Presbyopia: Effectiveness of correction strategies

Abstract

Presbyopia is a global problem affecting over a billion people worldwide. The prevalence of unmanaged presbyopia is as high as 50% of those over 50 years of age in developing world populations, due to a lack of awareness and accessibility to affordable treatment, and is even as high as 34% in developed countries. Definitions of presbyopia are inconsistent and varied, so we propose a redefinition that states "presbyopia occurs when the physiologically normal age-related reduction in the eye's focusing range reaches a point, when optimally corrected for distance vision, that the clarity of vision at near is insufficient to satisfy an individual's requirements". Strategies for correcting presbyopia include separate optical devices located in front of the visual system (reading glasses) or a change in the direction of gaze to view through optical zones of different optical powers (bifocal, trifocal or progressive addition spectacle lenses), monovision (with contact lenses, intraocular lenses, laser refractive surgery and corneal collagen shrinkage), simultaneous images (with contact lenses, intraocular lenses and corneal inlays), pinhole depth of focus expansion (with intraocular lenses, corneal inlays and pharmaceuticals), crystalline lens softening (with lasers or pharmaceuticals) or restored dynamics (with 'accommodating' intraocular lenses, scleral expansion techniques and ciliary muscle electrostimulation); these strategies may be applied differently to the two eyes to optimise the range of clear focus for an individual's task requirements and minimise adverse visual effects. However, none fully overcome presbyopia in all patients. While the restoration of natural accommodation or an equivalent remains elusive, guidance is given on presbyopic correction evaluation techniques.

Correction of presbyopia: old problems with old (and new) solutions

“…Radially symmetric or concentric design multifocal lenses are most common, but early multifocal contact lenses employed a segmented geometry inherited from spectacle lenses, as did the earliest bifocal IOL (a variant of which is still produced) . Segmented bifocal contact lenses, however, suffered from rotational instabilities, and are now typically only implemented as gas‐permeable lens designs utilised for a select patient group . Optical modelling reveals, however, that meridionally segmented optical designs may offer superior optical performance …”

“…Similar to some fish, 15 optical corrections in which optical power varies with spatial location across the pupil have been implemented in modern multifocal IOLs [84][85][86] and contact lenses. [87][88][89][90] Radially symmetric or concentric design multifocal lenses are most common, 20 but early multifocal contact lenses employed a segmented geometry inherited from spectacle lenses, [91][92][93] as did the earliest bifocal IOL (a variant of which is still produced). 94 Segmented bifocal contact lenses, however, suffered from rotational instabilities, 92 and are now typically only implemented as gas-permeable lens designs utilised for a select patient group.…”

“…94 Segmented bifocal contact lenses, however, suffered from rotational instabilities, 92 and are now typically only implemented as gas-permeable lens designs utilised for a select patient group. 20 Optical modelling reveals, however, that meridionally segmented optical designs may offer superior optical performance. 95,96 The core principle of a concentric multifocal design is that it will be rotationally insensitive and include two or more powers contained in geometrically separate zones located at different distances from the lens centre 97 (Figure 3).…”

“…Variants of these less common strategies are now being utilised by older humans who have lost the ability to adjust power of their lenses (presbyopes and pseudphakes 17,18 ), a senescent trait also observed in non-human primates and other mammals. 18,19 This paper builds upon recent comprehensive reviews 20,21 to examine the optical implications of current and potential strategies to focus the retinal image despite the loss of accommodative ability.…”

Monovision and the Misperception of Motion

“…far lens in left eye). The current standard is to place the far lens in the dominant eye 10,48 , but this does not appear to increase patient acceptance rate, patient satisfaction 48,49 , or quantitative measures of visual performance 6,50 . Although the scenarios just discussed are not the only scenarios that ought be considered, they may invite reexamination of standard optometric practice.…”