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Conjunctiva

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Conjunctiva

The conjunctiva lines the inside of the eyelids and covers the sclera.

The conjunctiva is composed of unkeratinized, stratified squamous epithelium with goblet cells, and stratified columnar epithelium.

It is highly vascularized.

The conjunctiva is divided into three parts:

Palpebral or tarsal conjunctiva-Lining the eyelids.

Bulbar or ocular conjunctiva-Covers the eyeball, over the anterior sclera:

Fornix conjunctiva-Forms the junction between the bulbar and palpebral conjunctivas:

The bulbar region of the conjunctiva is tightly bound to the underlying sclera by Tenon’s capsule and moves with the eyeball movements.

The average thickness of the bulbar conjuntival membrane is 33 microns.

The fornix conjunctiva is loose and flexible, allowing the free movement of the lids and eyeball.

Blood to the bulbar conjunctiva is primarily derived from the ophthalmic artery.

The blood supply to the palpebral conjunctiva is derived from the external carotid artery.

The circulations of the bulbar conjunctiva and palpebral conjunctiva are also linked by the ophthalmic artery and the external carotid artery, to varying extents.

Sensory innervation of the conjunctiva is divided into four parts:

Superior

Supraorbital nerve

Supratrochlear nerve

Infratrochlear nerve

Inferior Infraorbital nerve

Lateral Lacrimal nerve

Circumcorneal Long ciliary nerves

The conjunctiva consists of both stratified squamous and stratified columnar epithelium, with interspersed goblet cells.

Its epithelial layer contains blood vessels, fibrous tissue, and lymphatic channels.

The accessory lacrimal glands in the conjunctiva produce the aqueous portion of tears, helping to lubricate the eye by producing mucus and tears.

It produces a smaller volume of tears than the lacrimal gland

The conjunctival epithelium include melanocytes, T and B cell lymphocytes, and contributes to immune surveillance to prevent the entrance of microbes into the eye.

The conjunctival microvascular hemodynamics are affected by diabetic retinopathy.

Type II diabetes is associated with conjunctival hypoxia, resulting in increased average blood vessel diameter, and capillary loss.

With sickle-cell anemia with blood vessel sludging altered blood flow and blood vessel diameter, and capillary micro-haemorrhages.

There is an increase in the tortuosity of bulbar conjunctival blood vessels and loss of capillary and arterioles with hypertension.

Impaired carotid artery circulation is associated with slower conjunctival blood flow and apparent capillary loss.

As a result of aging the conjunctiva stretches and loosens from the underlying sclera, leading to conjunctival folds, a condition known as conjunctivochalasis.

It can be affected by benign, pre-malignant or malignant tumors.

Leptospirosis, can cause conjunctival suffusion.

The bulbar conjunctival microvasculature contains arterioles, meta-arterioles, venules, capillaries, and communicating vessels.

The bulbar conjunctival blood vessels being close to ambient air allows for diffusion from ambient air influencing blood oxygen saturation.

When the eyelid is closed it stops oxygen diffusion by placing a barrier between the bulbar conjunctival microvessels and ambient air.

The bulbar conjunctival microvessels are imaged with a high-magnification slit lamp with green filters,and it is possible to see groups of individual red blood cells flowing.

Fundus cameras may also be used for low-magnification wide field-of-view imaging of the bulbar conjunctival microvasculature, and can measure conjunctival blood flow and blood oxygen saturation.

Fluorescein angiography has been used to study the blood flow of the bulbar conjunctiva.

The bulbar conjunctival microvasculature dilates in response to several stimuli and external conditions : allergens, temperature, time-of-day, contact-lens wear, acute hypoxia, and emotional state changes.

Type 2 diabetes is associated with an increase in average bulbar conjunctival vessel diameter and capillary loss, while sickle-cell anemia is associated with altered average vessel diameter.

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