Crystalline Lens and Related Conditions

Flashcards covering key vocabulary related to the crystalline lens, its function, and common conditions like presbyopia and cataracts, based on the provided lecture notes.

Crystalline Lens

The transparent elastic structure behind the iris by which light is focused onto the retina of the eye (a part of the eye that focus things in the back of the eye)

Avascular

A descriptor for the crystalline lens, meaning it lacks blood vessels.

Zonular Fibers (Zonules of Zinn/Suspensory ligaments)

Thread-like fibers that suspend the crystalline lens from the surrounding ciliary body.

Malleable

A property of the crystalline lens, allowing its shape to change due to ciliary muscle contraction.

Accommodation

The mechanism by which ciliary muscle contraction changes the lens shape, increasing its dioptric power to allow near objects to be focused on the retina.

Refractive Power of Unaccommodated Lens

Approximately 20 diopters (D).

Maximum Accommodative Amplitude

14 diopters (D), typically reached between ages 8 and 12, decreasing with age to near zero after 50.

Lens Composition

The crystalline lens is composed of the Nucleus (center), the Cortex, and the Capsule.

Presbyopia

The age-related decrease in the eye's ability to focus at near (accommodate), due to the lens capsule becoming thicker, less elastic, and more brittle with age.

Cataracts

The opacity or 'clouding' of the crystalline lens, which is the greatest cause of blindness in the world.

Causes of Cataracts

Aging, disease, genetics, nutritional deficiencies, congenital factors, environmental stress, and radiation (especially UVR).

UV Radiation (UVR) Absorption by Lens

The lens absorbs most of the UVR our eyes are exposed to (300-400nm), highlighting the need for UV protection.

Diabetic Cataracts

Cataracts caused by elevated glucose levels, which cause lens fibers to swell and can develop rapidly.

Cortical Cataracts

An age-related cataract appearing 'spoke-like,' often associated with lifetime exposure to UVR.

Age Related Nuclear Cataracts

An age-related cataract where the lens color changes to hues of yellow and brown due to chemical changes.

Posterior Subcapsular (PSC) Cataracts

Cataracts formed by cells migrating from the equatorial portion of the lens to the posterior pole, often linked to radiation from cancer treatments.

Congenital Cataracts

Cataracts caused by the swelling of cortical fibers during pregnancy.

Steroid Induced Cataracts

Cataracts located in the Posterior Subcapsular region of the lens, caused by the use of steroid medications.

Cataract Surgery

A surgical procedure to remove the clouded crystalline lens and insert an Intraocular lens (IOL) to restore vision.

Intraocular Lens (IOL)

An artificial lens inserted into the eye during cataract surgery to replace the power of the missing natural lens.