Nastash continues with an overview of commonly used equipment. It is best to adhere to a systematic protocol, examining all parts of the eye in order, no matter what the presenting complaint. By following such a routine, it is less likely that problems will be missed. Both eyes require examination, even if only one has an obvious problem. Cats should be gently restrained, using a towel only if necessary.

Firstly, the animal is examined with the lights on and attention paid to facial symmetry, palpebral reflex, menace response, dazzle reflex and papillary light responses as discussed in Sally Turner’s article.

The lights are then turned off to minimise reflections.

Focal light source examination

Using a penlight, Finhoff transilluminator, or the light provided by a direct ophthalmoscope, a general examination of the eyelids and the eye is made, usually starting with the outside and working inwards.

Examination should include:

•   eyelids – look for injuries or entropion (eyelids rolling inwards)

•   ocular mucous membranes – the conjunctiva will be pale with anaemia, yellow with jaundice and congested with conjunctivitis. Petechiae may be a sign of clotting problems such as rat poisoning or haemolytic anaemia

•   cornea – check for cloudiness, redness (neovascularisation) and surface irregularities

•   anterior chamber. This should be clear with no cloudiness or blood in front of the iris

•   iris – the margins of the pupil should be smooth and not distorted, without blood or pigment spots

•   lens – within the pupil, the lens may appear white or cloudy if there are cataracts.

Distant direct ophthalmoscopy

This technique is quick and simple to perform and can provide very valuable information. It involves using the shiny tapetal reflection to highlight any abnormalities in front of it, which may appear as a dark shadow. It is performed in a darkened room.

The lens of the direct ophthalmoscope is set to zero. The examiner needs to be positioned an arm’s length distance from the patient. Then, holding the ophthalmoscope up to their own eye, they can examine the patient’s tapetal reflection (Figure 1).

Figure 1: Distant direct ophthalmoscopy

Note the size of the pupils (anisocoria is the term if they are different from each other). If there is a cataract in the lens, it will not be possible to get the tapetal reflection. The retina with its blood vessels may be observed ‘floating, if it is detached.

Examination with magnification

Using an otoscope, a direct ophthalmoscope changing the lens dial setting, or a slit-lamp, a more careful examination of the anterior chamber is carried out (Figure 2). Attention is paid to finer details, such as distichia or ectopic cilia on the eyelids, small opacities on the cornea, and so on.

Figure 2: Slit-lamp biomicroscopy

Examination of the fundus

The fundus should always be examined. The optic nerve should be assessed for colour (red or pale), size (smaller or enlarged) or appearance (raised, or depressed). The retina itself cannot be seen directly in the normal animal as it is transparent, but it will appear as a grey/white veil when it is detached. The retinal blood vessels can be examined for calibre (attenuated or not), colour and tortuosity.

The tapetum is a reflective structure sitting underneath one area of the retina. It should be examined for hyperreflectivity, hypo-reflectivity or haemorrhages. The non-tapetal fundus is the dark brown area of the fundus, excluding the tapetum and optic nerve. It should be examined for elevations, pigmentation or depigmentation.

To allow for the best view of the fundus, the pupils should be pharmacologically dilated with tropicamide. Dilation takes at least 20 minutes to achieve, and it is important to wait until it has taken effect.

The fundus may be examined using direct or indirect ophthalmoscopy (Figures 3 and 4). By using indirect ophthalmoscopy, the picture obtained is much larger than that obtained on close direct ophthalmoscopy. The technique takes a little longer to learn, but is very rewarding as the image obtained is so clear owing to the wide field of view.

Figure 3: Direct opthalmoscopy

Figure 4: Indirect ophthalmoscopy

Schirmer tear test (STT)

Nurses may perform the STT. It should be carried out before placement of other topical drops, such as local anaesthetic, which would reduce the reading.

Before opening the packet, bend the notched area over 90°. Then open the packet from the other end, where L and R are marked for left and right. Try to handle the strip only at this end, as oils on your fingers can be absorbed and prevent the passage of tears down the strip. Gently pull out the lower eyelid. Hook the notched section over the lateral aspect of the eyelid, so that it may contact the cornea. If possible, place the strip in the second eye immediately afterwards.

It is useful to place a hand on the cat’s neck area to prevent it from raising its paws to rub out the strips. The distance travelled by the tears on the test strip in 60 seconds is recorded. Cats have variable results. A value of <10mm wetting per minute is considered significant in the presence of ocular surface disease.

Figure 5: Schirmer tear test (STT)

Fluorescein stain

The vet will need to examine the eye before fluorescein is applied.

Fluorescein is a water-soluble ophthalmic dye. One drop is applied and excess dye must be then flushed from the eye – otherwise it pools in any irregularities on the corneal surface (Figure 6). The dye is orange in colour, but changes to bright green when in contact with the alkaline tear film.

Figure 6: Applying fluorescein

Uptake by the cornea indicates ulceration. Descemet’s membrane does not uptake fluorescein; therefore a clear area at the base of a deep defect in the cornea is a bad sign, as the ulcer is very deep and in danger of rupturing. Observing fluorescein stain uptake is greatly enhanced by examining with a blue light – using a Wood’s lamp, a blue filter attached to the end of your pen torch, or your ophthalmoscope may contain a blue filter.

The stained cornea may be shown to the owners, which can help them to understand their cat’s problem. The dye usually appears at the nose or mouth five minutes later, confirming the patency of the nasolacrimal duct – it is best to warn owners about this (Figure 7).

Figure 7: Fluorescein appearing at the nares and mouth

Concluding comments

Other ocular tests, include tonometry (measurement of intraocular pressure), and ultrasound (useful when the eye is cloudy or full of blood).

If the eye problem appears serious but the diagnosis cannot be made by your practice examination, it is strongly advised that the cat is referred to a veterinary ophthalmologist as soon as possible, as some conditions can only be successfully treated if presented early in the course of disease.

Author

Natasha Mitchell

MVB CertVOphthal MRCVS

Veterinary Nursing Journal • VOL 25 • Nol • January 2010 •