Brachycephalic pigmentary keratitis

28 Brachycephalic pigmentary keratitis

INITIAL PRESENTATION

Abnormal appearance – cloudy, blind

PRESENTING SIGNS

Brachycephalic pigmentary keratitis can present in a variety of ways. The most straightforward is where the owner has noticed a film appearing over the dog’s eyes with an apparent reduction in vision – particularly for things immediately in front or beneath them. Sometimes there has been recurrent ulceration and thus the dog could have a sore, watery red eye as the reason for seeking veterinary advice. Alternatively, the dog could be presented with a sticky ocular discharge. Normally dogs are young to middle aged and in good general health.

CASE HISTORY

It is not uncommon for a history of previous ulceration to have occurred in one or both eyes. The owners might have been aware of the change in appearance of the eyes associated with a dark film across them. Some increased lacrimation with tear overflow might have been noted; alternatively, the eyes could be slightly dry with a mucoid or mucopurulent discharge. The condition is chronic in nature, and it is possible that the owners were unaware of current problems – perhaps the dog was brought in for routine vaccination and the ocular abnormalities were found incidentally.

CLINICAL EXAMINATION

General clinical examination is usually normal. However, multiple, often quite subtle, abnormalities are detected on ophthalmic examination. The most striking feature is a film of dark pigment extending over the corneas. This is usually bilateral, but not necessarily symmetrical. It is normally most dense ventromedially and extends in a triangle with the apex centrally (Figure 28.1).

Figure 28.1 Bilateral pigmentary keratitis in a young Pug. Note the ventromedial pigment in both corneas.

However, other less obvious changes are likely to be present. The dog can probably see, so menace responses will be present, but these might be reduced, especially if directing the threatening gesture from a ventral or ventromedial direction. Palpebral reflexes should be checked – they are likely to be normal in that the animal will blink, but the eyelids might not fully meet on blinking due to some degree of lagophthalmos. Blink rates might be reduced and incomplete or partial blinks are not uncommon. It is sensible to ask the owners whether the dog sleeps with his eyes fully closed – sometimes they do not. Schirmer tear test readings should be evaluated. These could be normal, increased (especially if corneal ulceration is present) or reduced. Low grade keratoconjunctivitis sicca is not infrequent in brachycephalic dogs.

Careful evaluation of the lid margins should be undertaken. A ventromedial entropion is often present. The eyelid margins will appear tight against the cornea, with hairs from the lid touching the corneal surface. The third eyelid is not normally elevated or providing any corneal protection. Hairs are often also present on the caruncles – the small fleshy protuberances at the medial canthi – and these can both irritate the cornea and act as a wick to draw tears down the face rather than down the nasolacrimal punctae.

Nasal fold trichiasis can be present. Here the hairs from the skin over the nasal folds are in contact with the corneal surface. Viewing the patient from the side and above as well as directly in front will help to determine whether significant trichiasis is present. Close evaluation of the nasolacrimal punctae should be performed. These are normally present, and of normal size, but the medial entropion causes the openings to be physically closed (like a straw flattening on itself). This will contribute to any epiphora. The skin ventromedial to the eye should be checked – the epiphora could allow a low grade moist dermatitis to develop here. Distichia can be present – commonly in English bulldogs for example – but as these are often subclinical they must be carefully examined to see if they are actually in contact with the cornea or the tear film and are truly contributing to the corneal disease, or whether they are purely an incidental finding (Figure 28.2).

Figure 28.2 Ten-year-old Shih Tsu with pigmentary keratitis. Marked corneal scarring is present from previous ulceration and trichiasis from hair at the medial canthus is present. Subclinical distichia are visible on the upper lid. Tear production was normal. This patient was treated with just topical lubrication, including soft white paraffin ointment onto the medial canthal hairs to smooth them away from the cornea and reduce the irritation.

Conjunctival hyperaemia is not a consistent finding – it will be present if there is concurrent corneal ulceration but otherwise the conjunctiva is often normal. Detailed corneal examination is required. The pigment is normally superficial but can be quite thick in places. It will almost always be associated with some degree of corneal vascularization – this is best appreciated at the leading edge of the pigment since the dark colouration will obscure any blood vessels beneath it. If ulceration has occurred previously it is most common centrally in brachycephalics and so some white stromal scarring and/or irregular corneal outline might be present in this area. Active ulceration can be shallow or quite deep with a marked vascular reaction and all the signs typically present with any ulceration. It goes without saying that fluorescein testing is mandatory. As usual, the excess dye should be carefully flushed away using sterile saline solution – the surface of the cornea is likely to be irregular due to the pigment and previous scarring, and pooling of dye in these patches could lead to false positives.

Although intraocular contents are usually normal, evaluation of them can be difficult. Distant direct ophthalmoscopy can be used to assess pupil size and gain a tapetal reflex (albeit reduced). Indirect ophthalmoscopy offers the best way of evaluating the fundus since the view through semi-opaque ocular media is superior with this method over direct ophthalmoscopy.

CASE WORK-UP

Once a thorough ocular examination has been performed to determine the underlying reason for the pigment deposition, then a management plan can be drawn up. This will probably include both surgical and medical options and if the former is indicated a full general examination should be undertaken. Particular attention should be paid to the presence of other brachycephalic problems – notably upper airway conditions – which might require surgery as well as the eyes, or at least should be borne in mind when planning general anaesthesia. Apart from this, there is limited work-up necessary since the ophthalmic examination should be sufficient to reach a definitive diagnosis.

NURSING ASPECTS

The patient is likely to require both surgical and medical management. Thus the nurse will be involved perioperatively in patient preparation, anaesthesia and surgical recovery. Extensive treatment prior to surgery is not usually necessary unless some bacterial skin infection is present associated with the nasal folds for example, in which case a course of systemic antibiotics might be required as well as appropriate topical medication. Once anaesthetized, the nurse will be required to assist surgical preparation and positioning in theatre, along with monitoring the anaesthetic.

Careful monitoring is required during recovery with brachycephalics in particular due to their compromised upper airway anatomy. Prevention of self-trauma is required and sometimes an Elizabethan collar might be necessary. Postoperatively, topical and systemic medication is usually necessary, the former sometimes long term, and nurses are invaluable in instructing clients about this and checking their proficiency at medicating their pet.

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Tags: Saunders Solutions in Veterinary Practice Small Animal Ophthalmo

Sep 10, 2016 | Posted by admin in SMALL ANIMAL | Comments Off

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