Anatomy Of Cornea

• Outer & fibrous coat of EYEBALL.
• Transparent, anterior 1/6th segment of eyeball.
• Non-vascular
• Watch- glass like structure.
• The charaterstics of adult cornea are:

• Anterior surface is elliptical, posterior surface is circular.
• Horizontal diameter of both surfaces is same (11.7 mm).
• While vertical diameter of posterior surface (11.7 mm) is about 1 mm less than anterior surface (10.6 mm).
• Radius of curvature of anterior surface is 7.8 mm & of posterior surface is 6.5 mm.
• The vertical meridian of cornea is 0.05 D steeper than the horizontal meridian, resulting in Astigmatism with the rule.

• Refractive power of cornea is about 43-44 D (3/4 of total diopetric power of the eye).
• Most of the refraction in eye occur at anterior surface of cornea (air-tear interface) ,i.e., Anterior surface of cornea is the most important refractive structure of eye.
• Refractive index of Cornea is 1.376.

• Horizontal diameter of cornea at birth is about 10 mm & the adult 11.7mm is attained by the age of 2 years.
• Megalocornea is labelled when the horizontal diameter is of adult size at birth or ≥ 13 mm afterthe age of 2 years.
• Systemic diseases associated with megalcornea are Marfan syndrome, Ehler danlos syndrome, Apert syndrome & Down syndrome.
• Microcornia is labelled when the corneal diameter is < 10mm.

• Cornea requires energy for maintenance of its transparency and state of relative dehydration.
• Energy in form of ATP is generated by the breakdown of glucose.
• As cornea is is an avascular structure, major pathway of metabolism is anaerobic glycolysis.
• The most actively metabolising layers of the cornea are epithelium & endotheium the former being ten times thicker than the latter, requires a proportionately large supply of metabolic substrates.

Cornea is avascular structure. Source of nutrition are:

1.  Solutes (glucose & other): From aqueous humor & perilimbal capillaries.
2. Oxygen: From air (atmosphere) through the tear film.

Exam Question

• Avascular coat in eye is Cornea.
• Anterior surface of Cornea is elliptical, posterior surface is circular.
• Radius of curvature of anterior surface of Cornea is 7.8 mm
• Refractive power of cornea is about 43-44 D.
• Refractive index of Cornea is 1.376.
• Most of the refraction in eye occur at anterior surface of cornea (air-tear interface).
• The critical angel of cornea-air interface is 46°.
• Cornea gets its nourishment mainly from Aqueous humour.