Ocular dominance is the preference of one eye over the other in terms of sighting, sensory, and oculomotor tasks [
Contrast sensitivity is defined as the ability to differentiate between light and dark in a series of bands with no clear boundary [
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 years when compared to 20–30 years, there was a linear decline in contrast sensitivity with age for medium and high spatial frequencies, but sensitivity for low spatial frequencies was independent of age [
Monovision therapies like contact lens for near vision, corneal refractive surgery for near vision, and multifocal intraocular lens implantation in various cases generally come into consideration in middle-aged people. Since nondominant eye is usually chosen for near vision applications, it is important to reveal whether ocular dominance affects contrast sensitivity, because monovision therapies might also have a negative influence on it. In this study, we aimed to evaluate the effects of sighting ocular dominance on contrast sensitivity in middle-aged healthy people.
Ninety eyes of 45 healthy middle-aged subjects (30 males and 15 females) were included in this retrospective comparative study. The study and data collection conformed to all local laws and were compliant with the principles of the Declaration of Helsinki.
Patients who were aged between 40 and 60 years and were having uncorrected visual acuity (UCVA) of 20/25 or better (Snellen chart), keratometry values between 41 and 47 Diopters, and spherical or cylindrical refractive error values between +0.50 and −0.50 Diopters were eligible for inclusion in the study. Central corneal thickness and pupil diameter measurements were also performed. Those parameters were evaluated in order to eliminate other factors that might have an influence on contrast sensitivity other than ocular dominance. Both ocular dominance and contrast sensitivity measurements were done with spectacle correction. In order to avoid observer bias, contrast sensitivity testing had been performed before ocular dominance detection.
Exclusion criteria were any ocular surgeries, ocular diseases, such as corneal opacities or irregularity, dry eye, amblyopia, anisometropia, glaucoma, retinal abnormalities, any neurological disorder, diabetes mellitus, taking medications that might affect contrast sensitivity, insufficient mental capacity to perform the tests, and any physical disability that might make it difficult to perform the test.
Ocular dominance was stated by hole-in-the-card test. The participant is given a card with a small hole in the middle, instructed to hold it with both hands, and then told to view a distant object through the hole with both eyes open. The observer then alternates closing the eyes or slowly draws the opening back to the head to determine which eye is viewing the object (this is the dominant eye). This technique is used to detect sighting dominance. The test was performed three times in order to be sure.
Functional acuity contrast testing (F.A.C.T.) was measured using the Optec 6500 vision testing system (Stereo Optical Co. Inc., Chicago, IL, USA) with natural pupil under both the photopic condition (target luminance value of 85 cd/m2) and mesopic condition (target luminance value of 3 cd/m2). Sequence of testing was as follows: 1.5, 3, 6, 12, and 18 cpd (cycles per degree). Examinations under photopic conditions were done at first, and, after 10 minutes of dark adaptation, examinations under mesopic condition were performed. Contrast sensitivity values were converted to numerical values by using a conversion chart of F.A.C.T. Contrast sensitivity values of dominant and nondominant eyes were compared at all five spatial frequencies (1.5, 3, 6, 12, and 18 cpd). Since this test needs full concentration for appropriate results, all the measurements were repeated three times at all spatial frequencies. All the examinations were done by two researchers (GP and NA).
For statistical analysis, SPSS 17.0 software for Windows (SPSS Inc., Chicago, IL, USA) was used. Paired samples
The mean age was 51.26 (SD: 3.87) years. All the eyes had a mean UCVA of 20/25 or better. Best corrected visual acuity (BCVA) was 20/20 for all the eyes. Forty-three patients (96%) had their right eyes as dominant eye. Forty patients (91%) had their dominant eyes on the same side as the master hand.
All the eyes had keratometry values between 41 and47 Diopters. The mean central corneal thickness (CCT) of the dominant eyes was
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. However, among all of the differences between the values of the two groups, only mesopic 18 cpd spatial frequency measurements were statistically significant (
Figures
Mean photopic contrast sensitivity values of the dominant and nondominant eyes.
Spatial frequency |
Dominant eye |
Nondominant eye |
|
---|---|---|---|
1.5 |
|
|
0.76 |
3 |
|
|
1.00 |
6 |
|
|
0.56 |
12 |
|
|
0.20 |
18 |
|
|
0.15 |
cpd: cycles per degree.
Mean mesopic contrast sensitivity values of the dominant and nondominant eyes.
Spatial frequency |
Dominant eye |
Nondominant eye |
|
---|---|---|---|
1.5 |
|
|
0.92 |
3 |
|
|
0.20 |
6 |
|
|
0.58 |
12 |
|
|
0.74 |
18 |
|
|
0.035 |
cpd: cycles per degree.
Photopic contrast sensitivity curves of the dominant and nondominant eyes.
Mesopic contrast sensitivity curves of the dominant and nondominant eyes.
Ocular dominance is usually defined as the superiority of one eye over the other in some sensory or motor tasks. Ocular dominance is an important consideration in monovision therapies, because it helps us to decide which eye should be corrected for near or far. Ocular dominance has a strong effect on the success of monovision techniques [
There are several methods to determine ocular dominance [
In this study, functional acuity contrast testing (F.A.C.T.) was measured using the Optec 6500 vision testing system. In this test, the test targets were vertically oriented sine-wave gratings, so-named because the luminance of the vertical bars varied sinusoidally over space. The bar gratings presented to the test subject covered spatial frequencies of 1.5, 3, 6, 12, and 18 cycles per degree (cpd) of visual angle. In general, contrast sensitivity function had its peak sensitivity at intermediate spatial frequencies (3–6 cpd) with a steep decrease at high spatial frequencies and a more gradual decrease at lower frequencies [
Effects of ocular dominance on contrast sensitivity had been investigated previously to some extent. Suttle et al. found no significant interocular difference in contrast sensitivity or alignment sensitivity in their study [
In the F.A.C.T. chart, mild refractive disorders and early cataracts generally cause contrast sensitivity losses at higher spatial frequencies, whereas severe refractive disorders and advanced cataracts cause contrast sensitivity losses at lower spatial frequencies [
The present study is one of the few conducted to describe contrast sensitivity function values in a middle-aged population. There are several reports in the literature about the effect of age on contrast sensitivity [
Contrast sensitivity is affected by pupil diameter [
Since monovision therapies are usually applied in middle-aged people, it is important to make visual measurements of this age group. The presbyopic patients over the age of 40 years are the best candidates for monovision [
Our contrast sensitivity scores provided were slightly low when compared to some other FACT data in the literature [
The authors declare that there is no conflict of interests regarding the publication of this paper.