Mesopic foveal contrast sensitivity is impaired in diabetic patients without retinopathy.
BACKGROUND
Contrast sensitivity (CS) has been studied extensively to determine its effectiveness as a test for diagnosing early and advanced diabetic retinopathy. Various techniques have been adopted to measure CS, and most of them reported a significant difference between diabetic and normal eyes. Our purpose is to demonstrate differences in foveal CS between diabetic patients without retinopathy and healthy subjects under mesopic and photopic conditions, using a simple, rapid computerized test.


METHODS
Seventeen eyes of nine patients with type 2 diabetes without diabetic retinopathy were included. Fourteen eyes of seven non-diabetic patients served as controls. All the patients underwent a careful ophthalmologic examination, including ETDRS chart visual acuity, color photographs, and optical coherence tomography (OCT). Patients with any ocular disease were excluded. All eyes had a visual acuity of 20/25 or better, a normal eye examination and optical coherence tomography (OCT). Photopic and mesopic contrast sensitivity was tested using a computerized psychophysical static method involving four forced-choice procedures. The targets were Gabor patches with spatial frequencies of 3-12 cycles per degree (cpd). The mesopic testing was conducted in a completely darkened room; the monitor was covered with a neutral density filter, allowing luminance of only 0.9 cd/m(2).


RESULTS
The average age was similar: 59.1 ± 5.3 years in the diabetic group vs 61.4 ± 3.2 years in the control group. The average duration of diabetes was 16 years (range 6-26). The average visual acuity was 0.04 ± 0.01 logMAR and 0.01 ± 0.01 logMAR in the diabetic and control groups respectively. Photopic foveal CS was similar in both groups. Significantly lower CS was found in diabetic patients under mesopic conditions at a spatial frequency of 3 (p < 0.008). At higher spatial frequencies, the mesopic contrast sensitivity was very low in both groups and without a significant difference.


CONCLUSIONS
Mesopic foveal CS is impaired in diabetic patients despite good visual acuity, a normal fundus examination and normal OCT. Early central visual function impairment may occur in diabetic patients before the appearance of retinopathy.
Katz
Gabriel
G
Goldschleger Eye Institute, Sheba Medical Center, Tel-Hashomer, Tel-Aviv University, 52621, Tel-Aviv, Israel. gabrielkatz.dr@gmail.com
Levkovitch-Verbin
Hani
H
Treister
Giora
G
Belkin
Michael
M
Ilany
Jacob
J
Polat
Uri
U
D000368:Aged; D015350:Contrast Sensitivity / Q000502:physiology*; D003924:Diabetes Mellitus, Type 2 / Q000503:physiopathology*; D003930:Diabetic Retinopathy / Q000503:physiopathology; D005260:Female; D005584:Fovea Centralis / Q000502:physiology*; D006801:Humans; D008297:Male; D055255:Mesopic Vision / Q000502:physiology*; D008875:Middle Aged; D014786:Vision Disorders / Q000503:physiopathology*