Ocular surface diseases in dogs are frequently encountered in routine ophthalmology consultations. These include ulcerative keratitis, pigmentary keratitis and keratoconjunctivitis sicca, and are typically seen in brachycephalic dogs. The underlying cause is their abnormal conformation: large palpebral fissures (macroblepharon), prominent globes and corneal exposure due to shallow orbits, medial lower eyelid/canthal entropion and associated trichiasis, as well as caruncular trichiasis (Figure 1). Together, these conditions are also known as brachycephalic ocular syndrome (BOS) (Nutbrown-Hughes, 2021; Costa et al., 2021; Palmer et al., 2021; Sebbag and Sanchez, 2023). Although medical management can alleviate the clinical signs associated with this anatomical abnormality, it is usually insufficient, leading to the progression and worsening of ocular surface diseases. Medial canthoplasty is a surgical technique that corrects the anatomical abnormalities present in brachycephalic dogs, significantly improving overall ocular surface health.
Historically, medial canthoplasty has been performed by incising the eyelid margins (upper and lower) perpendicular to the medial canthus. The area of incision was limited by the puncta and canaliculi; however, this restriction reduced the extent to which the palpebral fissure could be shortened (Yi et al. 2006). Since macroblepharon and eyelid length vary among individual dogs, this original technique often resulted in under-correction in patients with more severe macroblepharon and greater corneal exposure.
A surgical technique described by Allgoewer (2024), which is also the author’s approach, allows for the removal of a greater length of both the upper and lower eyelids, resulting in a greater reduction of the palpebral fissure. This can be particularly beneficial for patients who require it. The length of the eyelid to be removed can be measured with a Schirmer tear test paper strip or callipers (Figure 2A). Increased visualisation of the canaliculi can be achieved using a Nettleship dilator if necessary (Figure 2B). Both the upper and lower puncta are incised with surgical scissors (Figure 2C), and the canaliculi are opened from the puncta down to the medial fornix.
The nictitans membrane is then exposed using von Graefe forceps or mosquito forceps, and the caruncle is excised (identified as pigmented or non-pigmented conjunctiva, sometimes with hair follicles in the medial rostral fornix). Upper and lower free eyelid margin incisions are made medially at a depth of 3 to 4mm (Figure 2D). These incisions are then extended towards the medial canthus, parallel to the eyelid margins, until they meet at the medial canthal skin, beyond the medial canthus. The distance from the incisions at the free eyelid margin to the medial canthus depends on the total initial eyelid length and the desired final size of the palpebral fissure, which is usually set at 20mm from the “new” medial to lateral canthus (author’s approach to medial canthoplasty). The medial canthal skin is released by cutting the medial canthal ligament, which can be identified at the medial canthus, extending from the medial orbital rim rostrolaterally to the orbicularis oculi muscle beneath the medial canthal skin.
The surgical wound is then closed in two layers. The tarsal suture brings together the “tarsal” plates (deeper layer) of both eyelid margins using a far-near-across-near-far loop technique. This is followed by suturing the subconjunctival layers with 6-0 absorbable suture material using a simple interrupted vertical U suture or a continuous suture pattern. A figure-of-eight suture, bringing together the free eyelid margins, is performed by entering the skin of one eyelid approximately 2mm from the eyelid margin and 1mm from the wound, directed obliquely to the opposite side of the surgical wound.
The needle then enters the contralateral eyelid wound and exits approximately two meibomian gland openings away from the wound margin. This movement is then repeated in reverse on the other side of the wound, entering approximately two meibomian gland openings from the wound margin and directed obliquely to the opposite side, exiting through the eyelid skin 2mm from the free margin and 1mm from the wound margin (Figure 3). All entry and exit points must be equidistant from the wound margins and symmetrical on both sides of the wound. The remainder of the skin incision (involving the skin and orbicularis muscle) is sutured with 6-0 absorbable or non-absorbable suture material using a simple interrupted pattern until the wound is fully closed.
This procedure for medial canthoplasty is usually performed bilaterally in dogs, which adds the challenge of achieving symmetrical results in both eyes. Although reducing the palpebral fissure is the primary goal of this procedure and is typically discussed with the owners, it is important to emphasise the change in appearance this will cause. When performed bilaterally, managing owner expectations regarding symmetry is crucial to avoid unexpected concerns or feedback.
The post-operative period and recovery in dogs are usually short, as the eyelids are well vascularised, allowing for rapid healing. Post-operative treatment typically includes the use of a hard buster collar, systemic pain relief (a combination of non-steroidal anti-inflammatories, paracetamol and gabapentin), systemic antibiotics (either empirical or based on skin culture and sensitivity testing prior to surgery) and topical antibiotics.
The complication rate is very low (1.01 percent), as reported by Allgoewer (2024). These complications include wound dehiscence, corneal ulceration secondary to suture irritation and wound infection. To minimise the risk of complications, an appropriately sized hard buster collar is essential. Other complications may include trichiasis, insufficient palpebral fissure reduction and medial lower entropion.
When performed appropriately, the medial canthoplasty procedure reduces the length of the palpebral fissure, enhancing globe protection by the eyelids, allowing for a complete blink and improving tear film distribution over the cornea (Figures 4D, 5D, 6D and 7). This helps reduce excessive evaporation of the tear film and minimises corneal exposure (Figures 4E, 4F, 5E and 5F). Medial entropion is resolved by removing the in-rolling skin and releasing the tension from the medial canthal ligament. Removing the caruncles eliminates caruncular trichiasis.
Some corneal changes associated with chronic corneal trauma and irritation (such as corneal fibrosis, vascularisation and pigmentation) have been reported to stop progressing and even improve following medial canthoplasty and topical treatment (Figures 6B, 6C, 6E, 6F and 8) (Allgoewer et al., 2016). It is common for these patients to be started on long-term treatment with topical lacrimostimulants/immunomodulators, such as cyclosporin A or tacrolimus, which have been shown to reduce corneal pigmentation and inflammation, thereby enhancing corneal transparency and improving vision (Crasta et al., 2023).
Medial canthoplasties have a significant impact on the conformation of patients who undergo this procedure, resulting in considerable changes to their appearance (Figures 6A, 6D, 9A and 9B). While this intended outcome does not influence the clinical decision to choose this surgical technique when indicated, it does significantly affect the owners. Therefore, it is important to ensure that owners are fully informed about the cosmetic results of the procedure.
A survey of owners of brachycephalic dogs that had undergone medial canthoplasty documented that owners were very satisfied with both the clinical and cosmetic outcomes. Following this procedure, owners reported a reduction in the need for periocular cleaning, decreased ocular discharge and improved ocular comfort (Andrews et al., 2023).
Medial canthoplasty is a surgical technique performed in brachycephalic dogs that corrects, with minimal complications, the anatomical abnormalities of the eyelids that cause ocular surface disease and vision impairment. It plays an important role in managing BOS and, alongside medication, improves the comfort and quality of life for individuals undergoing this procedure.
Although the literature on BOS and medial canthoplasty primarily documents canine cases, feline breeds with marked brachycephaly, such as the Persian, also present with associated ocular surface disease (O’Neill et al., 2019). Given that the anatomy of the cat’s medial canthus is similar to that of the dog, the surgical technique in cats is presumed to be similar to that described for dogs, with potentially similar benefits based on the authors’ experience.
Since medical management alone is insufficient to improve ocular surface health and halt the progression of clinical signs associated with BOS, medial canthoplasty should be recommended for all canine patients with BOS-related ocular surface disease. It should also be considered for brachycephalic patients without overt ocular surface disease to reduce the incidence of corneal disease associated with BOS.
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