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First Author: I.Van der Meulen THE NETHERLANDS
Co Author(s): R. Lapid-Gortzak C. Nieuwendaal T. van den Berg
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Patients with posterior polar cataracts may experience a decrease in visual quality, despite normal to excellent visual acuity. Frequent complaints are haloes, increased glare hindrance or difficulties with driving in the dark. As cataract surgery in these types of cataracts has a higher chance of intra-operative rupture of the posterior capsule, the need may be felt for increased support of an interventional decision in case of good visual acuity. Straylight denotes the visual effect of intraocular forward scattered light projected unto the patients retina, diminishing the contrast of the retinal image. Straylight and visual acuity are poorly correlated, and typical straylight complaints occur quite independently from visual acuity-associated complaints. Clinically, straylight is assessed functionally in a reliable and repeatable way with the Oculus C-Quant (Oculus GmbH, Wetzlar, Germany), based on the compensation comparison method. Previous studies have shown that straylight and visual acuity contribute almost equally to subjectively experienced quality of vision in patients with cataract, and that adding straylight measurements to the pre-operative considerations for cataract surgery improves the predictability of postoperative results. We investigated the value of straylight measurements in the pre-operative decision making process for patients with posterior polar cataracts and good visual acuity.
The Department of Ophthalmology of the Academic Medical Center (AMC) in Amsterdam, the Netherlands, which is a tertiary referral center.
Prospective interventional case series of three patients (five eyes) with posterior polar cataracts, who presented with complaints of decreased visual performance due to increased disability glare and more difficulty with functioning in the dark. Visual acuity was measured using the modified ETDRS protocol and straylight measurements were performed with the C-Quant. Measurement by the C-Quant results in a functional straylight parameter s, which expresses the amount of straylight as experienced by the patient. This parameter presents the relation between the amount of unwanted, scattered light, which causes the veil of light over the retinal image, and the wanted, focused, non-scattered light, which forms the retinal image. Usually the logarithm of the straylight parameter s is used and the result is denoted as log(s). Two of the three patients (four eyes) underwent cataract surgery. Visual acuity and straylight measurements were repeated postoperatively.
All three patients (60, 65 and 67 years old) experienced visual complaints due to posterior polar cataracts for several years and were severely disturbed by them. The complaints mostly consisted of increased glare hindrance and hazy vision at night. Snellen visual acuity was in all eyes around 20/30. Slitlamp examination showed mild nuclear cataract and dense posterior polar cataract in all eyes. Pre-operative straylight measurements were 5x increased compared to the levels of young, normal eyes, which can account for the complaints. By comparison, a doubling of the straylight level is usually experienced as a noticeable loss of quality of vision for patients. A 4x increase is considered as a limit value for safe driving. Four eyes underwent cataract extraction, which was uncomplicated in three eyes. In one eye, a rupture of the posterior capsule occurred with vitreous loss. Postoperatively, three eyes obtained an uncorrected distance visual acuity of 20/20, the eye with the complicated cataract surgery had a corrected distance visual acuity of 20/20 (refraction: S + 1.00 = C -1.00 x 135Ḟ). Postoperative straylight levels returned to normal or even better than normal values for age-related eyes. All patients were very satisfied with the postoperative outcome.
It might be difficult to estimate when cataract surgery is necessary in patients with posterior polar cataracts who present with subjective loss of visual quality and good visual acuity. The clinical challenges posed by this type of cataract are even larger than those of other cataract types, as cataract surgery has a higher risk of being complicated and the postoperative result is thus more unpredictable. Straylight measurements are known to be helpful in the pre-operative considerations of cataract surgery of normal cataracts, and this study has shown that they can contribute equally well to the pre-operative decision process in patients with posterior polar cataracts. Posterior polar cataracts lead to a huge increase in the amount of straylight, while visual acuity can remain reasonably normal. Cataract surgery can establish an improvement in straylight levels to those of healthy, age-related eyes, corresponding to a subjectively experienced major improvement in quality of vision for the operated patient. The postoperative improvement in straylight is larger than the improvement in visual acuity. When 50% or more of the pupil area is left clear by the cataract, the decrease in visual acuity will only be modest. However, the light scattering effect of cataract is proportional to the pupil area which is covered by the lens opacities and will occur even if only a small part of the pupil area is occupied by cataract. The significant effect on the amount of intraocular straylight can be explained by the considerable light scattering influence of posterior polar cataracts.