The lens is one of the main refractive media of the eye and adds a variable degree of refraction (10-20 diopters, depending on the person's fit) to the constant refractive power of the cornea (about 43 diopters).
Suspended by thin filamentous zonules from the ciliary processes located between the iris anteriorly and the vitreous posteriorly.
The loss of transparency of the crystalline lens and becoming opaque is called cataract.
Causes of Acquired Cataract
age-related cataracts
1. subcapsular cataract
(a) Anterior subcapsular cataract
(b) Posterior subcapsular cataract
2. Nuclear cataract
Myopia is seen due to an increase in the refractive index in the lens nucleus.
Some elderly patients with nuclear cataracts may have the opportunity to read closely again without eyeglasses, thanks to this resulting myopia (the elderly begin to see again).
3. Cortical cataract
Cortical opacities begin as slits and vacuoles between the lens fibers due to cortex hydration.
Patients often complain of light scattering.
presenile cataracts
Presenile cataracts may be associated with the following systemic diseases.
I. Diabetes
2. Myotonic dystrophy
3. Atopic dermatitis
4. Neurofibromatosis type 2
Traumatic cataracts
• Trauma is the most common cause of unilateral cataracts in young individuals.
1. Direct exposure of the lens to penetrating injury.
2. Blunt traumas - 'Vossius' ring characterized by the projection of the iris pigment onto the anterior capsule of the lens in the form of a stigma, as well as causing flower-shaped opacities in the lens
3. Electric shocks and lightning strikes
4. Application of ionizing radiation to ocular tumors
5. Infrared radiation (glassblower cataract)
Effects of Blunt Trauma to the Eye:
• Corneal erosion and edema
• hyphema
• Iridodialysis
• Hypertonia due to inflammation (high intraocular pressure)
• Hypotonia due to ciliary body depression (low intraocular pressure)
• Cataract
• Globe rupture
• Vitreous hemorrhage
• Retinal edema and detachments
• Traumatic optic neuropathy
• Optic nerve avulsion
• Central retinal artery occlusion (rare)
Toxic cataracts
1. Steroids: whether taken systemically or topically, they have catharogenic properties.
Lens opacities begin in the posterior subcapsular region, followed by the anterior subcapsular region.
2. Chlorpromazine, miotics, busulfan, amiodarone, gold
Secondary Cataracts
• Secondary or complicated cataract occurs as a result of another eye disease.
I. Chronic anterior uveitis is the most common cause of secondary cataract.
2. Acute congestive angle-closure glaucoma
3. High myopia
4. Hereditary fundus dystrophies (retinitis pigmentosa, Leber's congenital amaurosis, gyrate atrophy, Stickler syndrome)
Congenital Cataract Etiology
Systemic metabolic associations
I. galactosemia
2. Galactokinase deficiency
3. Mannosidosis
4. Lowe's oculocerebrorenal syndrome
5. Fabry disease
6. Other metabolic causes: Maternal diabetes, hypoparathyroidism, pseudohypoparathyroidism, hypoglycemia and hyperglycemia
Concomitant intrauterine infections
• Congenital rubella, toxoplasmosis, cytomegalovirus infection, syphilis, Herpes simplex infection and Varicella are included.
Concomitant chromosomal abnormalities
• Down syndrome (trisomy 21), Patau syndrome (trisomy 13), Edward's syndrome (trisomy 18), cri-du-chat syndrome (deletion of the fifth chromosome) and Turner syndrome.
