Diagnosis and treatment of common ophthalmic disorders in South American camelids

Camelid eyes are large relative to their head and body size. The axial length of the globe is approximately 38 mm. The cornea is ovoid with a prominent curvature, a horizontal diameter of about 25–30 mm, a vertical diameter of 18–22 mm and a thickness of 0.5–0.6 mm (Gionfriddo, 1994; Andrew et al, 2002). The epithelium is relatively thick, made up of 12–15 layers comprising 30% of corneal thickness. The relatively thick epithelium compared with other species is thought to be protective against UV light, dehydration and trauma. The limbus is often defined by a wide heavily pigmented band. The periocular vibrissae and cilia are long and prominent. The eyelid margins are pigmented and do not contain meibomian glands (Gionfriddo, 1993) (Figures 1 and 2).

A large haired caruncle of third eyelid contains sebaceous glands that likely contribute to the pre-ocular tear film (Figure 2). The nasolacrimal anatomy is similar to sheep and horses. The iris of camelids is unique with large pleated folds of posterior pigmented epithelium located dorsally and ventrally around the oval pupil rather than true corpora nigra (Figures 1 and 2). Pigmentation of the iris and fundus varies with coat colour where more heavily pigmented coat colours are associated with brown irides and a darker brown fundus colour. The fundus of South American camelids is characterised by a lack of a tapetum lucidum, a variably pigmented oval-shaped optic nerve head, a variably pigmented retinal pigmented epithelium that gives a dark appearance to the fundus (except in colour dilute animals), large prominent retinal blood vessels that lie superficially on the retinal surface, and commonly, a long, white hyaloid artery remnant (Bergmeister's papilla) visible extending from the center of the optic nerve (Figure 3). Vision in alpacas is nearly emmetropic (normal vision) while llamas, especially females, have been found to be slightly myopic (near-sighted) (Willis et al, 2000a).