Cataract Due To Mendelian Disorders - Congenital Cataracts, Clinical Types, Diagnosis, and Management

What Are Cataracts?

Cataracts are slowly progressing ocular diseases described by the opacification of the eye lens, thus blocking the transmission of light through the lens to the retina. It is the most common cause of reversible blindness worldwide.

What Are Congenital Cataracts?

Cataracts inherited or caused by changes in the gene sequence in infants and children are congenital cataracts. It is characterized by the opacity of the crystalline lens that impairs the normal development of the eye. Congenital cataracts are inherited in a Mendelian fashion and thus have high penetrance. Mendelian inheritance in biology is the pattern in which the traits or personalities are transferred from one generation to another.

What Causes Congenital Cataracts?

The exact cause for the genetic mutation in congenital cataracts is unclear. Transformation of the genes coding for eye proteins is hypothesized to be the leading cause of congenital cataracts. Mutation (change in gene sequence) of the various lens proteins is the source of congenital cataracts.

Risk factors linked with congenital cataracts include,

• An intrauterine insult, for example, maternal infection like rubella.

• Low socioeconomic status.

What Is the Mechanism for the Development of Congenital Cataracts?

• Damage to the lens architecture, breakdown of lens fibers, formation of the vacuole, and deposition of large molecular weight proteins in the lens causes a change in the lens's capacity to transmit light (optical density of lens) and its light scattering capacity.

• The declining capacity of the crystalline proteins in the lens due to genetic or age-related causes leads to abnormal folding of the proteins in the lens. These proteins get deposited abnormally as amyloid in the lens, causing opacification of the lens. The fluctuations in the optical density ultimately lead to the formation of cataracts.

• The most common genes associated with congenital cataracts encode proteins associated with several structural and functional aspects of the lens.

What Are the Different Patterns of Inheritance?

All congenital cataracts occur through the Mendelian model of inheritance. Congenital cataracts show an autosomal dominant pattern of inheritance. In autosomal dominant inheritance, the defective gene or the dominant gene is passed on to every generation and manifests clinically. In a sporadic form of inheritance, the disease occurs without any previous family history of the disease.

What Are the Clinical Types of Congenital Cataracts?

Congenital cataracts, based on their clinical appearance, are of seven types:

• A nuclear cataract occurs due to the opacification of the center of the lens. It is the most frequently occurring cataract characterized by glare and blurring of vision.

• Anterior polar cataracts are nonprogressive cataracts requiring only a follow-up. It presents as white spots in the anterior layer of the lens.

• Posterior polar cataracts appear as a discoid opaque mass in the center of the lens near the posterior capsule.

• Lamellar cataracts are the autosomal dominant cataracts present at the oldest and centremost part of the lens (embryonic nucleus level). They are bilateral and asymmetrical.

• Coralliform cataracts are a particular type of congenital cataracts with coral or stellate form.

• Blue and white opacifications are described by a blue dot in the nucleus region of the eye. Most of the patients are asymptomatic till twenty months.

• Cortical cataracts start at the edge of the lens and progress towards the center.

• A pulverulent cataract is a dominant variant of congenital cataracts. It appears as disc-shaped opacification involving the fetal nucleus and white dots in the lamellar portion of the eyelid.

How Do Congenital Cataracts Present Themselves?

Congenital cataracts primarily affect infants within one year after birth. Congenital cataracts may involve either one or both eyes.

• Congenital cataracts occur as an isolated entity or with other disease entities like microcornea (small cornea), microphthalmia (small eyes), and aniridia (partial or complete absence of the iris).

• Cataracts also occur in association with other multisystem disorders like chromosomal disorders, metabolic diseases, and developmental defects.

Congenital cataracts often occur with the following syndromes:

• Down's syndrome is a genetic disorder of chromosome 21.

• Lowe syndrome is a metabolic disorder affecting mainly the eyes, brain, and kidneys.

• Pierre-Robin syndrome is a congenital disability affecting the facial bones.

• An ectodermal dysplasia syndrome is a group of inherited disorders. It causes abnormal development of all structures originating from the outer germ layer (ectodermal origins), like hair, teeth, nails, and sweat glands.

How to Confirm Diagnosis for Congenital Cataract?

The diagnosis of congenital cataracts comprises clinical examination and tests.

• All newborns are screened for congenital cataracts through the red reflex technique. A red reflex test is ideal even in cases of an obstinate child. It is performed in a dark room using an ophthalmoscope and assesses the size and location of the cataract.

• Other eye tests to investigate the intraocular pressure, other eye parts, and the posterior pole of the eye are performed using the slit lamp technique and ultrasound.

Can Congenital Cataracts Be Cured?

Congenital cataracts are treated both medically and surgically.

• Medical or pharmacological management of congenital cataracts encompasses the use of Phenylephrine and Tropicamide.

• Surgical procedures for the newborn are performed at the age of six weeks in case of unilateral eye involvement cases. Bilateral cataracts are surgically corrected at ten weeks with a gap of one week between the two surgeries. The most significant surgeries performed to correct congenital cataracts are:

  • Extracapsular Cataract Extraction (ECCE) - The lens is removed by keeping the thin outer membrane covering it (lens capsule) intact.

  • Intracapsular Cataract Extraction (ICCE) - The lens is removed entirely from the capsule.

  • The affected lens is removed and replaced with intraocular lenses for best results. Putting intraocular lens after congenital cataract surgery at ten weeks is not advised as the eye is still growing. So the normal time to put an intraocular lens is after two years. Regular follow-up is crucial as children with intraocular lenses are at a greater risk of secondary opacification and myopia or shortsightedness.

What Are the Complications of Congenital Cataracts?

Delay in treatment of congenital cataracts leads to the following complication:

• Amblyopia is also known as the lazy eye, where one eye has reduced vision due to abnormal eye development.

• Strabismus is also known as the crossed eye. In this, both eyes look in different directions.

• Nystagmus is a visual condition in which the eyes make repeated and involuntary movements leading to blurred vision and perception.

• Glaucoma encompasses a group of eye diseases caused by damage to the optic nerve.

What Is the Overall Outlook of Congenital Cataracts?

Congenital cataracts are entirely curable with surgery. Complete restoration of visual acuity is achieved. In the case of other eye diseases linked to congenital cataracts, the improvement in vision is limited. Patients should follow up with their ophthalmologists.

Conclusion

Congenital cataracts are more prevalent in developing countries and affect newborns and infants. Most congenital cataracts are passed on from one generation. They occur due to the change in genetic sequence. Appropriate screening and surgical management of the disease entity improves a child's vision.