Congenital Squint (Infantile Strabismus)
Definition And Pathophysiology
- Condition where visual axes fail to meet at point of regard.
- Results in failure of normal binocular vision development.
- Immature visual system initiates active suppression of one image to prevent diplopia.
- Eliminates double vision but sacrifices stereopsis and binocularity.
- Prolonged suppression results in irreversible amblyopia.
- Normal infants display imperfect coordination early; proper coordination expected by 3 to 6 months.
- Persistent deviation at 6 months demands prompt evaluation.
Classification And Etiology
- Broadly divided into non-paralytic (comitant) and paralytic (non-comitant) forms presenting early in life.
Non-Paralytic Causes (Presentation Before 6 Months)
- Infantile esotropia.
- Nystagmus blockage syndrome.
- Infantile exotropia.
- Dissociated vertical deviation.
Paralytic Syndromes (Presentation Before 3 Months)
| Syndrome | Pathophysiology | Clinical Features |
|---|---|---|
| Duane syndrome | Absence of sixth nerve nucleus; aberrant lateral rectus innervation. | Globe retraction on adduction; abduction and adduction impairment; compensatory face turn. |
| Mobius syndrome | Bilateral sixth and seventh nerve palsies. | Mask-like facies; inability to abduct both eyes; difficulty closing eyes. |
| Brown syndrome | Restriction of superior oblique tendon passage through trochlea. | Inability to elevate eye in adduction; chin-up head posture. |
| Congenital fibrosis syndrome | Tight extraocular muscles. | Chin-up posture; inability to elevate eyes; ptosis. |
| Congenital nerve palsy | Third, fourth, or sixth cranial nerve defects. | Exotropia or hypertropia with third nerve; upshoot with fourth nerve; esotropia with sixth nerve. |
Infantile Esotropia (Most Common Presentation)
- Represents true congenital esotropia; confirmed onset before 6 months.
- Characterized by large, constant angle of deviation exceeding 40 prism diopters.
- Cross-fixation frequently observed; child uses left eye for right gaze and right eye for left gaze.
- Refractive error typically matches normal children of same age.
- Amblyopia commonly associated.
- Excludes prematurity, developmental delay, and paralytic strabismus.
Differential Diagnosis
Pseudostrabismus
- False appearance of misalignment despite aligned visual axes.
- Caused by flat broad nasal bridge, prominent epicanthal folds, narrow interpupillary distance.
- Differentiated by centered corneal light reflex and normal cover-uncover test.
- Resolves spontaneously with facial growth.
Diagnostic Evaluation
| Assessment Tool | Mechanism | Application |
|---|---|---|
| Hirschberg corneal reflex test | Light projected onto cornea. | Rapid screening; detects asymmetric light reflection. |
| Krimsky method | Prisms used to align corneal light reflections. | Measures exact degree of deviation. |
| Cover-uncover test | Covers one eye while patient views distant object. | Differentiates manifest tropias from latent phorias. |
| Alternate cover test | Rapidly shifts cover back and forth between eyes. | Detects subtle deviations and maximum misalignment angle. |
Management Strategies
Goals Of Therapy
- Restore clear vision and eliminate deviation.
- Facilitate development of normal binocular vision.
Medical Management
- Exclude and treat underlying refractive errors.
- Amblyopia therapy mandatory before surgical intervention.
- Occlusion therapy patching sound eye.
- Penalization therapy using atropine drops to blur sound eye.
Surgical Management
- Indicated for persistent, constant esotropia or exotropia.
- Early intervention before 2 years of age maximizes chances of binocular vision development.
- Involves extraocular muscle resection or recession to restore ocular alignment.
- Paralytic syndromes require specific muscle release or transposition surgeries.
Long-Term Complications
- Amblyopia persistence if untreated.
- Development of secondary vertical deviations post-surgery.
- Inferior oblique muscle overaction causing upshoot in adduction.
- Dissociated vertical deviation causing slow upward drift of one eye.
- Continuous monitoring required throughout visually immature period.