Ophthalmology – Microphthalmia

Basics

Description

Microphthalmia is a congenital developmental disorder in which one or both eyes are abnormally small, involving reduced axial length and/or corneal diameter.

It may occur:

• Unilaterally or bilaterally
• In isolation
• With other ocular malformations
• As part of a systemic genetic syndrome

Associated visual function ranges from near normal to profoundly impaired.

Epidemiology

Microphthalmia occurs in approximately:

1–2 per 10,000 newborns

Severity and associated abnormalities vary widely.

Risk Factors

Important associations include:

• Ocular coloboma
• Congenital cataract
• Persistent fetal vasculature
• Intrauterine infection, especially rubella
• Chromosomal abnormalities
• Congenital syndromes
• Teratogenic exposure

Potential teratogens include:

• Ionizing radiation
• Alcohol
• Isotretinoin

Genetics

Microphthalmia is genetically heterogeneous.

Genes associated with isolated ocular microphthalmia include:

• SOX2
• OTX2
• PAX6
• FOXE3
• GDF6
• SIX6
• RAX
• MAF
• CRYAA
• CRYBA4

Syndromic forms may involve genes such as:

• CHD7 – CHARGE syndrome
• HESX1 – septo-optic dysplasia
• SOX2 – syndromic microphthalmia
• BMP4
• STRA6
• HCCS – microphthalmia with linear skin defects
• BCOR – oculofaciocardiodental syndrome

Inheritance may be:

• Autosomal dominant
• Autosomal recessive
• X-linked dominant
• X-linked recessive

Some cases are sporadic.

Importantly, unilateral microphthalmia can still have a genetic cause.

General Prevention

Potential preventive measures include:

• Genetic counseling
• Prenatal genetic testing when a familial mutation is known
• Prevention of maternal infections
• Avoidance of known teratogens during pregnancy

Severe microphthalmia may sometimes be detected by prenatal ultrasound, including in the late first trimester.

Pathophysiology

Microphthalmia results from incomplete ocular development during embryogenesis.

Developmental gene abnormalities can disrupt:

• Optic vesicle formation
• Optic cup development
• Closure of the embryonic fissure
• Growth of the globe
• Formation of the anterior and posterior segments

Because many involved genes are transcription factors, abnormalities can affect multiple downstream developmental pathways.

Etiology

Causes include:

• Genetic mutations
• Chromosomal abnormalities
• Intrauterine infections
• Teratogenic exposure
• Ocular coloboma
• Persistent fetal vasculature
• Rare primary aphakia
• Idiopathic developmental abnormalities

Bilateral disease is particularly suggestive of a genetic or syndromic etiology.

Commonly Associated Ocular Conditions

Microphthalmia may be associated with:

• Ocular coloboma
• Congenital cataract
• Persistent fetal vasculature
• Anterior segment dysgenesis
• Optic nerve hypoplasia
• Retinal dysplasia
• Congenital retinal detachment
• Strabismus
• Nystagmus
• Refractive error
• Glaucoma

Anterior chamber depth is often normal in microphthalmia but is characteristically shallow in nanophthalmos.

Systemic Associations

Systemic abnormalities vary according to the underlying syndrome.

Possible associated findings include:

• Developmental delay
• Neurologic abnormalities
• Craniofacial malformations
• Cardiac disease
• Skeletal anomalies
• Endocrine abnormalities
• Hearing impairment

The presence of developmental delay or multiple congenital abnormalities increases suspicion for a syndromic or chromosomal disorder.

Diagnosis

History

Important questions include:

• Family history of small eyes, coloboma, congenital cataract, or blindness
• Maternal infections during pregnancy
• Medication or teratogen exposure
• Other congenital anomalies
• Developmental delay
• Previous ocular surgery

Physical Examination

A complete ocular examination should assess:

• Globe size
• Corneal diameter
• Axial appearance
• Palpebral fissure size
• Orbital and periocular development
• Anterior chamber depth
• Lens
• Iris
• Retina
• Optic nerve

Particular attention should be paid to the inferonasal peripheral fundus, where a coloboma is commonly found.

Visual Function

Assess:

• Fixation behavior
• Visual acuity
• Preferential looking in infants when appropriate
• Refractive error
• Amblyopia

Visual acuity can vary widely depending on associated structural abnormalities.

Refractive Error

Patients may have:

• High hyperopia
• High myopia
• Astigmatism

Refraction should be performed carefully because correct optical treatment may significantly improve visual development.

Strabismus and Nystagmus

Both are common, especially when there is:

• Asymmetric visual input
• Bilateral poor vision
• Optic nerve abnormalities
• Retinal dysplasia

Laboratory Evaluation

No routine laboratory tests are required in isolated microphthalmia without systemic abnormalities.

Consider:

• Chromosomal analysis if multiple congenital anomalies are present
• Targeted molecular genetic testing
• Syndrome-specific testing

Genetic evaluation is particularly appropriate when:

• Disease is bilateral
• There is developmental delay
• There are systemic malformations
• There is a positive family history

Imaging

A-Scan Ultrasonography

Useful for measuring:

• Axial length

This helps confirm reduced globe size.

B-Scan Ultrasonography

Useful when the fundus cannot be visualized.

It can evaluate:

• Retina
• Optic nerve
• Retinal detachment
• Persistent fetal vasculature
• Presence or absence of the lens

Ultrasound Biomicroscopy

UBM may help evaluate:

• Anterior segment anatomy
• Scleral thickness
• Ciliary body anatomy
• Shallow anterior chamber

Neuroimaging

Consider MRI when there is:

• Bilateral optic nerve abnormality
• Developmental delay
• Neurologic findings
• Suspected syndromic disease

Orbital Imaging

CT or MRI may be useful in severe cases to assess:

• Orbital size
• Bony development
• Associated craniofacial abnormalities

Differential Diagnosis

Important differential diagnoses include:

• Anophthalmia
• Nanophthalmia
• Microcornea without microphthalmia
• Phthisis bulbi

Anophthalmia

No identifiable globe is present clinically or on imaging.

