High AC/A Ratio Esotropia: Do We Really Need to Be Using Bifocals?

INTRODUCTION AND PURPOSE

Most strabismus specialists use bifocals for patients with convergence excess esotropia whose distance deviation is small. While this is a popular treatment modality, there is actually no good data to indicate that this should be considered a standard of care.

PATIENTS AND METHODS

In patients for whom the distance deviation is small enough to allow for the development of binocular vision, my preference is to simply observe these patients. Most will improve with time. For those who do not, or who decompensate, surgery may be indicated.

RESULTS

A careful review of the literature shows a lack of evidence to suggest that bifocals provide an effective treatment for this problem. Some data and theoretical concern may raise a concern over their use. Time and observation may be all that is necessary. There may be a role for surgical correction in these patients as well.

CONCLUSION

While there are theoretical advantages to the use of bifocals in patients with convergence excess esotropia, current data does not support the actual need for active treatment of these patients.

Mathematical Models of College Myopia

Experimental design phase of a pilot study at Annapolis is described, using reading glasses, +1.5 D. to +3.0 D. to alleviate college myopia. College students often become 1.0 to 2.0 diopters more myopic, so reading glasses were explored to partially cancel the effects of the study environment. N = 25 different sets of (+)Add lenses are evaluated, for required adjustment period and reading comfort. Three computer models are developed to predict refraction versus time. Basic control system equations predict exponential myopia shift of refractive state R(t) with time constant t0 = 100 days. Linear, exponential and Gompertz computer results are compared calculating refraction R(t) during the college years, showing correlation coefficients |r| = 0.96 to 0.97, accurate +/-0.31 D. over a 14 year interval. Typical college myopia rate is -0.3 to -0.4 D/yr. Reading glasses may be a simple, practical solution to stabilize college myopia.

Optical treatment strategies to slow myopia progression: effects of the visual extent of the optical treatment zone

In order to develop effective optical treatment strategies for myopia, it is important to understand how visual experience influences refractive development. Beginning with the discovery of the phenomenon of form deprivation myopia, research involving many animal species has demonstrated that refractive development is regulated by visual feedback. In particular, animal studies have shown that optically imposed myopic defocus slows axial elongation, that the effects of vision are dominated by local retinal mechanisms, and that peripheral vision can dominate central refractive development. In this review, the results obtained from clinical trials of traditional optical treatment strategies employed in efforts to slow myopia progression in children are interpreted in light of the results from animal studies and are compared to the emerging results from preliminary clinical studies of optical treatment strategies that manipulate the effective focus of the peripheral retina. Overall, the results suggest that imposed myopic defocus can slow myopia progression in children and that the effectiveness of an optical treatment strategy in reducing myopia progression is influenced by the extent of the visual field that is manipulated.

Optical control of myopia has come of age: or has it?

This article presents a clinical perspective on recent myopia research related to the development and testing of optical treatments for controlling myopia progression. The perspective is from that of a clinician in private practice and a clinician researcher, both with long-term involvement in myopia management and research.

Myopia: attempts to arrest progression

Previous studies have evaluated the efficacy of several interventions to decrease the progression of myopia. These include devices that alter the perception of the visual environment and pharmacological treatments. There is no conclusive evidence thus far that alteration of the pattern of spectacle wear, bifocals, ocular hypotensives, or contact lenses retards the progression of myopia. Several randomised clinical trials have demonstrated that the rate of progression of myopia is lower in children given atropine eye drops than those given placebo. However, atropine is associated with short term side effects such as photophobia and possible long term adverse events including light induced retinal damage and cataract formation. Other more selective antimuscarinic agents such as pirenzipine are presently being evaluated. Further well conducted randomised clinical trials with large sample sizes and adequate follow up designed to evaluate treatments to retard the progression of myopia should be conducted, since the identification of an effective intervention may have a greater public health impact on the burden and morbidity from myopia than the few treatments currently available.