P 157 Effects of morphine on the response of pain corneal fibers to chemical and mechanical stimulation

m To evaluate comeal sensitivity in 50% galactose-fed rats and explore its potential use in assessing diabetic keratopathy in this animal model. Mathods: Weanling male Sprague-DawleY rats were divided into two weight-matched groups and fed Purina laboratory chow (15001) plus 1) 50% alpha cellulose fiber (controls. n=9); or 2) 50% D-salactose (n= 12). Comeal sensitivity measurements were conducted after i2 months on the diets. A Cachet-Bonnet Aesthesiometer ILuneau) was mounted on a micromanipulator such that the end of the filament (0.012 mm diameter) was in the plane of focus of a slit-lamp biomicroscope (AO). The instrument was utilized to determine Comeal touch threshold (CTT). This index of comeal sensitivity was defined as the exerted pressure on the cornea which elicited a blink response to 50% of the stimuli (5/1Ol. Rats were restrained without medication in a specially designed restrainer. Left comeal sensitivity measurements were conducted sequentially at mean pressures of 11,lZ. 13, 16 mgI.0113 sq mm (filament lengths of 6, 5.5, 5.0, 4.5. respectivelv). Right comeal sensitivity measuremenis were conducted in the reverse order of ipplied pressures. The filament was applied perpendicularly to the central comeal surface (at pupil) and the first visible bending of the filament as well as blink responses were confirmed by two independent investigators. Fluorescein (0.25%) staining was utilized to examine comeal epithelial integrity following completion of sensitivity measurements on each eye. &~f& Paired T-tests comparing left and right comeal sensitivities within groups were not significantly different at any pressure. Comeal sensitivity was significantly decreased lp<O.OOOl) in the galactose-fed rats at all pressures compared to controls. Mean sensitivity of control rats was above CTT at each pressure. Mean comeal sensitivity of the galactose-fed rats was below CTT at each pressure. No clinically significant epithelial defects were noted by fluorescein staining. Condusionr: This study is the first to.demonstrate a decreased central comeal sensitivity in the galactose-fed rat model of diabetic complications. This model could be useful for investigating the pathogenic mechanism(s) involved in decreased comeal sensitivity associated with diabetic keratopathy.