Purchase this article with an account.
Pablo De Gracia, Carlos Dorronsoro, Alvaro Sanchez-Gonzalez, Lucie Sawides, Susana Marcos; Visual Performance Under Pure Simultaneous Vision. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6333.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
To evaluate visual performance with bifocal corrections using a custom-developed simultaneous vision simulator instrument. To test the effect of different adds on image contrast and visual acuity.
A compact instrument was developed with two collinear channels that provide the eye with two simultaneous images, focused at near and far. Independent motorized Badal systems allow control of the defocus level in each channel. Stimuli were displayed on a CRT at far distance (4.5 m). The system was first tested using an artificial eye (objective lens + CCD). High and low contrast Snellen E targets were projected on the CCD through both channels. Channel 1 was focused at far, while the focus of channel 2 was moved from -4 to 4 D (0.1D steps). Series of control thru-focus images were also obtained for only Channel 1. A total of 8910 images were obtained, and the letter Michelson contrast calculated. High (HC) and low contrast (LC, 0.33) decimal VA (tumbling E letters) were also measured on 4 normal subjects (age=34±6; cyclopleged to emulate presbyopia; 4 m artificial pupil). Measurements were obtained at subjective best focus (for each channel), and then keeping channel 1 at far, and moving channel 2 thru-focus (0 to ±4D, 0.5-1 steps). The positive defocus positions simulate far vision with different adds in pure bifocal corrections, and the negative defocus simulates near vision. A thru-focus control condition (-2 to 2 D in 0.5D steps) was also tested blocking channel 2 (monofocal vision).
Contrast degradation with simultaneous imaging varied with the amount of add. For HC condition, contrast was maximally degraded (23%) for 1.5-2D add ranges, while degradation was less than 15% in the 0-1D and 2.5-4D add ranges. The add that produced highest degradation was the same for LC but with a higher maximum degradation (41%). All subjects showed consistent visual performance among them, both for monofocal and pure bifocal vision. Monofocal VA decreased systematically with defocus (from 1.05 at 0 D to 0.35 at ±2D, on average). For simultaneous vision, VA decreased when increasing add with a minimum (0.64) at 1.68 D, and then increased for higher adds (0.78 for an add of 3.75 D). While, on average, VA for monofocal vision decreased below 0.8 for defocus higher than 0.51 D, VA with bifocal corrections remained above 0.72 for all of the 0-4D add range. LC VA under simultaneous vision tended to parallel HC VA, with an average reduction of 32%.
Visual Acuity was reduced (7-41%) in simultaneous vision, both for far and near. VA decrease is systematically highest for typical adds of bifocal corrections (1.5-2 D). A simultaneous vision instrument is an excellent tool to simulate bifocal vision and increase understanding/improvement of multifocal solutions for presbyopia.
This PDF is available to Subscribers Only