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A number of studies over the past 10 years have found differences in the prevalence of corneal staining response with different combinations of contact lens multipurpose solutions (MPS) and lens materials (Table 1).1-11 A majority of these reports refer to conventional hydrogels used in conjunction with MPS containing polyhexamethyl biguanide (PHMB).

With more than one in four silicone hydrogel lens users either removing the lenses daily or using them only occasionally overnight,12 corneal staining with these new materials and solution combinations continues to be relevant. With the PureVision lens, Jones et al 7 found 37 per cent of patients using the PHMB-preserved MPS ReNu MultiPlus had asymptomatic corneal staining, compared to 2 per cent with a polyquad-preserved OptiFree Express (Alcon).

Symptoms of lens awareness and discomfort with corneal staining have, however, been reported in patients switching to PureVision and ReNu MultiPlus, in some cases after two weeks' solution use.13 Fonn14 noted superficial circumferential staining with this combination which was usually asymptomatic. However, Levy15 presented company data that showed no significant difference in corneal staining levels between PureVision and a conventional hydrogel when used with ReNu MultiPlus.
In a previous study by the present author, the clinical performance of Ciba Vision's silicone hydrogel lens Focus Night & Day, worn on a daily wear basis, was compared using OptiFree Express and the peroxide-based AOSept Plus (Ciba Vision).11 Corneal staining was significantly greater with OptiFree Express.
Introduced to the UK market in February 2004, Focus Aqua is the latest MPS from Ciba Vision. Known in North America as AQuify MPS, this solution has the same concentration of PHMB as ReNu MultiPlus (0.0001 per cent) but incorporates different ingredients as surfactants, lubricants and buffering agents. In addition, Focus Aqua contains dexpanthenol (Pro-Vitamin B5), a moisturiser which, when combined with the humectant Sorbitol, has been shown to increase the water-holding capacity of traditional hydrogels.16
The purpose of this study was therefore to evaluate and compare the clinical performance of Focus Aqua with that of ReNu MultiPlus, when used in conjunction with Night & Day lenses worn on a daily wear basis.
METHODS AND MATERIALS
This was a one-month, 25-subject, randomised, single-masked (investigator), contralateral study in which subjects were optimally fit with Night & Day lenses and used ReNu MultiPlus in one eye and Focus Aqua in the other.
The study protocol is more fully described in the previous paper.11 The same inclusion/exclusion criteria were used as in the first study, ie no clinically significant slit-lamp findings and adequate tears. Subjects made three visits during the study: a fitting/dispensing visit and two-week and one-month follow-up visits. The performance of each solution was assessed for various clinical variables, including slit-lamp findings, aspects of lens comfort and symptoms, visual acuity at high and low contrast, vision quality, lens fit, non-invasive tear break-up time and pre-lens tear film quality.
Corneal staining was graded at the slit lamp by the investigator using a given 0-4 scale with 0.5 increments, and if ³Grade 1 and extending to three or more quadrants of the cornea, was considered as solution related. An objective method using captured image analysis was also employed to determine the surface area of the corneal staining in mm2. This system has been shown to be an effective objective method of evaluating different corneal staining responses.8
At each follow-up visit, investigators asked subjects about their overall preference between the two care systems and subjects also completed an exit questionnaire comparing the systems and indicating which performed better for a range of features. In addition, at the final visit only, the quantity of solution remaining in each bottle was measured and recorded to assess compliance.
The formulations of the lens care products used in the study are shown in Table 2. ReNu MultiPlus was used according to the manufacturer's instructions approved in the UK (ie no rub, pre-rinse). In the EU, Focus Aqua is approved as a no rub, no rinse solution; however, for the purposes of this study, the US-approved instructions were used for Focus Aqua, ie no rub but with a pre-rinse. For both solutions, the recommended soaking time is four hours. No saline rinse or lubricating drops were used for the duration of the study.
Subjects used the manufacturer's approved lens case with each solution and one lid of each lens case was removed to prevent errors in the solution used. Focus Aqua is packaged with the antimicrobial lens storage case, MicroBlock, which has been shown to reduce levels of case contamination and, potentially, the incidence of associated infections.17

Statistical analysis
For each visit, data for eyes randomised to each care system were compared using either the paired Students t-test, Wilcoxon's signed ranks test for matched pairs or chi-square test, depending on the distribution of the data. Preference data were analysed using Pearson's chi-square test. In all cases, a P-value of 0.05 or less was taken to indicate a statistically significant difference.

RESULTS
Of the 25 subjects enrolled, a majority (76 per cent) were female and the mean age was 45 years. All were previous contact lens wearers using a variety of care products prior to enrolment; 32 per cent were using OptiFree Express, 12 per cent used Complete (AMO), 16 per cent were using hydrogen peroxide systems and 20 per cent used generic own-label products. The remaining subjects were previously daily disposable lens wearers and used no lens care products.
A total of 23 subjects completed the study; one subject was discontinued by the investigator following an adverse event (contact lens peripheral ulcer) while using Focus Aqua, although this was regarded as unlikely to be solution-related. The other discontinued subject was found to have Grade 2.5 staining at the two-week visit while using ReNu MultiPlus.
The mean wearing times were more than 12 hours per day and more than 6.5 days per week at both the two-week and one-month visits.

Corneal staining
Investigator grading
Results for corneal staining graded by investigators at baseline, two weeks and one month are summarised in Table 3. At both follow-up visits there was greater extent, depth, maximum grade, proportion of eyes ³Grade 1, proportion showing solution sensitivity Grade 1 and solution sensitivity Grade 2, with ReNu MultiPlus than with Focus Aqua.
At the two-week visit, almost half of the ReNu MultiPlus eyes had clinically significant (³Grade 2) solution-related corneal staining in multiple quadrants versus none with Focus Aqua. There were fewer ReNu MultiPlus solution-related corneal staining eyes at one month than at two weeks but one subject had previously discontinued with Grade 2.5 staining at the two-week visit. One subject had Grade 3 corneal staining in the ReNu MultiPlus eye Ð the maximum recorded during the study Ð at the one-month visit. Seventy per cent of the ReNu MultiPlus eyes had ³Grade 1 corneal staining at one month compared with 26 per cent of the Focus Aqua eyes. Figure 1 shows this trend over the three visits.
The mean corneal staining grade (0-4 scale) was significantly higher with ReNu MultiPlus than with Focus Aqua at both follow-up visits: 1.5 vs 0.8 at two weeks (P(0.0001) and 1.2 vs 0.5 (P(0.0001) at one month. These values compare with mean corneal staining at baseline of 0.8 in the ReNu MultiPlus eyes and 0.7 in the Focus Aqua eyes.

