Structure and function of the eye Flashcards
Give 3 reasons for tear production?
Basal Tears
Reflex Tears – in response to irritation: Afferent – Cornea – CN V1, Efferent – Parasympathetic, Neurotransmitter – Acetylcholine
Crying (Emotional) Tears
Describe the lacrimal system?
Tear produced by the Lacrimal Gland
Tear drains through the two puncta, opening on medial lid margin
Tear flows through the superior and the inferior canaliculi
Tear gathers in the Tear Sac
Tear exits the Tear Sac through the tear duct into the nose cavity
What is the function and structure of the tear film?
Tear film maintains smooth cornea-air surface
Oxygen Supply to Cornea – Normal cornea has no blood vessels
Removal of Debris (Tear film and Blinking)
Bactericide
• Three Layers
– Superficial Oily Layer to reduce tear film evaporation (produced by a row of Meibomian Glands along the lid margins)
– Aqueous Tear Film (Tear Gland)
– Mucinous Layer on the Corneal Surface to maintain surface wetting
Describe the conjunctiva?
The conjunctiva is the thin, transparent tissue that
covers the outer surface of the eye. It begins at the outer edge of the cornea, covers the visible part of the eye, and lines the inside of the eyelids. It is nourished by tiny blood vessels
What are the 3 coats of the eye?
Sclera – Hard and Opaque
Choroid – Pigmented and Vascular
Retina – Neurosensory Tissue
What is the sclera?
Commonly known as “the white of the
eye,” is the tough, opaque tissue that serves as the eye’s protective outer coat. High water content
What is the cornea?
Front-most part of Anterior Segment Continuous with the Scleral Layer Transparent Refraction – 2/3 of power Convex curvature Higher refractive index than air Physical and Infection Barrier
What are the 5 layers of the cornea?
1 – Epithelium
2 – Bowman’s Membrane
3 – Stroma – regularity contributes towards transparency. Corneal nerve endings provides sensation and nutrients for healthy tissue. No blood vessels in normal cornea
4 – Descemet’s Membrane
5 – Endothelium – pumps fluid out of corneal and prevents corneal oedema, Doesn’t regenerate and dysfunction may cause cloudiness and oedema.
What is the UVEA?
Vascular coat of eye ball and lies between the sclera and retina. Uvea is composed of three parts. • Iris • ciliary body • choroid
What is the choroid?
Lies between the retina and sclera. It is composed of layers of blood vessels that nourish the back of the eye.
What is the iris?
It controls light levels inside the eye similar to the aperture on a camera.
The round opening in the centre of the iris is called the pupil.
The iris is embedded with tiny muscles that dilate (widen) and constrict (narrow) the pupil
size.
What is the structure and function of the lens?
Outer Acellular Capsule with regular inner elongated cell fibres
Transparency, Refractive Power, Accommodation
What is the Lens zonules?
Lens is suspended by a fibrous ring known as lens
zonules, consists of passive connective tissue
What is the macula?
The macula is located roughly in the centre of the retina, temporal to the optic nerve.
It is a small and highly sensitive part of the retina responsible for detailed central vision. The fovea is the very centre of the macula. The macula allows us to appreciate detail and perform tasks that require central vision such reading.
What divides the anterior and posterior segments of the eye?
The lens