Virtual Issue Editorial: Presbyopia – grappling with an age‐old problem

Millodot, in his “Dictionary of Optometry and Visual Science” defines presbyopia as “A refractive condition in which the accommodative ability of the eye is insufficient for near vision work, due to ageing”. While the onset of presbyopia for any individual is influenced by factors such as arm-length and the nature of their near visual tasks, it typically occurs when the subjective amplitude of accommodation is 3-4 D, at an age in the mid-forties in temperate countries. However, as was first systematically charted by Donders, the amplitude of accommodation starts to decline well before adulthood is reached. Thus presbyopia is only the last phase of a slow progressive loss in accommodative efficiency, which began long before. This decline, which in its later stages appears to be approximately linear with age for the individual, continues beyond the onset of presbyopia, so that by the mid-fifties most people have almost no ability to change the power of their eyes, although they still possess a small residual subjective amplitude of accommodation due to depth-of-focus effects. With life expectancies over much of the developed world approaching 80 years, most phakic individuals are likely to spend almost half their life as presbyopes and more than a quarter of it with virtually no active accommodation at all. Hence there is a huge demand for spectacle, contact lens, surgical and other strategies to enable the presbyope to see clearly over a range of distances, and much of the work of optometrists is directed towards meeting this need. In the less-developed world, uncorrected presbyopia remains a major cause of visual disability. What would we ideally like achieve in relation to the “correction” of presbyopia? Although the invention of spectacles in the 13 century introduced a brilliant and highly successful form of correction, few would deny that spectacles and other current methods of presbyopic correction have real limitations in terms of the visual performance achieved, ease of use and, for some patients, appearance. Further development is therefore required to minimise these problems. Beyond this, a more ambitious goal would be that the “ideal” correction should, if applied at the natural onset of presbyopia, be capable of restoring to pre-presbyopic levels the dioptric range within which accurate focus can be smoothly and rapidly achieved. It should also be able to maintain this range throughout the remaining decades of the life of the individual, without any further intervention, with the eye always being emmetropic at the lower end of the range. Schor suggests that a minimum target for the achievable subjective amplitude of accommodation should be 5.00 D. These focus changes should occur “naturally” and be appropriate to the convergence movements of the eyes, which probably implies that at least some of the components of the natural accommodation system must be utilised, if these are still functional, as is the case for, e.g., the ciliary muscle. Lastly the presence of the correction should be invisible to the outside observer. Evidently at present no method of correction approaches this goal, although designers of “accommodating” intraocular lenses have attempted to achieve it, on the assumption that increasing lenticular rigidity is the main cause of presbyopia. Their efforts have so far failed to lead to convincing success but it may be that in future a method based on the regeneration of the crystalline lens, using endogenous stem cells, offers greater potential. A helpful supplementary strategy would, in principle, be delay the onset of presbyopia by reducing the rate of decline in the natural amplitude of accommodation with age, perhaps by ocular exercises, diet, drugs or other means: as yet there is little evidence that this is possible. To understand the origins of presbyopia, and perhaps to develop more radical methods for its correction, we need to understand the structure and action of the accommodation system, and their changes with age. The possible importance to accommodation of changes in the shape of the crystalline lens was recognised in the 17 C by Kepler and Descartes. In the same century, Scheiner clearly demonstrated with his double-pinhole experiment that an active change in the optics of the eye must be involved. Subsequent studies in succeeding centuries revealed the importance of other ocular structures in relation to the lenticular changes. Nevertheless, Duke-Elder and Abrams in 1970 could still write “There are few subjects upon which so many diverse opinions have been entertained as the