Image analysis
Results for objective image analysis of corneal staining are summarised in Table 4. There was a greater mean staining area and average number of corneal staining spots with ReNu MultiPlus at both the follow-up visits than Focus Aqua. These results are in agreement with the investigator grading and are also strongly statistically significant.
At both follow-up visits, all peripheral quadrants showed greater staining extent and a greater number of staining spots in eyes exposed to ReNu MultiPlus and these differences were statistically significant. The greatest area of staining was found in the inferior quadrant for both care systems. Again ReNu MultiPlus showed a greater mean staining area than Focus Aqua in this quadrant: 0.082 mm2 vs 0.040 mm2 at two weeks (P=0.05) and 0.103 mm2 vs 0.026 mm2 at one month (P=0.001).
There were no significant differences between the two care systems with respect to any of the other slit-lamp findings.

Comfort, vision and lens fit
Comfort was rated at all visits using a 10cm visual analogue scale. The mean scores for 'comfort at visit' ranged from 9.5 to 9.7 and for 'average end of day comfort' from 8.3 to 8.8. The only significant difference in comfort was a higher score with ReNu MultiPlus at two weeks (9.7 vs 9.5, P=0.05). However, this trend was not consistent at the one-month visit, where Focus Aqua was graded higher (9.7 vs 9.6). There were no significant differences in the occurrence of symptoms between care systems.
Similarly, there were no significant differences with any assessment of vision or lens fit between eyes using the different care systems at any of the study visits. Tear film assessments were also similar.

Preference
Although at both follow-up visits a majority of subjects expressed a preference for Focus Aqua, these differences were not statistically significant. At the two-week visit, 46 per cent preferred Focus Aqua and 25 per cent preferred ReNu MultiPlus. After one month, the proportions were 43 per cent and 26 per cent respectively. The trend among patients who did comment about their preference was that they preferred Focus Aqua because the case and solution bottle were easier to use.
On completing the exit questionnaire, subjects again expressed a slight preference for Focus Aqua over ReNu MultiPlus (44 per cent vs 36 per cent). They were also asked which care system they preferred with respect to various features including dryness, lens cleanliness, comfort, quality and lens wearing time. In all cases, about half of the subjects found no difference between care systems and where preferences were expressed there were no statistically significant differences.

Solution usage
At the end of the study, the amount of solution used by subjects was estimated from the solution remaining in the returned bottles. There was a wide variation between subjects in the amount of solution used, some using, on average, less than 1ml per day and others using the theoretically correct amount of approximately 4ml per lens per day.
There was some evidence of a connection between solution usage and corneal staining. The five subjects who showed no significant staining with ReNu MultiPlus were all poorly compliant. The 'non-stainers' used, on average, 42 per cent of the theoretically correct amount (range: 13-56 per cent) while the 'stainers' used, on average, 104 per cent of the correct amount (range: 49-160 per cent).

DISCUSSION
The main finding of this study is a difference in the level of solution-related corneal staining between Focus Aqua and ReNu MultiPlus when used in conjunction with Night & Day lenses. ReNu MultiPlus resulted in high levels of solution-related corneal staining compared to Focus Aqua. None of the eyes exposed to Focus Aqua were judged to have clinically significant (³Grade 2) solution-related staining whereas with ReNu MultiPlus, nearly half of the eyes showed Grade 2 or more staining at the two-week visit.
Since the two systems contain similar levels of PHMB (0.0001 per cent) and similar instructions for use, corneal staining is not just due to the presence of PHMB and is likely related to the difference in surfactants, lubricants and buffer systems contained in the formulations (Table 2).
A previous study has also found that two multipurpose solutions Ð Complete and ReNu MultiPlus Ð that contain identical concentrations of the same biguanide preservative (Complete refers to the preservative as 'polyhexamethylene biguanide' and ReNu MultiPlus refers to 'polyaminopropyl biguanide' although they are chemically identical), can produce different levels of corneal staining in conventional daily wear hydrogel lens users.9
The present study suggests that the relationship between PHMB and corneal staining may have been overstated in the literature. Support for this relationship has been based on increased concentration of PHMB causing increased corneal staining.5,8 This may occur either by solution formulations containing a higher concentration of PHMB or due to increased accumulation of PHMB in the lens over time Ð which can be determined from in vitro laboratory uptake and release studies.
While it must be taken into account that silicone hydrogel lenses inherently have reduced uptake and release of PHMB than traditional hydrogels and that this is less with Night & Day lenses than with PureVision lenses,17 the results of the present study, along with those of the author's previous study with Night & Day lenses,11 diminish support for a simple relationship between PHMB and corneal staining. Objective analysis of change in corneal staining from baseline measurements showed almost a three-fold decrease at two weeks and almost a four-fold decrease at one month with Focus Aqua. For ReNu MultiPlus the opposite was the case, with a three-fold increase in corneal staining from baseline at two weeks and one month. With ReNu MultiPlus, the staining was apparent in multiple corneal quadrants whereas with Focus Aqua only the inferior quadrant showed any significant staining. As previously reported,13 the central cornea showed less staining response.
Subjects in the present study used a variety of MPS and other lens care products prior to enrolment. The mean extent of corneal staining, maximum grade and proportion of eyes ³Grade 1 were all lower in the Focus Aqua eye at one month than at baseline. This improvement is too small to be statistically significant but it is in contrast with the ReNu MultiPlus eyes, which showed an increase in these and other corneal staining measures.
The results of this study are in line with reports of solution-related staining with ReNu MultiPlus used in conjunction with PureVision silicone hydrogel lenses.13,14 In one report,14 a similar proportion of subjects showed a solution-based reaction to that noted in the present study, but the staining tended to be at a higher level. This difference may be due to the continuous surface coating of Night & Day while the PureVision lens has discrete islands of coating.18
Although there was a difference in the corneal staining response, there was no corresponding difference in other aspects of corneal physiology and this finding is consistent with other studies.7,14 However, as observed by previous authors,4 it is possible that periods longer than one month are required for clinical responses other than corneal staining to become evident. Similarly, there was no significant difference in comfort response between Focus Aqua and ReNu MultiPlus, despite significant differences in staining. This has been noted with other MPS staining studies.5,7,8 Several authors have noted an overall difference in comfort as well as staining but have not been able to make a direct correlation.7,9
An interesting finding from this study was that compliance with solution usage may be a factor in solution-related staining; subjects who showed no significant staining with ReNu MultiPlus were all poorly compliant with the volume of solution recommended. The reason for this probably relates to the reduced concentration of PHMB and other constituents in solution that is re-used or topped up. Paradoxically, poor compliance in this respect Ð though obviously undesirable Ð may therefore be an advantage in reducing exposure to the solution ingredients.
Finally, it is useful to look at the staining results compared to non-contact lens wearers. The mean level of naturally occurring corneal staining has been found to be equivalent to the 0.5 grade on a 0-4 scale with 0.5 steps.19 In one study, some degree of corneal staining was found in 79 per cent of the corneas of non-contact lens wearers.20 Putting the results of the present study in perspective, the combination of daily wear Night & Day lenses maintained with Focus Aqua lens care solution appears to cause less departure from normal physiological corneal staining than other lens and care system combinations.

