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Howard P Apple, Tina K Leonard-Green, Erin M Harvey, Joseph M Miller, Deborah Apple; Suitability of computer generated grating acuity stimuli for assessment of grating acuity in children. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2738.
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Determine if computer-generated grating acuity stimuli presented on high-resolution consumer displays are adequate for grating acuity testing in children.
As of 2010, the highest resolution consumer LCD monitor was the MacBookPro with Retina display (Apple, Inc). Display size is 13” wide x 8.2” high (2880 x 1800 pixels) with a native resolution of 220 pixels per inch (ppi) or 87 ppcm. A third-party app (SwitchResX, http://www.madrau.com) was required to allow display at that resolution. Programs written in Matlab R2012a (MathWorks, Inc) produced and presented 4” (10 cm) square acuity stimuli. Seventeen gratings with linewidths from 3 to 128 pixels were used, resulting in spatial frequencies of 1.18 to 50.39 cycles/deg at 2m in 0.1 log steps. Special attention was given to edge artifact blend algorithms. Testing was done on 261 non-astigmatic 2nd - 7th grade students using a 2AFC procedure to determine right eye grating acuity threshold while wearing their best correction. Analysis compared actual performance versus expected performance.
For horizontal gratings, 23.8% of subjects were able to see the highest frequency (50 cy/deg, approximately 20/12). For vertical gratings, 33.7% of subjects were able to see the highest frequency. Of the subjects able to see the highest spatial frequency, only 71% (for horizontal) and 65% (for vertical) were able to resolve the 20/12 +/- 1 logMAR line on the ETDRS letter acuity chart with their best correction.
The finding that some students were able to resolve the highest spatial frequency grating but did not have letter acuity of a similar threshold value suggests that there may be an artifact in the computer display that cues the subjects as to the location of the grating stimulus. To meet the requirements of Teller acuity at 55 cm, future development will use the higher-resolution Google Nexus 7 tablet (323 ppi) and will include further analysis. A preferential looking prototype using two Nexus 7 tablets (computer controlled right and left grating displays) against a framework the size of a standard Teller Acuity Card (22" x 10") (Stereo Optical Co, Inc) is currently under development; and a computer program simulating the Teller Acuity Card procedure has established a formal detailed flowchart of the procedure for further automation.
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