The role of veterinary nurses in canine cataracts

Canine visual impairment is commonly presented in first opinion practice resulting from a variety of acute and progressive diseases or trauma. Canine cataracts are one of the most common causes of blindness in dogs (Gould, 2002; Gelatt and Mackay, 2005). Cataracts have a highly variable nature and appearance and can be classified according to their progression, location, age of onset and aetiology (Petersen-Jones, 2002; Fischer, 2019). Owners may report ‘cloudiness’ or opacity of the lens or a grey appearance of the eyes accompanied by gradual or acute vision loss (Figure 1); although, many owners do not realise there are cataracts until very late in the disease process and often believe cataracts are part of the ageing process.

The canine lens is approximately 7 mm thick, 10 mm in equatorial diameter, and has a volume of 0.5 ml (Samuelson, 2013); it divides anterior and posterior segments of the eye and is involved with focusing light onto the retina. The lens is a transparent biconcave structure located behind the iris, surrounded by an outer capsule, supported by the suspensory ligament to the ciliary body (Figure 2). Contraction of the ciliary muscles allows the process of accommodation — the ability of the eye to change the focal length of the lens by changing the curvature of the lens — maintaining focus as the distance of an object from the eye varies (Busse, 2011). The anterior epithelial cells are located beneath the anterior lens capsule and actively divide by mitosis; as they multiply, they move towards the lens periphery and start to form lens fibres (Hyde, 2011). Lens fibres are constantly produced throughout life, resulting in the progressive compression of the lens nucleus. These fibres are partially responsible for the normal ageing change, known as nuclear sclerosis, where the lens nucleus becomes denser (Hyde, 2011). Nuclear sclerosis presents as a grey appearance of the eye however, the retina can still be easily examined (Figure 3).