CONCLUSIONS
This study has demonstrated differences in corneal staining response between multipurpose solutions when used with Focus Night & Day silicone hydrogel lenses in daily wear.
Corneal staining was shown to be significantly better with Focus Aqua than with ReNu MultiPlus, although the two care systems are preserved with the same preservative (PHMB) used in the same concentration. These findings suggest that PHMB is not the main ingredient of MPS implicated in corneal staining with silicone hydrogel lenses, and that other constituents are involved. The study also showed that patient compliance may be a factor in solution-related staining.
In this study no association was found between corneal staining and comfort or symptoms. However, differences in staining response between different formulations of MPS are certainly a factor to consider when choosing the optimum care system for use with daily wear silicone hydrogel lenses. In this respect, Night & Day lenses and Focus Aqua would appear to have less effect on corneal physiology than other combinations of products.
REFERENCES
1 Land JK and McKenney C. Corneal staining with three contact lens disinfection systems. In: Proceedings of the 9th Asian Pacific Optometric Congress on Science Programme, Hong Kong, 1993.
2 Begley CG, Edrington TB, Chalmers R. Effect of lens care systems on corneal fluorescein staining and subjective comfort in hydrogel lens wearers. Int Contact Lens Clin, 1994;21:7-13.
3 Bois A, Brazeau D, Goldberg S et al. Performance of two single-solution contact lens care systems. optician, 1996; 211(5533):37-42.
4 Soni PS, Horner DG, Ross J. Ocular responses to lens care systems in adolescent soft contact lens wearers. Optom Vis Sci 1996; 73(2):70-85.
5 Jones L, Jones D, Houlford M. Clinical comparison of three polyhexanide-preserved multipurpose solutions. Cont Lens Ant Eye, 1997;20:23-30.
6 Cho P, Lui T, Kee C. Soft contact lens care systems and corneal staining in Hong Kong-Chinese. Cont Lens Ant Eye, 1998;21:47-53.
7 Jones L, MacDougall N, Sorbara LG. Asymptomatic corneal staining associated with the use of balafilcon silicone hydrogel contact lenses disinfected with a biguanide-preserved care regimen. Optom Vis Sci, 2002; 79:753-761.
8 Pritchard N, Young G, Coleman S et al. Subjective and objective measures of corneal staining related to multipurpose care systems. Cont Lens Ant Eye, 2003;26:3-9.
9 Lebow KA, Schachet JL. Evaluation of corneal staining and patient preference with use of three multipurpose solutions and two brands of soft contact lenses. Eye Cont Lens, 2003; 29:213-220.
10 Lutzi D, Cedrone R, Evans D et al. Differences in corneal staining between two 'no-rub' multipurpose solutions. Review of Cont Lenses, 2004; Jan 28-31.
11 Amos C. A clinical comparison of two soft lens care systems used with silicone hydrogel contact lenses. optician, 2004; 227(5933):16-20.
12 www.siliconehydrogels.com.
13 Epstein AB. SPK with daily wear of silicone hydrogel lenses and MPS. Cont Lens Spectrum, 2002; 17(11)30.
14 Fonn D. Observations of corneal staining with MPS and silicone hydrogel lenses. Cont Lens Spectrum, 2002; 17(11)32.
15 Levy B. Contact lens solution manufacturer responds with data. Cont Lens Spectrum, 2002;17(11):34.
16 Kendig S. The effects of lens care products on the dehydration of hydrogel contact lenses measured by dynamic vapour sorption. Invest Ophthalmol Vis Sci, 2004;45:ARVO E-abstract 1545.
17 George M. MicroBlock: a new antimicrobial lens case. optician, 2003; 226: 5930: 18-20.
18 Tighe B. Silicone hydrogel materials Ð how do they work. In: Silicone Hydrogels: The Rebirth of Continuous Wear (Ed. Sweeney D). Butterworth-Heinemann, Oxford 2000.
19 Schwallie J, McKenney C, Long B and McNeil A. Corneal staining patterns in normal non-contact lens wearers. Optom Vis Sci, 1997; 74(2):92-98.
20 Dundas M, Walker A and Woods R. Clinical grading of corneal staining of non-contact lens wearers. Ophthal Physiol Opt, 2001; 21(1):30-35.

Chris Amos is project manager, lens care products, at Ciba Vision Corp, Duluth, Georgia, USA number of studies over the past 10 years have found differences in the prevalence of corneal staining response with different combinations of contact lens multipurpose solutions (MPS) and lens materials (Table 1).1-11 A majority of these reports refer to conventional hydrogels used in conjunction with MPS containing polyhexamethyl biguanide (PHMB).
With more than one in four silicone hydrogel lens users either removing the lenses daily or using them only occasionally overnight,12 corneal staining with these new materials and solution combinations continues to be relevant. With the PureVision lens, Jones et al 7 found 37 per cent of patients using the PHMB-preserved MPS ReNu MultiPlus had asymptomatic corneal staining, compared to 2 per cent with a polyquad-preserved OptiFree Express (Alcon).
Symptoms of lens awareness and discomfort with corneal staining have, however, been reported in patients switching to PureVision and ReNu MultiPlus, in some cases after two weeks' solution use.13 Fonn14 noted superficial circumferential staining with this combination which was usually asymptomatic. However, Levy15 presented company data that showed no significant difference in corneal staining levels between PureVision and a conventional hydrogel when used with ReNu MultiPlus.
In a previous study by the present author, the clinical performance of Ciba Vision's silicone hydrogel lens Focus Night & Day, worn on a daily wear basis, was compared using OptiFree Express and the peroxide-based AOSept Plus (Ciba Vision).11 Corneal staining was significantly greater with OptiFree Express.
Introduced to the UK market in February 2004, Focus Aqua is the latest MPS from Ciba Vision. Known in North America as AQuify MPS, this solution has the same concentration of PHMB as ReNu MultiPlus (0.0001 per cent) but incorporates different ingredients as surfactants, lubricants and buffering agents. In addition, Focus Aqua contains dexpanthenol (Pro-Vitamin B5), a moisturiser which, when combined with the humectant Sorbitol, has been shown to increase the water-holding capacity of traditional hydrogels.16
The purpose of this study was therefore to evaluate and compare the clinical performance of Focus Aqua with that of ReNu MultiPlus, when used in conjunction with Night & Day lenses worn on a daily wear basis.
METHODS AND MATERIALS
This was a one-month, 25-subject, randomised, single-masked (investigator), contralateral study in which subjects were optimally fit with Night & Day lenses and used ReNu MultiPlus in one eye and Focus Aqua in the other.
The study protocol is more fully described in the previous paper.11 The same inclusion/exclusion criteria were used as in the first study, ie no clinically significant slit-lamp findings and adequate tears. Subjects made three visits during the study: a fitting/dispensing visit and two-week and one-month follow-up visits. The performance of each solution was assessed for various clinical variables, including slit-lamp findings, aspects of lens comfort and symptoms, visual acuity at high and low contrast, vision quality, lens fit, non-invasive tear break-up time and pre-lens tear film quality.
Corneal staining was graded at the slit lamp by the investigator using a given 0-4 scale with 0.5 increments, and if ³Grade 1 and extending to three or more quadrants of the cornea, was considered as solution related. An objective method using captured image analysis was also employed to determine the surface area of the corneal staining in mm2. This system has been shown to be an effective objective method of evaluating different corneal staining responses.8
At each follow-up visit, investigators asked subjects about their overall preference between the two care systems and subjects also completed an exit questionnaire comparing the systems and indicating which performed better for a range of features. In addition, at the final visit only, the quantity of solution remaining in each bottle was measured and recorded to assess compliance.
The formulations of the lens care products used in the study are shown in Table 2. ReNu MultiPlus was used according to the manufacturer's instructions approved in the UK (ie no rub, pre-rinse). In the EU, Focus Aqua is approved as a no rub, no rinse solution; however, for the purposes of this study, the US-approved instructions were used for Focus Aqua, ie no rub but with a pre-rinse. For both solutions, the recommended soaking time is four hours. No saline rinse or lubricating drops were used for the duration of the study.
Subjects used the manufacturer's approved lens case with each solution and one lid of each lens case was removed to prevent errors in the solution used. Focus Aqua is packaged with the antimicrobial lens storage case, MicroBlock, which has been shown to reduce levels of case contamination and, potentially, the incidence of associated infections.17

