PRESENTING SIGNS

The patient will be presented due to a sudden change in appearance of the eye and the owner will have noticed a pink fleshy mass at the medial canthus (Figure 8.1). Patients are normally young dogs, 3–12 months old, although sometimes cats (e.g. Burmese) can be affected. Very occasionally an older dog will present which does not fit into the normal signalment. In this instance it is necessary to look for an underlying predisposing cause such as keratoconjunctivitis sicca which will be discussed briefly later. The condition is initially unilateral but has a definite bilateral risk. The patient is normally unconcerned about the appearance of the lump, with minimal discomfort and usually only a very mild serous ocular discharge. The mass can become very inflamed in appearance and slightly swollen within a couple of days and the discharge can become mucopurulent due to secondary bacterial infection.

Figure 8.1 Prolapsed nictitans gland of the left eye in an Old English (or Victorian) bulldog.

CASE HISTORY

Usually there is no previous history prior to the appearance of the mass. The owners typically are alarmed by the sudden appearance and seek veterinary attention quickly. However, a few do leave the dog for a week or more since the pet does not show any symptoms of pain or visual disturbance. By this time a mucopurulent ocular discharge has often developed. The mass can appear overnight or sometimes the dog will have been out playing and returns with the strange appearance, making the owners think that the pup has been injured.

CLINICAL EXAMINATION

General clinical examination is typically normal. On ophthalmic examination the most obvious abnormality is the presence of a smooth, pink mass at the medial canthus. Mild conjunctival hyperaemia and a slight serous discharge might be present but no overt blepharospasm or discomfort is usually noted.

On close examination the mass can be seen extending from the bulbar aspect of the third eyelid, and the leading edge of the nictitans membrane cannot be seen. Sometimes there is kinking, or scrolling, of the cartilage of the nictitans membrane (Figure 8.2), although this might not be appreciated in the conscious patient when the gland is fully prolapsed. No ulceration is usually present. Schirmer tear tests should be performed and are usually normal or marginally reduced (presumably due to inflammation in the gland restricting the secretion of aqueous tears). Intraocular contents are also typically unremarkable.

Figure 8.2 Scrolled cartilage in a young Labrador retriever – this can be mistaken for a prolapsed nictitans gland so careful ophthalmic examination is essential.

The fellow eye should be fully evaluated since the condition has a strong tendency to be bilateral (although not necessarily at the same time).

The globe should be retropulsed to examine the nictitans membrane. Any scrolling or weakness of the cartilage can be examined. The bulbar aspect of the membrane should be examined if there is any concern about the gland’s position. A cotton bud soaked in topical anaesthetic is held against the third eyelid for 30–60 seconds and then it can be grasped with fine fixating forceps (e.g. Von Graefe forceps, Figure 13.1) and the underside examined. In addition to checking the position of the gland, its size is evaluated and the presence of any follicles or inflammatory lesions on the bulbar aspect noted.

CASE WORK-UP

Since the condition is readily diagnosed on clinical examination there is little requirement for case work-up. The Schirmer tear test should be recorded in the notes since many of the breeds predisposed to prolapsed nictitans glands are also those which suffer from keratoconjunctivitis sicca later in life. The fellow eye should be fully evaluated and discussions with the owners over the risk to the second eye, and whether it should undergo prophylactic surgery at the same time as correction on the affected eye, should be considered.

EPIDEMIOLOGY

Prolapse of the nictitans gland is a breed-related condition. Thus, there must be some genetic aspects, although as with so many adnexal diseases in dogs the exact genetic abnormalities have not been established. Pre-disposed breeds are many, and include the English bull-dog, great Dane, Neapolitan mastiff and other mastiff breeds, English and American cocker spaniels, Lhasa Apso and Shih Tsu, and Pekingese among others. Burmese cats are also affected but it is rare in other feline breeds. Typically dogs are a few months old when presented – bulldogs are frequently very young, sometimes less than 3 months – while the larger breeds such as the mastiffs are often 6–9 months before the prolapse develops.

Although the condition is very common, the actual pathogenesis remains poorly understood. The standard wisdom is that there are anatomical anchoring abnormalities such that the gland is not properly attached to the orbital fascia, allowing it to pop out of position. A local adenitis is often present, but this is probably secondary to the abnormal anatomy rather than being the primary underlying problem. However, once the gland becomes displaced it rapidly becomes swollen and inflamed, which further affects its positioning and can result in lowered aqueous tearing as well as predisposing to secondary bacterial infections.

ANATOMY AND PHYSIOLOGY REFRESHER

See introduction. The nictitans gland is found deep within the ventromedial third eyelid and is attached loosely to the periorbital tissue and base of the nictitans cartilage. It secretes the aqueous portion of the tear film, contributing up to one-third of this (the remainder comes from the main lacrimal gland).