Download Eyes - The George Veterinary Group

Lens:
This is the structure at the back of the anterior chamber that focuses
images onto the back of the eye (the retina). The main problem we see
here is degenerative changes leading to opacities on the previously clear
lens. These are commonly known as cataracts.
Cataract surgery is increasingly available as a treatment but each case is
different and some cases are not appropriate for surgical treatment.
Cataracts normally develop slowly and the horse is generally quite used
to his level of impaired vision. However there are safety concerns associated with these cases and they are a particular concern if found at a
pre-purchase examination.
Cataract
Eyes
Fundus:
Normal Fundus of the eye
The fundus of the eye is the interior surface of the eye, opposite the lens, and includes the
retina (the light sensitive area which processes images) and the optic disc. Normally it
should look like this (see picture to the left).
We use an ophthalmoscope to visualise the fundus.
Normal variations can include a sunburst effect
(where nerve cells are seen more prominently
around the optic nerve head) - see picture to the
right.
But we can see a variety of genuine problems including detachment of the retina which obviously
will have catastrophic effects on vision.
Enucleation:
Dr Tom Hunton BVSc MRCVS
If you’ve ever had any sort of problem with your own eyes you will know
how painful they can be and you probably sought medical help pretty
fast. Your horse is no different and as vets we always want to see eye
conditions as early as possible to help alleviate the associated pain and
prevent any damage from worsening.
The eye is a complex organ so in this article we will look at the individual
parts of the eye and describe some of the problems that we see in each area.
Eyelids
The vast majority of eye problems can be corrected to a very good degree, especially if we get
to see them early. However there are a small number of cases where this is not possible and
the eye needs to be removed (enucleation):
This horse collided with a fence post causing severe and irreparable damage to the left eye
The horse was operated on under General Anaesthetic but these operations can be performed with standing sedation and appropriate
ocular nerve blocks.
The eye is removed, the skin is sutured back
together and it’s even possible to implant a
prosthetic eyeball.
Two weeks later the eye looked like this when
the sutures were removed. There were no further problems.
Whilst this is a dramatic and upsetting event for
all concerned, it removes the problem of a very
painful condition and horses always seem to
adapt very well to losing one eye.
“Sunburst” effect on the fundus
Any problems here need to be approached very seriously because it is vital that
the upper eyelid meets the lower eyelid perfectly when the horse blinks. If this
does not happen then the ‘dry’ eye can suffer considerable damage.
This means that wounds in this area need very careful management and nearly
always require suturing (with the horse still and sedated).
We can also see tumours develop around the eyelids.
These tumours will generally require surgical removal and reconstruction of the
affected eyelid so that the eyelids meet correctly.
A nasty laceration to the lower eyelid
Third eyelid
In horses, a third eyelid also exists. It is generally concealed under the medial
canthus (where the eyelids meet or at the inside cover). If this third eyelid protrudes to any significant degree then it can indicate a problem.
External trauma to the eye can lead to swelling of the conjunctiva (inner lining of
the eyelid) and prolapse of the third eyelid.
Often these will respond to anti-inflammatory medication and rest but the eye
needs to be fully examined under sedation.
Foreign bodies such as thorns can get stuck under the third eyelid and this can
cause a lot of damage when they are drawn across the cornea as the horse blinks.
The other problem we occasionally see in this area is another tumour: a squamous cell carcinoma of the third eyelid.
And after surgical repair
Tel: 01666 826456
Email: [email protected]
www.georgevetgroup.co.uk
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Tumour on the lower eyelid.
Third eyelid prolapse.
Third eyelid tumour requiring surgery
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Conjunctiva
The conjunctiva is the inner lining of the eyelid. It is normally pink
(see picture 1) but in cases of conjunctivitis it can become reddened and quite inflamed (see picture 2). This may be due to trauma or infection.
Occasionally, we see nasty tumours on the conjunctiva and just
like wounds or tumours on the eyelids, these can affect normal
closure of the eye and require surgical treatment.
(2) Tumour on the conjunctiva
(1) Conjunctivitis
Cornea:
The cornea is the clear lining of the eyeball. Injuries to this area are always painful and generally we see a lot of discharge and closing of
the eyelids. The most common problem associated with the cornea is a corneal ulcer which has stripped the outer lining of the cornea.

