Lens SAQS

1. Congenital Cataract

Congenital and developmental cataracts arise from disturbances in the normal growth of the lens.

• Definition: If the disturbance occurs before birth, the opacity is limited to the embryonic or fetal nucleus and is termed congenital cataract. If it occurs from infancy to adolescence, it is called developmental cataract.

• Etiology: Approximately one-third are idiopathic, one-third are hereditary, and one-third are due to maternal or fetal causes.

    ◦ Maternal factors: Malnutrition, infections (Rubella, toxoplasmosis), drugs (thalidomide, corticosteroids), and radiation. Maternal rubella infection in the first trimester causes cataract in 50% of cases.

    ◦ Fetal/Infantile factors: Metabolic disorders (galactosemia, Lowe’s syndrome), anoxia, birth trauma, and ocular anomalies like persistent hyperplastic primary vitreous (PHPV) or aniridia.

• Morphological Types: These include Capsular, Polar (anterior or posterior), Nuclear (e.g., cataracta pulverulenta, lamellar), and Generalized (e.g., coronary, blue dot).

• Management: This involves detailed clinical evaluation (TORCH test, urine analysis), assessment of visual function, and surgery (lens aspiration or lensectomy) followed by optical correction (IOL, contact lenses) and amblyopia therapy.

2. Zonular Cataract (Lamellar Cataract)

• Definition: It is the most common type of congenital cataract presenting with visual impairment, accounting for 50% of cases.

• Features: The opacity occupies a discrete zone of the fetal nucleus surrounding the embryonic nucleus. The area internal and external to this zone remains clear, except for small linear opacities called "riders" (like spokes of a wheel) extending toward the equator.

• Etiology: It can be genetic (usually autosomal dominant) or environmental. Environmental causes include Vitamin D deficiency, hypocalcemia, and maternal rubella infection between the 7th and 8th week of gestation.

• Impact: It is usually bilateral and frequently causes severe visual defects.

3. Complications of Hypermature Cataract

If a mature cataract is left untreated, it progresses to hypermaturity, leading to potential complications:

• Phacolytic Glaucoma: Lens proteins leak through the intact capsule of a Morgagnian cataract. These proteins are engulfed by macrophages, and the resulting debris clogs the trabecular meshwork, causing secondary open-angle glaucoma.

• Phacoanaphylactic Uveitis: Lens proteins leaking into the anterior chamber act as antigens, inducing an antigen-antibody reaction that leads to severe granulomatous anterior uveitis.

• Lens-Induced Glaucoma (Phacotopic): Degeneration of zonules in the hypermature stage can lead to subluxation or dislocation of the lens, which may cause glaucoma by blocking the pupil or the angle of the anterior chamber.

4. Complicated Cataract

• Definition: Opacification of the lens secondary to some other intraocular disease.

• Causes: The most common cause is anterior uveitis (iridocyclitis). Other causes include degenerative conditions (retinitis pigmentosa), retinal detachment, primary or secondary glaucoma, and intraocular tumors (retinoblastoma, melanoma).

• Clinical Features:

    ◦ Typically starts as a posterior subcapsular cataract (PSC).

    ◦ Characteristic signs include a "breadcrumb" appearance and "polychromatic luster" (rainbow cataract) seen on slit-lamp examination.

    ◦ The opacity is irregular and variable in density, eventually spreading to involve the entire lens.

5. Intraocular Lenses (IOLs)

• Definition: An artificial lens implanted to correct aphakia.

• Types:

    ◦ Based on Fixation: Anterior Chamber IOL (e.g., Kelman multiflex), Iris-supported lenses (e.g., Singh-Worst’s iris claw), and Posterior Chamber IOL (PCIOL). PCIOL is the most ideal and can be fixed in the capsular bag or ciliary sulcus.

    ◦ Based on Material: Rigid (PMMA), Foldable (silicone, acrylic, hydrogel), and Rollable (ultra-thin hydrogel).

    ◦ Focusing Ability: Unifocal, Multifocal (pseudoaccommodative), and Accommodative.

• Advantages: IOLs avoid the magnification (30% with spectacles) and prismatic aberrations of aphakic glasses, provide a wider field of vision, prevent anisometropia in unilateral cases, and are cosmetically acceptable.

• IOL Power Calculation: Calculated using biometry, which measures the axial length of the eyeball (A-scan ultrasound) and corneal curvature (keratometry). The SRK formula is commonly used: P=A−2.5L−0.9K (where P is power, A is a constant, L is axial length, and K is corneal curvature).

