Cornea congenital anomalies

Megalocornea
Horizontal diameter of cornea at birth is about 10 mm and the adult size of about 11.7 mm is attained by the age of 2 years. Megalocornea is labelled when the horizontal diameter of cornea is of adult size at birth or 13 mm or greater after the age of 2 years. The cornea is usually clear with normal thickness and vision. The condition is not progressive. Systemic association include Marfan's, Apert, Ehlers Danlos and Down syndromes.

Differential diagnosis
1. Buphthalmos. In this condition IOP is raised and the eyeball is enlarged as a whole. The enlarged cornea is usually associated with

cornea anatomy

APPLIED CORNEA ANATOMY
The cornea is a transparent, avascular, watch-glass like structure. It forms anterior one-sixth of the outer fibrous coat of the eyeball.

Dimensions

• The anterior surface of cornea is elliptical with an average horizontal diameter of 11.7 mm and vertical diameter of 11 mm.
• The posterior surface of cornea is circular with an average diameter of 11.5 mm.
• Thickness of cornea in the centre is about 0.52 mm while at the periphery it is 0.7 mm.
• Radius of curvature. The central 5 mm area of the cornea forms the powerful

Grading of trachoma

McCallan's classification
McCallan in 1908, divided the clinical course of the
trachoma into following four stages:

• Stage I (Incipient trachoma or stage of infiltration). It is characterized by hyperaemia of palpebral conjunctiva and immature follicles.
• Stage II (Established trachoma or stage of florid infiltration). It is characterized by appearance of mature

CHLAMYDIAL CONJUNCTIVITIS

Chlamydia lie midway between bacteria and viruses,
sharing some of the properties of both. Like viruses,
they are obligate intracellular and filterable, whereas
like bacteria they contain both

Glands of conjunctiva

The conjunctiva contains two types of glands
(Fig. 1):


1. Mucin secretory glands. These are goblet cells
(the unicellular glands located within the epithelium),
crypts of
Henle (present in the tarsal conjunctiva)
and glands of Manz (found in limbal conjunctiva).
These glands secrete mucus which is  
essential for wetting the

Structure of conjunctiva

Histologically, conjunctiva consists of three layers
namely, (1) epithelium, (2) adenoid layer, and (3)
fibrous layer (Fig. 1 below ).


1. Epithelium. The layer of epithelial cells in
conjunctiva varies from region to region and in its
different parts as
follows:

• Marginal conjunctiva has 5-layered stratified squamous type of epithelium.
• Tarsal conjunctiva has

ANATOMY of Conjunctiva

The conjunctiva is a translucent mucous membrane
which lines the posterior surface of the eyelids and
anterior aspect of eyeball. The name conjunctiva
(conjoin: to join) has been given to this mucous
membrane owing to the fact that it joins the eyeball
to the lids. It stretches from the lid margin to the
limbus, and encloses a complex space called
conjunctival sac which is open in front at the
palpebral fissure.

Parts of conjunctiva
Conjunctiva can be divided into three parts (Fig. 1):
1. Palpebral conjunctiva. It lines the lids and can be
subdivided into marginal, tarsal and orbital
conjunctiva.
i. Marginal conjunctiva extends from the

contact lens use Indications & Contraindications

Indications of contact lens use

1. Optical indications include anisometropia, unilateral aphakia, high myopia, keratoconus and irregular astigmatism. Optically they can be used by
every patient having refractive error for cosmetic purposes.

Advantages of contact lenses over spectacles:
(i) Irregular corneal astigmatism which is not possible to correct with glasses can be corrected with contact lenses.

(ii) Contact lenses provide normal field of vision.

(iii) Aberrations associated with spectacles (such as peripheral aberrations and prismatic distortions) are eliminated.

(iv) Binocular vision can be retained in high anisometropia (e.g., unilateral aphakia) owing to less magnification of the retinal image.
 

 (v) Rain and fog do not condense upon contact lenses as

Regular Astigmatism Refractive types

Depending upon the position of the two focal lines in relation to retina, the regular astigmatism is further
classified into three types:

1. Simple astigmatism, wherein the rays are focused on the retina in one meridian and either in front (simple myopic astigmatism – Fig. 1 a) or behind (simple hypermetropic astigmatism  Fig. 1 b "BELOW") the retina in the

DERIVED STRUCTURES FROM EMBRYONIC LAYERS OF THE EYE

1. Surface ectoderm

•  The crystalline lens
•  Epithelium of the cornea
•  Epithelium of the conjunctiva
•  Lacri

lacrimal apparatus and Conjunctiva introduction

What is Conjunctiva
Conjunctiva develops from the ectoderm lining the lids and covering the globe .
Conjunctival glands develop as growth of the basal cells of upper conjunctival fornix. Fewer glands
develop from the lower fornix.

The lacrimal apparatus
Lacrimal gland is formed from about 8 cuneiform epithelial buds which grow by the end of 2nd month
of fetal life from the superolateral side of the
conjunctival sac .
Lacrimal sac,

VISUAL PATHWAY , ORBIT, EXTRAOCULAR MUSCLES OF THE EYE

 VISUAL PATHWAY

Each eyeball acts as a camera; it perceives the images   
and relays the sensations to the brain (occipital
cortex) via visual pathway which comprises optic
nerves, optic chiasma, optic tracts, geniculate bodies
and optic radiations

 
ORBIT, EXTRAOCULAR MUSCLES AND APPENDAGES OF THE EYE

Each eyeball is