Statistical analysis
For each visit, data for eyes randomised to each care system were compared using either the paired Students t-test, Wilcoxon's signed ranks test for matched pairs or chi-square test, depending on the distribution of the data. Preference data were analysed using Pearson's chi-square test. In all cases, a P-value of 0.05 or less was taken to indicate a statistically significant difference.

RESULTS
Of the 25 subjects enrolled, a majority (76 per cent) were female and the mean age was 45 years. All were previous contact lens wearers using a variety of care products prior to enrolment; 32 per cent were using OptiFree Express, 12 per cent used Complete (AMO), 16 per cent were using hydrogen peroxide systems and 20 per cent used generic own-label products. The remaining subjects were previously daily disposable lens wearers and used no lens care products.
A total of 23 subjects completed the study; one subject was discontinued by the investigator following an adverse event (contact lens peripheral ulcer) while using Focus Aqua, although this was regarded as unlikely to be solution-related. The other discontinued subject was found to have Grade 2.5 staining at the two-week visit while using ReNu MultiPlus.
The mean wearing times were more than 12 hours per day and more than 6.5 days per week at both the two-week and one-month visits.

Corneal staining
Investigator grading
Results for corneal staining graded by investigators at baseline, two weeks and one month are summarised in Table 3. At both follow-up visits there was greater extent, depth, maximum grade, proportion of eyes ³Grade 1, proportion showing solution sensitivity Grade 1 and solution sensitivity Grade 2, with ReNu MultiPlus than with Focus Aqua.
At the two-week visit, almost half of the ReNu MultiPlus eyes had clinically significant (³Grade 2) solution-related corneal staining in multiple quadrants versus none with Focus Aqua. There were fewer ReNu MultiPlus solution-related corneal staining eyes at one month than at two weeks but one subject had previously discontinued with Grade 2.5 staining at the two-week visit. One subject had Grade 3 corneal staining in the ReNu MultiPlus eye Ð the maximum recorded during the study Ð at the one-month visit. Seventy per cent of the ReNu MultiPlus eyes had ³Grade 1 corneal staining at one month compared with 26 per cent of the Focus Aqua eyes. Figure 1 shows this trend over the three visits.
The mean corneal staining grade (0-4 scale) was significantly higher with ReNu MultiPlus than with Focus Aqua at both follow-up visits: 1.5 vs 0.8 at two weeks (P(0.0001) and 1.2 vs 0.5 (P(0.0001) at one month. These values compare with mean corneal staining at baseline of 0.8 in the ReNu MultiPlus eyes and 0.7 in the Focus Aqua eyes.

Image analysis
Results for objective image analysis of corneal staining are summarised in Table 4. There was a greater mean staining area and average number of corneal staining spots with ReNu MultiPlus at both the follow-up visits than Focus Aqua. These results are in agreement with the investigator grading and are also strongly statistically significant.
At both follow-up visits, all peripheral quadrants showed greater staining extent and a greater number of staining spots in eyes exposed to ReNu MultiPlus and these differences were statistically significant. The greatest area of staining was found in the inferior quadrant for both care systems. Again ReNu MultiPlus showed a greater mean staining area than Focus Aqua in this quadrant: 0.082 mm2 vs 0.040 mm2 at two weeks (P=0.05) and 0.103 mm2 vs 0.026 mm2 at one month (P=0.001).
There were no significant differences between the two care systems with respect to any of the other slit-lamp findings.

Comfort, vision and lens fit
Comfort was rated at all visits using a 10cm visual analogue scale. The mean scores for 'comfort at visit' ranged from 9.5 to 9.7 and for 'average end of day comfort' from 8.3 to 8.8. The only significant difference in comfort was a higher score with ReNu MultiPlus at two weeks (9.7 vs 9.5, P=0.05). However, this trend was not consistent at the one-month visit, where Focus Aqua was graded higher (9.7 vs 9.6). There were no significant differences in the occurrence of symptoms between care systems.
Similarly, there were no significant differences with any assessment of vision or lens fit between eyes using the different care systems at any of the study visits. Tear film assessments were also similar.

Preference
Although at both follow-up visits a majority of subjects expressed a preference for Focus Aqua, these differences were not statistically significant. At the two-week visit, 46 per cent preferred Focus Aqua and 25 per cent preferred ReNu MultiPlus. After one month, the proportions were 43 per cent and 26 per cent respectively. The trend among patients who did comment about their preference was that they preferred Focus Aqua because the case and solution bottle were easier to use.
On completing the exit questionnaire, subjects again expressed a slight preference for Focus Aqua over ReNu MultiPlus (44 per cent vs 36 per cent). They were also asked which care system they preferred with respect to various features including dryness, lens cleanliness, comfort, quality and lens wearing time. In all cases, about half of the subjects found no difference between care systems and where preferences were expressed there were no statistically significant differences.

Solution usage
At the end of the study, the amount of solution used by subjects was estimated from the solution remaining in the returned bottles. There was a wide variation between subjects in the amount of solution used, some using, on average, less than 1ml per day and others using the theoretically correct amount of approximately 4ml per lens per day.
There was some evidence of a connection between solution usage and corneal staining. The five subjects who showed no significant staining with ReNu MultiPlus were all poorly compliant. The 'non-stainers' used, on average, 42 per cent of the theoretically correct amount (range: 13-56 per cent) while the 'stainers' used, on average, 104 per cent of the correct amount (range: 49-160 per cent).

