Impact of acute conjunctivitis on ocular surface homeostasis in dogs

Abstract

Objective To investigate the effects of acute conjunctivitis on tear film characteristics and corneal sensitivity in dogs. Animals studied Eight female spayed Beagle dogs (1.5‐2 years old, 7.5‐10 kg). Procedures On two consecutive days, one randomly selected eye in each dog received 1 or 375 mg/mL histamine solution to induce mild or severe conjunctivitis, while the contralateral eye served as control. Diagnostic tests were performed in the following order: fluorescein instillation and repeated tear collection over 20 minutes (to determine tear volume [TV] and turnover rate [TTR] by fluorophotometry), Schirmer tear test‐1 (STT‐1), tear ferning, corneal esthesiometry, and tear film breakup time (TFBUT). Results Results are presented as median values for severe conjunctivitis, mild conjunctivitis, and control eyes. Eyes with severe conjunctivitis had significantly higher STT‐1 (24, 19.5, 17.5 mm/min; P = .002) and significantly lower TFBUT (10.5, 13.5, 15.5 s; P = .002), but no changes were noted in corneal tactile sensation (2, 2.5, 2.5 cm) or tear ferning (grades 2, 2, 2.5). Severe conjunctivitis significantly increased TV by nearly 10‐fold (631, 97, 65 µL) initially (reflex tearing), although basal TV returned rapidly (<5 minutes) in all eyes (46, 58, 48 µL). Finally, there was a nonsignificant trend for higher reflex TTR in the conjunctivitis vs control eyes (68, 58, 43%/min). Conclusions Experimentally induced conjunctivitis increases tear quantity and decreases tear quality in dogs, but has no impact on corneal sensitivity. Changes in tear film dynamics could affect ocular pharmacology (eg, precorneal retention time), although homeostasis of lacrimal volume and drainage is rapidly restored.

Impact of diurnal variation, sex, tear collection method, and disease state on tear protein levels in dogs

“…Residual reflex tearing may play a role by diluting protein content with excess tear fluid, although tear film dynamics (tear volume, tear turnover rate) typically return to baseline values in less than 20 minutes. 24,27 Despite an overall reduction in TPC, serum albumin levels increased in canine tears with experimentally induced conjunctivitis, consistent with findings in animals and humans with naturally acquired ocular inflammatory conditions. 14,17,23 Ocular disease disrupts the blood-tear barrier and allows leakage of plasma compounds into the tear film, as previously described in dogs 14,28 and other species.…”

“…Disease state was mimicked in canine eyes following a reliable in vivo model using topical histamine solutions. 14 The following precautions were taken to minimize bias in protein quantification due to collection methods or experimental induction of conjunctivitis: (i) 20 minutes elapsed between topical administration of histamine and sampling, allowing ample time for ocular surface homeostasis to return 27 ; and (ii) protein levels were compared to baseline measurements to account for variability inherent to the tear collection methods. 14 Tear film TPC generally decreased with experimentally induced conjunctivitis, especially when tears were sampled with Schirmer strips.…”

An eye on the dog as the scientist's best friend for translational research in ophthalmology: Focus on the ocular surface

“…• A transient increase in tear quantity and decrease in tear quality occur, although tear film homeostasis is rapidly restored in ≤5 min. 304 Levels of serum albumin are increased in tear film of canine eyes with experimentally induced or naturally acquired conjunctivitis, 200,273 a physiological variation caused by the breakdown of the blood-tear barrier ( Figure 6). Disruption of the blood-tear barrier is also described in human patients with spontaneous ocular surface disorders (e.g., dry eye, allergic conjunctivitis) 226,305-307 and other animal species (rabbits, horses, and guinea pigs).…”

“…The duration of conjunctivitis can be lengthened by repeating topical histamine administration at set intervals 215 Topical histamine is safe and generally well‐tolerated, although selected eyes receiving the highest dose of histamine (375 mg/ml) can develop mild ocular irritation (lasting <1 min), blepharitis or miosis. Tear film composition changes in eyes with experimentally induced conjunctivitis (e.g., higher levels of serum albumin and inflammatory cytokines), mimicking clinical patients with ocular surface inflammation. A transient increase in tear quantity and decrease in tear quality occur, although tear film homeostasis is rapidly restored in ≤5 min 304 …”

“…A transient increase in tear quantity and decrease in tear quality occur, although tear film homeostasis is rapidly restored in ≤5 min 304 …”