Ophthalmology: Latent Squint and Heterophoria

Latent Squint (Heterophoria)

• Characterized by a tendency for the eye to deviate due to extraocular muscle (EOM) imbalance while being held straight by binocular vision.
• Occurs in 70-80% of the population, with incidence increasing with age.
• Causes include mild weakness in the EOM or errors of refraction.

Types of Heterophoria

• Exophoria: Tendency for eye to deviate outward.
• Esophoria: Tendency for eye to deviate inward.
• Hyperphoria: Tendency for eye to deviate upwards.
• Hypophoria: Tendency for eye to deviate downwards.
• Excyclophoria: Tendency for eye to roll outward.
• Incyclophoria: Tendency for eye to roll inward.

Symptoms

• Most cases are compensated, showing no symptoms.
• Decompensated cases might show manifest squint.

Diagnosis

• Cover-Uncover Test: Assessing eye for deviation by covering one eye to disrupt binocular vision.
• Maddox Rod Test (Far): Evaluates how a red line appears when an eye is covered; deviation indicates heterophoria strength.
• Maddox Wing Test (Near): Assesses vertical and horizontal phoria at a distance of 40 cm using prismatic lenses.

Treatment

• Minor errors may require no treatment.
• Correct refractive errors.
• Consider strengthening weak eye muscles; surgery is a last resort.

Paralytic Squint

• Occurs due to paralysis of one or more extraocular muscles, can be partial (paresis) or complete.

Functions of Extra-Ocular Muscles

• Horizontal Muscles: Lateral rectus (abduction), medial rectus (adduction).
• Vertical Muscles: Superior rectus (elevation), inferior rectus (depression), superior oblique (intorsion), inferior oblique (extorsion).

Ocular Motility Terms

• Ductions: Monocular movements controlled by agonist and antagonist muscles.
  • Adduction: Movement in one direction.
  • Abduction: Movement in the opposite direction.
• Version Movement: Simultaneous movement of both eyes in the same direction.
• Vergence Movement: Coordinated eye movement, includes convergence (inward) and divergence (outward).

Sherrington's Law

• States that when one muscle contracts (agonist), the antagonist relaxes simultaneously.

Angle of Squint Measurement

• Corneal Light Reflex (Hirschberg Test): Uses light reflection to assess squint angle.
• Prism-Cover Test: Measures angle deviation by determining how much a prism affects the squinting eye.

Inflammation of the Sclera

• Episcleritis: Inflammation of superficial sclera, more common, usually unilateral, associated with collagen diseases.
• Scleritis: Inflammation of all scleral layers, can be bilateral, often seen in elderly females.

Symptoms of Scleral Inflammation

• Episcleritis: Painful not tender, presents with a red eye.
• Scleritis: Painful and tender, red eye, may lead to complications like glaucoma and keratitis.

Staphyloma

• Bulging of sclera or cornea due to conditions such as keratitis or high intraocular pressure.
• Types include anterior (corneal) and posterior staphyloma.

Amblyopia

• Defined as decreased visual acuity without correctable pathology.
• Develops during critical visual development, primarily in children under 6 years of age.

Treatment of Amblyopia

• Occlusion therapy to encourage usage of the amblyopic eye.

Congenital Glaucoma (Buphthalmos)

• Caused by developmental anomalies in the anterior chamber angle, it usually manifests during the first 6 months of life.
• Symptoms include lacrimation and photophobia; signs include large globe, corneal edema, and increased intraocular pressure.

Strabismus

• Types include refractive and non-refractive exotropia, often corrected surgically.
• Can occur due to various underlying diseases.

Autoimmune Diseases

• Sjögren Syndrome: Autoimmune condition affecting lacrimal and salivary glands, presenting with dry mouth and eyes.
• Rheumatoid Arthritis: Autoimmune disease causing symmetrical joint inflammation with ocular manifestations like scleritis and secondary Sjögren syndrome.
• Sarcoidosis: Granulomatous inflammation affecting the eye, can lead to various uveitis types.

Multiple Sclerosis

• Demyelinating disease with ocular features like optic neuritis.
• Typically presents in the 3rd-4th decades of life.

Uveitis

• Inflammation of the uveal tract; classified anatomically, clinically, and etiologically.
• Acute anterior uveitis is common, caused by infections and autoimmune disorders, causing rapid painful loss of vision and photophobia.

Explore the condition of latent squint, or heterophoria, in this quiz. Understand its epidemiology, causes, and different types, including exophoria, esophoria, and hyperphoria. Test your knowledge on how this common eye condition affects the population.