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

## TL;DR

This study shows that general anesthesia significantly reduces tear film quantity and quality in healthy dogs, with incomplete recovery by discharge.

## Contribution

The study is the first to comprehensively evaluate both quantitative and qualitative tear film changes in dogs under general anesthesia.

## Key findings

- Tear volume and osmolarity significantly decreased during general anesthesia.
- Tear ferning scores increased, indicating structural deterioration of the tear film.
- Punctate epithelial lesions were found in 34.4% of dogs at discharge.

## Abstract

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.

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.

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).

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.