Visual recognition in contact lenses. Part 2 - Dryness signs and symptons

Bill Harvey and David Ruston describe clinical appearances that may be indicative of contact lens-related dryness which are important to assess and record either prior to fitting or in assessing the success of lens wear (C1630).

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Dry eye is a somewhat vague term that encompasses a wide range of clinical scenarios, ranging from a situation where tear coverage of the anterior ocular surface is insufficient to maintain adequate lubrication and therefore comfort and integrity, to an eye that appears absolutely normal yet feels dry when certain contact lenses are worn. This condition may be as a result of insufficient tear production, production of tears that are of an inappropriate consistency, excessive evaporation of the tears (possibly linked to an irregular surface or external or environmental evaporative influences) or inability for the tears to be maintained within the precorneal interpalpebral reservoir or for other as yet unknown reasons.

It is perhaps worth remembering that 'dryness' is the most commonly reported symptom among contact lens wearers,1 though this in itself does not always relate to a problem with the tear film. For example, where a lens surface is heavily deposited or scratched, this may result in uneven tear flow, but equally may result in a direct mechanical irritation which results in vasodilation and a symptom reported as dryness irrespective of the nature of the tear film present. Additionally, there may be absolutely no signs of any physical anomaly present, yet the patient reports dryness. For the contact lens practitioner, the ability to detect signs of tear imbalance prior to fitting is important if the appropriate lens material and wearing modality is to be selected. Once lens wear is established, it is equally important to recognise signs and symptoms of dryness which are either already causing or may develop into complications for a given wearer.

PRE-FITTING ASSESSMENT
As with any clinical assessment, a general history is important. There are many systemic diseases which have a strong association with tear abnormalities. Connective tissue disorders, particularly seropositive diseases such as rheumatoid arthritis, have a strong association with keratoconjunctivitis sicca.

The triad of dry eye, dry mouth and joint disorders (Sjgren's syndrome) may be present and needs to be established. Occasionally, a systemic disease may have a less direct influence upon the tear balance, for example acne rosacea (Figure 1). Patients with rosacea often present with blepharitis which may adversely affect the tear film. Adequacy of treatment, for example with systemic tetracyclines, must be established if any potential compromise is to be minimised.
Certain systemic drugs, such as systemic beta-blockers, anti-histamines and anti-depressants, may also have a deleterious effect upon the tear film.

TEAR FILM EVALUATION 
The six S's describes a useful mnemonic for remembering the six techniques that may be used to assess a patient's tear film.2 These S categories are as follows:

Symptoms
As already described, a full history and symptoms is essential and, because of the breadth of symptoms that might be initially described as 'dry', a more detailed questioning as to the exact nature and extent of the symptom is important. There are several questionnaires designed specifically for this purpose, such as the McMonnies Dry Eye Questionnaire (or DEQ),3 or one like that of Edwards reproduced in Efron.4

Chalmers and Begley (optician May 6 2005, 6000 vol 229, pp25-31) show that contact lens wearers typically have more frequent and more severe symptoms of dryness than non-wearers and that the onset of symptoms is most commonly late in the day. The lack of correlation between symptoms and signs of dryness makes the importance of good communication between practitioner and patient more important than ever.

Slit-lamp assessment
Direct observation of the tear film and related adnexa is able to usefully indicate signs that may interfere with an adequate tear film. The meniscus along the lower lid may be viewed for its regularity (Figure 2) and its height may be recorded. One suggested method involves the measurement of the tear prism height immediately below the pupil centre and at 5mm either side of this central point.5 This would indicate both an inadequate tear prism height (0.22mm is the peak expected height) and also irregularity of the height along the lid margin.

Much work has been done on the assessment of the tear film using polarised light with the Keeler Tearscope to observe interference fringes from irregular tear-film layers. Though this is now again available, it is not often found in general practice. However, observation with simple white light on a slit lamp occasionally reveals an 'oil on water' pattern which may indicate instability of the lipid layer of the tears (Figure 3).

Similarly, gross tear changes, such as excess debris, mucus strands or excessive greasiness (Figure 4) may also indicate the potential for future lens deposition or dryness symptoms. The speed by which fluorescein dissolves into the entire tear film is also a useful indicator or the state of normality of the tear film, where a rapid tear dilution time is more likely to be normal than a slow one. Useful indicators of lipid layer instability would also include evidence of meibomian gland blockage (Figure 5) or foamy tears (Figure 6), the latter a sign indicative of disrupted lipid layer.

Stability of the tear film
Fluorescein assessment is possibly the most commonly used technique for assessing the stability of the tear film. Instillation of fluorescein allows the tear film to be viewed under blue light immediately after blinking and the time taken for gaps in the fluorescing film to be recorded (Figure 7). This is best done using a yellow Wratten 42 filter, as in Figure 7. This tear break up time (BUT) is useful and easy to perform and certainly shows reduced time to break up in cases of unstable tear films. However, it is important to remember that the test is invasive, so the actual measurement is of the stability of the tears with fluorescein in them. Furthermore, the presence of the fluorescein itself may lead to some reactive tearing, so corrupting the observation. Generally, a break up time of 20 seconds is accepted as normal and significantly lower values (eg less than 10 seconds) must be assumed to be significant.

Attempts at overcoming the limitations of an invasive quality assessment have been made. They usually involve the assessment of the tear surface immediately post-blink by observation of a reflected pattern. This may be done simply by observing the quality of reflection of the keratometer mires, distortion of which indicates tear break up. Other more controlled projection targets include the HirCal Grid and the Loveridge Grid, both viewed in a dark field, or the light field observed grid producible with a Tearscope (Figure 8).

