Assessment of Vision Behind Cataracts

Ophrhal. Physiof. Opt. Vol. 16, Suppl. 2, pp. S26-S32, 1996 Copyright Q 1996 The College of Optometrists. Published by Elsevier Science Ltd Printed in Great Britain 0275-.5408/96 $15.00 +O.OO Assessment of vision behind cataracts Paul V. McGraw*, Brendan T. Barrett* and David Whitaker” Department of Optometry, University of Bradford, Richmond Road, Bradford BD7 1 DP, West Yorkshire, UK Introduction therapy is implemented to treat estab- ophthalmoscopic view of the fundus. lished retinal/neural disease. If the Clinical assessmentof the effect of Causes of reduced visual function can cataract is the limiting factor determin- lenticular opacification on vision is be grouped into three broad categories, ing visual function between visits, highly subjective and unreliable. In pre-retinal (i.e. optical), retinal/neural, then progression of retinal/neural addition, the presence of identifiable and a combination of the two. It is disease may go unnoticed, giving the retinal pathology does not preclude now widely accepted that one of the ophthalmologist a misplaced confidence improvement in visual acuity following penalties of longevity is the eventual in the treatment regime. Conversely, cataract surgery. Over the past three development of cataracts, which scatter any progression in the density of the decades, the problem of assessing light and reduce visual performance. cataract between visits may erroneously retinal/neural function in the presence To date, the generally accepted form lead the clinician to conclude that of ocular media opacities has attracted of treatment is the surgical removal of therapy directed at the retinal/neural considerable attention. The large the cataractous lens and compensation disease is ineffective. number of techniques which have for its refractive power by either Cataract extraction and insertion of been developed and the voluminous spectacles, contact lenses or, more an intra-ocular lens has become an body of literature in this field are commonly, by insertion of an intra- extremely successful procedure, with indicative of the difficulty posed by ocular implant lens. There are a number approximately 90% of patients achiev- this problem. of clinical investigative techniques ing a post-operative acuity of 6112 or To assessthe functional capability employed by practitioners to detect better (Cataract Manage-ment Guide- of the macula in the presenceof media and evaluate lenticular opacification. line Panel, 1993). When cataract opacities, a test must be employed Similarly, retinal/neural disease, in surgery is completed without significant which has one or more of the follow- isolation, is readily identified using a complications, the success of the ing features: does not require the number of established investigative surgery depends upon two main factors: ocular systemto produce a high quality techniques. Considerable problems the degree of optical degradation image; projects an image through the exist, however, when optical and produced by the cataract, and the opacity; or bypassesthe optical system retinal/neural defects co-exist, since functional capabilities of the retina and of the eye. This review will be divided the clinician is faced with the arduous its neural system. Presumably cataract into three broad categories. The first task of attempting to quantify the surgery, a group of procedures with section will contain basic clinical tests. relative contribution of each factor to significant risks, would not be employ- These rudimentary techniquesprovide the observed loss in vision. This ed if the degree of optical degradation qualitative rather than quantitative in- problem is confounded since the like- is extremely small or if retinal function formation. The second category des- lihood of cataract and retinal/neural is severely impaired, since the surgery cribes techniques which require addi- disease co-existing increases rapidly will be of little benefit. The most tional dedicated instrumentation and with age (Courtney, 1992). common cause of ‘unsuccessful’ sur- are most commonly used by ophthal- A related problem is faced by the gery remains underlying retinal/neural mologists. The final category describes ophthalmologist when patients present disease. However, assessment of two relatively new approachesto the with dense media opacification and retinal integrity in the presence of problem. While these are essentially dense opacification is often problematic still research methods, both have *MCOptom due to the absence of an adequate recently made important inroads into S26 Assessment of vision behind cataracts: P. V. McGraw et al. S27 the clinical domain. For a more grid; the latter group comprised more detailed treatment of this area the than a quarter of the patients in the interested