Dr Frank Eperjesi reports from one of the major events on the optometric calendar, held by the American Academy of Optometry, in Tampa, Florida, last month
The American Academy of Optometry met last month in Tampa, Florida for a four-day conference entitled 'Today's research, tomorrow's practice - Technology's impact on standards of care'. Speakers revealed numerous interesting research findings on topics such as glaucoma, including new thoughts on visual field analysis, the HRT II and tonometry. The programme also included useful presentations on near vision disorders and reading rehabilitation, refining refraction techniques and contact lenses.
DETECTION AND TREATMENT OF GLAUCOMA AND TONOMETRY
A group of researchers from Albuquerque investigated whether central corneal thickness (CCT) could be used to predict the severity of glaucoma.
It is known that CCT can be used to predict the development of POAG, but little is known about the predictive value of CCT for glaucoma severity.
They found that CCT was higher in glaucoma subjects without field loss than in those with field loss, but that there was no statistical difference in CCT between subjects with mild, moderate and advanced visual field loss. Therefore, CCT was useful in predicting the presence of field loss but not in predicting the severity of this loss.
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| Interesting new research findings on glaucoma and visual field analysis were aired in Tampa |
Frequency doubling technology (FDT) has been around for several years now and many UK practitioners use this technique for visual field analysis, so it is interesting to see data on how reproducible FDT results are when compared to standard (white-on-white) automated perimetry.
The researchers defined an abnormal FDT visual field loss as two or more locations depressed to the 5 per cent level on the pattern deviation plot. They found that only half the visual field defects detected at the first visit were detected again at the second visit one year later, but that this was still better than for standard perimetry.
Another group was interested in determining if FDT screening of large populations can be reserved for high risk patients based on age, race and family history of glaucoma. They reported that the increased sensitivity of performing FDT perimetry on all persons in a mass screening of a low-risk population may not be justified by the loss of specificity and recommended that the FDT is best used on high risk patients who seem to have normal discs and intraocular pressure.
Another piece of technology that is slowly starting to appear in optometric practice is the HRT II. A group from New York reported on a study in which they attempted to find out why the HRT sometimes failed to identify patients with glaucoma. They defined a failure as a normal HRT result in a subject with POAG visual field loss.
The HRT makes use of a reference plane in its scanning paradigm, which is set 50 microns beneath the papillo-macular bundle. If this is thinned, or is sitting at the base of a staphyloma or deep crescent, the reference plane will be placed much deeper into the retina.
Although there is no doubt that the HRT is a useful tool, some myopic subjects with deep temporal crescents demonstrated less cupping with the HRT than with ophthalmoscopy and were often misclassified, as were subjects with central visual field loss, disc drusen, angle-closure glaucoma and pigmentary glaucoma.
Interestingly, investigators from Bradford reported that intraocular pressure (IOP) is not directly related to corneal thickness (central and peripheral), nor is optic nerve head diameter related to corneal thickness and that this lack of a relationship held for all ages and both genders.
On the subject of intraocular pressure, workers from Boston compared the results of the Proview pressure phosphene tonometer (this takes the ocular pressure reading through the closed eye and does not require anaesthetic) with the Goldmann applanation tonometer. They found that there was a close agreement between the results from the two tests and suggested that the Proview offered a practical and cost-effective alternative for IOP measurement.
Another relatively new tonometer is the Pascal dynamic contour tonometer (DCT). The DCT has already been proven to accurately reflect true IOP readings as measured by manometry. One study reported that for post-Lasik patients with a corneal thickness of more than 520 microns it was more accurate than Goldmann tonometry
A research group headed by a researcher from Pennsylvania College of Optometry investigated the effects of topical hypotensive medication in delaying or preventing the onset of POAG among African-American participants with ocular hypertension.
This study was part of the ground-breaking and much larger Ocular Hypertensive Treatment Study and proved that starting patients, who had these two risk factors for POAG, on topical hypotensive medication is effective in preventing or delaying the onset of POAG.
NEAR VISION DYSFUNCTION AND READING REHABILITATION
There is very little published data on the most effective treatment for convergence insufficiency (CI), so it was good to see a report on the findings from a clinical trial designed to compare the effectiveness of base-in prism and placebo reading glasses for treatment of symptomatic CI.
Rather surprisingly, base-in prism reading glasses (based on Sheard's criterion) were found to be no more effective than the placebo glasses.
These results were supported by those from another study in which lateral phorias were compensated using prisms for a group of poor readers. No statistical or clinical difference was found in reading speed when the phorias were compensated for.
Along similar lines, a group from Illinois College of Optometry studied the effects of vision therapy on eye movements for reading underachievers. After vision therapy, all subjects had improved fixations, reduced regressions, a higher reading rate, improved average duration of fixation, saccadic accuracy and reading grade level.
REFINEMENT OF REFRACTION TECHNIQUES
The results from an interesting study investigating the effect of ambient luminance on refraction results were presented by a group from London.
They reported that there were significant differences in refraction at low luminance in 20 per cent of their subjects, compared to normal luminance testing, and went on to recommend that patients reporting difficulties at low luminance (for example, driving at night) should be refracted under such conditions.
Researchers from Manchester reported on a study designed to determine the incidence on non-severe keratitis and severe keratitis among contact lens wearers and used a clinical severity matrix (based on severity of presenting symptoms and signs) to differentiate between the two.
They found that those patients who choose to sleep in contact lenses should be advised to wear silicone hydrogel lenses, as they carry a five times lower risk of severe keratitis compared with hydrogel lenses.
In another study, the same group found that males and smokers carried an increased risk for experiencing 'corneal infiltrative events' in general contact lens wear. Meanwhile, a group based in Canada found that refitting existing low Dk soft daily lens wearers with high Dk silicone hydrogels resulted in a decrease in hyperaemia and improvements in symptoms of dryness and discomfort.
The same group reported that rewetting drops containing surfactants were likely to be beneficial for patients using continuous wear silicone hydrogel lenses, in terms of greater subject satisfaction, reduced protein deposition and reduced denatured lysosome compared to a saline drop.