Microphthalmia is a condition in which the eyeball is congenitally small. It occurs when abnormal development of the cornea, lens, retina, vitreous body, and other structures impairs the growth of the eyeball. No definitive treatment has been established.
Anophthalmia is a condition in which the eyeball is absent, and it is classified into the following three types.
The definition of microphthalmia in adults (Majima criteria) is an axial length of 20.4 mm or less in men and 20.1 mm or less in women. Age-based axial length criteria are described below.
It is a rare disease affecting 1 to 3 people per 10,000, with no sex difference, and the frequencies of bilateral and unilateral cases are almost the same. This article focuses especially on oculoplastic approaches (expander, prosthetic eye, and orbital reconstruction surgery).
Anophthalmia is a condition in which the eyeball is completely absent, and microphthalmia is a condition in which the eyeball is smaller than normal. Anophthalmia results from a defect in early optic vesicle formation, while microphthalmia results from abnormalities at various stages of development. In clinical practice, the main approach for both is reconstructive treatment to promote orbital growth (expanders and prosthetic eyes), but anophthalmia often involves severe orbital malformation.
Severe microphthalmia with associated anomalies can cause serious vision loss. In cases with a corneal diameter of 6 mm or less, or a marked difference between the two eyes, visual acuity is often below 0.02. Severe refractive errors are common, and early, regular use of glasses is essential for visual development.
In anophthalmia, extreme microphthalmia, and severe unilateral microphthalmia, abnormal development of the affected eye affects the growth of the tissues around the eye. This leads to delayed growth of the orbit and facial bones, and facial asymmetry. The reason is that the presence of the eye is essential for normal orbital bone development.
Anophthalmia
Definition: Complete absence of the eyeball
Three-type classification: primary (orbital socket not formed), secondary (abnormal forebrain development), and degenerative (the eye vesicle develops and then degenerates and disappears)
Features: It is often accompanied by severe orbital malformations. Conservative treatment is difficult, and many cases require orbital reconstruction surgery.
Microphthalmia
Definition: a condition in which the eyeball is congenitally smaller than normal
Duke-Elder 4-type classification: true microphthalmia (nanophthalmos), coloboma-associated type, type associated with ocular congenital anomalies, and type associated with systemic disease
Features: Management differs depending on severity. In mild cases, visual function development can be expected.
| Type | Characteristics |
|---|---|
| True microphthalmia (nanophthalmos) | The structure of the eyeball is almost normal, but it is small overall. The risk of angle-closure glaucoma is high |
| Microphthalmia with coloboma | Associated with failure of embryonic fissure closure. Accompanied by coloboma of the optic nerve, choroid, and iris |
| Microphthalmia associated with ocular congenital anomalies | Accompanied by various intraocular structural anomalies (such as Peters anomaly) |
| Microphthalmia associated with systemic diseases | CHARGE syndrome, Hallermann-Streiff syndrome, chromosomal abnormalities, etc. |
| Time period | Normal (male) | Normal (female) | Microphthalmia (male) | Microphthalmia (female) |
|---|---|---|---|---|
| At birth | 16.85mm | 16.60mm | 14.70mm | 14.44mm |
| 2 years old | 20.60mm | 20.29mm | 17.97mm | 17.65mm |
| 6-7 years old | 22.00mm | 21.68mm | 19.19mm | 18.86mm |
| Adult | 23.40mm | 23.06mm | 20.42mm | 20.06mm |
It depends on severity. If the corneal diameter is 6 mm or less, visual acuity is predicted to be below 0.02. In mild cases, early refractive correction and amblyopia treatment can support visual development. Because severe refractive errors are common, early and continuous use of glasses is important. Coexisting complications such as cataract (34%), glaucoma (13%), and retinal detachment (7%) affect the visual prognosis.
It is a rare disease, affecting 1 to 3 people per 10,000. There is no sex difference, and the frequency of bilateral and unilateral cases is about the same.
Associated systemic abnormalities occur in 31% of cases and are more common in bilateral cases. Central nervous system abnormalities are seen in about 13%.
The main associated diseases and syndromes are listed below.
As genetic factors, mutations in transcription factor genes such as SOX2, PAX6, OTX2, and RAX are involved. Environmental factors include TORCH syndrome (congenital infections such as toxoplasmosis, rubella, cytomegalovirus, and herpes), exposure to drugs during pregnancy, radiation exposure, and alcohol.
The basic test is axial length measurement by A-mode ultrasound. In principle, the difference between the two eyes is emphasized. The following values are used as a guide for diagnosis.
Assess according to the Majima criteria (a table of normal age-specific axial length values and microphthalmia 기준 values).
Evaluate side-to-side differences in ocular volume ratio, orbital volume, and orbital transverse diameter.
| Assessment item | Clinical significance |
|---|---|
| Eye volume ratio (50% or less of the healthy eye) | Orbital volume reduced to 80% or less of the healthy eye |
| Left-right difference in orbital transverse diameter (2 mm or more) | Indicator of cosmetic problems |
| Orbital CT/MRI | Used to evaluate the morphology of the orbital bones, globe, and optic nerve |
Orbital CT/MRI are essential for quantifying the eye volume ratio, orbital volume, and orbital transverse diameter.