DISCUSSION
The main finding of this study is a difference in the level of solution-related corneal staining between Focus Aqua and ReNu MultiPlus when used in conjunction with Night & Day lenses. ReNu MultiPlus resulted in high levels of solution-related corneal staining compared to Focus Aqua. None of the eyes exposed to Focus Aqua were judged to have clinically significant (³Grade 2) solution-related staining whereas with ReNu MultiPlus, nearly half of the eyes showed Grade 2 or more staining at the two-week visit.
Since the two systems contain similar levels of PHMB (0.0001 per cent) and similar instructions for use, corneal staining is not just due to the presence of PHMB and is likely related to the difference in surfactants, lubricants and buffer systems contained in the formulations (Table 2).
A previous study has also found that two multipurpose solutions Ð Complete and ReNu MultiPlus Ð that contain identical concentrations of the same biguanide preservative (Complete refers to the preservative as 'polyhexamethylene biguanide' and ReNu MultiPlus refers to 'polyaminopropyl biguanide' although they are chemically identical), can produce different levels of corneal staining in conventional daily wear hydrogel lens users.9
The present study suggests that the relationship between PHMB and corneal staining may have been overstated in the literature. Support for this relationship has been based on increased concentration of PHMB causing increased corneal staining.5,8 This may occur either by solution formulations containing a higher concentration of PHMB or due to increased accumulation of PHMB in the lens over time Ð which can be determined from in vitro laboratory uptake and release studies.
While it must be taken into account that silicone hydrogel lenses inherently have reduced uptake and release of PHMB than traditional hydrogels and that this is less with Night & Day lenses than with PureVision lenses,17 the results of the present study, along with those of the author's previous study with Night & Day lenses,11 diminish support for a simple relationship between PHMB and corneal staining. Objective analysis of change in corneal staining from baseline measurements showed almost a three-fold decrease at two weeks and almost a four-fold decrease at one month with Focus Aqua. For ReNu MultiPlus the opposite was the case, with a three-fold increase in corneal staining from baseline at two weeks and one month. With ReNu MultiPlus, the staining was apparent in multiple corneal quadrants whereas with Focus Aqua only the inferior quadrant showed any significant staining. As previously reported,13 the central cornea showed less staining response.
Subjects in the present study used a variety of MPS and other lens care products prior to enrolment. The mean extent of corneal staining, maximum grade and proportion of eyes ³Grade 1 were all lower in the Focus Aqua eye at one month than at baseline. This improvement is too small to be statistically significant but it is in contrast with the ReNu MultiPlus eyes, which showed an increase in these and other corneal staining measures.
The results of this study are in line with reports of solution-related staining with ReNu MultiPlus used in conjunction with PureVision silicone hydrogel lenses.13,14 In one report,14 a similar proportion of subjects showed a solution-based reaction to that noted in the present study, but the staining tended to be at a higher level. This difference may be due to the continuous surface coating of Night & Day while the PureVision lens has discrete islands of coating.18
Although there was a difference in the corneal staining response, there was no corresponding difference in other aspects of corneal physiology and this finding is consistent with other studies.7,14 However, as observed by previous authors,4 it is possible that periods longer than one month are required for clinical responses other than corneal staining to become evident. Similarly, there was no significant difference in comfort response between Focus Aqua and ReNu MultiPlus, despite significant differences in staining. This has been noted with other MPS staining studies.5,7,8 Several authors have noted an overall difference in comfort as well as staining but have not been able to make a direct correlation.7,9
An interesting finding from this study was that compliance with solution usage may be a factor in solution-related staining; subjects who showed no significant staining with ReNu MultiPlus were all poorly compliant with the volume of solution recommended. The reason for this probably relates to the reduced concentration of PHMB and other constituents in solution that is re-used or topped up. Paradoxically, poor compliance in this respect Ð though obviously undesirable Ð may therefore be an advantage in reducing exposure to the solution ingredients.
Finally, it is useful to look at the staining results compared to non-contact lens wearers. The mean level of naturally occurring corneal staining has been found to be equivalent to the 0.5 grade on a 0-4 scale with 0.5 steps.19 In one study, some degree of corneal staining was found in 79 per cent of the corneas of non-contact lens wearers.20 Putting the results of the present study in perspective, the combination of daily wear Night & Day lenses maintained with Focus Aqua lens care solution appears to cause less departure from normal physiological corneal staining than other lens and care system combinations.

CONCLUSIONS
This study has demonstrated differences in corneal staining response between multipurpose solutions when used with Focus Night & Day silicone hydrogel lenses in daily wear.
Corneal staining was shown to be significantly better with Focus Aqua than with ReNu MultiPlus, although the two care systems are preserved with the same preservative (PHMB) used in the same concentration. These findings suggest that PHMB is not the main ingredient of MPS implicated in corneal staining with silicone hydrogel lenses, and that other constituents are involved. The study also showed that patient compliance may be a factor in solution-related staining.
In this study no association was found between corneal staining and comfort or symptoms. However, differences in staining response between different formulations of MPS are certainly a factor to consider when choosing the optimum care system for use with daily wear silicone hydrogel lenses. In this respect, Night & Day lenses and Focus Aqua would appear to have less effect on corneal physiology than other combinations of products.
REFERENCES
1 Land JK and McKenney C. Corneal staining with three contact lens disinfection systems. In: Proceedings of the 9th Asian Pacific Optometric Congress on Science Programme, Hong Kong, 1993.
2 Begley CG, Edrington TB, Chalmers R. Effect of lens care systems on corneal fluorescein staining and subjective comfort in hydrogel lens wearers. Int Contact Lens Clin, 1994;21:7-13.
3 Bois A, Brazeau D, Goldberg S et al. Performance of two single-solution contact lens care systems. optician, 1996; 211(5533):37-42.
4 Soni PS, Horner DG, Ross J. Ocular responses to lens care systems in adolescent soft contact lens wearers. Optom Vis Sci 1996; 73(2):70-85.
5 Jones L, Jones D, Houlford M. Clinical comparison of three polyhexanide-preserved multipurpose solutions. Cont Lens Ant Eye, 1997;20:23-30.
6 Cho P, Lui T, Kee C. Soft contact lens care systems and corneal staining in Hong Kong-Chinese. Cont Lens Ant Eye, 1998;21:47-53.
7 Jones L, MacDougall N, Sorbara LG. Asymptomatic corneal staining associated with the use of balafilcon silicone hydrogel contact lenses disinfected with a biguanide-preserved care regimen. Optom Vis Sci, 2002; 79:753-761.
8 Pritchard N, Young G, Coleman S et al. Subjective and objective measures of corneal staining related to multipurpose care systems. Cont Lens Ant Eye, 2003;26:3-9.
9 Lebow KA, Schachet JL. Evaluation of corneal staining and patient preference with use of three multipurpose solutions and two brands of soft contact lenses. Eye Cont Lens, 2003; 29:213-220.
10 Lutzi D, Cedrone R, Evans D et al. Differences in corneal staining between two 'no-rub' multipurpose solutions. Review of Cont Lenses, 2004; Jan 28-31.
11 Amos C. A clinical comparison of two soft lens care systems used with silicone hydrogel contact lenses. optician, 2004; 227(5933):16-20.
12 www.siliconehydrogels.com.
13 Epstein AB. SPK with daily wear of silicone hydrogel lenses and MPS. Cont Lens Spectrum, 2002; 17(11)30.
14 Fonn D. Observations of corneal staining with MPS and silicone hydrogel lenses. Cont Lens Spectrum, 2002; 17(11)32.
15 Levy B. Contact lens solution manufacturer responds with data. Cont Lens Spectrum, 2002;17(11):34.
16 Kendig S. The effects of lens care products on the dehydration of hydrogel contact lenses measured by dynamic vapour sorption. Invest Ophthalmol Vis Sci, 2004;45:ARVO E-abstract 1545.
17 George M. MicroBlock: a new antimicrobial lens case. optician, 2003; 226: 5930: 18-20.
18 Tighe B. Silicone hydrogel materials Ð how do they work. In: Silicone Hydrogels: The Rebirth of Continuous Wear (Ed. Sweeney D). Butterworth-Heinemann, Oxford 2000.
19 Schwallie J, McKenney C, Long B and McNeil A. Corneal staining patterns in normal non-contact lens wearers. Optom Vis Sci, 1997; 74(2):92-98.
20 Dundas M, Walker A and Woods R. Clinical grading of corneal staining of non-contact lens wearers. Ophthal Physiol Opt, 2001; 21(1):30-35.

