Scotoma Simulation in Healthy Subjects

Abstract

Significance: This article shows a successful concept for simulating central scotoma, which is associated with age-related macular degeneration (AMD), in healthy subjects by an induced dark spot at the retina using occlusive contact lenses. The new concept includes a control mechanism to adjust the scotoma size through controlling pupil size without medication. Therefore, a miniaturized full-field adaptation device was used.

Purpose: The aim of this study was to design a novel concept to simulate AMD scotoma in healthy subjects using occlusive contact lenses.

Methods: To define an optimal set of lens parameters, we constructed an optical model and considered both the anatomical pupil diameter and the opaque central zone diameter of the contact lens. To adjust the scotoma size, we built a miniaturized full-field adaptation device. We demonstrate the validity of this novel concept by functional measurements of visual fields using automated threshold perimetry. Finally, we conducted a perception study including two tasks, consisting of pictograms and letters. The stimuli were presented at different eccentricities and magnifications.

Results: The visual fields of all 10 volunteers exhibited absolute scotomas. The loss of contrast sensitivity ranged within 27 and 36 dB (P < .05), and the scotoma localizations were nearly centered to the macula (mean variation, 2.0 ± 4.8° horizontally; 3.5 ± 4.7° vertically). The eccentric perception of letters showed the largest numbers of correctly identified stimuli. The perception of pictograms showed significantly reduced numbers (P < .0001) and revealed a dependency on magnification. The results suggest that best perception is possible for magnified stimuli near the scotoma.

Conclusions: We demonstrated that the creation of an absolute simulated AMD scotoma is possible using occlusive contact lenses combined with a miniaturized full-field adaptation device.

FIGURE 1

(A) Optical model in Zemax OpticStudio. It consists of the contact lens (CL) with an opaque central zone (OZ) and all components of the schematic eye including the cornea (C), the anatomical pupil (P), the eye lens (L), and the fundus (F). (B) Relative illumination at the retina (half field) caused by an occlusive contact lens.

FIGURE 2

(A) Scotoma obscuration as a function of the opaque central zone diameter (OZD) (OZD, 4 mm solid line; OZD, 3 mm dashed line; OZD, 2 mm dotted line). (B) Scotoma obscuration as a function of the pupil diameter (PD) (PD, 4 mm dotted line; PD, 3 mm solid line; PD, 2 mm dashed line). The proportions of OZD and PD as well as the relative illumination at the retina are depicted next to the curves.

FIGURE 3

(A) Miniaturized full-field adaptation device used with the non–lens-covered eye. The upper half sphere (HS) is removed to show the location of the light-emitting diode (LED) in the tube (T). (B) Nearly homogenous illuminated field (IF) induced by the Lambertian sphere and the LED. The power supply cable (PS) is on the right side.

FIGURE 4

(A, B) Miniaturized full-field adaptation device applied to the perimeter (Humphrey Field Analyzer II). (C) Single field analysis of the left eye without any contact lens. The red arrow indicates the restricted visual field caused by the adaptation device. The dark spot in the left hemisphere indicates the papilla.

FIGURE 5

Illumination chamber (IC) with liquid crystal display (LCD) on the rear side and miniaturized full-field adaptation device (AD) and its power supply (PS) in the front. The digitally addressable lighting interface is connected to the control unit (CU). One of the pictograms (cat) and the fixation point (underneath the cat) are visible on the LCD screen.

FIGURE 6

The randomly selected pictograms (upper two rows) and letters (lower two rows). Graphic and cultural aspects of the pictograms were taken into account, considering the work of Spinillo. Complexity of the pictograms is higher than the complexity of the letters.

FIGURE 7

(A) Opaque central zone optical density of various contact lenses. We analyzed one lens from Ultravision CLPL (Ultravision lens) and three lenses from Falco Linsen AG (Falco lens F1, Falco lens F2, Falco lens F3). (B) The selected lens type (FASP iris: O-EXTREM ICE) with its corresponding opaque zone optical density of F1.

FIGURE 8

Functional measurements of 10 volunteers (grouped into two rows) using 30-2 SITA standard automated perimetry. For each volunteer, grayscale results (left side) and total deviations (right side) are depicted. The numeric total deviation values represent the differences in decibels between the volunteer's test results and the age-corrected normal values at each tested point.

FIGURE 9

Correctly identified stimuli for each volunteer (black rectangle with number) for the different eccentricities (10° blue, 20° red) and the different magnifications (3× solid lines, 5× dotted lines). (A) Perception of the different letters. (B) Perception of the different pictograms.