Strabismus – Back To Basics:
What is Strabismus?
Strabismus is the medical term for misalignment of the eyes, a wandering eye, and what is often called a squint, lazy eye, cross eyed, or wall eyed. It occurs when the eyes do not align when looking at an object. Strabismus has many causes, classifications and types, and can occur in both children and adults. Treatment options for strabismus depend largely on the type of strabismus a patient has. In this section we will delve into detail on both adult strabismus and paediatric (childhood) strabismus.
A child with a Right Esotropia. Photo courtesy of AAPOS
Classification of Strabismus:
Strabismus is classified using many factors, including the onset, direction, laterality, nature, features and cause.
Below we outline the most important aspects of classifying strabismus:
Onset:
– Acquired: Where the onset of the eye turn occurs as an adult. Conditions such as thyroid eye disease, stroke, or tumours can cause strabismus, as can trauma to the brain, eye muscles, or the eye itself.
– Decompensated: Where the onset of symptoms is as an adult, but the underlying cause of the problem started earlier than this.
– Congenital/infantile: Where the eye turn presents during childhood.
Direction:
– Esotropia: When the eye turns in towards the nose. People often refer to this as being cross-eyed. There are many types of esotropia including primary esotropia, congenital esotropia, accommodative esotropia, partially and fully refractive esotropia, intermittent and constant esotropia and cyclical esotropia.
– Exotropia: Where the eye turns out towards the temple. Often referred to as wall-eyed. Exotropia can be intermittent or constant.
– Hyper/Hypotropia: A vertical strabismus where one eye drifts up towards the hairline or down towards the feet. There are many types of vertical strabismus, and vertical strabismus is often found in conjunction with horizontal strabismus.
Laterality:
– Right, Left, or alternating: Used to describe which eye is turning. Alternating refers to the ability for each eye to misalign in turn.
Features:
– Intermittent: When the eye turn occurs only some of the time, and at other times the eyes are aligned well.
– Constant: Where the eye turn is present all of the time.
– Unilateral: When only one eye has strabismus.
– Bilateral: Where either eye can have the eye turn.
– Concomitant: Where the size of the deviation remains similar in all positions of gaze. Usually due to childhood strabismus or less commonly, a long-standing adult-onset eye turn.
– Incomitant: When there is variance in the strabismus when the eyes are taken into different positions of gaze. Usually neurological and paralytic in cause.
– Heterophoria: A latent form of strabismus which is only seen when the eyes are made to work individually (dissociated). This form of strabismus can often cause eye strain and headaches. Heterophorias are not normally noticed by lay-people, but are found under expert clinical testing.
– Heterotropia: A manifest form of strabismus where misalignment is noticed without too much dissociation.
Size:
– Generally recorded as micro, small, medium or large. Deviation size is an important factor in the strabismus assessment. Most treatments are dependant on accurate measurements of the angle of the eye turn. Detailed measurements of the size of the turn will be taken by your ophthalmologist or orthoptist. Sometimes measurements are taken over several visits to ensure angle stability. Large angle strabismus can be very obvious and easy for most casual observers to notice. Strabismus can also come in the form of very small angles, or micro strabismus, whose effects can be just as troublesome for the patient as the larger angle eye turns. A competent eye health professional will be able to find, diagnose and treat all forms of strabismus, including the smaller angle micro strabismus.
Cause:
– Primary: An eye turn that occurs without other obvious co-existing, causal eye abnormalities.
– Secondary: Strabismus caused by other co-existing eye disease such as congenital cataract or retinal disease. Any eye disease that causes a significant decrease to vision can potentially cause secondary strabismus. An eye with very poor vision is more likely to develop an exotropia. We call this exotropia due to very poor vision a sensory exotropia.
– Consecutive: An overcorrection of strabismus that can occur after strabismus surgery.
– Certain patterns of strabismus have been given names such as Duanes syndrome and Browns syndrome. Other forms of strabismus that follow a certain pattern are attributed to cranial nerve palsies.
Now that we have completely exhausted you with medical jargon, tomorrow we will move on to something more interesting and less jargon filled – all about adult strabismus.
References:
https://aapos.org/terms/conditions/11