Assessment of vision behind cataracts.

Causes of reduced visual function can be grouped into three broad categories, pre-retinal (i.e. optical), retinal/neural, and a combination of the two. It is now widely accepted that one of the penalties of longevity is the eventual development of cataracts, which scatter light and reduce visual performance. To date, the generally accepted form of treatment is the surgical removal of the cataractous lens and compensation for its refractive power by either spectacles, contact lenses or, more commonly, by insertion of an intraocular implant lens. There are a number of clinical investigative techniques employed by practitioners to detect and evaluate lenticular opacification. Similarly, retinal/neural disease, in isolation, is readily identified using a number of established investigative techniques. Considerable problems exist, however, when optical and retinal/neural defects co-exist, since the clinician is faced with the arduous task of attempting to quantify the relative contribution of each factor to the observed loss in vision. This problem is confounded since the likelihood of cataract and retinal/neural disease co-existing increases rapidly with age (Courtney, 1992). A related problem is faced by the ophthalmologist when patients present with dense media opacification and