Evaluation And Management Of Squint
Definition And Pathophysiology
- Visual Axes Of Two Eyes Do Not Meet At Point Of Regard.
- Motor And Sensory Alignment Of Eyes Lack Synchronization.
- Child Initially Suffers Diplopia Due To Different Images Presented To Visual Cortex.
- Brain Suppresses One Image To Eliminate Diplopia.
- Constant Suppression Causes Amblyopia (Lazy Eye), Leading To Loss Of Binocularity And Stereopsis.
Classification Of Strabismus
Comitant Versus Noncomitant Strabismus
| Feature | Comitant Strabismus | Noncomitant Strabismus |
|---|---|---|
| Basic Defect | No Defect In Individual Extraocular Muscles. | Extraocular Muscle Paretic, Palsied, Or Restricted. |
| Ocular Motility | Full Motility In All Positions Of Gaze. | Limited In Direction Of Paretic Or Restricted Muscle. |
| Angle Of Deviation | Constant Irrespective Of Direction Or Position Of Gaze. | Varies According To Direction Of Gaze. |
| Common Etiologies | Infantile Esotropia, Accommodative Esotropia, Intermittent Exotropia. | Cranial Nerve Palsies, Duane Syndrome, Brown Syndrome. |
Types By Direction Of Deviation
- Esotropia: Inward Or Convergent Deviation.
- Exotropia: Outward Or Divergent Deviation.
- Hypertropia: Upward Vertical Deviation.
- Hypotropia: Downward Vertical Deviation.
Clinical Evaluation
History And General Assessment
- Note Age Of Onset. Early Detection Essential To Prevent Permanent Visual Impairment.
- Evaluate Abnormal Head Postures. Face Turns Or Head Tilts Strongly Suggest Diplopia Or Specific Muscle Palsies.
Visual Acuity And Refraction
- Assess Visual Acuity To Detect Amblyopia.
- Perform Cycloplegic Refraction And Fundus Evaluation.
Ocular Alignment Tests
Corneal Light Reflex Tests
- Ideal For Uncooperative Children Or Those With Poor Fixation.
- Hirschberg Test: Project Light Source Onto Cornea. Asymmetric Reflex Indicates Strabismus.
- Krimsky Method: Use Prisms Over Eyes To Align Light Reflections. Accurately Measures Degree Of Deviation.
Cover Tests
- Requires Patient Attention, Good Motility, And Adequate Vision.
- Cover-Uncover Test: Differentiates Manifest Deviations (Tropias) From Latent Deviations (Phorias).
- Alternate Cover Test: Rapidly Shift Cover Back And Forth. Identifies Total Deviation Magnitude.
Specific Strabismus Syndromes
Esodeviations
- Infantile Esotropia: Onset Before Six Months. Characterized By Large Constant Angle And Frequent Cross-Fixation.
- Accommodative Esotropia: Onset Between Two And Three Years. Uncorrected Hyperopia Drives Excessive Accommodative Convergence.
- Pseudoesotropia: False Appearance Of Strabismus Due To Flat Nasal Bridge Or Epicanthal Folds. Corneal Light Reflex Remains Centered.
Exodeviations
- Intermittent Exotropia: Most Common Exodeviation. Outward Drifting During Distance Fixation. Worsens With Fatigue Or Illness.
Cranial Nerve Palsies
- Third Nerve Palsy: Presents With Exotropia, Hypotropia, And Ptosis.
- Fourth Nerve Palsy: Presents With Hypertropia. Child Exhibits Head Tilt To Opposite Shoulder.
- Sixth Nerve Palsy: Presents With Esotropia And Defective Abduction. Head Turned Toward Palsied Muscle.
Management Principles
Non-Surgical Management
- Amblyopia Therapy: Must Precede Surgical Realignment.
- Institute Part-Time Or Full-Time Patching (Occlusion) Of Sound Eye.
- Utilize Penalization Therapy (Atropine Drops Or Fogging Lenses) For Selected Patients.
- Refractive Correction: Prescribe Spectacles Or Contact Lenses Based On Cycloplegic Refraction.
- Accommodative Esotropia Management: Prescribe Full Hyperopic Correction To Eliminate Accommodative Effort And Correct Deviation.
Surgical Management
- Surgical Indications: Restore Ocular Alignment, Maintain Binocular Vision, Eliminate Abnormal Compensatory Head Postures.
- Infantile Esotropia: Align Eyes Surgically After Successfully Treating Associated Amblyopia.
- Accommodative Esotropia: Surgery Reserved For Residual Nonaccommodative Component Not Corrected By Glasses.
- Intermittent Exotropia: Perform Surgery If Deviation Becomes Large Or Increases In Frequency To Prevent Loss Of Binocularity.