they eye and vision Flashcards
describe the sclera
- tough fibrous outer coat, protection, made of collagen
- Forms whit capsule, except anterior surface where it is specialised into the clear cornea
- Serves as an insertion point for the external muscles of the eye
- Continuation of dura mater and cornea
describe the cornea
- Light transmission, must be transparent
- Barrier to trauma and infection – must be tough
- refraction
- smooth spherical surface
describe the iris
- contains dilator (sympathetic, radial fibres) and sphincter pupillae muscles (parasympathetic, circular fibres)
- both innervated by oculomotor nerve via ganglion
- pupillary reflexes
- specialised section of choroid
describe the ciliary body
- Glandular epithelium produces aqueous humour – processes; aqueous humour & nutrients for cornea & lens
- Ciliary (smooth) muscle controls accommodation
choroid
- blood supply/nutrition to outer third of retina (photoreceptors)
- Heat sink
- Darkly pigmented so that it can absorb stray photons
what is in the middle layer of the eye? (uvea)
iris
ciliary body
choroid
describe how the retina works
- Light passes through the pupil from the visual field to project an image onto the retina. An object that attention is focused on, projects an image that is centred near the posterior pole of the eye along the visual axis – fovea centralis. The surrounding 1cm is known as the Macula lutea at these points the retina is specifically modified for maximal visual acuity
- Medial to the macula is a region where retinal axons accumulate to leave the eye this is the optic disc (where the optic nerve forms) photoreceptors are absent in this region – blind spot
- Retinal pigment epithelium (RPE) – contains photoreceptors so it is able to convert light into electrical impulses – photoelectric transducer
aqueous humour
contains water and electrolytes
• Nutrition to lens and cornea
• Maintains intraocular pressure, by production and drainage
• Produced by glandular epithelium of ciliary body – travels forward
• Drain – trabecular meshwork
• Contains both anterior and posterior chambers
• Made of smooth muscle which controls accommodation
• Parasympathetic
lens
- Biconvex
- Responsible 1/3 refractive power of eye
- Accommodation
hypermetropia
Underpowered to focus near objects on retina May be due to: • Corneal curvature too shallow • Lens not flexible enough • Axial length of eyeball too short • Fixed with converging lens
myopia
Overpowered so cant focus objects on retina
May be due to
• Corneal curvature to steep
• Axial length of eyeball too long
what is in the posterior segment
- Vitreous humour
- Avascular viscoelastic gel
- Hyaluronic acid (GAG)
- Collagen
what makes up the Adnexae
eyelids, conjunctiva, tear film
lids
protect the eye
• Orbicularis oculi muscle – closure of eyelid
• Levator palpebrae superioris (oculomotor, opens eyelid) & sympathetic muscle
conjunctiva palpebral
- Conjunctival fornix
- Limbal stem cells
- Mucous membrane (goblet cells)
- Lymphoid cells (protective)
- Highly vascular
tear film
- 3 layers: anterior lipid (oils – secreted by meibomium glands, hydrophobic barrier to prevent the aqueous layer evaporating), middle aqueous (water, electrolytes, proteins – secreted by lacrimal glands, regulates transport through the cornea and prevent infection) , posterior mucous (secreted by goblet cells, hydrophilic layer that allows for the even distribution of the tear film)
- Protective
- Nutrition for cornea
layers through which a photon must travel through the eye
1) Tear film (transmission)
2) Cornea (transmission & 2/3 refraction)
3) Aqueous humour (transmission)
4) Lens (transmission & refraction)
5) Vitreous humour (transmission)
6) Ganglion cell (transmission)
7) Amacrine cell (transmission)
8) Bipolar cell (transmission)
9) Horizontal cell (transmission)
10) Cone (transduction)
11) Rods (transduction)
12) Pigmented epithelium (absorption of excess photons)
arterial supply of eye
Internal carotid a. → ophthalmic a.
• Branches of ophthalmic a. (ocular group):
Central retinal a.
Posterior ciliary a. → long and short posterior ciliary a.
Muscular a. → anterior ciliary a.
• branches of ophthalmic artery (orbital group)
lacrimal a.
several other arteries supply face and lips
external carotid a.→ facial a.→ angular a.
blood supply - inner retina
blood supply – inner retina
• inner 2/3 retina supplied by central retinal a.
• branches into superior/inferior/temporal/nasal branches
• drained by branch retinal veins → central retinal v.→ ophthalmic retinal v.→ cavernous sinus→ internal jugular v.
blood supply - outer retina
• outer 1/3 supplied by choroid
• posterior ciliary a. → choroidal a.→ choriocapillaris
• blood-retinal barrier at RPE
regulates movement of nutrition and solutes from choroid into subretinal space
lymphatics of eye
No lymphatic drainage from the globe
Conjunctiva and lids do have lymphatic drainage to submandibular and pre-auricular nodes
