Eso Deviations

An eso deviation is the inward turn of an eye.

An esophoria is a latent squint. This means the eyes are straight without dissociation (covering of the eyes) and corneal reflections will be symmetrical.

• On cover-uncover test, the fixing eye will not move.
• On alternate cover test, both eyes will move with an outwards motion to fix – meaning they have a tendency to turn in.

An esotropia is a manifest squint. This means one eye is turning inwards all the time and corneal reflections will show a misalignment.

• On cover-uncover test, the eyes will move out to fix.
• On alternate cover test, the outwards movement may increase.

Some of the main causes of an esotropia (turn in of the eye) include:

• Congenital/infantile – these patients have had a turn since birth/very young age. They will supress (not process vision) the strabismic eye so they may not develop binocular vision and are at risk of amblyopia (reduced visual development).
• Convergence excess – when accommodating (focusing on a target), the eyes over-converge and turn inwards.
• Associated with accommodation – plus lenses relax the eyes outwards. Therefore, some esotropia’s may reduce in size or straighten with a hypermetropic (longsighted) prescription.
• Associated with myopia – myopia (shortsightedness) is when the eye is too big. This can result in the extraocular muscle functions to change, pulling the eye inwards.
• 6th cranial nerve palsy – the lateral rectus muscle is weak so the eye can’t be turned outwards fully and may sit inwards.
• Consecutive/residual – the surgical overcorrection of an exotropia, or undercorrection of an esotropia.

It is the role of an Orthoptist to diagnose and differentiate these aetiologies.