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M. Brookes, P. E. M. Smith, F. A. Ennis, J. M. Wild; Binocular Disability Rating of Patients With Vigabatrin-Attributed Visual Field Loss. Invest. Ophthalmol. Vis. Sci. 2007;48(13):936.
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Firstly, to apply existing binocular summation algorithms, used in the production of binocular functional fields (BFF), to the fields of patients exhibiting vigabatrin-attributed visual field loss (VAVFL). Secondly, to develop a binocular disability rating (BDR) based upon the BFF.
The visual field results, recorded with Program 30-2 and the FASTPAC strategy and with the Three Zone 135 Point Screening Test of the Humphrey Field Analyzer, from 20 randomly selected patients exhibiting a range of VAVFL, were analysed retrospectively using 4 different binocular summation algorithms (Best Summation, Best Location, Average Eye and Worst Location). For the central field, monocular fields were produced in terms of 10dB and 0dB cut-offs and monocular isopters equivalent to Goldmann III-4e and V-4e stimuli generated. For the peripheral field, a monocular isopter equivalent to the Goldmann V-4e, only, was generated. The given monocular isopter for each eye was then binocularly overlapped, evaluated for ocular convergence, to produce a BFF. The area of the BFF isopter was measured with custom software to determine the BDR as a proportion of the area of the given normal isopter.
The lowest BDRs occurred with the Best Summation and Best Location algorithms and the highest BDR with the Worst Location algorithm. The disparity between stimulus location and actual location, resulting from ocular convergence, increased with eccentricity; however this effect was not significant within the central field out to a radius of 30o. Isoptric BFF analysis generated a stimulus-dependent BDR for the central and peripheral fields that correlated with VAVFL grading.
Best Summation and Best Location algorithms provided the best representation of BFF in patients with VAVFL. The BDR demonstrates why, in mild VAVFL, patients are often asymptomatic, and why the visual field loss is more disabling in later stages.
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