Evaluation is needed with awareness that systemic abnormalities are present in 31%.
The three mainstays of reconstructive treatment are: (1) promoting orbital growth with expanders, (2) fitting an ocular prosthesis, and (3) orbital reconstruction surgery.
Promoting orbital growth with expanders
Purpose: To enlarge the conjunctival sac and promote development of the orbit and facial bones
When to start: Start as early as possible after birth (within 6 months is the guideline)
Method: Insert an expander into the conjunctival sac, increasing its size every 1 to 2 weeks, and gradually expand it
Important: After 6 months of age, there is a risk of irreversible asymmetry and deformity of the orbit and facial bones
Fitting an ocular prosthesis
Indication: Once the conjunctival sac has expanded sufficiently
Procedure: Referral to an ocular prosthetics center → temporary prosthesis fitting → adjustments (3 or more times, adjustment period of at least 6 months) → fabrication of the final prosthesis
Insurance coverage: In principle, ocular prostheses for microphthalmia are not covered by insurance benefits. This places a major financial burden on the family
Growth-period management: As the child grows, the prosthetic eye needs ongoing adjustment and remaking
Orbital reconstruction surgery
Indications: When conservative treatment (conformers/prosthetic eye) is difficult
Procedure: Surgery to form the orbital bones and prosthetic eye socket. Securing orbital volume with bone grafts or artificial materials
Candidates: Anophthalmia and microphthalmia with severe orbital malformation
Purpose: To improve appearance and create an orbital base for prosthetic eye fitting
The purpose of fitting a conformer is to expand the conjunctival sac (prosthetic eye socket). Starting as early as possible after birth is most important; after 6 months of age, the risk of irreversible asymmetry and deformity of the orbit and facial bones increases.
Different sizes of conformers are prepared, and every 1–2 weeks they are replaced with a larger size and inserted into the conjunctival sac. Repeating this gradually enlarges the conjunctival sac.
Once the conjunctival sac has expanded enough, the patient is referred to a prosthetic eye specialist. A temporary prosthesis is fitted and adjusted, and then the final prosthesis is made and fitted. In children, the prosthesis often needs to be adjusted at least three times, and the adjustment period may last 6 months or more. Ongoing adjustment and remaking of the prosthesis are needed throughout growth.
Insurance coverage note: A prosthetic eye after eye removal is covered by insurance, but a prosthetic eye for microphthalmia is generally not covered. The financial burden on families is large, so support including consultation with a medical social worker and use of disability welfare services is important.
Microphthalmia is often accompanied by significant refractive error. It is important to wear glasses consistently from an early stage to support visual development. Amblyopia treatment should also be carried out at the same time.
Regular follow-up is also needed for complications such as cataracts (34%), glaucoma (13%), and retinal detachment (7%).
Start as early as possible after birth. After 6 months of age, there is a risk of irreversible left-right asymmetry of the orbit and facial bones. Increase the size every 1 to 2 weeks, gradually expanding the conjunctival sac in preparation for prosthetic eye fitting. Early evaluation at an ophthalmology specialty facility and starting intervention directly improve the prognosis.
A prosthetic eye after eye removal is covered by insurance, but a prosthetic eye for microphthalmia is generally not covered. Because the financial burden on families is large, it is advisable to consult a medical social worker, including about using welfare support systems. The details of these systems may change, so check the latest information with the attending physician or consultation desk.
Eye development begins with the formation of the optic vesicle derived from neuroectoderm, followed by invagination into the optic cup, closure of the embryonic fissure, and differentiation of each ocular structure. If an abnormality occurs at any stage in this series of processes, anophthalmia or microphthalmia develops.
| Classification | Features |
|---|---|
| optic vesicle developmental disorder | anophthalmia and severe microphthalmia. Abnormality in the stage of formation from the eye pit to the optic vesicle |
| optic cup formation disorder | congenital cystic eye. Failure of invagination into the optic cup |
| anterior segment mesenchymal dysgenesis | Peters anomaly, Axenfeld-Rieger syndrome, etc. |
| lens-derived | ocular developmental disorder caused by abnormal lens development |
| vitreous-derived | persistent fetal vasculature (PHPV), etc. |
| failure of embryonic fissure closure | formation of coloboma (iris, choroid, optic nerve) |
| Abnormal development of the eyeball wall | True microphthalmia (nanophthalmos). The structure is normal, but the eyeball is small |
As genetic factors involved in the development of anophthalmia and microphthalmia, mutations in transcription factor genes essential for eye development are known.
The following factors during pregnancy may disrupt eye development.
The presence of the eyeball is essential because it provides the mechanical stimulus needed for normal orbital bone development. If the eyeball is absent or severely underdeveloped, that mechanical stimulus is lost and orbital growth is impaired. This directly causes facial asymmetry. Using an expander early after birth to make up for the lost mechanical stimulus is the basis of expander therapy, which helps promote the development of the orbit and facial bones.
