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Vandana C. Reddy, Jacqueline A. Leavitt, Sanjay V. Patel; Corneal Sensitivity, Blink Rates, Ocular Surface Disease, and Corneal Nerve Density in Progressive Supranuclear Palsy and Parkinson Disease. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1974.
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Progressive supranuclear palsy (PSP) and Parkinson disease are associated with motor and non-motor features. PSP and Parkinson disease patients are frequently diagnosed with dry eye syndrome, but these patients rarely complain of dry eye symptoms. We hypothesized that lack of dry eye symptoms might be related to decreased corneal sensitivity. The aim of this study was to determine the relationships between blink rates, dry eye, and corneal sensitivity in PSP and Parkinson disease, and to compare these findings to those of normal control eyes.
In a cross-sectional clinical study, 14 eyes of 7 patients with PSP, and 8 eyes of 4 patients with Parkinson disease were examined and compared to 8 normal eyes of 4 age-matched control subjects. The primary outcome was corneal sensitivity, measured by using a Cochet-Bonnet esthesiometer. Blink rate, meibomian gland disease, tear meniscus height, tear film breakup time, and ocular surface staining, were determined according to established grading scales. Corneal subbasal nerve density was also measured by using confocal microscopy in vivo. Comparisons between variables were made by using generalized estimating equation models to account for possible correlation between fellow eyes of the same subject.
Corneal sensitivity in both PSP (2.5 ± 1.6 cm, mean ± SD) and Parkinson disease (4.2 ± 1.6 cm) was lower than that in controls (5.9 ± 0.2 cm, p<0.001). Blink rates were lower in PSP (1.9 ± 1.3 blinks/sec) and Parkinson disease (8.5 ± 2.9 blinks/sec) than in controls (12.4 ± 0.8 blinks/sec, p<0.001). Abnormalities of the dry eye tests were more common in both PSP and Parkinson disease compared to controls (p<0.001). In PSP and Parkinson patients, blink rate was correlated with corneal sensitivity (r = 0.67, p <0.001). Corneal subbasal nerve density in PSP and Parkinson disease did not differ from that in controls (p=0.39 and p= 0.06, respectively).
Corneal sensitivity was markedly reduced in patients with PSP and Parkinson disease, and this might explain why these patients manifest signs of dry eye yet remain asymptomatic. The reason for decreased corneal sensitivity in PSP and Parkinson disease is unknown, but is not explained by decreased corneal nerve density. It is unknown whether the decreased blink rate is a manifestation of decreased corneal sensitivity, or if decreased sensitivity is a manifestation of dry eye caused by decreased blink rate.
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