Chris Amos is project manager, lens care products, at Ciba Vision Corp, Duluth, Georgia, USA number of studies over the past 10 years have found differences in the prevalence of corneal staining response with different combinations of contact lens multipurpose solutions (MPS) and lens materials (Table 1).1-11 A majority of these reports refer to conventional hydrogels used in conjunction with MPS containing polyhexamethyl biguanide (PHMB).
With more than one in four silicone hydrogel lens users either removing the lenses daily or using them only occasionally overnight,12 corneal staining with these new materials and solution combinations continues to be relevant. With the PureVision lens, Jones et al 7 found 37 per cent of patients using the PHMB-preserved MPS ReNu MultiPlus had asymptomatic corneal staining, compared to 2 per cent with a polyquad-preserved OptiFree Express (Alcon).
Symptoms of lens awareness and discomfort with corneal staining have, however, been reported in patients switching to PureVision and ReNu MultiPlus, in some cases after two weeks' solution use.13 Fonn14 noted superficial circumferential staining with this combination which was usually asymptomatic. However, Levy15 presented company data that showed no significant difference in corneal staining levels between PureVision and a conventional hydrogel when used with ReNu MultiPlus.
In a previous study by the present author, the clinical performance of Ciba Vision's silicone hydrogel lens Focus Night & Day, worn on a daily wear basis, was compared using OptiFree Express and the peroxide-based AOSept Plus (Ciba Vision).11 Corneal staining was significantly greater with OptiFree Express.
Introduced to the UK market in February 2004, Focus Aqua is the latest MPS from Ciba Vision. Known in North America as AQuify MPS, this solution has the same concentration of PHMB as ReNu MultiPlus (0.0001 per cent) but incorporates different ingredients as surfactants, lubricants and buffering agents. In addition, Focus Aqua contains dexpanthenol (Pro-Vitamin B5), a moisturiser which, when combined with the humectant Sorbitol, has been shown to increase the water-holding capacity of traditional hydrogels.16
The purpose of this study was therefore to evaluate and compare the clinical performance of Focus Aqua with that of ReNu MultiPlus, when used in conjunction with Night & Day lenses worn on a daily wear basis.
METHODS AND MATERIALS
This was a one-month, 25-subject, randomised, single-masked (investigator), contralateral study in which subjects were optimally fit with Night & Day lenses and used ReNu MultiPlus in one eye and Focus Aqua in the other.
The study protocol is more fully described in the previous paper.11 The same inclusion/exclusion criteria were used as in the first study, ie no clinically significant slit-lamp findings and adequate tears. Subjects made three visits during the study: a fitting/dispensing visit and two-week and one-month follow-up visits. The performance of each solution was assessed for various clinical variables, including slit-lamp findings, aspects of lens comfort and symptoms, visual acuity at high and low contrast, vision quality, lens fit, non-invasive tear break-up time and pre-lens tear film quality.
Corneal staining was graded at the slit lamp by the investigator using a given 0-4 scale with 0.5 increments, and if ³Grade 1 and extending to three or more quadrants of the cornea, was considered as solution related. An objective method using captured image analysis was also employed to determine the surface area of the corneal staining in mm2. This system has been shown to be an effective objective method of evaluating different corneal staining responses.8
At each follow-up visit, investigators asked subjects about their overall preference between the two care systems and subjects also completed an exit questionnaire comparing the systems and indicating which performed better for a range of features. In addition, at the final visit only, the quantity of solution remaining in each bottle was measured and recorded to assess compliance.
The formulations of the lens care products used in the study are shown in Table 2. ReNu MultiPlus was used according to the manufacturer's instructions approved in the UK (ie no rub, pre-rinse). In the EU, Focus Aqua is approved as a no rub, no rinse solution; however, for the purposes of this study, the US-approved instructions were used for Focus Aqua, ie no rub but with a pre-rinse. For both solutions, the recommended soaking time is four hours. No saline rinse or lubricating drops were used for the duration of the study.
Subjects used the manufacturer's approved lens case with each solution and one lid of each lens case was removed to prevent errors in the solution used. Focus Aqua is packaged with the antimicrobial lens storage case, MicroBlock, which has been shown to reduce levels of case contamination and, potentially, the incidence of associated infections.17

Statistical analysis
For each visit, data for eyes randomised to each care system were compared using either the paired Students t-test, Wilcoxon's signed ranks test for matched pairs or chi-square test, depending on the distribution of the data. Preference data were analysed using Pearson's chi-square test. In all cases, a P-value of 0.05 or less was taken to indicate a statistically significant difference.

RESULTS
Of the 25 subjects enrolled, a majority (76 per cent) were female and the mean age was 45 years. All were previous contact lens wearers using a variety of care products prior to enrolment; 32 per cent were using OptiFree Express, 12 per cent used Complete (AMO), 16 per cent were using hydrogen peroxide systems and 20 per cent used generic own-label products. The remaining subjects were previously daily disposable lens wearers and used no lens care products.
A total of 23 subjects completed the study; one subject was discontinued by the investigator following an adverse event (contact lens peripheral ulcer) while using Focus Aqua, although this was regarded as unlikely to be solution-related. The other discontinued subject was found to have Grade 2.5 staining at the two-week visit while using ReNu MultiPlus.
The mean wearing times were more than 12 hours per day and more than 6.5 days per week at both the two-week and one-month visits.

