The Crystalline Lens Anatomy and Nutrition

Questions and Answers

What metabolic process occurs in the lens due to its avascular nature?

Oxidative phosphorylation

Fermentation

Aerobic respiration

Anaerobic metabolism (correct)

What is the primary function of the lens in regard to UV protection?

It enhances blood flow to the retina.

It produces retinal cells.

It absorbs harmful UV rays. (correct)

It disperses light rays evenly.

Which protein carrier is critical for the oxidation process in the lens?

Vitamin E

Vitamin C (correct)

Vitamin B12

Vitamin D

Which type of cataract is classified as 'acquired'?

Traumatic cataract Signup and view all the answers

What percentage of the lens's composition is made up of water?

65% Signup and view all the answers

What does the accommodation process help achieve?

Focus at various distances Signup and view all the answers

What is the approximate refractive index of the lens nucleus?

1.42 Signup and view all the answers

What change in the lens occurs as a person ages from young to old?

Decreased elasticity Signup and view all the answers

Which of the following best describes the anterior surface of the crystalline lens?

Less convex with a radius of 10 mm Signup and view all the answers

What is the primary structural feature that suspends the crystalline lens in position?

Zonules Signup and view all the answers

What is the average refractive power of the lens for unaccommodated vision at birth?

+15 D to +18 D Signup and view all the answers

How does the color of the lens change from childhood to old age?

Colorless to yellowish to grayish Signup and view all the answers

Which characteristic is commonly associated with congenital cataracts?

Bilateral occurrence Signup and view all the answers

What is the typical treatment if a congenital cataract is large and impacts vision?

Da visual iridectomy Signup and view all the answers

What distinguishes congenital anterior polar cataract from acquired types?

Present since birth Signup and view all the answers

Which symptom is least likely to be associated with anterior polar cataract?

Severe pain around the eye Signup and view all the answers

What type of opacity is typically seen in congenital anterior polar cataract?

Disc-shaped opacity Signup and view all the answers

What is a likely etiology for anterior polar cataract?

Prolonged contact between cornea and lens Signup and view all the answers

What is a common characteristic of congenital cataracts?

They are often associated with chromosomal abnormalities. Signup and view all the answers

Which type of cataract progresses to total opacification?

Total cataract Signup and view all the answers

What is a distinguishing feature of soft cataracts compared to hard cataracts?

They contain soluble proteins that can be digested. Signup and view all the answers

Which statement correctly describes anterior polar cataract symptoms?

Symptoms are asymptomatic in most cases. Signup and view all the answers

Which of the following is considered a risk factor for congenital cataracts?

Maternal exposure to teratogenic drugs. Signup and view all the answers

What type of cataract is associated with maternal malnutrition, particularly a deficiency of Vitamin D and Calcium?

Congenital cataract Signup and view all the answers

How does the presence of a hard nucleus in hard cataracts affect post-surgery outcomes?

The nucleus remains, potentially causing after cataracts. Signup and view all the answers

Which of the following features is NOT typical of soft cataracts?

Presence of a large hard nucleus. Signup and view all the answers

What is the primary function of the lens capsule?

Acts as a semi-permeable membrane Signup and view all the answers

Which type of fiber is pushed inward and undergoes sclerosis?

Central fibers Signup and view all the answers

What type of suture is typically found in the adult lens?

Star-shaped suture Signup and view all the answers

What is the primary metabolic process in the lens?

Anaerobic metabolism Signup and view all the answers

What characterizes the embryonic nucleus of the lens?

Forms within the first three months of intrauterine life Signup and view all the answers

Which cells are responsible for secreting lens fibers?

Equatorial cells Signup and view all the answers

What is the correct classification of lens opacity due to age?

Senile Signup and view all the answers

What is a significant characteristic of lens fibers with age?

New fibers remain nucleated Signup and view all the answers

What is a significant risk during cataract surgery in patients with congenital cataract?

Associated cardiac anomalies Signup and view all the answers

Which type of cataract is characterized by small blue dots scattered in the lens?

Blue dot cataract Signup and view all the answers

What are the common features associated with congenital rubella syndrome?

