Purpose. Our aim was to compare contrast sensitivity values of the dominant and nondominant eyes of healthy middle-aged subjects. Material and Methods. Ninety eyes of 45 healthy middle-aged subjects (30 males and 15 females) were included in this study. Patients were aged between 40 and 60 years, having uncorrected visual acuity (UCVA) of 20/25 or better (Snellen chart). Ocular dominance was determined by hole-in-the-card test. Functional acuity contrast testing (F.A.C.T.) was measured using the Optec 6500 vision testing system (Stereo Optical Co. Inc., Chicago, IL, USA) under both photopic and mesopic conditions. Results. At all spatial frequencies (1.5, 3, 6, 12, and 18？cpd), under mesopic conditions, the contrast sensitivity values of the dominant eyes were slightly greater than those of the nondominant eyes; but only 18？cpd spatial frequency measurements’ difference was statistically significant . Under photopic conditions, the contrast sensitivity values of the dominant eyes and non-dominant eyes were similar at all spatial frequencies . Conclusions. The photopic and mesopic contrast sensitivity values of dominant and nondominant eyes of healthy middle-aged people were similar at all spatial frequencies, except at mesopic 18？cpd spatial frequency. 1. Introduction Ocular dominance is the preference of one eye over the other in terms of sighting, sensory, and oculomotor tasks [1, 2]. Ocular dominance is clinically important in sports vision and vision therapy, but the most important application of the principles of ocular dominance is fitting of monovision contact lenses and applying monovision excimer laser refractive surgery for near vision [2, 3]. Contrast sensitivity is defined as the ability to differentiate between light and dark in a series of bands with no clear boundary [4]. It is revealed that impaired contrast sensitivity may be present in cases of normal visual acuity [5]. It is important to know the difference between spatial contrast sensitivity and visual acuity. Visual acuity is a measure of the spatial-resolving ability of the visual system under conditions of very high contrast (at least 85%); all targets are presented at the same contrast, but their sizes vary during the test, whereas contrast sensitivity is a measurement of the threshold contrast for seeing a target; but contrast is not kept constant during the test [6]. Contrast sensitivity is affected by various different conditions. Age and ocular dominance are some of the investigated parameters affecting contrast sensitivity. Ross et al. found that, in the age range 50–87
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