Corneal staining
Investigator grading
Results for corneal staining graded by investigators at baseline, two weeks and one month are summarised in Table 3. At both follow-up visits there was greater extent, depth, maximum grade, proportion of eyes ³Grade 1, proportion showing solution sensitivity Grade 1 and solution sensitivity Grade 2, with ReNu MultiPlus than with Focus Aqua.
At the two-week visit, almost half of the ReNu MultiPlus eyes had clinically significant (³Grade 2) solution-related corneal staining in multiple quadrants versus none with Focus Aqua. There were fewer ReNu MultiPlus solution-related corneal staining eyes at one month than at two weeks but one subject had previously discontinued with Grade 2.5 staining at the two-week visit. One subject had Grade 3 corneal staining in the ReNu MultiPlus eye Ð the maximum recorded during the study Ð at the one-month visit. Seventy per cent of the ReNu MultiPlus eyes had ³Grade 1 corneal staining at one month compared with 26 per cent of the Focus Aqua eyes. Figure 1 shows this trend over the three visits.
The mean corneal staining grade (0-4 scale) was significantly higher with ReNu MultiPlus than with Focus Aqua at both follow-up visits: 1.5 vs 0.8 at two weeks (P(0.0001) and 1.2 vs 0.5 (P(0.0001) at one month. These values compare with mean corneal staining at baseline of 0.8 in the ReNu MultiPlus eyes and 0.7 in the Focus Aqua eyes.

Image analysis
Results for objective image analysis of corneal staining are summarised in Table 4. There was a greater mean staining area and average number of corneal staining spots with ReNu MultiPlus at both the follow-up visits than Focus Aqua. These results are in agreement with the investigator grading and are also strongly statistically significant.
At both follow-up visits, all peripheral quadrants showed greater staining extent and a greater number of staining spots in eyes exposed to ReNu MultiPlus and these differences were statistically significant. The greatest area of staining was found in the inferior quadrant for both care systems. Again ReNu MultiPlus showed a greater mean staining area than Focus Aqua in this quadrant: 0.082 mm2 vs 0.040 mm2 at two weeks (P=0.05) and 0.103 mm2 vs 0.026 mm2 at one month (P=0.001).
There were no significant differences between the two care systems with respect to any of the other slit-lamp findings.

Comfort, vision and lens fit
Comfort was rated at all visits using a 10cm visual analogue scale. The mean scores for 'comfort at visit' ranged from 9.5 to 9.7 and for 'average end of day comfort' from 8.3 to 8.8. The only significant difference in comfort was a higher score with ReNu MultiPlus at two weeks (9.7 vs 9.5, P=0.05). However, this trend was not consistent at the one-month visit, where Focus Aqua was graded higher (9.7 vs 9.6). There were no significant differences in the occurrence of symptoms between care systems.
Similarly, there were no significant differences with any assessment of vision or lens fit between eyes using the different care systems at any of the study visits. Tear film assessments were also similar.

Preference
Although at both follow-up visits a majority of subjects expressed a preference for Focus Aqua, these differences were not statistically significant. At the two-week visit, 46 per cent preferred Focus Aqua and 25 per cent preferred ReNu MultiPlus. After one month, the proportions were 43 per cent and 26 per cent respectively. The trend among patients who did comment about their preference was that they preferred Focus Aqua because the case and solution bottle were easier to use.
On completing the exit questionnaire, subjects again expressed a slight preference for Focus Aqua over ReNu MultiPlus (44 per cent vs 36 per cent). They were also asked which care system they preferred with respect to various features including dryness, lens cleanliness, comfort, quality and lens wearing time. In all cases, about half of the subjects found no difference between care systems and where preferences were expressed there were no statistically significant differences.

Solution usage
At the end of the study, the amount of solution used by subjects was estimated from the solution remaining in the returned bottles. There was a wide variation between subjects in the amount of solution used, some using, on average, less than 1ml per day and others using the theoretically correct amount of approximately 4ml per lens per day.
There was some evidence of a connection between solution usage and corneal staining. The five subjects who showed no significant staining with ReNu MultiPlus were all poorly compliant. The 'non-stainers' used, on average, 42 per cent of the theoretically correct amount (range: 13-56 per cent) while the 'stainers' used, on average, 104 per cent of the correct amount (range: 49-160 per cent).

DISCUSSION
The main finding of this study is a difference in the level of solution-related corneal staining between Focus Aqua and ReNu MultiPlus when used in conjunction with Night & Day lenses. ReNu MultiPlus resulted in high levels of solution-related corneal staining compared to Focus Aqua. None of the eyes exposed to Focus Aqua were judged to have clinically significant (³Grade 2) solution-related staining whereas with ReNu MultiPlus, nearly half of the eyes showed Grade 2 or more staining at the two-week visit.
Since the two systems contain similar levels of PHMB (0.0001 per cent) and similar instructions for use, corneal staining is not just due to the presence of PHMB and is likely related to the difference in surfactants, lubricants and buffer systems contained in the formulations (Table 2).
A previous study has also found that two multipurpose solutions Ð Complete and ReNu MultiPlus Ð that contain identical concentrations of the same biguanide preservative (Complete refers to the preservative as 'polyhexamethylene biguanide' and ReNu MultiPlus refers to 'polyaminopropyl biguanide' although they are chemically identical), can produce different levels of corneal staining in conventional daily wear hydrogel lens users.9
The present study suggests that the relationship between PHMB and corneal staining may have been overstated in the literature. Support for this relationship has been based on increased concentration of PHMB causing increased corneal staining.5,8 This may occur either by solution formulations containing a higher concentration of PHMB or due to increased accumulation of PHMB in the lens over time Ð which can be determined from in vitro laboratory uptake and release studies.
While it must be taken into account that silicone hydrogel lenses inherently have reduced uptake and release of PHMB than traditional hydrogels and that this is less with Night & Day lenses than with PureVision lenses,17 the results of the present study, along with those of the author's previous study with Night & Day lenses,11 diminish support for a simple relationship between PHMB and corneal staining. Objective analysis of change in corneal staining from baseline measurements showed almost a three-fold decrease at two weeks and almost a four-fold decrease at one month with Focus Aqua. For ReNu MultiPlus the opposite was the case, with a three-fold increase in corneal staining from baseline at two weeks and one month. With ReNu MultiPlus, the staining was apparent in multiple corneal quadrants whereas with Focus Aqua only the inferior quadrant showed any significant staining. As previously reported,13 the central cornea showed less staining response.
Subjects in the present study used a variety of MPS and other lens care products prior to enrolment. The mean extent of corneal staining, maximum grade and proportion of eyes ³Grade 1 were all lower in the Focus Aqua eye at one month than at baseline. This improvement is too small to be statistically significant but it is in contrast with the ReNu MultiPlus eyes, which showed an increase in these and other corneal staining measures.
The results of this study are in line with reports of solution-related staining with ReNu MultiPlus used in conjunction with PureVision silicone hydrogel lenses.13,14 In one report,14 a similar proportion of subjects showed a solution-based reaction to that noted in the present study, but the staining tended to be at a higher level. This difference may be due to the continuous surface coating of Night & Day while the PureVision lens has discrete islands of coating.18
Although there was a difference in the corneal staining response, there was no corresponding difference in other aspects of corneal physiology and this finding is consistent with other studies.7,14 However, as observed by previous authors,4 it is possible that periods longer than one month are required for clinical responses other than corneal staining to become evident. Similarly, there was no significant difference in comfort response between Focus Aqua and ReNu MultiPlus, despite significant differences in staining. This has been noted with other MPS staining studies.5,7,8 Several authors have noted an overall difference in comfort as well as staining but have not been able to make a direct correlation.7,9
An interesting finding from this study was that compliance with solution usage may be a factor in solution-related staining; subjects who showed no significant staining with ReNu MultiPlus were all poorly compliant with the volume of solution recommended. The reason for this probably relates to the reduced concentration of PHMB and other constituents in solution that is re-used or topped up. Paradoxically, poor compliance in this respect Ð though obviously undesirable Ð may therefore be an advantage in reducing exposure to the solution ingredients.
Finally, it is useful to look at the staining results compared to non-contact lens wearers. The mean level of naturally occurring corneal staining has been found to be equivalent to the 0.5 grade on a 0-4 scale with 0.5 steps.19 In one study, some degree of corneal staining was found in 79 per cent of the corneas of non-contact lens wearers.20 Putting the results of the present study in perspective, the combination of daily wear Night & Day lenses maintained with Focus Aqua lens care solution appears to cause less departure from normal physiological corneal staining than other lens and care system combinations.