Microcephaly, MR, Deafness, PDA Signup and view all the answers

Which of the following cataract types does not affect vision but is usually discovered during routine examination?

Blue dot cataract Signup and view all the answers

What treatment is recommended for unilateral congenital cataracts at the age of 4-6 weeks?

Immediate surgery to prevent amblyopia Signup and view all the answers

Which complication arises from bilateral opacity in congenital cataract?

Nystagmus with non-fixing eye Signup and view all the answers

What should be done if bilateral cataracts are equal in density?

Conduct visual acuity assessments Signup and view all the answers

What symptom is commonly reported by a mother if the cataract in the infant is extensive?

White pupil Signup and view all the answers

What is the primary cause of senile cataract's development?

Unknown etiology with contributing factors Signup and view all the answers

Which type of cataract is the most common in senile cataracts?

Cortical (75%) Signup and view all the answers

Which factor is NOT typically associated with the pathogenesis of senile cataracts?

Exposure to cold temperatures Signup and view all the answers

What is a significant consequence of disturbed capsular permeability in the lens?

Increased calcium levels Signup and view all the answers

In what way does the aging process influence the lens structure in senile cataract?

Causes lens protein instability Signup and view all the answers

What examination method is commonly used to assess the lens for cataracts?

Oblique illumination Signup and view all the answers

What defines lamellar cataract?

Lens opacification involving one or more lamellae Signup and view all the answers

Which condition is not commonly associated with lamellar cataract due to deficiency?

Vitamin A deficiency Signup and view all the answers

What is the most prominent clinical feature of posterior polar cataract?

Disc-shaped opacity at the posterior pole Signup and view all the answers

What is the nodal point in the eye?

The point through which light rays must pass to fall on the fovea Signup and view all the answers

Which of the following is a common feature of congenital rubella syndrome?

Microcephaly Signup and view all the answers

What complication is particularly associated with cataract surgery in patients with total cataract due to rubella?

Viral endophthalmitis Signup and view all the answers

What is a characteristic appearance of lens opacity in lamellar cataract?

Steering wheel or cart wheel Signup and view all the answers

Which type of cataract consists of small blue dots?

Blue dot cataract Signup and view all the answers

What feature differentiates sutural cataract from other cataract types?

Opacities at the Y-shaped suture Signup and view all the answers

What is the appropriate treatment option for posterior polar cataract?

Lensectomy Signup and view all the answers

What is the purpose of performing cataract extraction if visual acuity remains poor after initial treatment?

To remove dense lens material causing opacity Signup and view all the answers

Which of the following is a consequence of operating on a dense opacity before 3 months of age?

Interference with eye development Signup and view all the answers

In cases of uncorrected hyperopia, which method of aphakia correction is least suitable?

Glasses Signup and view all the answers

What is a significant disadvantage of using vitrectomy for lens removal?

Retinal detachment risk Signup and view all the answers

Why should visual acuity be assessed before performing surgery on a non-dense opacity?

To prevent unnecessary surgical intervention Signup and view all the answers

What advantage does the irrigation/aspiration operation provide over vitrectomy?

Reduced rate of retinal detachment Signup and view all the answers

Which feature of an IOL is preferred by children according to the treatment guidelines?

Aspheric IOLs Signup and view all the answers

What factor may complicate the dilation of the pupil during early surgery in infants?

Underdeveloped dilator muscles Signup and view all the answers

What is the major disadvantage of lensectomy compared to aspiration operation for cataract extraction in infants?

Higher risk of retinal detachment and vitreous loss due to very strong zonules and hyalo-capsular ligament Signup and view all the answers

What is the recommended IOL type to reduce the incidence of posterior capsule opacification (PCO) in children?

Acrylic hydrophobic IOLs with square edges Signup and view all the answers

What is a major disadvantage of using glasses for correction of aphakia in children?

Heavy weight and constricted visual field Signup and view all the answers

Why is a posterior capsulotomy and anterior vitrectomy performed during aspiration operation for congenital cataract?

To prevent posterior capsular opacity (PCO) Signup and view all the answers

Which of the following statements about piggyback IOLs in children is TRUE?

They are a recently developed option for aphakia correction Signup and view all the answers

What visual acuity outcome is considered better in children after cataract surgery and why?

