Research Article | 27 Dec 2025

Perioperative decline in quantitative and qualitative tear film parameters in clinically healthy mesocephalic Canis familiaris under general anesthesia: A prospective study

Liga Kovalcuka1 , Grēta Elīza Gaile1, Laura Voiko1 , Ilze Dūzena1, Madara Nikolajenko1 , and Ivars Lūsis2 Show more
VETERINARY WORLD | pg no. 4082-4092 | Vol. 18, Issue 12 | DOI: 10.14202/vetworld.2025.4082-4092
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Abstract

          
Background and Aim: General anesthesia (GA) suppresses the blink reflex and lacrimal gland activity, making animals more vulnerable to precorneal tear film (PTF) issues. Although decreases in tear volume during GA are well documented, changes in PTF quality are not well understood. This study examined both the quantity and quality of PTF, including the Schirmer Tear Test-1 (STT-1), tear osmolarity (TO), tear ferning (TF), and punctate fluorescein staining (PFS), in healthy mesocephalic Canis familiaris undergoing routine non-ophthalmic surgery under GA. 
Materials and Methods: A prospective, randomized, pre–post study was conducted on 16 client-owned mesocephalic dogs (32 eyes). All subjects were clinically and ophthalmologically normal and classified as American Society of Anesthesiologists (ASA) I–II. Tear film parameters were evaluated at five perioperative time points: 30 min preoperatively (T0), 10 min post-premedication (T10), 5 min post-induction (T5), at first surgical incision (TS), and at discharge (TD). STT-1, TF, and TO were measured at each time point; PFS was performed at TD. GA consisted of methadone and dexmedetomidine premedication, propofol induction, and isoflurane maintenance. Mixed-effects regression, paired t-tests, and correlation analyses were applied, with p < 0.05 considered significant. 
Results: STT-1 values significantly decreased from baseline (21.2 ± 3.3 mm/min) to T10 (13.5 ± 5.9 mm/min; p < 0.001), T5 (6.4 ± 6.3 mm/min; p < 0.001), and TS (0.8 ± 1.6 mm/min; p < 0.001). TO decreased from 374.4 ± 29.3 mOsm/L at T0 to 354.7 ± 28.2 mOsm/L at TS (p < 0.001). TF grades increased from 0.8 ± 1.0 at T0 to 1.5 ± 1.3 at T10 and 2.3 ± 1.4 at T5 (p < 0.001), indicating deterioration of PTF structure. Moderate correlations were observed among STT-1, TF, and TO. At TD, tear parameters remained significantly altered compared with T0, and PFS identified punctate epithelial lesions in 34.4% of dogs. Age showed a moderate negative relationship with STT-1 (b = –0.41 mm/min; p = 0.038). 
Conclusion: GA causes a significant decline in the quantity and quality of the PTF, with incomplete recovery by discharge despite the return of spontaneous blinking. These findings emphasize the need for proactive perioperative ocular surface protection and highlight TF and TO as useful early indicators of anesthesia-related ocular surface impairment in mesocephalic Canis familiaris. 
          
Keywords: canine anesthesia, corneal protection, dog tear film, ophthalmic complications, Schirmer tear test, tear ferning, tear osmolarity, tear film quality.