AIM: To investigate the physiological asymmetry of retinal parameters with cirrus high-definition optical coherence tomography(Cirrus HD-OCT)in healthy young adults.

METHODS: In this cross-sectional observational study we included 146 normal young adults. Bilateral eyes retinal parameters such as retinal nerve fiber layer thickness, optic nerve head and macula were assessed with OCT and mean differences for all parameters were established by subtracting the values of left eye from the right eye parameters and evaluated by paired sample t-test. Interocular differences were evaluated and cut off points at 2.5^th and 97.5^th percentiles were produced. Retinal parameters were correlated. Effects of gender and blood pressure on retinal parameters were evaluated by regression analysis.

RESULTS:Average retinal nerve fiber layer(RNFL)thickness was not statistically significant(+0.7 μm, P=0.09). Significant thickness was present in temporal quadrant(+2.51 μm, P=0.02), nasal quadrant(+2.50 μm, P=0.04), clock hours 2/10(+5.85 μm, P=0.002), 3/9(+3.20 μm, P=0.005), 11/1(+3.80 μm, P=0.024), average(-0.034 μm, P=0.013)and vertical cup-to-disc ratio(-0.028 μm, P=0.008), macular inner nasal quadrant(+7.76 μm, P=0.003)in right eyes. Superior quadrant was significantly thicker in left eyes(-2.40 μm, P=0.03). Cut-off values for average RNFL and macular thicknesses were 11.00 μm and 18.00 μm, respectively. Bilateral eyes have moderate interocular correlation(0.41-0.6)for retinal parameters and not correlated with gender and blood pressure(P<0.05 regression). The interocular differences in average RNFL and macular thickness of normal adults should not exceed 11 μm and 18 μm, respectively, if measured with Cirrus HD-OCT.

CONCLUSION: Asymmetry in retinal parameters exists in healthy eyes and provides valuable assessments in diagnosing retinopathies at early stage.