Predicting and Testing for Ocular Disease

Predicting Cataract Risk

Cataract is the most common cause of blindness in the world and is expected to double in many developed countries in the next 20 years due to the aging of the population. McCarty et al. (p. 3720) report that information about attributable risk, the percentage of cataract that is due to a given risk factor, can be used for primary and secondary prevention of cataract. For example, successful smoking interventions have the potential to decrease by 17% the amount of nuclear cataract. Use of sunglasses and hats could potentially decrease the prevalence of cortical cataract by 10%. 

Predicting PRK Haze

Some photorefractive keratectomy (PRK) patients develop haze several months after surgery. At present, there is no presurgical predictor of the potential for haze formation. Csutak et al. (p. 3743) find that there is a normal pattern of plasminogen activator (PA) activity in tear film for patients who have a normal (no haze) outcome to PRK surgery. However, a different pattern manifests itself on the third postoperative day for those patients who develop haze several months later. Monitoring PA in tears three days after surgery might be used to predict which patients are vulnerable to future development of haze. 

Predicting Tear Volume

Meniscometry is a powerful method of evaluating tear volume over the ocular surface by measuring tear meniscus radius. Using video-meniscometry, Yokoi et al. (p. 3748) have studied the effect of the cotton thread and Schirmer tests on the radius of tear meniscus in severe dry eye patients with therapeutically occluded puncta. The wetting length of the Schirmer strip was found to significantly correlate with the change in tear meniscus radius. However, such correlation was not found for the cotton thread, suggesting that the cotton thread test does not accurately indicate tear volume. 

Predicting Amblyopia

Although observations in both human infants and laboratory animals have suggested that depth of amblyopia is influenced by the degree of retinal image degradation, establishing this relationship has proven difficult due to temporal variations in the amount of image degradation in previous studies. Smith et al. (p. 3775) reared infant monkeys with diffuser lenses that produced varied amounts of image degradation and demonstrated a corresponding variation in severity of the resulting spatial vision deficits. This study establishes that the degree of retinal image degradation experienced during infancy is an important factor, in addition to the age of onset and the duration of anomalous vision, influencing the depth of amblyopia that develops. 

Assessing PCO

Posterior capsule opacification (PCO) is the most common complication of cataract surgery with ophthalmic, social, and economic consequences, and is a major bar to intraocular lens implantation in underdeveloped countries where the facilities for laser capsulotomy are not available. Preventative strategies are being developed and the problem remains of how to assess their benefit. Nd:YAG capsulotomy rates are subjective and reflect such factors as when the patient asks for treatment, when the surgeon offers it, financial considerations, and equipment availability. Retroillumination images demonstrate PCO and lend themselves to image analysis, but low contrast changes cannot be satisfactorily quantified by intensity segmentation. Barman et al. (p. 3882) describe an image analysis technique based on texture segmentation which is the relationship, rather than absolute values of intensity, between groups of pixels that overcome these problems. 

Visual Assessment in Retinal Dystrophies

The aim of the work by Hetherington et al. (p. 3979) was to use a number of easily-administered visual functional tests on rodents. As such, any researchers could use these tests to establish the efficacy of transplantation or other potential therapeutic approaches which they may wish to use. A battery of simple neurological tests revealed visual deficits in dystrophic animals, but no auditory problems. A similar visual impairment of photophobia was also observed in dystrophic animals. Visual acuity tests are much more difficult to behaviorally assess in dystrophic animals as a result of the ongoing degeneration at the time of testing. 

Assessing Optic Neuritis

Optic neuritis (ON) is often an early manifestation of multiple sclerosis. With the advent of experimental drugs designed to impede the course of multiple sclerosis, it is increasingly important to follow changes in visual function following acute episodes of ON. Hood et al. (p. 4032) show that the multifocal visual evoked potential (mVEP) can be used to track local optic nerve damage after unilateral ON. This technique should prove useful in the studying the local effects of drug therapies. 

Testing for Macular Edema

By measuring the directional sensitivity and visual pigment density of centrally located photoreceptors, Lardenoye et al. (p. 4048) were able to identify the eyes with retinal damage due to cystoid macular edema before the loss of visual acuity has occurred. These techniques could be important tools for distiction of patients at risk of visual loss due to macular edema and need for treatment.