Congenital Cataract

A cataract is an opacification of the lens. Congenital cataracts usually are diagnosed at birth. If a cataract goes undetected in an infant, permanent visual loss may ensue. ^[1] Not all cataracts are visually significant. If a lenticular opacity is in the visual axis, it is considered visually significant and may lead to blindness. If the cataract is small, in the anterior portion of the lens, or in the periphery, no visual loss may be present.

Unilateral cataracts usually are isolated sporadic incidents. They can be associated with ocular abnormalities (eg, posterior lenticonus, persistent hyperplastic primary vitreous, anterior segment dysgenesis, posterior pole tumors), trauma, or intrauterine infection, particularly rubella.

Bilateral cataracts often are inherited and associated with other diseases. They require a full metabolic, infectious, systemic, and genetic workup. The common causes are hypoglycemia, trisomy (eg, Down, Edward, and Patau syndromes), myotonic dystrophy, infectious diseases (eg, toxoplasmosis, rubella, cytomegalovirus, and herpes simplex [TORCH]), and prematurity. ^[1]

See What the Eyes Tell You: 16 Abnormalities of the Lens, a Critical Images slideshow, to help recognize lens abnormalities that are clues to various conditions and diseases.

The lens forms during the invagination of surface ectoderm overlying the optic vesicle. The embryonic nucleus develops by the sixth week of gestation. Surrounding the embryonic nucleus is the fetal nucleus. At birth, the embryonic and fetal nuclei make up most of the lens. Postnatally, cortical lens fibers are laid down from the conversion of anterior lens epithelium into cortical lens fibers.

The Y sutures are an important landmark because they identify the extent of the fetal nucleus. Lens material peripheral to the Y sutures is lens cortex, whereas lens material within and including the Y sutures is nuclear. At the slit lamp, the anterior Y suture is oriented upright, and the posterior Y suture is inverted.

Any insult (eg, infectious, traumatic, metabolic) to the nuclear or lenticular fibers may result in an opacity (cataract) of the clear lenticular media. The location and pattern of this opacification may be used to determine the timing of the insult as well as the etiology.

In 2019, Shiels and Hejtmancik wrote that cataract typically "is caused by the presence of high-molecular-weight (HMW) protein aggregates or disruption of the lens microarchitecture. In general, genes involved in inherited cataracts reflect important processes and pathways in the lens including lens crystallins, connexins, growth factors, membrane proteins, intermediate filament proteins, and chaperones." ^[2]  

Typically, mutations that severely damage proteins are responsible for congenital cataracts; however, milder variants that make a person more vulnerable to environmental factors are linked to age-associated cataracts. Pathogenic mechanisms may vary; congenital cataracts initiate the unfolded protein response and aptoptosis, whereas denatured crystallins in patients with age-related cataracts bind to α-crystallin and create light-scattering HMW aggregates. New treatments for age-related cataracts employ "chemical chaperones" to solubilize HMW aggregates, whereas work is ongoing to utilize endogenous stem cells to regenerate lenses in patients with congenital cataracts. ^[2]

Frequency

United States

Incidence is 1.2-6 cases per 10,000.

International

Incidence is unknown. Although the World Health Organization and other health organizations have made outstanding strides in vaccinations and disease prevention, the rate of congenital cataracts is probably much higher in underdeveloped countries.

Genetics

A 2020 review of the genetics of congenital cataracts found that cataracts have various causes, with genetic defects being responsible for approximately one fourth of congenital cataracts; multiple mutations have been identified in upwards of 100 genes in congenital cataracts.{ref3}

Mortality/Morbidity

Visual morbidity may result from deprivation amblyopia, refractive amblyopia, glaucoma (as many as 10% post surgical removal), and retinal detachment.

Metabolic and systemic diseases are found in as many as 60% of bilateral cataracts.

Mental retardation, deafness, kidney disease, heart disease, and other systemic involvement may be part of the presentation.

Age

Congenital cataracts usually are diagnosed in newborns.

Of persons with unilateral congenital cataracts, 40% develop visual acuity of 20/60 or better.

Of persons with bilateral congenital cataracts, 70% develop visual acuity of 20/60 or better.

A 2019 study from France looked at 56 consecutive procedures performed in 37 infants. Overall, unilateral cataracts were found in 26.8% of babies, and bilateral cataracts were seen in 73.2%. The median age at surgery was 1.0 years [IQR (interquartile range): 0.3-5.2] for unilateral cataracts and 2.7 years [IQR: 0.4-9.5] for bilateral cataracts.  At the last follow-up documented, the median best-corrected visual acuity (BCVA) was 0.5logMAR [IQR: 0.2-0.8] and 0.1logMAR [IQR: 0.0-0.8]. The top postoperative complication was posterior capsule opacification (PCO) (Unilateral cataract, 60%; bilateral cataract, 46.3%; P=0.019), and the mean follow-up was 2.0 years (IQR, 1.0-5.0). ^[4]

The prognosis is poorer in persons with other ocular or systemic involvement.

Removal of the cataract is only the beginning. Visual rehabilitation requires many years of refractive correction (eg, contact lenses, aphakic glasses), possible patching for amblyopia, possible strabismus surgery, and glaucoma screenings.

Patients must be made aware of the risk of potential visual loss from amblyopia, retinal detachment, or glaucoma.

Repeated surgical procedures, including a secondary lens implant if other modalities of refractive correction fail, may be needed.

If this is a de novo chromosomal change or a familial abnormality, all siblings and future offspring are at risk.

For excellent patient education resources, visit eMedicineHealth's Eye and Vision Center. Also, see eMedicineHealth's patient education article Cataracts.