CONCLUSIONS
This study has demonstrated differences in corneal staining response between multipurpose solutions when used with Focus Night & Day silicone hydrogel lenses in daily wear.
Corneal staining was shown to be significantly better with Focus Aqua than with ReNu MultiPlus, although the two care systems are preserved with the same preservative (PHMB) used in the same concentration. These findings suggest that PHMB is not the main ingredient of MPS implicated in corneal staining with silicone hydrogel lenses, and that other constituents are involved. The study also showed that patient compliance may be a factor in solution-related staining.
In this study no association was found between corneal staining and comfort or symptoms. However, differences in staining response between different formulations of MPS are certainly a factor to consider when choosing the optimum care system for use with daily wear silicone hydrogel lenses. In this respect, Night & Day lenses and Focus Aqua would appear to have less effect on corneal physiology than other combinations of products.
REFERENCES
1 Land JK and McKenney C. Corneal staining with three contact lens disinfection systems. In: Proceedings of the 9th Asian Pacific Optometric Congress on Science Programme, Hong Kong, 1993.
2 Begley CG, Edrington TB, Chalmers R. Effect of lens care systems on corneal fluorescein staining and subjective comfort in hydrogel lens wearers. Int Contact Lens Clin, 1994;21:7-13.
3 Bois A, Brazeau D, Goldberg S et al. Performance of two single-solution contact lens care systems. optician, 1996; 211(5533):37-42.
4 Soni PS, Horner DG, Ross J. Ocular responses to lens care systems in adolescent soft contact lens wearers. Optom Vis Sci 1996; 73(2):70-85.
5 Jones L, Jones D, Houlford M. Clinical comparison of three polyhexanide-preserved multipurpose solutions. Cont Lens Ant Eye, 1997;20:23-30.
6 Cho P, Lui T, Kee C. Soft contact lens care systems and corneal staining in Hong Kong-Chinese. Cont Lens Ant Eye, 1998;21:47-53.
7 Jones L, MacDougall N, Sorbara LG. Asymptomatic corneal staining associated with the use of balafilcon silicone hydrogel contact lenses disinfected with a biguanide-preserved care regimen. Optom Vis Sci, 2002; 79:753-761.
8 Pritchard N, Young G, Coleman S et al. Subjective and objective measures of corneal staining related to multipurpose care systems. Cont Lens Ant Eye, 2003;26:3-9.
9 Lebow KA, Schachet JL. Evaluation of corneal staining and patient preference with use of three multipurpose solutions and two brands of soft contact lenses. Eye Cont Lens, 2003; 29:213-220.
10 Lutzi D, Cedrone R, Evans D et al. Differences in corneal staining between two 'no-rub' multipurpose solutions. Review of Cont Lenses, 2004; Jan 28-31.
11 Amos C. A clinical comparison of two soft lens care systems used with silicone hydrogel contact lenses. optician, 2004; 227(5933):16-20.
12 www.siliconehydrogels.com.
13 Epstein AB. SPK with daily wear of silicone hydrogel lenses and MPS. Cont Lens Spectrum, 2002; 17(11)30.
14 Fonn D. Observations of corneal staining with MPS and silicone hydrogel lenses. Cont Lens Spectrum, 2002; 17(11)32.
15 Levy B. Contact lens solution manufacturer responds with data. Cont Lens Spectrum, 2002;17(11):34.
16 Kendig S. The effects of lens care products on the dehydration of hydrogel contact lenses measured by dynamic vapour sorption. Invest Ophthalmol Vis Sci, 2004;45:ARVO E-abstract 1545.
17 George M. MicroBlock: a new antimicrobial lens case. optician, 2003; 226: 5930: 18-20.
18 Tighe B. Silicone hydrogel materials Ð how do they work. In: Silicone Hydrogels: The Rebirth of Continuous Wear (Ed. Sweeney D). Butterworth-Heinemann, Oxford 2000.
19 Schwallie J, McKenney C, Long B and McNeil A. Corneal staining patterns in normal non-contact lens wearers. Optom Vis Sci, 1997; 74(2):92-98.
20 Dundas M, Walker A and Woods R. Clinical grading of corneal staining of non-contact lens wearers. Ophthal Physiol Opt, 2001; 21(1):30-35.

Chris Amos is project manager, lens care products, at Ciba Vision Corp, Duluth, Georgia, USA number of studies over the past 10 years have found differences in the prevalence of corneal staining response with different combinations of contact lens multipurpose solutions (MPS) and lens materials (Table 1).1-11 A majority of these reports refer to conventional hydrogels used in conjunction with MPS containing polyhexamethyl biguanide (PHMB).
With more than one in four silicone hydrogel lens users either removing the lenses daily or using them only occasionally overnight,12 corneal staining with these new materials and solution combinations continues to be relevant. With the PureVision lens, Jones et al 7 found 37 per cent of patients using the PHMB-preserved MPS ReNu MultiPlus had asymptomatic corneal staining, compared to 2 per cent with a polyquad-preserved OptiFree Express (Alcon).
Symptoms of lens awareness and discomfort with corneal staining have, however, been reported in patients switching to PureVision and ReNu MultiPlus, in some cases after two weeks' solution use.13 Fonn14 noted superficial circumferential staining with this combination which was