Eye

Eye – lecture plan • Layers of eye• Chambers of eye• Segments of eye• Retractile (Dioptric) Media of Eye

• Development ( embryology) of Eye• Histology of

– Corneo-scleral part– Uvea ( Iris, Ciliary body, choroid)– Retina – (layers, rods & cones)– Lens

outer: corneo – scleral

Middle: Urea with its choroid, ciliary body and Iris

Inner: Retina has two layers (outer pigment and inner neuronal)

Layers

Chambers of Eye

Segments of Eye

• Anterior segment– Cornea – Contents of anterior chamber– Contents of posterior chamber

• Posterior segment– Vitreous chamber– Retinal layers, posterior sclera– uvea

Retractile (Dioptric) Media of Eye

• 1. Cornea –

– anterior window of light

– chief refractive element (1.378)

• 2. Aqueous humor –

– watery fluid in anterior and posterior chambers

– minor role in retractile media

– important in nutrition of cornea & lens (avascular organs)

• 3. Lens

– transparent, crystalline,

– important refractive part after cornea,

– suspended by zonules of Zinn

• 4. Vitreous body

– transparent gel,

– 99% is water with water soluble proteins, Hyaluronic acid, glycoproteins,

– acts as shock absorber (protects retina & maintains shape of eyes)

Development of Eye

Histology of Corneo – scleral coat

Histology of Corneo – scleral coat

• Cornea – has five layers– Epithelium – nonkeratinized stratified squamous , basal layer

cells ( like skin) proliferate and replace the lost suface epithelial cells

– Bowman’s membrane – fibrillar, ends at limbus, main role in limiting the spread of infections

– Connective tissue stroma – 90% of corneal thickness, contains proteoglycans, So4 GAGs (Keratan and chodroitin So4)

– Decemet’s membrane – basal lamina of endothelial cells, made of meshwork of fibers and pores, regenerates after injury (unlike Bowman’s)

– Endothelium – single layer of squamous cells, all metabolic exchanges takes place here,

Corneo – scleral coat

Histology of Corneo – scleral coat

• Cornea– How cornea is transparent?– By precise regulation of water in stroma, if there is

endothelial damage corneal edema and corneal opacity

• Sclera – Dense connective tissue of flat collagen fibers and

meshwork of elastic fibers• Limbus

– transition zone – Has irido- corneal angle for drainage of aqueous

humor ( canal of schlemn)

Uvea - iris

Vascular coat (Uvea)

• Iris- most anterior part, forms diaphragm, pupil is central aperture, posterior pigment epithelium and myoepithelial layer next, two muscles (dilator and constrictor pupillae)

• Muscle of adaptation– Sphincter pupillae – circular band of SMC, parasympathetic

control ( CN III), causes reduced size of pupil in response to light– Dilator pupillae – radially oriented pigmented myoepithelial

cells, form anterior pigment epithelium, under sympathetic control (superior cervical ganglion), causes increased pupillary size in response to dim light

• Ciliary body – has ora serrata, anterior part is ciliary process, has ciliary muscle with three functional groups ( longitudinal – for drainage of aqueous, radial – flatten the lens for distant vision, circular- reduce tension on lens for near vision

Retina

• Inner most layer• Consists of 10 layers of cells• Functionally two regions

– Non photosensitive (non visual) region– Photosensitive ( optic) region

• Optic disc or fovea centralis or blind spot in visual field – where optic nerve joins retina

• Retinal pigment epithelium – has important functions (absorb light and reduce glare, blood- retina barrier, Phagocytosis)

• Nuclei of Rods and cones form outer nuclear layer

Retina

Rods & Cones

Rods & Cones

• Rods – more in # (12 million), more sensitive to light, used in dim or night light), have maximum absorption at 496 nm of light ( black and white pictures)

• Cones – less in # (7million), three classes (L,M,S), less sensitive to light ( for day vision), have absorption at 420 (blue), 531(green) and 588 nm (red) of light, for color vision

Crystalline lens

Crystalline lens

• Transparent, avascular, biconvex, • Lens capsule – type IV collagen, • New lens fibers are produced through out the

life• Presbyopia – decreased elasticity and power

of accommodation with age• Cataract – loss of transparency, causes can

be infections, metabolic, hereditary, trauma, UV light