Discussion
The surgical indication was given in all four ulcers of this retrospective study because of the depth of the corneal defect (4/4), signs of melting (2/4), big diameter of the ulcus (4/4) and poor healing conditions because of BOS (4/4).
Most commonly isolated bacteria in infected corneal ulcers are Staphylococcus and Streptococcus spp. In this study Streptococcus canis could be detected in two cases. In contrast, the corneal swab sample of the melting ulcer in case 4 was negative.
While waiting for the antibiotic test results all ulcers in this study were treated with systemic antibiotics and topical application of preservative free antibiotic eyedrops before and after surgery.
Ulcerative keratitis has a vast range of causes in dogs. Brachycephalic breeds have the highest prevalence of corneal ulcers with a twenty times higher likelihood to be affected than non-brachycephalic dogs. The predisposing factors include macroblepharon, shallow orbits with subsequent lagophthalmos, medial canthal entropion, trichiasis, tear film deficits and reduced corneal sensitivity. These factors are collectively known as brachycephalic ocular syndrome (BOS). In one study most of the mean values of ocular surface diagnostic tests were lower in brachycephalic compared to non-brachycephalic dogs.
This study consisted of cases in which a therapeutic compromise had to be found. Therapeutic management was limited due to financial restraints (cases 2 and 4), compliance of the owners (cases 1 and 2) and anaesthetic restraints due to the severe respiratory brachycephalic syndrome (all cases). Surgical therapy was imperative in all four cases because of the deep of the ulcers. The compromise was to use a xenogenic biomaterial as scaffold and for replacing missing tissue without suturing in combination with a third eyelid flap for providing bandage and mechanical stability. These biomaterials have been used successfully for surgical therapy of corneal defects in dogs and cats and replace missing tissue und and serve for regeneration. They were applied either alone or in combination with covering by a conjunctival flap , with temporary lateral tarsorrhaphy and a temporary nictitating membrane flap . All these grafts were placed in the defect and sutured in the peripheral intact cornea tissue. This takes time and is an expensive surgery. In some instances a short procedure time is imperative and/or financial restrictions exist. Furthermore, suturing the cornea requires microsurgical equipment and experience of the surgeon. Sometimes one or both of these requirements are not met.
The main disadvantage of the third eyelid flap is to monitor progress or worsening.
However the third eyelid flap is superior to a temporary lateral tarsorrhaphy for full coverage of the nonfixated piece of SIS. In addition, in case of worsening pain and increasingly discharge would be expected and couldn’t be seen in all four cases.
Further limitations of the study were the small sample size and the short follow up time in two cases. Studies with more patients and a comparison group for further research into this technique should be performed in future. But the first results presented in this case report are promising that the modified surgical technique may be useful in very selected cases because it makes the procedure easier and faster. In all cases of this study the cosmetic and visual outcome was very good to excellent.