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Classify squint. Describe concomitant squint with its types and management.

Ophthalmology · 3rd Professional

Classification and Terminology

Strabismus (squint) is a misalignment of the visual axes, such that the two foveae are not directed at the same object.
A concomitant (comitant) squint is one in which the angle of deviation is the same in all directions of gaze and with either eye fixing.
By manifest or latent — a tropia is a manifest deviation present under binocular conditions; a phoria is a latent deviation held in check by fusion and revealed only on dissociating the eyes, as by covering one

Esodeviations

Type	Features and management
Infantile (congenital) esotropia	Onset before 6 months, with a large and stable angle (over 30 prism dioptres), a low hypermetropic refraction, cross-fixation (using the right eye to look left and vice versa. Amblyopia in about half. Treated by early surgery, ideally before 2 years, to give any chance of binocularity
Refractive accommodative esotropia	Onset 2 to 3 years, often intermittent at first and precipitated by illness or fatigue. The child is significantly hypermetropic (+3 to +6 D) and over-accommodates to see clearly, driving excess convergence. Fully corrected BY glasses after cycloplegic refraction — and surgery is wrong. The glasses must be worn constantly and the full cycloplegic correction given
Non-refractive (convergence excess) esotropia	A high AC/A ratio: the eyes converge excessively for the accommodation exerted. The deviation is greater for near than for distance. Treated with bifocals (an executive bifocal with the segment bisecting the pupil) or miotics, and surgery for the residual angle
Partially accommodative esotropia	Glasses reduce but do not eliminate the deviation; surgery is performed for the non-accommodative residue only, and the glasses continue afterwards
Sensory esotropia	Follows unilateral visual loss — cataract, corneal opacity, retinoblastoma, optic nerve disease. The cause OF the visual loss must BE found; a squint is not a diagnosis
Consecutive esotropia	Following over-correction of an exotropia surgically

The AC/A ratio (accommodative convergence per dioptre of accommodation) is normally about 3 to 5 prism dioptres per dioptre. A high ratio produces convergence excess esotropia; a low ratio contributes to convergence insufficiency
The most important practical rule IN childhood squint: every child with an esotropia must have a cycloplegic refraction with atropine or cyclopentolate before anything else. A child’s powerful accommodation conceals hypermetropia entirely on dry refraction, and a fully accommodative esotropia is cured by spectacles — so operating on one is both unnecessary and harmful

Exodeviations

Intermittent exotropia is the commonest exodeviation and the commonest childhood squint in Asian populations including India
Its characteristic history — the deviation appears on distance fixation, in bright sunlight, when tired, unwell or daydreaming, and the child closes one eye in bright light, which is a classical and highly suggestive symptom. It is controlled by fusion at other times
Classified by the distance-near relationship — basic (distance equals near); divergence excess (distance greater than near); and convergence insufficiency type (near greater than distance)
The essential assessment is control, not the angle — how readily the child regains fusion after dissociation, and what proportion of waking hours the eye is manifest. Deteriorating control is the indication for surgery
Management — correct any refractive error (and minus over-correction may stimulate convergence in the young); treat amblyopia; orthoptic exercises for convergence insufficiency; part-time occlusion as anti-suppression; and surgery (bilateral lateral rectus recession) when control deteriorates
Constant exotropia — congenital (rare, often with neurological disease), sensory, or decompensated from an intermittent form
Convergence insufficiency — distinct from squint: asthenopia, blurring and diplopia on prolonged near work, with a remote near point of convergence and reduced fusional convergence. It is common in students, is a frequent cause of "eye strain" attributed to refractive error, and responds well to convergence exercises (pencil push-ups, stereograms)
A tropia is manifest and a phoria is latent, revealed only by dissociating the eyes with a cover
Alternating squint spares vision and unilateral squint does not, so laterality should always be recorded

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