Anatomy of Eye Flashcards
External structure of eye
Sclera (outermost layer)
Choroid
Retina
Cornea
- Main structure responsible for refraction of light entering eye
Layers of the cornea
From outermost to innermost
1. Epithelium
2. Bowman’s layer
3. Stroma
4. Descemet’s membrane
5. Endothelium
- Pumps water out of cornea to keep it dry and clear
- Number of cells decrease with age, does not regenerate
- Diseases affecting endothelium cause corneal edema and hazy cornea
Nerve supply of the cornea
Ophthalmic division of trigeminal nerve
Flow of aqueous humour
- Produced at the ciliary body
- Flows anterior to the lens and through the pupil
- Drains into Schlemm’s canal (10% drains into uveo-scleral pathway)
Where can aqueous humour be found?
Anterior and posterior chamber
Function of aqueous humour
- Maintenance of intraocular pressure and structural form of the globe
- Provides nutrition to surrounding tissues
- For its refractive index
Fovea contains which photoreceptor only?
Cones
Blood supply of the retina
Central retinal artery is a branch of ophthalmic artery
- supplies inner 6 layers of retina
Choroidal vessels
- supplies outer 4 layers
Retinal veins drains into cavernous sinus directly or via superior ophthalmic vein
Orbicularis oculi muscle
Function: Closure of eyelids
Nerve supply: zygomatic branch of facial nerve
Levator palpebrae superioris
Function: elevates upper eyelid
Nerve supply: oculomotor nerve
Neurons at the retina
3 main groups of neurons: Photoreceptors (rods and cones)
- Rods for vision in dim light
- Cones for vision in bright light, fine details and colour
- Rods are absent at fovea, ↑ in
number towards peripheral retina
- Cones of highest density at fovea, ↓ in number in periphery
Bipolar cells
Ganglion cells
How are tears produced and drained?
Tears are secreted by main and accessory lacrimal gland, pass along the ocular surface and enter the upper and lower canaliculi and enters lacrimal sac and nasolacrimal duct
Lens
- Transparent biconvex structure located behind iris and pupil and in front of vitreous body
- Equator of lens encircled by ciliary processes of ciliary body and kept in position by suspensory ligaments
Accommodation of lens
When looking at far objects, ciliary muscles relax -> lens zonules pull on lens -> lens become flatter/less convex -> focus light from far objects onto retina
When looking at near objects, ciliary muscles contract -> lens zonules slacken -> lens become more convex -> focus light from near objects into retina