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Tressa L. Larson, Stephen Sinclair; Field Acuity Analyzer and Various Types of Refractive Correction. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5574.
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A new instrument, the Field Acuity Analyzer (FAA), from Vimetrics LLC, is an interactive computer program that measures a patient’s visual acuity at twenty-five points within the central twenty degree visual field under conditions that mimic real world environments.
Measurements reveal startling variations in vision among various types of corrections.A twenty-nine year old female (OD -5.25DS, OS -6.00DS) underwent examination with the instrument while wearing each of four refractive corrections (BCVA in each case): standard spectacles, iZon spectacles, RGP contact lenses, and soft contact lenses. For each correction nine trials were completed, three at each of three contrast levels; high contrast (99% white on black), dim restaurant conditions (64% grey against 3cd/m2), and driving at dusk (47% grey against 3cd/m2).
The field area of best visual acuity was consistent among the three trials but varied widely between eyes and among corrections. In the right eye the acuities at high contrast were equivalent among all four correction types, but at mid and low contrasts, the acuities with standard spectacles were superior to those with contact lenses. The acuities in the left eye (which had greater HOA than OD) were clearly superior with RGP contact lenses at high and mid contrast levels, but at low contrast the field acuity with either the standard or iZon spectacles was superior to that with contact lenses.
These findings suggest a variety of future investigations that may alter the tenets of vision evaluation. By measuring an index of macular acuity, rather than simply the acuity at fixation, it was determined that in these mesopic environments vision at lowered contrast in this case was actually superior to her vision at high contrast. The variability of the size of the field of best acuity also has clear implications for defining visual function in eyes with macular disease as well as in eyes undergoing refractive surgery or correction with different optical means.
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