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 .
it is revealed that impaired contrast sensitivity may be present in cases of normal 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 .
ross et al . found that , in the age range 5087 years when compared to 2030 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 . in the aspect of ocular dominance , suttle et al .
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 .
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 ,
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 .
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 ) .
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 / m ) and mesopic condition ( target luminance value of 3  cd / m ) .
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 t - test was used to compare contrast sensitivity values of the dominant and nondominant eyes .
forty patients ( 91% ) had their dominant eyes on the same side as the master hand .
the mean central corneal thickness ( cct ) of the dominant eyes was 567.04  23.86  m and the mean cct of the nondominant eyes was 563.70  28.84  m ( p = 0.21 ) .
the mean pupil diameter of the dominant eyes was 5.68  0.55  mm and the mean pupil diameter of the nondominant eyes was 5.69  0.54  mm ( p = 0.75 ) .
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 ( p = 0.035 ) . under photopic conditions ,
the contrast sensitivity values of the dominant eyes and nondominant eyes were similar at all spatial frequencies ( p > 0.05 ) .
tables 1 and 2 show numerical contrast sensitivity values and p values under photopic and mesopic conditions .
when the data were transformed into logarithmic units , the p value for the comparison of dominant and nondominant eyes became 0.08 at mesopic 18 cpd .
for all the other comparisons at photopic and mesopic states , p value was > 0.05 similar to using cs scores .
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 . when with both eyes open , people with normal binocular vision have no sense that one eye or the other contributes more strongly to the combined binocular vision ; it is only sensed when normal binocular vision is deteriorated .
generally , blurring the dominant eye causes more discomfort when compared with blurring the nondominant eye at far , so it seems convenient to choose the nondominant eye for near correction .
this is an easy , repeatable , and reliable test for sighting ocular dominance detection .
the dominant eye is often , but not always , on the same side as the master hand ; this statement was also acceptable for our patients . 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 ( 36  cpd ) with a steep decrease at high spatial frequencies and a more gradual decrease at lower frequencies .
suttle et al . found no significant interocular difference in contrast sensitivity or alignment sensitivity in their study .
handa et al . investigated the effects of ocular dominance on binocular summation after monocular reading adds and found that , with strong ocular dominance , defocus results in a greater loss of contrast sensitivity than with weak ocular dominance . in this study , there was not statistically significant difference at all spatial frequencies in mean photopic contrast sensitivity values between dominant and nondominant eyes .
but , in mesopic condition , at 18  cpd , there was statistically significant difference that dominant eye had greater contrast sensitivity function values . 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 [ 13 , 14 ] . although it was not previously reported that interocular difference occurred on higher spatial frequencies like 18  cpd , we found that dominant eye had better contrast sensitivity function values at mesopic 18  cpd spatial frequency .
this result might be interpreted as deterioration of stereopsis and decrease of reading capacity ( if near monovision therapy was performed ) at mesopic 18  cpd .
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 [ 15 , 16 ] .
found that age - related decrease in contrast sensitivity was confirmed at all frequencies in japanese population , even when adjusted for visual acuity , and added that contrast sensitivity tests , especially at high frequencies , assessed aspects of visual function that could not be determined in the elderly population from visual acuity tests alone .
revealed that statistically significant age - related declines in contrast sensitivities occurred due to age - related changes in the magnocellular pathway . in this study ,
contrast sensitivity curves both under photopic and mesopic conditions did not show any pathological patterns in middle - aged population .
found that senile miosis was not responsible for older adults ' loss in spatial vision ; rather , older adults ' miotic pupil tended to have a positive effect on their spatial vision in that it slightly improved their contrast sensitivity . in this study , in order to avoid pupil diameter influences , we tried to do measurements under similar pupil diameter values . 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 . beyond the past literature , this study investigated contrast sensitivity and other ocular parameters in people whose age ranged between 40 and 60 years .
some of the factors contributing to better results in monovision therapies include good interocular blur suppression , posttreatment anisometropia of less than 2.50 diopters , successful distance correction of the dominant eye , good stereoacuity , and motivation to adapt to this visual system .
although we did not measure the degree of ocular dominance in this study , the degree of ocular dominance plays a strong role in monovision success .
handa et al . reported that patients with strong sighting preference tended to have reduced interocular blur suppression and decreased binocular depth of focus that makes monovision less tolerable .
schor et al . have found that interocular blur suppression is more effective under photopic viewing conditions than high contrast mesopic and scotopic conditions .
horn revealed that suppression of the out of focus image in the near eye is easier under lower contrast viewing situations .
our contrast sensitivity scores provided were slightly low when compared to some other fact data in the literature .
some concerns about statistical analysis might come to one 's mind that it would be better to use logarithmic units while interpreting the data ; but according to us there is no definitive superiority of using logarithmic units instead of cs scores . in conclusion ,
in the present study , at mesopic 18 cpd , contrast sensitivity of a nondominant eye was slightly lower than that of the dominant eye .
although this parameter is not the best indicator of monovision treatment success , it is worth giving importance .
 
 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 ( p = 0.035 ) . under photopic conditions , 
 the contrast sensitivity values of the dominant eyes and non - dominant eyes were similar at all spatial frequencies ( p > 0.05 ) . 
 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
2. Material and Methods
3. Results
4. Discussion