What is a squint?

A “squint” is the common name for ‘strabismus’ which is the medical term used to describe eyes that are not pointing in the same direction, or which are misaligned. Squints are also sometimes called ‘lazy eye’, to refer to a turned eye, but this is not an accurate description. Squints can be classified according to the direction of the turn of the eye: esotropia (convergent) refers to an eye that turns inwards towards the nose; exotropia (divergent) refers to an eye that points outwards; hypertropia is when the eye is in an upward direction. Binocular vision occurs when both eyes are looking towards the same direction, to produce a single, combined image at the brain.

Types of squint

The classification of squint may be based on a number of features including the relative position of the eyes, whether the deviation is latent or manifest, intermittent or constant, concomitant or otherwise and according to the age of onset (congenital -at birth, or acquired- later in life) and the relevance of any associated refractive error. The type of strabismus is established by a detailed history and examination.

The squint may be present all or only part of the time, in only one eye or alternating between the two eyes. A squint can occur for a number of reasons: these separately or together cause squint.

• Refractive (focusing) abnormality
• Eye muscle imbalance
• It can run in families
• Illness can make it obvious
• Fatigue, stress or extended work load
• Injury
• Rarely, it can be due to other diseases or illness

Why do squints need correction in adults?

A major concern of individuals with squints is the effect on their cosmetic appearance. Double vision (diplopia) is one of the most troublesome visual disorders a patient can experience. This is when a person sees two images of the same object some or all of the time. The two images may be vertically separated (one on top of the other) or horizontally separated (side by side) or both (oblique). The ability to read, walk and perform common activities is suddenly disrupted. The management goal is to establish clear binocular single vision.

Compared to binocular vision, adults with strabismus may have a decrease in their field of vision, absence of stereopsis or depth vision, decreased visual acuity and impaired spatial orientation. Individuals with squints are disadvantaged in visual motor skills, form and colour, and of appreciation of the dynamic relationship of the body to the environment, which facilitates control of manipulation, reaching and balance.

Squints may manifest as difficulties in eye hand coordination, clumsiness, bumping into objects and / or people, ascending or descending stairs or kerbs, crossing the street, driving, various sports and other activities of daily living which require stereopsis and peripheral vision.

Surgical correction for squints

The type and amount of surgery to perform for a particular squint is a decision for our surgeons. This demands an accurate pre-operative decision and necessitates meticulous surgical planning and accurate prediction of surgical outcome.

The surgical aims are re-alignment of the eye muscles where necessary to achieve satisfactory function and cosmetic appearance. This can mean that the non-squinting eye may be operated on. Since some patients may recover function over time, surgery may not be considered initially. Patients need to be advised that, whilst accuracy in measuring and operating upon strabismus is essential, the response to surgery is variable and cannot be guaranteed. Our surgeons employ good practice and discuss the actions necessary if the desired surgical outcome is not achieved.

Non-surgical correction for squints

Prisms, refractive lenses, vision therapy, eye patching and pharmacologic measures have been used to help patients achieve fusion (alignment of the eyes) and alleviate diplopia, in addition to surgery. Some patients will adapt by suppressing the vision of one eye to eliminate their diplopia. An additional technique is the use of Botulinum toxin.