corneal ulcer Pathogenesis and pathology

Pathology of corneal ulcer Once the damaged corneal epithelium is invaded by the offending agents the sequence of pathological changes which occur during development of corneal ulcer can be described under four stages, viz., infiltration, active ulceration, regression and cicatrization. The terminal course of corneal ulcer depends upon the virulence of infecting

Pathology of sloughing corneal ulcer and formation of anterior staphyloma

When the infecting agent is highly virulent and/or body resistance is very low, the whole cornea sloughs with the exception of a narrow rim at the margin and
total prolapse of iris occurs. The iris becomes inflamed and exudates block the pupil and cover the iris surface; thus a false cornea is formed. Ultimately these exudates organize and form a thin fibrous layer over which the conjunctival or corneal epithelium rapidly grows and thus a pseudocornea is

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

OPHTHALMIA NEONATORUM

Ophthalmia neonatorum is the name given to bilateral inflammation of the conjunctiva occurring in an infant, less than 30 days old. It is a preventable disease usually occurring as a result of carelessness at the time of birth. As a matter of fact any discharge or even watering from the eyes in the first week of life should arouse suspicion of ophthalmia neonatorum, as tears are not formed till then.
Etiology
Source and mode of infection
Infection may occur in three ways: before birth, during birth or after birth.

1. Before birth infection is very rare through infected liquor amnii in mothers with ruptured membrances.

2. During birth. It is the most common mode of infection from the

ACUTE FOLLICULAR CONJUNCTIVITIS

Acute follicular conjunctivitis is an acute catarrhal conjunctivitis"OR KNOWN AS ACUTE MUCOPURULENT CONJUNCTIVITIS" associated with marked follicular hyperplasia especially of the lower fornix and lower palpebral conjunctiva.

General clinical features
Symptoms are similar to acute catarrhal conjunctivitis and include: redness, watering, mild mucoid discharge, mild photophobia and feeling of

VIRAL CONJUNCTIVITIS

Most of the viral infections tend to affect the epithelium, both of the conjunctiva and cornea, so, the typical viral lesion is a 'keratoconjunctivitis'. In some viral infections, conjunctival involvement is more prominent (e.g., pharyngo-conjunctival fever), while in others cornea is more involved (e.g., herpes simplex).

Viral infections of conjunctiva include:

• Adenovirus conjunctivitis
• Herpes simplex keratoconjunctivitis
• Herpes zoster conjunctivitis
• Pox virus conjunctivitis
• Myxovirus conjunctivitis
• Paramyxovirus conjunctivitis
• ARBOR virus conjunctivitis

Clinical presentations. Acute viral conjunctivitis may
present in

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

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

ANGULAR CONJUNCTIVITIS

ANGULAR CONJUNCTIVITIS is a type of chronic conjunctivitis characterised by mild grade inflammation confined to the conjunctiva and lid margins near the angles (hence the name) associated with maceration of the surrounding skin.

Etiology
1. Predisposing factors are same as for 'simple chronic conjunctivitis'.
2. Causative organisms. Moraxella Axenfeld is the commonest causative organism. MA bacilli are placed end to end, so the disease is also called

CHRONIC CATARRHAL CONJUNCTIVITIS

Chronic catarrhal conjunctivitis’ also known as
‘simple chronic conjunctivitis’ is characterised by
mild catarrhal inflammation of the conjunctiva.

Etiology
A. Predisposing factors
1. Chronic exposure to dust, smoke, and chemical
irritants.
2. Local cause of irritation such as trichiasis,
concretions, foreign body and seborrhoeic scales.
3. Eye strain due to 

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

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 

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

SPECTACLES

The lenses fitted in a frame constitute the spectacles. It is a common, cheap and easy method of prescribing corrective lenses in patients with refractive errors and presbyopia. Some important aspects of the spectacles
are as follows:

Lens materials
1. Crown glass of refractive index 1.5223 is very commonly used for spectacles. It is ground to the appropriate curvature and then polished to await the final cutting that will enable it to

ANOMALIES OF ACCOMMODATION

Anomalies of accommodation are not uncommon.
These include: (1) Presbyopia, (2) Insufficiency of accommodation, (3) Paralysis of accommodation, and (4) Spasm of accommodation.(last three anomalies discussed in other posts)

PRESBYOPIA
Pathophysiology and causes:

Presbyopia (eye sight of old age) is not an error of refraction but a condition of physiological
insufficiency of accommodation leading to a progressive fall in near vision.

Pathophysiology. To understand the pathophysiology of presbyopia a working knowledge about
accommodation (as described in this post) is mandatory. As we know, in an emmetropic eye far point is infinity and near point varies with

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