Surface evaluation of ocular structure
Even using white light, irregularities of the ocular surface may be noted as potential disruptors of tear film. Common conjunctival degenerations such as pinguecula (Figure 9), pterygia (Figure 10) or excessive scarring (Figure 11) may all contribute to tear problems. These will be typically seen as areas of fluorescein staining in the region affected by the lesion.

The lid margin, particularly in cases where blepharitis is present (Figure 12), needs careful assessment for irregularity. Chronic blepharitis often leads to irregular lid margins, as in Figure 13 where the red telangiectasis is also evidence of long-term lid mechanical irritation. This will interfere with the normal action of the lid during blinking.

Staining of the ocular surface is important. Typically this is done with fluorescein, though the ability of rose bengal to stain denatured tissue and mucus means it should still have a place in dry eye assessment (Figure 14 shows localised conjunctival epithelial denaturation). Yet to be established in general practice but useful in surface evaluation is the stain lissamine green. Fluorescein staining on the conjunctiva may reveal evidence of cell damage due to desiccation (as in Figure 15) but may also aid in the observation of lid-parallel conjunctival folds or LIPCOF as they are often described (Figure 16). The presence of LIPCOF or pleating of the conjunctiva has been shown to be a 'dependable diagnostic sign of dry eye'.6

Surfacing of the lids
The observation of the completeness and frequency of the blink is important. Incomplete closure of the lids, lagophthalmos, is quite common and may result in a characteristic exposure or smile stain as in Figure 17.

The rate of blink may be easily assessed, and a reduction may occur, for example in RGP lens wear. It must also be remembered that many factors, psychological as well as physical, may influence rate of blink. The rate may also be related to the BUT slow blink rate and rapid BUT may increase problems.

Secretion tests
Measurements of tear volume indicate tear secretion rates. Classically this was done with Schirmer strips (Figure 18).
The filter paper strips are inserted into the lower fornix and left for a period of time allowing absorption of tears. Failure of 5mm or more of the strip to be wetted is indicative of a poor tear volume. Most authors and practitioners are now critical of this test as it causes significant discomfort and may be more a measure of reactive tearing rather than normal volume. More recently, thread tests - such as the phenol red test (Figure 19) - have been used to again show absorption rates and, being much more comfortable, should be preferred to Schirmer.

AFTERCARE ASSESSMENT
As well as the investigation of symptoms reported by the patient, evidence of desiccation should always be looked for in wearers. A classic stain related to drying in a soft lens wearer is the Smile stain. This should be graded for severity according to a recognised grading system, such as that of Efron, and remedial action taken. Figure 20 shows such a stain graded as grade 1, and Figure 21 shows a more severe grade 2. Remedial action may include ceasing wear, especially with more severe grades, until epithelial recovery and then consideration of a material less likely to allow such desiccation, such as changing from a conventional hydrogel to a silicone hydrogel.

With RGP lenses, disruption of tear flow by inappropriate lens fit (typically a small low-riding lens) or poor surface quality leads to the familiar 3 and 9 o'clock stain (Figure 22). Such staining may occur with soft lenses too, particularly where the lens allows corneal exposure intermittently, as may be the case with a flat-fitting lens. In both cases, refit of the lens may help to alleviate the sign. The dryness may show up as localised vasodilation or redness on white light examination (Figure 23).

The quality of the lens surface is important as deposition or surface defects may hinder tear flow and integrity. Less of a problem with soft lenses, as most are regularly replaced, surface deposition is still a potentially significant problem with less often replaced RGP lenses. Figure 24 shows a poor RGP surface due to scratches and deposition. Figure 25 shows protein deposition which may result in poor wetting of the lens surface (Figures 26 for an RGP lens and 27 for a soft lens).

Calculi (now known to be primarily comprised of lipid) are much less seen now but represent a significant cause of tear-film disruption (Figures 28 and 29). More common, particularly with silicone hydrogels, are smeary lens surfaces and smaller punctate deposits that remain translucent. The use of a surfactant cleaner or at least a 'rub and rinse' step can be crucial to maximising patient comfort with these lenses.

It is worth noting that the fit of the RGP lens is a major factor in eliciting some staining, as with Figure 30 where a thick RGP edge has resulted in staining, There is also the possibility that what may appear to be a dry appearance (Figure 31) is actually due to solution toxicity and this needs to be identified.

A bilateral fairly symmetrical form of staining that tends to reduce as the day wears on is generally indicative of a solution-related toxicity stain in both RGP and soft lens wearers. Solution and lens interactions are certainly fairly common and make the role of the lens fitter more important than ever in maximising patient success and retention.

CONCLUSION
Dryness symptoms and indeed signs are still a major feature of contact lens practice. The alert practitioner will seek, by a combination of communication and careful slit lamp examination, to identify those patients who present with signs and symptoms prior to fitting and select appropriate lens materials and replacement schedules likely to maximise their success. As a general principle, the more frequently lenses are replaced, the lower the tendency of the lens to exacerbate existing signs and symptoms. Thus, daily and two-weekly replacement may be more successful than monthly or less frequent replacement.7 It is also appropriate to set patient expectations based on the pre-fitting assessment. When these are exceeded the patient is generally more satisfied than when no warning of potential difficulties was given.

Where the problem is identified at a routine aftercare, the practitioner will want to seek to minimise the impact on patient satisfaction, ocular health and long-term tolerance. Improvements can be made by altering lens material, with new and existing materials designed to reduce dryness signs and symptoms now available, reducing replacement frequency, incorporating better lens care systems and avoidance of certain preservatives, use of contact lens rewetting drops and modification of challenging environments such as air conditioning by increasing ambient humidity.

Success in contact lens practice is exemplified by an ability to combine effective communication skills with heightened observational abilities. Nowhere is this better illustrated than in dryness management.