The vet will start by carrying out a basic clinical examination on your horse, to make sure there are no other problems.  If your horse’s eye is very painful, or for example they are somwhat head-shy, then sedation may be needed to make the exam less stressful for your horse, and to enable the vet to examine the eye fully and carefully.  Occasionally horse’s eyes can be so painful that they cannot be opened, and in this situation the vet may place a nerve block to temporarily paralyse the upper eyelid.

The examination of the eye will start from a distance, and will assess the degree of eyelid closure, the position of the eye, and any swelling or discharge.  Vision must next be assessed, and this will be done using a combination of a few tests:

• Menace response – does the horse try to avoid a hand moving toward their eye?
• Dazzle response – does the horse move away from an extremely bright light?
• Pupillary Light Response – do the pupils respond normally to light?
• Obstacle course – in horses where the above tests reveal a possible vision problem, the vet may create an obstacle course and see if the horse can negotiate it

The vet will now use a bright light to examine the eyelids and the front of the eye, including the cornea and iris.  They will also examine the granula iridica – these are the black structures found above the pupil.

Examination of the lens and the back of the eye, including the retina will then be carried out using an ophthalmoscope.  In order to examine as much of the retina as possible, it may be necessary to temporarily dilate your horse’s pupil with drops.  This will last up to 6 hours, so they will probably appreciate being kept in a darkened box for this time, and shouldn’t be ridden.

The final step in a routine eye examination is application of stain called fluoroscein to the horse’s eye.  This stain shows up any defects in the surface of the cornea, which is vitally important to know.  It can also test whether the tear duct is working, as normally the stain should drain into the nose within 15-20 minutes.  Be careful – it is not called a stain for nothing, and will stain hands for days, and clothes forever!

Various other tests can be carried out, which your vet will explain if they are needed.