‘Lazy eye’ may be used when strabismus (squint) is present but it is a loose term used for a variety of conditions.

Lets first clarify the terms:

1. It could refer to an eye with a droopy upper lid (‘ptosis’ – which may have been present from birth), so the eye looks smaller or ‘lazy’.  If the upper lid is droopy, it may require an operation, which may be done ‘urgently’ to allow the vision in the underlying eye to develop, or more usually at pre-school age if the droop is mild.

2. It may refer to an eye which has a squint (does not align with the fellow eye, on the same target).  The squinting (‘lazy’) eye may be turned in, out, up or down in relation to the fellow eye.  A squint is also known as strabismus.  It may be possible to re-align the eye by wearing glasses or by surgery to reposition the attachment of the eye muscles to the eyeball (see below); treatment depends on what has caused the squint.  Glasses may be prescribed after drops which dilate the pupils have been inserted, and the focal point of the eye has been determined.  The glasses are magnifying lenses, so they make the eyes look bigger and are used when the eye turns in.  There are many causes of strabismus, some which are very rare.  Adults who develop strabismus (due to a nerve supply problem or a reduced range of movement of the eye muscles) usually have double vision which is very troublesome.  Again, treatment depends on the cause of the strabismus.

3. An ophthalmologist may use the term ‘lazy eye’ when a condition known as amblyopia is present.  Amblyopia refers to a ‘normal’ eye which doesn’t have normal vision even when it is focussed correctly (using glasses).  Amblyopia may arise if light is not entering the eye normally (for example, where the upper lid is very droopy), or when the eyes are not aligned (squint/strabismus – an adult would see double but the immature brain ‘switches off’ the second image so vision may not develop properly) or may develop when the focal length of each eye is substantially different (in this case there is no external clue that something might be wrong; pre-school screening should detect this problem).  Amblyopia can only be treated during early childhood and usually requires patching the eye which sees normally.  Attention is also given to the underlying cause, and often requires the use of glasses.

Strabismus surgery aims to re-align the eyes relative to one another, by repositioning the attachment of the muscles of the eye, which either ‘weakens’ or ‘strengthens’ the muscle.  The procedure is usually performed under general anaesthesia but there is no need to spend the night in hospital.  When the patient is asleep the outer layer of the eye (conjunctiva) is ‘lifted’ and the eye rotated to expose the site where the muscle attaches to the wall of the eye (sclera).  There is No incision through the skin and the eyeball is NOT removed from the socket.

A muscle is ‘weakened’ when it is detached from the eye and re-attached further back from the front of the eye (figure 1).  A muscle is ‘strengthened’ when it is detached from the eye and a pre-determined section of the muscle is removed, thereby shortening the muscle, before it is re-attached at the same site (figure 2).  If the surgery is performed on an adult, the procedure can be ‘fine tuned’ if an ‘adjustable suture technique’ is used.  Eye muscles are usually secured to the wall of the eye with a permanent knot, but a temporary knot in an accessible position, makes it possible to adjust the position of the eye, when the patient is awake!  The temporary knot can be adjusted with minimal discomfort before it is tied permanently.  This adjustment would be done on the day or the day after the operation.

It is normal for the eyes to be a little scratchy for a few days, and the white of the eye may remain red for several weeks after the operation.

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