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  • Author or Editor: Gui-Shuang Ying x
  • Ophthalmology x
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Objective—To evaluate the effect of head position on intraocular pressure (IOP) in horses.

Animals—30 horses.

Procedures—Horses were sedated with detomidine HCl (0.01 mg/kg, IV). Auriculopalpebral nerve blocks were applied bilaterally with 2% lidocaine HCl. The corneas of both eyes were anesthetized with ophthalmic 0.5% proparacaine solution. Intraocular pressures were measured with an applanation tonometer with the head positioned below and above heart level. The mean of 3 readings was taken for each eye at each position for data analysis. The effect of head position on IOP was assessed and generalized estimating equations were used to adjust for the correlation from repeated measures of the same eye and intereye correlation from the same horse.

Results—Of the 60 eyes, 52 (87%) had increased IOP when measured below the heart level. A significant difference (mean ± SE, 8.20 ± 1.01 mm Hg) was seen in the mean IOP when the head was above (17.5 ± 0.8 mm Hg) or below (25.7 ± 1.2 mm Hg) heart level. No significant effect of sex, age, or neck length on IOP change was found.

Conclusions and Clinical Relevance—Head position has a significant effect on the IOP of horses. Failure to maintain a consistent head position between IOP measurements could potentially prevent the meaningful interpretation of perceived aberrations or changes in IOP.

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in American Journal of Veterinary Research


Objective—To develop a quantifiable behavioral test for identification of achromatopsic dogs based on visual performance.

Animals—14 dogs.

Procedures—A 3.6-m-long obstacle-avoidance course with 6 obstacle panels was developed from a preliminary 2.4-m-long course. Achromatopsic and visually normal control dogs were run through the course at 4 ambient light intensities (from dim to bright: 0.2, 25, 65, and 646 lux). Completion of 4 runs ranging from dimmest to brightest light intensity constituted 1 complete trial. Each dog underwent 3 trials. Transit times were measured and compared between dog groups and between light intensities by use of a generalized linear model and ANOVA.

Results—At the 3 highest light intensities, the achromatopsic dogs needed significantly more time to pass through the obstacle course than the control animals. Compared with the mean transit time at the lowest light intensity, mean transit times were 2.6 times as long at 25 lux, 3.2 times as long at 65 lux, and 5.7 times as long at 646 lux. The achromatopsic dogs had signs of increasing difficulty navigating around the obstacle panels with increasing light intensities; this was not the situation for the control dogs.

Conclusions and Clinical Relevance—A 3.6-m-long obstacle-avoidance course with 6 movable obstacle panels allowed identification of achromatopsic dogs at ambient light intensities ≥ 25 lux based on transit times. This test could be helpful in the evaluation of new cone photoreceptor specific treatments.

Full access
in American Journal of Veterinary Research