HYPERMETROPIA - A Comprehensive Essay

(Ophthalmology MBBS - NTRUHS Long Essay, 15 Marks)

DEFINITION

Kanski's Clinical Ophthalmology (10th ed.) - Hypermetropia results from a mismatch between the optical power of the eye and its axial length, requiring accommodation even for distant vision.

AETIOLOGY / CAUSES

1. Axial hypermetropia - The most common cause; the anteroposterior diameter of the eyeball is shorter than normal. Each 1 mm reduction in axial length results in approximately +3 D of hypermetropia.
2. Curvature hypermetropia - The cornea or lens (or both) has a flatter than normal curvature, reducing its refractive power.
3. Index hypermetropia - Decrease in the refractive index of the lens (e.g., nuclear sclerosis in early cataract).
4. Positional hypermetropia - Posterior displacement of the lens (rare).
5. Absence of the lens (Aphakia) - After cataract extraction without IOL implantation; produces very high hypermetropia (~+10 D).
6. Pathological - Due to disease, trauma, or abnormal development; e.g., microphthalmos, nanophthalmos, scleral buckling procedures displacing the eyeball posteriorly.

TYPES OF HYPERMETROPIA

A. Clinical / Functional Classification

• Total Hypermetropia = Latent + Manifest (Facultative + Absolute)
• As age advances: latent component decreases, absolute component increases.

B. Aetiological / Structural Classification (EyeWiki)

1. Simple hypermetropia - Due to decreased axial length or decreased converging power (flat cornea, decreased curvature). The most common form.
2. Pathological hypermetropia - Due to atypical development, trauma, or ocular disease (microphthalmos, nanophthalmos, aniridia, cataract, posterior scleritis).
3. Functional hypermetropia - Due to paralysis of accommodation (cycloplegic drugs, third nerve palsy).

C. Grading by Degree (Augsburger's Classification)

• Low hypermetropia: Up to +2.00 D
• Moderate hypermetropia: +2.25 D to +5.00 D
• High hypermetropia: More than +5.00 D

SYMPTOMS

In Young Adults (Mild-to-Moderate Hypermetropia)

• Asthenopia (Eye strain) - The most characteristic symptom. Results from sustained, excessive accommodative effort to maintain clear vision, especially for near work.
• Headache - Frontal or brow-ache, classically worse after prolonged near work (reading, writing, screen use), relieved by rest.
• Blurring of near vision - Difficulty reading small print, thread work, or close detail tasks.
• Photophobia - Mild, due to ciliary spasm.
• Watering of eyes - Due to accommodative spasm.
• Burning sensation and tired eyes - After sustained near work.

In High/Absolute Hypermetropia

• Blurring of both near AND distant vision - Once accommodation is exhausted or overpowered.
• Accommodative convergent squint (Esotropia) - A classic complication in children. Excessive accommodation triggers excessive convergence through the AC/A reflex, causing the eyes to turn inward.
• Amblyopia (Lazy eye) - May develop, especially in children who cannot compensate by accommodation.

In Infants and Children

• Parents may notice deviation of one or both eyes (esotropia is the commonest type).
• Reduced visual acuity on screening.
• The child may squint (screw up) the eyes when reading or doing near work.
• Anisometropic hypermetropia (one eye more hypermetropic) is a major cause of anisometropic amblyopia.

Kanski's Clinical Ophthalmology - The most common refractive error to cause strabismus is hypermetropia. Accurate measurement necessitates effective cycloplegia to neutralize the masking effect of accommodation.

SIGNS

On External Examination

• Small-appearing eye (Microphthalmos) in high hypermetropia.
• Esotropia (convergent squint) may be evident.
• Narrow palpebral fissure appearance.

Visual Acuity

• Near vision more affected than distant vision (in mild-moderate cases).
• Both near and distance vision impaired in absolute hypermetropia.

Retinoscopy

• Positive (With) movement of the reflex in ALL meridians - the hallmark finding.
• Neutralized with convex (plus) lenses.
• Must be done under cycloplegia (cyclopentolate 1% or atropine 1%) to reveal the full (total) extent of hypermetropia. Atropine is preferred in children with high hypermetropia or heavily pigmented irides.

Ophthalmoscopy / Fundus Examination

• Pseudopapilloedema - The optic disc appears blurred at its margins, hyperaemic, and slightly elevated (due to the small eyeball causing crowding of optic disc tissue). There is no true disc oedema.
• Small disc with indistinct margins.
• Blood vessels may appear tortuous.
• No actual cupping or obscuration of vessels.

Slit Lamp / Anterior Segment

• Shallow anterior chamber - Due to the short axial length; predisposes to angle-closure glaucoma in later life.
• Small corneal diameter.

Keratometry / Corneal Topography

• May reveal flat corneal curvature in curvature-type hypermetropia.

