Effects of oral administration of diphenhydramine on pupil diameter, intraocular pressure, tear production, tear film quality, conjunctival goblet cell density, and corneal sensitivity of clinically normal adult dogs.

To evaluate the effects of oral administration of diphenhydramine on pupil diameter, intraocular pressure (IOP), tear production, tear film quality, corneal sensitivity, and conjunctival goblet cell density (GCD) in clinically normal adult dogs. 12 healthy adult dogs. All dogs received diphenhydramine (2.2 mg/kg, PO, q 12 h) for 21 days. Conjunctival biopsy samples were obtained immediately before (day 1) and after (day 21) treatment with diphenhydramine and conjunctival GCDs were determined. Gross ophthalmic examinations and fluorescein staining of corneas were performed, and pupil diameter, corneal sensitivity, IOP, tear production, and tear film breakup time were determined prior to administration of diphenhydramine on days 1 through 5 and on day 21; pupil diameter and IOP measurements were repeated on each of those days at 20 and 40 minutes and 1, 3, 6, and 8 hours after administration of diphenhydramine. Data were analyzed to detect differences among values for dogs. Clinically important increases in pupil diameter were not detected after administration of diphenhydramine to dogs. Day 1 corneal sensitivity and tear film breakup time for dogs were significantly higher than day 21 values for those variables. Results of this study suggested that oral administration of diphenhydramine to healthy adult dogs was not likely to acutely induce glaucoma or keratoconjunctivitis sicca. However, effects of diphenhydramine in dogs with keratoconjunctivitis sicca or primary glaucoma or dogs genetically predisposed to development of those conditions were not determined. Administration of diphenhydramine to dogs decreased corneal sensitivity and tear film breakup time, although these effects were not clinically important.