6. Post-Operative Complications of Cataract Surgery

• Early Complications: Hyphema (blood in anterior chamber), Iris prolapse (inadequate suturing), Striate keratopathy (corneal edema), Flat anterior chamber (wound leak or pupil block), and Bacterial endophthalmitis (pain, redness, hypopyon 48–72 hours post-op). Toxic Anterior Segment Syndrome (TASS) is a sterile inflammation caused by toxic substances.

• Late Complications: Cystoid Macular Edema (CME), Delayed chronic endophthalmitis, Pseudophakic Bullous Keratopathy (PBK), Retinal Detachment (higher risk in aphakia), Epithelial ingrowth, and After-cataract.

• IOL-Related Complications: Malpositions (Sunset/Sunrise syndrome, lost lens), UGH syndrome (Uveitis-Glaucoma-Hyphema), and Toxic lens syndrome.

7. Hyphema

• Definition: Collection of blood in the anterior chamber.

• Causes: Ocular injuries (blunt or penetrating), postoperative complications (cataract surgery), spontaneous causes (rubeosis iridis, intraocular tumors), and infections like gonococcal iritis or herpes zoster iritis.

• Complications: Secondary glaucoma and blood staining of the cornea.

• Management: Most absorb spontaneously. Conservative treatment prevents IOP rise and secondary hemorrhage. Surgical drainage (paracentesis) is indicated if the blood does not absorb, causes raised IOP, or risks corneal staining.

8. After Cataract (Secondary Cataract)

• Definition: It is the most common postoperative complication, referring to opacity that persists or develops after extracapsular lens extraction.

• Types:

    ◦ Dense membranous: Proliferation of anterior epithelial cells.

    ◦ Soemmerring’s ring: A thick ring of after-cataract behind the iris.

    ◦ Elschnig’s pearls: Vacuolated subcapsular epithelial cells clustered like soap bubbles.

• Management: Thin membranous types and Elschnig's pearls are best treated by Nd:YAG laser capsulotomy. Dense membranes may require surgical membranectomy.

9. Senile Immature Cataract (ISC)

• Etiology: It is part of the age-related (senile) cataract process.

• Clinical Features:

    ◦ Vision: Visual acuity ranges from 6/9 to counting fingers.

    ◦ Color: The lens appears greyish white.

    ◦ Iris Shadow: A shadow of the pupillary margin of the iris is formed on the lens opacity, indicating clear cortex is present (a sign of immature cataract).

    ◦ Intumescent Stage: The lens may become swollen due to hydration, causing the anterior chamber to become shallow.

• Management: Surgical removal (ECCE, SICS, or Phacoemulsification) is the primary treatment. Non-surgical measures like changing glasses or using mydriatics may help in early stages.

10. Cortical Cataract

• Etiology: It is an age-related process involving decreased protein levels and increased hydration and sodium content in the lens, followed by protein coagulation.

• Stages:

    1. Stage of Lamellar Separation: Formation of vacuoles and water clefts.

    2. Stage of Incipient Cataract: Early detectable opacities, appearing as wedge-shaped (cuneiform) or saucer-shaped (cupuliform) opacities.

    3. Immature Senile Cataract (ISC): Opacification progresses, lens appears greyish white, iris shadow is visible.

    4. Mature Senile Cataract (MSC): Complete opacification, lens becomes pearly white ("ripe").

    5. Hypermature Senile Cataract (HMSC): Can be Morgagnian (liquefied cortex) or Sclerotic (shrunken).

• Symptoms: Glare, uniocular diplopia/polyopia, colored halos, and gradual loss of vision.

11. Macular Function Test

These tests are performed to predict visual potential in patients with dense cataracts where the fundus cannot be visualized.

• Tests include:

    ◦ Two-light discrimination test: Patient identifies two pin-hole lights 2 inches apart at 2 feet distance.

    ◦ Maddox rod test: Accurate perception of a red line from a distant bright light indicates normal function.

    ◦ Entoptic visualization: Patient perceives retinal vascular pattern when a light is rubbed against closed eyelids.

    ◦ Color perception: Indicates macular function.

    ◦ Laser Interferometry: The most accurate method for predicting macular potential.

    ◦ Potential Acuity Meter (PAM).

    ◦ Electrophysiological tests: ERG (Electroretinogram) and VER (Visually Evoked Response)