6/18 with some accommodation Signup and view all the answers

What is the purpose of using a double way cannula during the aspiration of lens matter in congenital cataract surgery?

To avoid collapse of the lens bag Signup and view all the answers

Which of the following is NOT a line of treatment for congenital cataract?

Laser capsulotomy Signup and view all the answers

Study Notes

The Crystalline Lens

Definition: A transparent, avascular, biconvex structure held in place by zonules.
Anatomical Relations:
- Anteriorly - Iris, separated by posterior chamber containing aqueous.
- Posteriorly - Vitreous, separated by retro-lental space also containing aqueous.
Shape:
- Biconvex and disc-shaped; anterior surface less convex (radius of 10 mm), posterior surface more convex (radius of 6 mm).
- Equatorial diameter ranges from 9-10 mm.
Consistency:
- Softer in youth, becomes harder with aging.
Color:
- Colorless in children, yellowish in adults, grayish in old age (physiological lens sclerosis).
Refractive Index:
- Cortex: 1.39, nucleus: 1.42, average lens: 1.4.
Refractive Power:
- +15 to +18 D in eye (decreases to +1 D by age 60); +70 D outside the eye.

Nutrition

After Birth: Nutrients acquired through diffusion from aqueous humor due to avascularity.
Before Birth: Vascular with both anterior and posterior supply from the hyaloid artery.

Composition

Contains 65% water, 34% proteins, and 1% minerals.

Metabolism

Primarily anaerobic due to lack of blood supply; oxidation facilitated by Vitamin C and Glutathione.

Functions of the Lens

Serves as one of the refractive media.
Responsible for accommodation.
Protects retina from harmful UV rays.

Accommodation

Ability of the eye to adjust its focusing power for different distances.

Cataract

Definition: Opacification of the lens leading to loss of transparency.
Classifications:
- Congenital and acquired, with acquired varying by cause (traumatic, complicated, senile).

Minute Anatomy

Capsule: Highly elastic membrane, thicker anteriorly, secreted by anterior subcapsular epithelium.
Lens Fibers: Created by equatorial cells, older fibers compressed towards the nucleus, producing sclerosis.
Sutures: Articulate lens fibers; fetal: Y-shaped, adult: star-shaped.

Anterior Polar Cataract

Etiology: Delayed formation, irritation leading to mass cell formation.
Symptoms and Signs: Typically asymptomatic; may appear as disc or pyramidal shape.

Congenital Cataract

Etiology: Hereditary, chromosomal abnormalities (e.g., Down syndrome), maternal malnutrition, intra-uterine infections, teratogenic exposure.

Types of Cataract

Soft Cataracts: Present before age 2, usually congenital, traumatic, or complicated.
Hard Cataracts: Develop after age 25, mainly senile.
Incidence: Nuclear, lens pin.

Clinical Features of Congenital Cataract

Symptoms include white pupil (if dense) and defective vision.
Treatment varies by opacity density, with early surgery preferred in unilateral cases.

Senile Cataract

Definition: Bilateral, asymmetrical, slowly progressive lens opacity in elderly people.
Age Incidence: Commonly above 50 years.
Pathogenesis: Altered water content, protein coagulation due to metabolic issues, and oxidative stress leading to lens opacity.

Method of Examination

Oblique illumination using torches and slit lamps for magnification and illumination.

Treatment Options

Surgical: Aspiration or lensectomy.
- Post-operative considerations include the risk of retinal detachment.
Correction of Aphakia:
- Glasses: Heavy with limited field; not suitable for unilateral cases.
- Contact Lenses: Difficult to manage with complications.
- Intraocular lenses (IOL): Preferred for corrections; various options assessed for pediatric patients.

Preoperative Evaluation

Assess opacity and visual acuity using objective methods; timing of surgery dictated by visual needs and eye development considerations.

Conclusion

Balanced approach for cataract treatment focusing not only on the surgical correction but also on long-term visual outcomes and potential complications.

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Description

Explore the structure and nutritional aspects of the crystalline lens through this informative quiz. Understand its anatomical relations, refractive properties, and changes over age, as well as how it acquires nutrients. Perfect for students studying ocular anatomy.