Vision and Refraction Eugene M. Helveston MD (2010) by Orbit International PDF

Description

The World Health Organization estimates that 333 million people are blind or visually impaired. Nearly half of these, 154 million are suffering from uncorrected refractive error, with more than 13 million of them children. Individuals so affected are handicapped in a variety of ways from being deprived of educational opportunities to being limited in the workplace and even being burdens to their families. The economic impact both personally and in terms of society at large is huge. In contrast to how “blindness” is usually defined, the vision reduction from uncorrected refractive errors must be considered in a different light. It differs from other physical inborn or acquired blinding conditions for two important reasons: 1) in instances of vision loss from uncorrected refractive error, vision can in most cases be corrected to normal with proper optical correction provided with glasses or contact lenses, and 2) eyes are normal except for the improper focus. The most commonly affected person, the myope or nearsighted individual, can usually see well even without correction if objects are held closer to the eye at what is called the far point. Vision reduction from uncorrected hyperopia (especially if it is high) and astigmatism can cause reduction in vision at all distances and in certain circumstances can lead to permanent vision loss from amblyopia. In rare cases, prolonged uncorrected high hyperopia (farsightedness) early in life can cause permanent reduction in vision from bilateral amblyopia. More commonly, unequal refractive errors, if uncorrected, can cause permanent loss of vision in one eye, anisometropic amblyopia, affecting the eye with the higher refractive error. Acquired refractive errors occur with aging as an involutional change called presbyopia. This affects another 150 million people. Presbyopia causes individuals in the mid to late fifth decade to experience difficulty seeing at near because of decreased focusing power of the eye. This can be remedied by use of reading glasses. Some people with a low to moderate degree of farsightedness (hyperopia) are able to see clearly in younger years because they can accommodate, but have difficulty seeing at both distance and near at age 40 and beyond because of the loss of accommodation occurring with presbyopia. Another important cause for acquired loss of vision from uncorrected refractive error has been failure to provide adequate optical correction after surgical removal of a senile cataract, or by loss of glasses something which has been said to occur in nearly 75% of cases in the first year after cataract surgery. However with the advent of properly selected intraocular lenses placed at the time of cataract surgery, this type of vision loss is occurring less often. The reduction in quality of life caused by uncorrected refractive error cannot be calculated with accuracy, but it is significant and deserves attention to the following details that will be discussed in the pages that follow. v Understanding how we see and how uncorrected refractive error affects vision v Identifying those at risk for vision reduction from uncorrected refractive error v The technique and methods for measuring refractive error (refraction) v The importance of prescribing and dispensing suitable glasses, and following up for the individual’s ongoing needs

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