Impact of Presbyopia and Its Correction in Low- and Middle-Income Countries.

Presbyopia affects more than 1 billion people worldwide, and the number is growing rapidly due to the aging global population. Uncorrected presbyopia is the world's leading cause of vision impairment, and as with other causes. The burden falls unfairly on low- and middle-income countries (LMICs), in which rates of presbyopic correction are as low as 10%. The importance of presbyopia as a cause of vision impairment is further underscored by the fact that it strikes at the heart of the productive working years, although it can be safely and effectively treated with a pair of inexpensive glasses. To galvanize action for programs to address uncorrected presbyopia in the workplace and beyond LMICs, it is crucial to build a solid evidence base detailing the impact of presbyopia and its correction in important areas such as work productivity, activities of daily living, visual function, and quality of life. The aim of this review was to provide an up-to-date reference for program planners and policymakers seeking to build support for programs of presbyopia correction, particularly in low-resource settings.

Reproducibility of sphero-cylindrical prescriptions.

PURPOSE: To investigate the reproducibility of the sphero-cylindrical prescriptions provided by 40 optometrists. METHODS: Forty registered optometrists were randomly selected from the cities of Oxford and Westminster in the UK to perform a sphero-cylindrical refraction on an asymptomatic 29-year-old male subject. The 95% limits of reproducibility for each component of refraction were assessed and are presented together with scatterplots, distribution ellipsoids and polar profiles of dioptric power. RESULTS: The mean stigmatic (spherical equivalent) refraction for the right eye was -0.83 D (S.D. = 0.28 D) with 95% limits of agreement -1.38 and -0.28 D. The 95% reproducibility limits for stigmatic data [1.96(square root of 2) (S.D.)] was 0.78 D. The average inter-ocular difference in the stigmatic components of refraction was -0.044 D (S.D. = 0.20 D) but estimates ranged from -0.50 to +0.50 D. Mean ortho- and oblique antistigmatic refractions were -0.23 D (S.D. = 0.084 D) and -0.14 D (S.D. = 0.086 D) respectively. CONCLUSIONS: The findings of this paper suggest that refractions performed by multiple optometrists on a single eye will differ in their stigmatic component by over 0.78 D on average not more than once in 20 refractions. The reproducibility of refractions reported here, approximately twice as variable as those reported under repeatability conditions, has profound implications for the analysis of refractive data collected by multiple optometrists over the course of replication, longitudinal and epidemiological studies.

Compensation of aniseikonia in astigmatic pseudophakic eyes.

PURPOSE: A recently published manuscript addressed the problem of compensating for aniseikonia between pseudophakic astigmatic eyes using a least-squares calculation scheme. The purpose of this paper is to revisit this topic with the specific aim of providing explicit formulae for the determination of the intra-ocular lens required to produce a specified transverse image size at the plane of the retina and the characteristics of the contact or spectacle lens required to realize some desired refractive outcome. METHODS: The 4 x 4 ray transference is central to the development of all formulae presented in this paper. Specifically, the formula for the determination of the power of the intra-ocular lens required to achieve some transverse image size at the retina is derived directly from the disjugacy of the pseudophakic eye. RESULTS: The formula is applicable to both stigmatic and astigmatic systems without restriction. A detailed numerical example for an unusual eye is provided. CONCLUSION: A formula for the determination of the intra-ocular lens required to produce any given transverse image size at the retina is derived. This approach does not require the application of the Moore-Penrose pseudo-inverse and one is able to work rather with the properties of the optical system directly without further modification.