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Purpose: Severe entropion of the medial canthus results in ocular surface diseases and tear staining syndrome. However, detailed anatomical structures of the medial canthus and lacrimal ducts in dogs are poorly understood. We aimed to understand the anatomical structures of the medial canthus by analyzing the distances from the medial palpebral commissure to the superior lacrimal punctum (DSP) and to the inferior lacrimal punctum (DIP) and by histological examinations of the medial canthal anatomy. Methods: Dogs that underwent modified medial canthoplasty (MMC) between April 2017 and March 2021 were studied. As a reference, non‐brachycephalic dogs that underwent other surgeries were also examined. DSP and DIP were measured preoperatively in all dogs in both the non‐everted and everted positions. Histological examinations of the medial canthal anatomy were performed in four eyes isolated from beagles. Results: The ratios of DIP to DSP (mean ± SD) at the non‐everted and everted positions in 242 MMC eyes of 126 dogs were 2.05 ± 0.46 and 1.05 ± 0.13, respectively (p <.01). The ratios of everted to non‐everted positions for DIP and DSP were 0.98 ± 0.21 and 1.93 ± 0.49, respectively (p <.01). Histological findings indicated that the orbicularis oculi muscle (OOM) circumjacent lacrimal canaliculus transformed into collagen fibers and were attached to the lacrimal bone. Conclusions: Histological studies revealed that the OOM circumjacent lacrimal canaliculus transformed into collagen fibers and these collagen fibers may be related to the difference between DSP and DIP. [ABSTRACT FROM AUTHOR]

Dry eye disease (DED) is a complex multifactorial condition caused by loss of ocular surface homeostasis from quantitative and/or qualitative tear film deficiency. Schirmer tear test (STT) is often the only diagnostic test used to assess for DED in veterinary practice. STT is invaluable in the diagnosis and monitoring of quantitative tear film deficiency (i.e., keratoconjunctivitis sicca); however, it is not sufficient to optimize therapy and fully recognize other contributing factors for the disturbance in ocular surface homeostasis. The present work reviews diagnostic tests for assessing aqueous tear production in veterinary medicine, as well as the quality of tears, corneal epithelial barrier integrity, and the lacrimal functional unit. [ABSTRACT FROM AUTHOR]

Objective: To compare the superficial punctate fluorescein staining in dogs with and without aqueous tear deficiency. Procedures: An eye from each client‐owned dogs presented to Triangle Animal Eye Clinic between January and December 2018 underwent tear and ocular surface tests, which included the Schirmer tear test (STT), phenol red thread test (PRT), and strip meniscometry tube tear test (SMT). Punctate fluorescein staining of the cornea (PFS‐C) and the upper palpebral conjunctiva (PFS‐UPC) were also performed. Fifty‐seven dogs with STT results of <15 mm/min had aqueous tear deficiency (AD); 31 dogs had <10 mm/min and 26 dogs had ≥10 mm/min. The 162 dogs with STT results of ≥15 mm/min did not have AD. The test results of the groups were compared using Kruskal‐Wallis and Steel‐Dwass multiple comparison tests. Results: Two hundred and nineteen eyes from 219 dogs were enrolled in this study. The PRT and SMT results, presented as mean ± SD, were significantly lower in the AD group than in the non‐AD group (PRT: 29.5 ± 8.1 vs 36.9 ± 5.6 mm/15 s; SMT: 6.2 ± 3.8 vs 10.8 ± 2.8 mm/5 s). The PFS scores were significantly higher in the AD group than in the non‐AD group (PFS‐C: 4.4 ± 0.7 and 3.7 ± 0.8; PFS‐UPC: 2.3 ± 0.5 and 1.7 ± 0.5). Conclusions: These results suggest that aqueous tear deficiency is not only reflected by PRT and SMT but also PFS‐C and PFS‐UPC. [ABSTRACT FROM AUTHOR]

Objective: To investigate meibomian gland (MG) morphology by noncontact infrared meibography in Shih Tzu dogs with or without keratoconjunctivitis sicca (KCS). Procedures: Fourteen eyes of 12 Shih Tzu dogs (mean age of 10.7 years, range of 7‐13 years) presented to Yakumo Animal Hospital or Triangle Animal Eye Clinic from 2011 to 2017 with clinical signs and a Schirmer tear test (STT) result consistent with KCS (<10 mm/min) were examined. Twenty‐eight eyes of 16 Shih Tzu dogs (mean age of 12.4 years, range of 8 to 15 years) with a STT > 15 mm/min served as healthy controls. Both groups of dogs underwent routine slitlamp biomicroscopy followed by noncontact infrared meibography of the upper eyelid with both desktop‐type and mobile‐type systems. Results: Meibography revealed morphological abnormalities of MGs in 13 eyes of 11 dogs with KCS. The abnormalities included gland shortening in 64% and gland dropout in 64% of the 14 eyes in the KCS group. Morphological changes were also observed in MGs of 16 eyes of 10 dogs in the control group. These changes included shortening in 46% and dropout in 17.8% of the 28 eyes in the control group. Dropout was significantly more common in eyes with KCS than in control eyes (P < 0.01). Conclusions: The frequency of MG abnormalities is increased in Shih Tzus with KCS compared with control animals. A reduced quality of the tear film associated with increased evaporation and reduced retention of tear fluid likely exacerbates the effects of a reduced tear volume in animals with aqueous deficiency. [ABSTRACT FROM AUTHOR]