Effects of experimentally induced hypothyroidism on the eye and ocular adnexa of dogs

Paul E. Miller From the Departments of Surgical Sciences (Miller) and Medical Sciences (Panciera), School of Veterinary Medicine, University of Wisconsin-Madison, 2015 Linden Dr West, Madison, WI 53706.

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David L. Paneiera From the Departments of Surgical Sciences (Miller) and Medical Sciences (Panciera), School of Veterinary Medicine, University of Wisconsin-Madison, 2015 Linden Dr West, Madison, WI 53706.

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Summary

Schirmer tear test (stt), intraocular pressure (iop) measurement, slit-lamp biomicroscopy, and indirect ophthalmoscopy were performed on 8 dogs with 131I-induced hypothyroidism and 4 euthyroid control dogs at weeks 0, 9, 13, 17, immediately prior to treatment with levothyroxine, after 5 weeks of levothyroxine administration (0.022 mg/kg of body weight, po, q 12 h), and at euthanasia 7 weeks after discontinuation of replacement therapy. Although the control group had higher baseline stt values than the hypothyroid group after randomization of dogs into the 2 groups (P < 0.01), stt values remained unchanged from their respective baseline values at all time intervals for both groups. Hypothyroid and control dogs had significant (P < 0.05) reduction in iop from baseline values at all subsequent time points, but differences were not observed when hypothroid dogs were compared with controls. Goblet cell indices determined from biopsy samples of the inferiornasal conjunctival fornix obtained before induction of hypothyroidism (baseline), immediately prior to and at conclusion of levothyroxine therapy, and at euthanasia were not significantly different when values for hypothyroid dogs were compared with their own baseline values or with values for control dogs. Histologic examination of the globes and adnexa at euthanasia also failed to indicate consistent qualitative differences between hypothyroid and control dogs. Marked reduction in serum thyroid hormone concentrations had little effect on the eye and ocular adnexa over the course of the study.

Summary

Schirmer tear test (stt), intraocular pressure (iop) measurement, slit-lamp biomicroscopy, and indirect ophthalmoscopy were performed on 8 dogs with 131I-induced hypothyroidism and 4 euthyroid control dogs at weeks 0, 9, 13, 17, immediately prior to treatment with levothyroxine, after 5 weeks of levothyroxine administration (0.022 mg/kg of body weight, po, q 12 h), and at euthanasia 7 weeks after discontinuation of replacement therapy. Although the control group had higher baseline stt values than the hypothyroid group after randomization of dogs into the 2 groups (P < 0.01), stt values remained unchanged from their respective baseline values at all time intervals for both groups. Hypothyroid and control dogs had significant (P < 0.05) reduction in iop from baseline values at all subsequent time points, but differences were not observed when hypothroid dogs were compared with controls. Goblet cell indices determined from biopsy samples of the inferiornasal conjunctival fornix obtained before induction of hypothyroidism (baseline), immediately prior to and at conclusion of levothyroxine therapy, and at euthanasia were not significantly different when values for hypothyroid dogs were compared with their own baseline values or with values for control dogs. Histologic examination of the globes and adnexa at euthanasia also failed to indicate consistent qualitative differences between hypothyroid and control dogs. Marked reduction in serum thyroid hormone concentrations had little effect on the eye and ocular adnexa over the course of the study.

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