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Subjects blinded by outer retinal dystrophies are able to differentiate a range of common objects using the Argus? II retinal prosthesis system

Session Details

Session Title: New drug treatment and technology

Session Date/Time: Friday 27/09/2013 | 14:30-16:00

Paper Time: 14:30

Venue: Hall 3 (Level 0)

First Author: Y.Luo UK

Co Author(s):    L. daCruz   F. Merlini   F. Anaflous   M. Arsiero     

Abstract Details

Purpose:

To determine if subjects blinded by outer retinal dystrophies and fitted with the Argus™ II Retinal Prosthesis System, can differentiate a range of common objects chosen by the subjects.

Setting:

The seven subjects were patients from two tertiary referral specialist vitreoretinal units in the UK. The tests were performed over both sites.

Methods:

Seven blind subjects fitted with the Argus® II Retinal Prosthesis were asked to identify 8 common objects in a forced-choice, closed-set series of tests. The subjects were interviewed regarding object preferences and from whence 8 testing objects were chosen. All objects were of white or metallic hue, and were presented to the subjects against a black felt worktop to maximize contrast. Before the test, each object was presented to the subject to allow visual familiarization. During the test, each object was presented in random order and the subject was allowed up to 30 seconds for object identification. The tests were performed under the following conditions: a) eyes patched, device switched on; b) eyes patched, device switched on but signals were scrambled; c) eyes unpatched, device switched on; d) eyes unpatched, device switched on but signals were scrambled; e) eyes unpatched, device switched off. The order of performing each testing conditions was also randomised. Within each condition, each object was presented twice, giving a total of 16 presentations per condition. The body of the 8 objects were then covered with cut-out black cardboards, so as to produce objects with white outlines. The above testing conditions were then repeated.

Results:

In the tests with solid objects (SOb), all the subjects performed better with the Argus® II Retinal Prosthesis device switched on (correct identification 13-69%, median 31.3%) compared with off (correct identification 6 – 25%, median 18.8%; P = 0.071 Wilcoxon Signed Rank Test). This difference is exaggerated in the tests performed with outlined objects (OOb), with 25 – 75% correct object identification (median 43.8%) when the device was switched on, compared with 0 – 19% (median 6.3%; P = 0.026) when the device was off. Scrambling of device signals showed that the subjects performed better with SOb (correct identification 13 – 56%; median 25%) than with OOb (6 – 25%; median 18.8%). There is a statistically significant difference in the results of the device-on versus device signal-scrambled group with OOb, (P = 0.043), but not with SOb (P = 0.891). This could be due to the fact that when the signals were scrambled, the subjects use other cues such as the reflectivity rather than the shape of the object to help them with identification. As the body of each object was covered in OOb, the difference in reflectivity of each object was diminished, thus rendering them more difficult to differentiate.

Conclusions:

This is a follow-on study from the previously presented geometric shapes recognition study on the same cohort of subjects. Results indicate that the Argus™ II Retinal Prosthesis System improves the subjects’ ability to visually identify a range of daily subjects, using both shapes and reflectivity as cues. Better results were obtained when the objects have a distinct high-contrast outline to their body, consistent with previous shapes recognition study findings. The results of this study could be use to advise Argus™ II subjects in the choice of purchasing daily objects to enhance their identification.

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