Ocular surface temperature measurement in diabetic retinopathy

Infrared thermography provides functional imaging by picturing the temperature pattern of the region imaged. The temperature correlates to the blood flow pattern and is used in the diagnosis of diseases like breast cancer, peripheral vascular disorders, diabetic neuropathy and fever screening. In the present study, the usage of ocular thermography for diagnosis of diabetic retinopathy is explored. Ocular thermograms using infrared imaging camera were obtained for normal subjects (80 volunteers - 40 males and 40 females) age groups 21-30, 31-40, 41-50 and 51-60 years, non-proliferative diabetic retinopathy (NPDR) patients (50 volunteers -25 males and 25 females) and proliferative diabetic retinopathy (PDR) patients (20 volunteers -10 males and 10 females) belonging to age group of 51-60 years. The temperature at various points of interest (POIs) and horizontal temperature profiles were studied. Ocular surface temperature (OST) and effect of eye dilation on OST was studied for control, age matched NPDR and PDR. Statistical analyses were carried out to find the significance of correlation between OST of controls and NPDR and PDR. The global minimum temperature on the ocular surface for controls (21-60 years) was found to be at cornea which is about 34.79 ± 0.68 °C, and maximum at the inner canthus viz. 36.08 ± 0.62 °C. Dilation studies showed an average increase of 0.82 ± 0.13 °C in cornea and 0.75 ± 0.14 °C in conjunctiva and limbus (p < 0.001). The temperature of cornea is around 33.22 ± 0.12 °C and 32.64 ± 0.12 °C for NPDR and PDR patients respectively, in the age group of 51-60 years. OST of NPDR patients was 0.60 ± 0.15 °C lesser than that of age matched normal eyes (p < 0.001) at cornea and limbus regions and 0.71 ± 0.20 °C at inner canthus. The OST of PDR patients was lesser than age matched controls by 1.18 ± 0.12 °C at cornea, 0.9 ± 0.13 °C at inner canthus and 1.0 ± 0.14 °C at other POIs. During dilation studies a positive variation of 0.61 ± 0.12 °C in cornea and 0.48 ± 0.13 °C in conjunctiva and limbus was observed (p < 0.001) in NPDR eyes. Similarly an average increase of 0.62 ± 0.11 °C in cornea and an average increase of 0.47 ± 0.15 °C in conjunctiva and limbus were observed (p < 0.001) in PDR eyes. The OST of NPDR and PDR patients was less compared with age matched counterparts in both pre and post dilation studies. Dilation of eye showed increase in OST for both controls and diabetic retinopathy patients. The degree of increase is less compared with controls. The variation in OST observed during pre and post dilatation studies of diabetic retinopathy patients is a functional marker of pathology, and can be used as a parameter for diagnosis.