ABSTRACT

A. INTRODUCTION Presbyopia, or age-related loss of accommodation, becomes noticeable between 40 and 45 years (1). It is one of the first signs of aging and results from the age-related decline in the amplitude of accommodation. Some feel that presbyopia becomes apparent when the near point is greater than 22 cm (2). Since the middle 1800s, Helmholtz’s theory of accommodation (3) and its modifications (4-8) have attributed accommodation to a decrease in zonular tension and presbyopia to lens sclerosis and/or ciliary muscle atrophy. A recent theory proposed by Ronald Schachar (9-16), however, states that during accommodation the lens equatorial zonules are under increased rather than decreased tension, as postulated by Helmholtz (Fig. 1). Furthermore, Schachar attributes presbyopia to a continuous age-related increase in the equatorial diameter of the lens, with a subsequent decrease in the effective working distance of the ciliary muscle. As a direct deduction from his theory, Schachar proposed scleral expansion for the treatment of presbyopia (16). The goal of this paper is to describe the technique of scleral expansion. The descriptions of the theories of accommodation and presbyopia are presented in Chapter 4, on Schachar’s theory of the mechanisms of accommodation.