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Simulation of a central scotoma using contact lenses with an opaque centre
Author(s) -
Almutleb Essam S.,
Bradley Arthur,
Jedlicka Jason,
Hassan Shirin E.
Publication year - 2018
Publication title -
ophthalmic and physiological optics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.147
H-Index - 66
eISSN - 1475-1313
pISSN - 0275-5408
DOI - 10.1111/opo.12422
Subject(s) - blind spot , opacity , central scotoma , pupil , optometry , perimeter , entrance pupil , fixation (population genetics) , ophthalmology , optics , luminance , octopus (software) , medicine , physics , mathematics , geometry , population , environmental health , quantum mechanics
Purpose This study evaluated the feasibility of using soft contact lenses ( CL s) with an opaque centre to induce absolute central scotomas that move with the eye. We examined the geometrical optics prediction that scotoma size will vary with the size of the CL 's opaque centre and with ocular pupil size. We also tested the hypothesis that high environmental light levels will ensure that the ocular pupil will remain small enough, even with opaque centre CL s, to generate absolute scotomas representative of those experienced by patients with age‐related macular disease. Methods Using an Octopus 900 Perimeter ( www.Haag-Streit.com ), kinetic visual fields ( VF s) were measured in five normally‐sighted subjects using a V4e Goldmann target with CL s that had central opaque areas with diameters of 2.8, 3.0, and 3.2 mm. To control pupil size, VF s were measured with background perimeter bowl luminances of 10, 585, and 1155 cd m −2 . Subjects attempted to (i) fixate the bowl centre; and (ii) place the scotoma edge at the bowl fixation target (eccentric viewing). Results As predicted, there was a direct relationship between scotoma size and both luminance level and diameter of the opacity. Mean scotoma diameters were 0°, 17.6° and 22°, for the low, medium and high bowl luminances, respectively. Scotoma size was determined primarily by the difference between the diameters of CL opacity and the entrance pupil of the eye and the axial separation between them, and between‐subject differences in pupil diameters contributed most to the between‐subject variability in scotoma diameter at each light level ( SD : 6.01°). Scotoma displacement during eccentric fixation confirmed the gaze‐contingent characteristics of this experimental model. Conclusion It is possible to induce a gaze‐contingent absolute scotoma and hence mimic central vision loss using centrally‐opaque CL s provided that the CL opacity is larger than the entrance pupil of the eye. This simulation tool will, therefore, be ineffective at low environmental light levels (as shown previously) if the entrance pupil of the eye is larger than the CL opacity.