VN August 2023

Vetnuus | August 2023 38 lower in brachycephalic dogs compared with mesocephalic and dolichocephalic dogs. Corneal nerves play an important role in the blink reflex, tear production, corneal wound healing, and maintenance of corneal epithelial health. Inherently, low corneal innervation in healthy brachycephalic dogs has been theorized to lead to a reduced blink rate, reduced aqueous tear secretion, and decreased epithelial integrity, all of which are risk factors for developing recurrent erosions, impaired wound healing, and infections. Limbal epithelial thickness was lower, nasally and temporally in brachycephalic dogs compared with non-brachycephalic dogs. The nasal and temporal regions of the limbus might be more vulnerable to damage because of reduced eyelid coverage when compared to superior and inferior regions, and this might be particularly pronounced in brachycephalic dogs with excessively large palpebral fissures and poor corneal protection. Physiological changes: The most commonly described disorder related to blinking in brachycephalic dogs is lagophthalmos (i.e., incomplete closure of the eyelids]. This leads to anomalies in the secretion of meibomian lipids and facilitates the spreading, mixing, and distribution of tear film constituents over the ocular surface The muscular action of blinking also drives the lacrimal pump to allow for adequate drainage of tear fluid via the nasolacrimal duct. The normal apposition of the lids during a complete blink promotes the secretion of meibomian lipids and facilitates the spreading, mixing, and distribution of tear film constituents over the ocular surface. The muscular action of blinking also drives the lacrimal pump to allow for adequate drainage of tear fluid via the nasolacrimal duct. Aqueous tear secretion [the STT] is considered to be 14% lower in brachycephalic dogs compared with non-brachycephalic dogs without clinical complaints of ocular disease. This is mainly attributed to the lower corneal sensitivity of brachycephalic dogs and its negative impact on the afferent pathway of lacrimation. Ageing can also play a role. Tear film homeostasis is also compromised in many brachycephalic dogs owing to insufficient pre-ocular mucins and/or lipids. For every additional year of life, the risk for dogs to develop KCS or corneal pigmentation each increase by 10%. Meibomian gland dysfunction leads to increased tear film break-up time [TFBUT] and lower tear film quality gets worse with increasing age. Ocular Surface Disease: Dry eye disease (DED) is an inflammatory condition of the ocular surface caused by a reduction in the aqueous layer (i.e., quantitative tear film deficiency, also known as keratoconjunctivitis sicca; KCS) and/or reduction in the pre-ocular mucins or lipids that cause an unstable tear film that rapidly evaporates (i.e., qualitative tear film deficiency, also known as evaporative dry eye). DED then leads to corneal fibrosis, pigmentation and vascularization, as well as the frequently seen excessive tacky mucous and conjunctivitis. Measuring the Schirmer tear test is necessary in brachycephalics and the TFBUT may be a further test that can be performed. It is reported that brachycephalic breeds had 11.18 times the odds of developing corneal ulceration compared with cross-breed dogs, while spaniel types had 3.13 the odds and purebred dogs had 2.23 times the odds. Pigmentary keratitis is highly prevalent in Pugs with a reported rate of 82.4%and 71.8% in two studies based in the United States, 70% in a study from Austria, and 91% in a study from the United Kingdom. It is not surprising that brachycephalic dogs are over-represented in veterinary studies that describe surgical corrections of deep ulcers with conjunctival pedicle flaps, corneal grafts, corneo-limbo- conjunctival transpositions or other treatment options. Brachycephalic breeds havemuch higher odds (6.71 times the odds] compared with mesocephalic breeds of developing a prolapsed gland of the third eyelid and this condition may have a bearing on the tear film quality. Management: Because Brachycephalic Ocular Syndrome can manifest through various signs, including excessive tearing, eye redness, squinting, eye discharge, corneal opacity, sensitivity to light, and changes in behaviour, a thorough examination with additional tests and good magnification is required. Ectopic cilia are microscopic structures!The management of Brachycephalic Ocular Syndrome typically involves a combination of medical treatment and, in some cases, surgical intervention. The treatment plan depends on the specific eye conditions present in the dog. Here are some common approaches: 1. Medications: Eye drops, ointments, or artificial tears may be prescribed to lubricate the eyes, reduce inflammation, and prevent infections. If KCS has been diagnosed then Tacrolimus 0.02% eyedrops would be required. 2. Surgical Correction: In cases of severe proptosis, entropion, or distichiasis, surgical procedures may be recommended to correct the abnormalities and alleviate discomfort. 3. Preventive Measures: Owners of brachycephalic dogs can take proactive steps to minimize the risk and severity of Brachycephalic Ocular Syndrome. Regular eye hygiene, such as gentle cleaning of the eye area [Pet Wipes], can help prevent infections and maintain ocular health. Additionally, avoiding situations that may lead to eye trauma, such as rough play or exposure to irritants, is essential. In the authors’ opinion, when BOS is confirmed and anatomical problems are present, especially the most common medial lower lid entropion, the most profound treatment option which can assist by managing most of the problems associated with BOS in one surgical procedure, is medial canthoplasty surgery. Ideally, this should be performed in younger dogs before the severe and vision-threatening pigmentary keratitis develops. Regulars I Ophthalmology Column