As in picture (3), you can sometimes see a bit of cloudiness under the surface of the cornea but this condition is best diagnosed
when we apply a dye (fluorescein) to the corneal surface, see
picture (4). Fluorescein runs off a normal cornea but stains
any defect to the surface.
These cases need treating as soon as possible with a combination of medications to prevent infection causing further
damage.

One example of a corneal ulcer that wasn’t ideally
managed is shown in pictures (5 & 6). The owner of this pony
saw that the eye was swollen and painful but unfortunately
chose to apply old eye drops left over from a previous problem, instead of getting prompt veterinary help. Unfortunately
(4) The above eye after dye was applied. this resulted in the development of a stromal abscess.
(3) Corneal ulcer

On the first examination the surface of the cornea was
starting to heal over but the infection had developed into an abscess underneath the outer layer.

New blood vessels (4) were branching across the eye as part of the healing process but this was going to be inadequate. The abscess was causing the eye to change shape; rupture of the eyeball was a real risk and so surgical intervention was required.

Under General Anaesthetic the surface of the cornea was cut away (a Keratectomy) to expose the abscess (7). The eye was then
lavaged before a section of the conjunctiva was cut and dragged down to cover the abscess (8).
This is called a conjunctival pedicle graft. It covers the abscess and provides the necessary blood supply to the area to allow healing to
take place.

Six weeks later the attachment to the upper conjunctiva was cut. The eye is left with permanent scarring from
the graft (9) however the pony was back competing within
another month and vitally his eye was pain free. However all
this could have been avoided had we been called at the first
New blood
sign of pain. Because the eye is normally closed when painful
vessels
it’s often only once we sedate the animal that we can diagAbscess
nose the problem.
(5)
This is generally the case when foreign bodies are stuck in
the eye (picture 10).
A blade of hay was removed from this eye (picture 11). The
hay had caused an ulcer, as shown by the dye (picture 12),
but this responded rapidly to appropriate treatment.
(6)
(10) A corneal foreign body
(11) Foreign body removed from eye
Anterior chamber:
This is the ‘shop window’ of the eye. It is the bit that you can see externally between
the cornea and the pupil. We occasionally have opacities floating in this area. Normally
they can only be seen with an ophthalmoscope and they generally cause no obvious
problems. We do however see a lot of other problems in this ‘shop window’ (1).
Inflammation and oedema can be seen as
white or blue cloudiness within the anterior chamber. This may be due to injury to
the cornea, it may be scarring or it can be
part of a generalised inflammation called
uveitis. Uveitis can be a recurrent problem
in the equine eye and if unsuccessfully
treated it can lead to blindness as in pic(1)
ture (2).
In other cases, especially those involving
external trauma, we see bleeding within the anterior chamber (hyphaema) (3).
Although the bleed often resolves in time, these cases obviously need seeing to ascertain
why it has happened and whether there is any ongoing damage.
Within the normal anterior chamber are structures called the Granula Iridica (4). These
brown spheres are outpouchings of the iris and sit above the pupil where they are thought (2)
to act as a parasol, shading the pupil and back of the eye from the sun.
But we can see problems associated with the
Granula iridica. They can fill with fluid and
cysts can form.
These can sometimes become so large that
they obscure vision to some degree.
Inflammatory events can also lead to the detachment of these Granula iridica within the
eye
In picture (5) we can see an inflammatory
event is occurring. It then leads to the granula
iridica detaching and dropping to the bottom
of the anterior chamber in picture (6).
(4)
(7)
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(8)
(12) Eye ulcer shown by dye
(3)
(9)
(5)
(6)
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