L. Jay Katz

BASICS

DESCRIPTION

• Nanophthalmos (simple microphthalmos) is a rare developmental disorder characterized by a small eye with short axial length (14.5–20 mm), shallow anterior chamber, high hypermetropia (+7.25-+20.50 diopter), thick sclera, a normal or thick lens, high lens-to-eye volume ratio, and crowded optic disc (pseudopapilledema).

• Rarely, some patients have emmetropia or myopia secondary to increased refractive power of the cornea and lens.

EPIDEMIOLOGY

Prevalence

• An uncommon condition

• Equal prevalence in men and women

RISK FACTORS

Nanophthalmos is a congenital malformation without risk factor for acquisition.

Genetics

• Most cases are not inherited and are not heritable.

• Both patterns of autosomal dominant (more common) and recessive isolated nanophthalmos have been reported.

• Mutations of MFRP (membrane frizzled-related protein) that regulates axial length in autosomal recessive nanophthalmos and NNO1 on chromosome 11, an autosomal dominant locus.

PATHOPHYSIOLOGY

• It may result from an arrest in ocular development after closure of the embryonic fissure.

• A smaller than normal optic vesicle growing from the forebrain may be the cause of the reduced size of the eye, and scleral thickening could be explained by the development of a normal amount of scleral cells surrounding a smaller optic vesicle, resulting in a proportionately denser population of cells.

COMMONLY ASSOCIATED CONDITIONS

• Ocular: Hypermetropia, retinal folds and yellow macular pigmentation, macular hypoplasia, pigmentary retinal degeneration, retinitis pigmentosa, pigmentary retinal dystrophy, acquired retinoschisis, retinitis pigmentosa, and optic nerve head drusen

• Systemic: Cryptorchidism, Hallermann-Streiff syndrome

DIAGNOSIS

HISTORY

• Glasses with thick convex lenses since childhood

• Amblyopia in those who did not receive appropriate treatment in childhood

• Family history of glaucoma

PHYSICAL EXAM

• Slit lamp exam: Corneal diameter usually <12 mm, lens and iris bulging forward into a shallow anterior chamber.

• Refraction: Hyperopia

• Gonioscopy: Occludable angle

• Funduscopy: Crowded optic discs (pseudopapilledema), pigmentary retinal changes.

• Tonometry: Elevated intraocular pressure (IOP), wide pulse amplitude of mires

DIAGNOSTIC TESTS & INTERPRETATION

Lab

Initial lab tests

Ocular sonography: Axial length <20 mm, shallow anterior chamber depth, thickened sclerochoroidal wall (>1.5 mm), possible optic nerve head drusen.

Follow-up & special considerations

• In childhood, correction of refractive error to prevent amblyopia is mandatory.

• Adults without glaucoma need follow-up examination every 6 months for early glaucoma detection.

• Avoid any intraocular surgery unless absolutely necessary.

• Patients are at risk of spontaneous uveal effusion.

• High risk of malignant glaucoma and uveal effusion intra- and postoperatively.

Imaging

• Full ophthalmic examination with particular attention to possibility of angle-closure glaucoma

– Review of systems to identify other possible syndrome findings

• A scan ocular sonography to determine the ocular axial length

– B-scan ocular sonography to evaluate for choroidal thickening and choroidal effusion

Diagnostic Procedures/Other

Orbital MRI is done to evaluate choroidal thickening or detachment and choroidal effusion. Usually not required.

Pathological Findings

Thickened sclera with an abnormal arrangement of collagen, reduced levels of glycosaminoglycan, and elevated levels of fibronectin.

DIFFERENTIAL DIAGNOSIS

• Anterior segment microphthalmos

• Microphthalmos

TREATMENT

• Narrow angle with a normal IOP: Follow-up every 3–6 months and consider early laser iridotomy.

• Closed angle with a normal IOP: Laser iridotomy

• Closed angle after laser iridotomy with normal or high IOP: Do ocular sonography.

– Choroidal effusion: Treat the effusion.

– No choroidal effusion: Peripheral iridoplasty

• High IOP without response to laser iridotomy or iridoplasty and no choroidal effusion: Start medical therapy like a case of open angle glaucoma.

– Miotics can worsen angle obstruction by producing a relative papillary block and by relaxing lens zonules

• High IOP accompanied with peripheral anterior synechia without response to laser therapy and maximum medical therapy: Trabeculectomy, possible lens extraction in those who do not have peripheral anterior synechia.

• Modification of the trabeculectomy to avoid postoperative hypotony and perform prophylactic posterior sclerotomies in both lower quadrants. The sclerotomies should be left unsutured to allow continued drainage of suprachoroidal fluid.

• Uveal effusion, choroidal detachment, or serous retinal detachment: Systemic steroid or surgical vortex vein decompression

ADDITIONAL TREATMENT

General Measures

• Any patient with nanophthalmos by the fourth decade should have ocular sonography for detecting possible choroidal separation or effusion and gonioscopic evaluation for angle closure.

• Performing any kind of surgery including laser iridotomy may be associated with uveal effusion and exudative retinal detachment.

Issues for Referral

• Angle-closure glaucoma.

• Cataract. Holladay 2 and Hoffer Q formulas are appropriate for IOL power calculation.

• Choroidal or retinal pathologies.

ONGOING CARE

FOLLOW-UP RECOMMENDATIONS

• All patients should be followed regularly for early glaucoma detection, especially after their fourth decade.

• Nanophthalmos associated with any ocular or systemic problems should be followed for those conditions.

PROGNOSIS

Those who develop uncontrolled glaucoma and need surgery have poor visual prognosis secondary to common posterior segment intra- and postoperative complications.

COMPLICATIONS

• Glaucoma.

• Spontaneous and intra- or postoperative uveal effusion or exudative retinal detachment.

ADDITIONAL READING

• Tay T, Smith JE, Berman Y, et al. Nanophthalmos in a Melanesian population. Clin Experiment Ophthalmol 2007;35(4):348–354.

• Yuzbasioglu E, Artunay O, Agachan A, et al. Phacoemulsification in patients with nanophthalmos. Can J Ophthalmol 2009;44(5):534–539.

• MacKay CJ, Shek MS, Carr RE, et al. Retinal degeneration with nanophthalmos, cystic macular degeneration, and angle closure glaucoma. A new recessive syndrome. Arch Ophthalmol 1987;105(3):366–371.

• Singh OS, Simmons RJ, Brockhurst RJ, et al. Nanophthalmos: A perspective on identification and therapy. Ophthalmology 1982;89(9):1006–1012.

CODES

ICD9

• 743.10 Microphthalmos, unspecified

• 743.11 Simple microphthalmos

CLINICAL PEARLS

• Nanophthalmos is a congenital ocular finding and may be associated with cryptorchidism and Hallermann-Streiff syndrome.

• High possibility of posterior segment complications with any surgical intervention

• The patients usually develop angle-closure glaucoma after the fourth decade.

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