reader should consult a study conducted by Bernth-Petersen comprehensive review by Hurst and (1981). Douthwaite (1993). Tests using entoptic imagery Basic clinical tests Entoptic images arise from optical The earliest attempts to investigate phenomenawithin the eye. Most types retinal/neural function behind ocular occur when the retina is stimulated media opacities include Maddox-rod with light in someunusual way. These orientation discrimination, colour dis- imagesare sufficiently novel that their crimination, two-point light discrimi- description by a naive patient is per- nation, the light-projection test and suasive evidence that a significant Figure 1. Purkinje vascular shadow. Comberg’s inter-ocular brightness test level of macular function exists (Brodie, (Comberg, 1938). For a review of 1987). However, the perception of may be produced by illuminating the these methods see Fuller and Hutton many entoptic phenomena does not globe either trans-sclerally (Brodie, (1982). While quick and simple to depend on fovea1 function alone 1987), or through closed eyelids with perform, these techniques are of (Guyton, 1987). Hence, description the patient looking up (Fuller and limited predictive value. However, of the image by a patient with ocular Hutton, 1982). The image arises from they do remain useful in locations media opacities cannot be taken as a the suddenillumination by the oblique where more modern methods are un- guarantee of normal fovea1 function. light source of photoreceptors which available (Minkowski, 1983). Equally, the inability of a cataract are normally in the shadow of the patient to describe an entoptic pheno- retinal vessels. To prevent image menon does not necessarily imply a fading, the light source must be con- Trans-illuminated amsler grid poor post-surgical visual prognosis; tinuously moved. This results in a This is a modified version of the there may simply be poor communi- constant shifting of the position of the standard Amsler test, first described cation between clinician and patient, vascular shadowson the retina. Astute by Miller, Lanberts and Perry (1978). or even an inability of the patient to observers will identify not only the The trans-illuminated grid is identical articulate such a novel sensation shadowsof the retinal vasculature, but in size to the standard Amsler test, but (Brodie, 1987). also the avascular fovea1 area and the has 1 mm holes located at the inter- The diagnostic value of entoptic optic disc area. section of the horizontal and vertical imagery may be improved if the test is The advantagesof using this test to grid lines. The grid is mounted on a first administered to the cataractous evaluate retinal/neural function behind light box containing two 15watt neon eye, and subsequently to the normal media opacities include the ease and tubes, and contains a 4mm fixation fellow eye. If the entoptic images are speed with which the test may be hole at its centre. Patients with media perceived in the fellow eye, but not in carried out. Other advantages are opacities, who often cannot see the the cataractous eye, the visual prog- that this test may prove useful in lines on the standard Amsler grid, can nosis is less favourable. patients with dense cataracts, and the be consideredas having normal macular There are many types of entoptic general reliability of a positive test function if all the lines joining the phenomena. These include Maxwell’s result when the image is reported retro-illuminated holes are perceived spot, Haidinger brushes, the Purkinje without the need for prompting from as being straight; metamorphopsiasor vascular shadow and the blue-field the clinician (Minkowski, 1983). How- scotomas are suggestive of abnormal entoptic phenomenon (also known as ever, 20% of patients with normal macular function. The predictive ability the Flying Corpuscle Phenomenon). posterior segments and 616 acuity of this technique has been investigated Purkinje vascular shadow and blue- cannot seethe Purkinje entoptic pheno- by Bernth-Petersen (198 1) who found field entoptic phenomenaare the most menon, even after leading remarks that the technique correctly identified suitable for investigating retinal/neural from the examiner (Goldmann, 1972). reduced retinal/neural function in function behind ocular media opacities The possibility of leading or confusing more than two-thirds of patients with (Brodie, 1987). the patient is not the only disadvantage cataract and co-existent macular The Purkinje tree is an image of the of this test. Since the macroscopically pathology. However, a significant retinal vasculature seen in fluctuating visible vesselsdo not closely approach disadvantage of the test is the high positive and negative contrast, and the fovea, the Purkinje

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