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

ADULT INCLUSION CONJUNCTIVITIS

Adult Inclusion conjunctivitis is a type of acute follicular conjunctivitis associated with mucopurulent discharge. It usually affects the
sexually active young adults.

Etiology
Inclusion conjunctivitis is caused by serotypes D to
K of Chlamydia trachomatis. The primary source of
infection is urethritis in males and cervicitis in

Trachoma Management

Management of trachoma should involve curative as
well as control measures.

A. Treatment of active trachoma
Antibiotics for treatment of active trachoma may be
given locally or systemically, but topical treatment is
preferred because:

• It is cheaper,
• There is no risk of systemic side-effects, and

TRACHOMA Complications & Diagnosis

Complications
The only complication of trachoma is corneal ulcer
which may occur due to rubbing by concretions, or
trichiasis with superimposed bacterial infection.

Diagnosis
A. The clinical diagnosis of trachoma is made from
its typical signs; at least two sets of signs should be
present out of the following:

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

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

Refractive surgery of myopia

Surgery to correct refractive errors has become very
popular. It should be performed after the error has
stabilized; preferably after 20 years of age.

Refractive surgery of myopia
1. Radial keratotomy (RK) refers to making deep (90 percent of corneal thickness) radial incisions in the peripheral part of cornea leaving the central 4 mm optical zone (Fig 1).

Fig. 1. Radial keratotomy. (A) configuration of radial
incisions; (B) depth of incision.

These incisions on healing; flatten the central cornea thereby reducing its
refractive power. This procedure gives very good correction in low to moderate myopia (2 to 6 D).

Disadvantages. Note: Because of its disadvantages
RK is not recommended presently. (i) Cornea is
weakened, so chances of globe rupture following
trauma are 

IRREGULAR ASTIGMATISM

It is characterized by an irregular change of refractive power in different meridia. There are multiple meridia which admit no geometrical analysis.
Etiological types
1. Curvatural irregular astigmatism is found in patients with extensive corneal scars or
keratoconus.
2. Index irregular astigmatism due to variable refractive index in different parts of the crystalline lens may 

What is ASTIGMATISM

Astigmatism is a type of refractive error wherein the refraction varies in the different meridia. Consequently, the rays of light entering in the eye cannot converge to a point focus but form focal lines. Broadly, there are two types of astigmatism: regular and irregular.

REGULAR ASTIGMATISM
The astigmatism is regular when the refractive power changes uniformly from one meridian to another (i.e., there are two principal meridia).
Etiology
1. Corneal astigmatism is the result of 

ACUTE PURULENT CONJUNCTIVITIS OF ADULTS

ACUTE PURULENT CONJUNCTIVITIS
Acute purulent conjunctivitis also known as acute
blenorrhea or hyperacute conjunctivitis is
characterised by a violent inflammatory response. It
occurs in two forms: (1) Adult purulent conjunctivitis
and (2) Ophthalmia neonatorum in newborn

ACUTE PURULENT CONJUNCTIVITIS
OF ADULTS
Etiology
The disease affects adults, predominantly males. Commonest causative organism is Gonococcus; but rarely it may be Staphylococcus aureus or Pneumococcus. Gonococcal infection directly spreads from genitals to eye. Presently incidence of gonococcal conjunctivitis has markedly decreased.

Clinical picture
It can be divided into three stages:
1. Stage of infiltraton. It lasts for 4-5 days and is
characterised by:

• Considerably painful and tender eyeball.
• Bright red velvety chemosed conjunctiva.
• Lids are

varieties of myopia

Clinical varieties of myopia
1. Congenital myopia
2. Simple or developmental myopia
3. Pathological or degenerative myopia
4. Acquired myopia which may be: (i) post-traumatic; (ii) post-keratitic; (iii) drug-induced, (iv)
pseudomyopia; (v) space myopia; (vii) night myopia; and (viii) consecutive myopia.
 
1. Congenital myopia
Congenital myopia is present since birth, however, it is usually diagnosed by the age of 2-3 years. Most of the time the error is unilateral and manifests as anisometropia. Rarely, it may be bilateral. Usually the error is of about 8 to 10 which mostly remains constant. The child may develop convergent squint in order to preferentially see clear at its far point
(which is about 10-12 cms). Congenital myopia may sometimes be associated with

Types of lenses

Lenses are of two types: the spherical and cylindrical
(toric or astigmatic).
1. Spherical lenses. Spherical lenses are bounded by two spherical surfaces and are mainly of two types : convex and concave.
(i) Convex lens or plus lens is a converging lens. It may be of biconvex, plano-convex or concavo-convex (meniscus) type .


Identification of a convex lens. (i) The convex lens is thick in the centre and thin at the periphery (ii) An object held close to the lens, appears magnified. (iii) When a convex lens is moved, the object seen through it moves in the opposite direction to the lens.
Uses of convex lens. It is used

continue vision physiology (2)

VISUAL PERCEPTION

It is a complex integration of light sense, form sense, sense of contrast and colour sense. The receptive field organization of the retina and cortex are used to encode this information about a visual image.

1. The light sense
It is awareness of the light. The minimum brightness required to evoke a sensation of light is called the light minimum. It should be measured when the eye is dark adapted for at least 20-30 minutes. The human eye in its ordinary use throughout the day is capable of functioning normally over an exceedingly wide range of illumination by a

Continue vision physiology (1)

PROCESSING AND TRANSMISSION OF VISUAL
IMPULSE
The receptor potential generated in the photoreceptors is transmitted by electrotonic
conduction (i.e., direct flow of electric current, and not as action potential) to other cells of the retina viz. horizontal cells, amacrine cells, and ganglion cells. However, the ganglion cells transmit the visual signals by means of action potential to the neurons of lateral geniculate body and the later to the primary visual cortex. The phenomenon of processing of visual impulse is very complicated. It is now clear that visual image is deciphered and analyzed in both serial and parallel fashion. Serial processing. The successive cells in the visual pathway starting from the photoreceptors to the

DERIVED STRUCTURES FROM EMBRYONIC LAYERS OF THE EYE

1. Surface ectoderm

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

iris eye , vitreous eye , eyelid anatomy

Iris

• Both layers of epithelium are derived from
  the marginal region of optic cup (neuroectodermal)
• Sphincter and dilator pupillae muscles are
  derived from the anterior epithelium (neuroectodermal).
• Stroma and blood vessels of the iris develop
  from the vascular mesenchyme present anterior
  to the optic cup.

Vitreous
1. Primary or primitive vitreous is mesenchymal in
origin and is a vascular structure having the
hyaloid system of vessels...

what is Cornea , Sclera , Choroid , Ciliary body

Cornea
1. Epithelium is formed from the surface ectoderm.
2. Other layers viz. endothelium, Descemet's..

what is optic nerve

It develops in the framework of optic stalk as
below:

• The neuroectodermal cells forming the walls of optic stalk develop into glial system of the nerve.
• Fibres from the nerve fibre layer of retina grow into optic stalk by passing through the choroidal fissure and form the optic nerve fibres.
• The fibrous septa of the optic nerve are developed from the vascular layer of mesenchyme which invades the nerve at 3rd fetal month.
• Sheaths of optic nerve are formed from the layers of mesenchyme like meninges of other parts of central nervous system.
• Myelination of nerve fibres takes place from brain distally and reaches the lamina cribrosa just before birth and stops there. In some cases, this extends up to around the optic disc and presentsas congenital opaque nerve fibres. These develop after birth.