sclera


sclera



 The sclera is the white, opaque outer coat of the eyeball – often called the "white of the eye." It is strong and protective, giving the eye its shape.


🔹 Key Features of the Sclera

  • Location:
    Forms the posterior 5/6 of the eyeball’s outer coat, continuous in front with the cornea and behind with the dura mater of the optic nerve.

  • Structure:

    • Dense connective tissue (mainly collagen & elastic fibers).

    • Avascular (no blood vessels), which makes it appear white.

    • Covered by episclera (outer connective tissue layer) and conjunctiva.

  • Thickness:

    • Thickest near the posterior pole (~1 mm).

    • Thinnest just behind the rectus muscle insertions (~0.3 mm).

  • Openings:

    • Anterior scleral foramina → for cornea.

    • Posterior scleral foramina → for optic nerve fibers.

    • Numerous small channels for nerves & blood vessels.


🔹 Functions

  • Maintains the shape of the eyeball.

  • Provides attachment for extraocular muscles.

  • Protects the delicate intraocular structures.

  • Transmits vessels and nerves into the eye.


Color Variations

  • Normal → white.

  • Infants → bluish (sclera thin, underlying uveal pigment shows through).

  • Elderly → yellowish (fatty deposits).

  • Pathological:

    • Blue sclera → osteogenesis imperfecta, Ehlers–Danlos, severe anemia.

    • Icteric (yellow) sclera → jaundice.

Reasons for White Color of the Sclera

  1. Dense Collagen Fibers

    • The sclera is made up of irregularly arranged collagen bundles.

    • Unlike the cornea (where collagen fibers are uniformly arranged → transparency), the scleral fibers are disorganized.

    • This irregularity scatters all wavelengths of light equally → giving it an opaque, white appearance.

Low Water Content

  • Cornea has ~78% water (kept in a precise state of dehydration by endothelium).

  • Sclera has less water (~65%), and no special dehydration mechanism, contributing to opacity.

Poor Vascularity

  • The sclera is almost avascular, so it lacks a pink/red tinge from blood vessels.

  • This adds to its white appearance.

🔹 Variations in Color

  • Bluish sclera → seen in infants (thin sclera, underlying uveal pigment shows through) or in diseases like osteogenesis imperfecta, Ehlers–Danlos, iron deficiency anemia.

  • Yellowish sclera → in elderly (lipid deposition) or in jaundice (bilirubin deposition).


bluish sclera 



The bluish sclera in babies is a normal finding in the first few months of life.

🔹 Why it happens

  1. Thin sclera in infants

    • In newborns and young infants, the sclera is not fully developed and is thinner than in adults.

    • Because of this, the underlying uveal tissue (choroid, rich in dark pigment and blood) shows through.

  2. Light scattering effect

    • The thin sclera allows shorter wavelengths (blue light) to scatter more, making the sclera appear bluish (similar to why veins look blue under the skin).

🔹 Clinical Aspect

  • Normal: Bluish sclera is common in babies and usually disappears as the sclera thickens with age (around 1 year).

  • Abnormal / Pathological (if persists or is very intense):

    • Osteogenesis imperfecta (brittle bone disease).

    • Ehlers–Danlos syndrome (connective tissue disorder).

    • Severe iron deficiency anemia.



Yellowish Sclera in Old Age



When eyes look yellowish in old age, it usually involves the sclera.

🔹 Causes of Yellowish Sclera in Old Age

Fat & Lipid Deposition

    • With aging, the sclera gradually accumulates lipids (cholesterol, fats).

    • This gives the sclera a yellowish tinge (similar to arcus senilis seen at the corneal periphery).

    • It is a benign, age-related change and does not affect vision.

Elastic Tissue Degeneration

  • Age causes changes in the connective tissue of the sclera.

  • Degeneration of elastin fibers → yellow-brown discoloration.

Conjunctival Changes

  • The overlying conjunctiva may also become thinner and allow underlying yellowish sclera to show more.

🔹 Important to Differentiate

  • Physiological (normal aging) → gradual, uniform yellowing, no other symptoms.

  • Pathological (disease):

    • Jaundice (bilirubin deposition in sclera) → sudden yellowing, usually with systemic illness (liver disease, bile duct obstruction).

    • Needs medical attention.


 Jaundice & Yellow Sclera

  • In jaundice, there is excess bilirubin in the blood (hyperbilirubinemia).

  • Bilirubin is a yellow pigment formed from the breakdown of hemoglobin.

Mechanism:

  1. High bilirubin in blood → diffuses into tissues.

  2. The sclera has a high content of elastin.

  3. Bilirubin has a high affinity for elastin fibers → it deposits in scleral tissue.

  4. This deposition gives the sclera a deep yellow color (sometimes golden or even greenish in chronic cases).

🔹 Clinical Significance

  • Yellow sclera is often the first visible sign of jaundice, sometimes before skin discoloration.

  • It indicates bilirubin levels are usually > 2 mg/dL in the blood.

🔹 Causes of Jaundice (broad categories)

  1. Pre-hepatic (excess breakdown of RBCs, e.g., hemolytic anemia).

  2. Hepatic (liver diseases, e.g., hepatitis, cirrhosis).

  3. Post-hepatic (bile duct obstruction, e.g., gallstones, tumors).



🔹 Clinical Importance

  • Scleritis → painful inflammation (often autoimmune).

  • Episcleritis → mild, localized, self-limiting inflammation.

  • Staphyloma → scleral thinning and bulging (seen in glaucoma, trauma, or infection).

Sclera = “Shield of the eye” → tough, white, protective layer.

For further process. click https://medorbis.ai



Comments

Post a Comment

Popular posts from this blog

MYOPIA

What is Myopia? Myopia (commonly called nearsightedness) is a vision condition where a person can see nearby objects clearly but distant objects appear blurry. What Causes Myopia? It usually occurs when: The eyeball is too long from front to back. The cornea (the clear front surface of the eye) is too curved. As a result, light rays focus in front of the retina, instead of directly on it. Symptoms of Myopia: Blurred vision when looking at distant objects. Squinting to see clearly. Eye strain or headaches (especially after focusing on distant objects). Difficulty seeing while driving, especially at night (night myopia). Risk Factors: Genetics : If one or both parents are myopic, the risk increases. Excessive near work : Prolonged reading, computer, or phone use. Lack of outdoor time: Spending less time in natural light, especially in childhood. Treatment and Management Corrective Lenses: Eyeglasses or contact lenses with minus (–) power lenses. Refractive Surgery: LASIK, PRK, SMILE – re...
Read more

Important of colour check

  Why is it important to check colour vision? Checking colour vision is important for several reasons: 1. Early Detection of Vision Disorders It helps detect congenital colour blindness, especially in children. Can also reveal acquired conditions due to eye diseases (e.g., glaucoma, optic neuritis). 2. Career Requirement Certain professions require normal colour vision, such as: Pilots Electricians Military personnel Police officers Graphic designers Drivers Railway and maritime workers 3. Safety and Daily Functioning Correct colour recognition is vital for identifying traffic lights, warning signs, and colour-coded materials. Difficulty distinguishing colours can impact school performance, cooking, clothing choices, and reading charts or graphs. 4. Monitoring Disease Progression Colour vision testing helps track changes in patients with: Diabetic retinopathy Multiple sclerosis Macular degeneration Medication side effects (e.g., ethambutol) 5. Educational Guidance In children, dete...
Read more