Nanophthalmia

The eye is globally small but structurally relatively complete and often has:

• Very short axial length
• Marked hyperopia
• Thick sclera
• Shallow anterior chamber
• Increased angle-closure risk

Phthisis

Represents acquired shrinkage of a previously developed eye following:

• Trauma
• Infection
• Severe inflammation
• Surgery

Treatment

There is no medication that can enlarge or normalize the congenitally small globe.

Management focuses on:

• Maximizing vision
• Preventing amblyopia
• Treating associated ocular disease
• Supporting normal orbital and facial development

Amblyopia Treatment

Amblyopia therapy should be initiated when appropriate.

Treatment may include:

• Full refractive correction
• Patching
• Penalization

This is particularly important in asymmetric or unilateral disease.

Optical Rehabilitation

Options include:

• Spectacles
• Contact lenses
• Low-vision devices

In a mildly microphthalmic but poorly functioning eye, a plus spectacle lens can sometimes enlarge the cosmetic appearance of the eye.

Orbital Growth and Cosmetic Rehabilitation

A severely microphthalmic eye may not adequately stimulate normal orbital growth.

In a nonfunctional eye, treatment may include:

• Conformer
• Scleral shell
• Progressive prosthetic expansion

These help encourage growth of:

• Eyelids
• Conjunctival socket
• Orbit
• Periocular tissues

Severe cases may require expandable orbital implants or tissue expanders coordinated with craniofacial or oculoplastic specialists.

Early intervention is especially important during the first years of life.

Cataract Surgery

Congenital cataract may require surgery when visually significant.

Visual prognosis depends heavily on associated retinal and optic nerve abnormalities.

Glaucoma Management

Glaucoma may occur particularly with:

• Aphakia
• Persistent fetal vasculature
• Anterior segment dysgenesis

Management may include:

• Medical therapy
• Laser treatment
• Surgery

Patients at risk require long-term IOP monitoring.

Shallow Anterior Chamber

In nanophthalmic-type anatomy with a very shallow anterior chamber, management requires special caution.

Miotics such as pilocarpine can worsen anterior displacement and angle crowding in some situations.

Treatment should be directed by a glaucoma/anterior-segment specialist.

Retinal Detachment

Colobomatous eyes have an increased risk of retinal detachment.

Retinal surgery may be considered for acquired rhegmatogenous detachment.

However, surgery is generally not beneficial for:

• Congenital retinal nonattachment
• Severe retinal dysplasia
• Some congenital tractional detachments

Strabismus Surgery

Strabismus surgery may be considered for:

• Functional alignment
• Abnormal head posture
• Cosmetic improvement

The visual potential of each eye should be taken into account.

Referral

Appropriate referrals may include:

• Pediatric ophthalmology
• Ocular genetics
• Medical genetics
• Retina specialist
• Glaucoma specialist
• Low-vision services
• Oculoplastic/craniofacial surgery
• Developmental pediatrics

Follow-Up

Follow-up depends on associated abnormalities.

Children require monitoring for:

• Amblyopia
• Refractive error
• Cataract
• Glaucoma
• Retinal detachment
• Strabismus
• Orbital growth

Patients with coloboma or glaucoma risk may require examinations approximately every 6 months, depending on severity.

Patient Monitoring

Monitor:

• Visual development
• School performance
• Developmental milestones
• Orbital and periocular growth
• Cosmetic concerns
• Psychosocial impact

Orbital growth is particularly important during the first 5 years of life.

Patient Education

Families should receive counseling regarding:

• Visual potential
• Possibility of associated systemic disease
• Genetic implications
• Importance of amblyopia treatment
• Retinal detachment symptoms
• Long-term glaucoma monitoring
• Low-vision resources

Genetic counseling is especially useful in bilateral or familial cases.

Prognosis

Visual prognosis is highly variable.

Better prognosis is generally seen when microphthalmia is mild and the:

• Retina
• Optic nerve
• Lens
• Macula

are relatively normal.

Poor visual prognosis is associated with:

• Primary aphakia
• Severe retinal dysplasia
• Congenital retinal detachment/nonattachment
• Severe optic nerve abnormalities

Complications

Important complications include:

• Amblyopia
• Strabismus
• Nystagmus
• Refractive error
• Cataract
• Glaucoma
• Retinal detachment, especially with coloboma
• Poor orbital development
• Cosmetic asymmetry
• Low vision

Key Clinical Pearls

• Microphthalmia = congenitally small eye involving reduced globe size, often including reduced axial length.
• It can be unilateral or bilateral and may be isolated or syndromic.
• Always search carefully for an inferonasal ocular coloboma.
• Bilateral microphthalmia strongly raises suspicion for a genetic or syndromic cause.
• A-scan measures axial length; B-scan evaluates posterior anatomy when there is no fundus view.
• Distinguish microphthalmia from nanophthalmia, anophthalmia, and phthisis.
• Visual prognosis depends much more on associated retinal, optic nerve, and lens abnormalities than on globe size alone.
• Early treatment of refractive error and amblyopia is essential.
• In a severely small nonfunctional eye, conformers or scleral shells can promote orbital and periocular growth.
• Coloboma increases the risk of retinal detachment, while aphakia/PFV/anterior segment dysgenesis increase the risk of glaucoma.