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Can reversed contrast affect the accommodative response?

Poster Details

First Author: J.Esteve-Taboada SPAIN

Co Author(s):    A. Del Águila-Carrasco   T. Ferrer-Blasco   N. López-Gil   R. Montés-Micó     

Abstract Details



Purpose:

To evaluate if printed media with reversed contrast (white letters on a black background) may or not affect the accommodative response of the human eye in comparison to the response obtained for the commonly used printed media (black letters on a white background).

Setting:

University of Valencia, Spain

Methods:

The normal situation in most of the texts used in daily life is given by dark letters on a white background. The same occurs with the frequently used visual acuity charts. But it is well known that for patients with reduced vision there exist special charts to evaluate their visual acuity that use reversed contrast charts given by white letters on a black background. Moreover, most of the closed-circuit television (CCTV) solutions to be used by subjects with reduced vision include the option to reverse the contrast of the image that they are capturing and displaying on the screen. This reversed contrast image is perceived better by reduced vision patients than commonly used printed media. By using an adaptive optics visual simulator (crx1, Imagine Eye), which combines high-quality Hartmann-Shack wavefront technology with an electromagnetic deformable mirror, it is possible to measure, correct and manipulate the optical aberrations and the accommodative response of the eyes with extreme precision. Several targets were used as fixation patterns containing different spatial frequencies and considering both standard and reversed contrast.

Results:

The targets included were a Malta cross, a Sloan letter chart corresponding to a visual acuity of 0.8, and a ring target with a central fixation circle both with sinusoidal profiles to maximize the accommodative response given at the spatial frequency of 3 cycles/degree. The 10 subjects involved in this experiment, aged 22-38, had all their refractive errors corrected. They had all clear intraocular media and no known ocular pathology. Wavefront aberrations and accommodative response were measured with natural pupil. The pupil diameter was always larger than 3.0 mm. The light of the room was dimmed during the experiments. Three different vergences, 0, 2 and 4 D, were used for each of the targets tested. A sequence of 5 measurements, with 5 s of time span between each of them, was obtained in order to characterize the ability of the subjects in maintaining their accommodative response for each of the targets used.

Conclusions:

The accommodative response depends on the individuals. Slight differences were found in the measured accommodative response for each of the targets used at different vergences. Some of the individuals manifested their difficulty to maintain the required level of accommodation when a reversed contrast target with high spatial frequencies was displayed in the visual simulator's screen. Project funded by: ERC-2012-StG 309416-SACCO FINANCIAL INTEREST: NONE

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