Biometry / A-Scan Ultrasound

• Reduced axial length confirms axial hypermetropia.

INVESTIGATIONS

1. Visual acuity - Snellen's chart (distance) and Jaeger's chart (near).
2. Retinoscopy - Under cycloplegia (atropine 1% ointment BD x 3 days); with movement of reflex.
3. Subjective refraction - Phoropter or trial frame with plus lenses.
4. Autorefraction - Quick objective screening, followed by subjective confirmation.
5. Slit lamp examination - To assess anterior chamber depth and rule out other pathology.
6. Fundoscopy - To assess optic disc, rule out true papilloedema.
7. Gonioscopy - In adults with high hypermetropia to assess angle and risk of angle-closure glaucoma.
8. Corneal topography / Keratometry - If surgical correction is planned.
9. Biometry (A-scan) - To measure axial length.

MANAGEMENT

1. Optical Correction (Spectacles / Glasses)

• Children without squint (mild hypermetropia < 4 D): Need not be corrected unless symptomatic. Physiological emmetropization may reduce it naturally. Full correction may interfere with normal emmetropization.
• Children with high hypermetropia (> 4 D): A two-thirds correction is usually given initially, with gradual increase.
• Children with accommodative esotropia: Full cycloplegic refraction correction is essential - this may reduce or eliminate the squint.
• Adults: The full manifest correction is given. As accommodation diminishes with age (presbyopia), more of the total hypermetropia becomes absolute and requires full correction.
• Astigmatic hypermetropia: Corrected with appropriate spherocylindrical (plus sphere + plus cylinder) lenses.

Kanski's Clinical Ophthalmology - Up to 4 D of hypermetropia should not be corrected in a child without a squint unless there are problems with near vision; with hypermetropia greater than this, a two-thirds correction is usually given.

2. Contact Lenses

• Convex (plus power) contact lenses provide an alternative to spectacles.
• Preferred by older children and adults for cosmetic reasons.
• Not generally recommended below adolescence unless absolutely indicated.
• Higher oxygen-permeable (rigid gas-permeable or silicone hydrogel) lenses are preferred.

3. Refractive Surgery (Surgical Management)

A. Laser Procedures

• PRK / LASEK (Surface ablation): Can correct low degrees of hypermetropia by applying laser to the corneal surface to increase its curvature.
• LASIK: Can correct up to +4 D of hypermetropia. A corneal flap is created, and the stroma is ablated to steepen the central cornea. Quicker recovery than surface ablation.

B. Conductive Keratoplasty (CK)

• Uses radiofrequency energy delivered via a micro-needle probe to peripheral corneal stroma in one or two concentric rings.
• Thermal shrinkage of stroma steepens the central cornea.
• Corrects low-to-moderate hypermetropia and hypermetropic astigmatism.
• Disadvantages: early overcorrection, significant regression, induced astigmatism.
• Also used for presbyopia correction.

Kanski's Clinical Ophthalmology - Conductive keratoplasty involves the application of radiofrequency energy to the corneal stroma in order to correct low-moderate hypermetropia and hypermetropic astigmatism. Burns are placed in one or two rings in the corneal periphery using a micro-needle high-frequency probe.

C. Intraocular Procedures (for High Hypermetropia > +4 D)

• Clear Lens Extraction (CLE) with IOL implantation - Removal of the natural lens and replacement with an appropriate high-plus power intraocular lens. Good results but irreversible loss of accommodation; risk of retinal complications is very low in hypermetropia (unlike myopia).
• Phakic IOL implantation - Implanting a plus power IOL in front of the natural lens (anterior chamber or posterior chamber), preserving accommodation. Options include angle-supported, iris-fixated (iris claw), and posterior chamber phakic IOLs.

4. Management of Complications

COMPLICATIONS OF UNTREATED HYPERMETROPIA

1. Amblyopia (refractive or anisometropic) - Especially in children; permanent vision loss if not treated before the critical period.
2. Accommodative convergent squint (esotropia) - Due to excessive AC/A-linked convergence.
3. Acute angle-closure glaucoma - Due to shallow anterior chamber in highly hypermetropic eyes.
4. Chronic headache and asthenopic symptoms - Affecting quality of life and academic performance.

SUMMARY TABLE

DIAGRAM (Optical Principle)

Light rays → Cornea → Lens → [retina] · · · FOCUS (behind retina)

Light rays → (+) Convex Lens → Cornea → Lens → FOCUS [on retina]

• Kanski's Clinical Ophthalmology: A Systematic Approach, 10th Edition, Jack J. Kanski & Brad Bowling
• Majumdar S, Tripathy K. Hyperopia. StatPearls [Internet]. Updated August 2023.
• EyeWiki - Hyperopia, American Academy of Ophthalmology