Structure and function of the eye Flashcards

Question

Describe the sclera

Answer 1

The white of the eye tough opaque tissue that is protective high water content

Answer 2

Fracture of the floor of the orbit and so eyeball can fall into the cheek a bit, maxilla fracture

Answer 3

``` Front most anterior part of ant. seg. continuous with sclera transparent 2/3 of refractive power convex curvature and higher refractive index than air physical barrier from opportunistic inf. ```

Answer 4

Epithelium Bowman's membrane Stroma - regularity contributes to transparency (corneal nerve endings, no blood vessels) Descemet's membrane Endothelium - pumps fluid out of the corneal and prevent corneal oedema ( only 1 cell layer, no regeneration power, density down with age, dysfunction = oedema/cloudy) IF YOU HYDRATE CORNEA GOES WHITE BECAUSE CORNEA H20 IS DOWN AND SCLERA H20 UP

Answer 5

Composed of iris, ciliary body and choroid | Disease of one part of uvea can affect other parts

Answer 6

Between the sclera and retina

Answer 7

Between retina and sclera Layers of blood vessels Nourish the back of the eye Retina requires 2 ways of feeding some vessels for outer and inner retina

Answer 8

The coloured part of the eye Controls light levels inside the eye Round opening = pupil Iris is embedded with tiny muscles that dilate and constrict the pupil size SPHINCTER PUPILLAE Anterior – stromal layer containing muscle fibres Posterior – epithelium

Answer 9

``` Structure – Outer Acellular Capsule – Regular inner elongated cell fibres – transparency – May loose transparency with age – Cataract ``` ``` Function – Transparency • Regular structure – Refractive Power • 1/3 power • Higher refractive index than aqueous fluid and vitreous – Accommodation • Elasticity Increases refractive power by CN3, can vary thickness and shape working as biconvex lens controlled by ciliary body ```

Answer 10

Lens is suspended by lens zonules consisting of passive connective tissue These fibres don't stretch at all, they merely transmit force from the contraction of the ciliary muscles

Answer 11

Ciliary muscle contraction is pushing towards themselves making lens thicker When ciliary relaxed the choroid acts like a spring pulling on lens and zonulae fibres causing the lens to flatten THICKER LENS = increased refractive and closer viewing THINNER LENS = decreased refractive power and further viewing

Answer 12

Thin layer of tissue that lines the inner part of the eye Capturing light rays that enter the eye These light impulses then sent to brain via the optic nerve

Answer 13

Macula ( red circle) | Optic nerve head (yellow circle)

Answer 14

Retinal arteries and veins provide circulation to inner 2/3 and outer 1/3 is by choroid vasculature 4 branches of vessel arcades: sup and inf temporal sup and inf nasal

Answer 15

Roughly in centre of the retina temporal to the optic nerve Small highly sensitive part of retina reported for detailed central vision Fovea is the very centre of the macula, allows us to appreciate detail and perform tasks that require central vision - reading

Answer 16

1st cause of irreversible blinding disease, silent and asymptomatic Cataract = highest cause of reversible blindness glaucoma linked to degeneration of retina and optic nerve

Answer 17

Ring shaped tissue surrounding the lens | Between anterior and posterior segments and is located behind the iris

Answer 18

Retina gives rise anteriorly to ciliary body epithelium and posterior layer of iris (epithelial) Choroid gives rise to ciliary body stroma and the stromal Ant. layer of iris

Answer 19

Ciliary body secretes aq. fluid Aq. fluid then travels anteriorly into ant. chamber Trabecular network drains the fluid out of the eye into canals of schlemm 10-20% = uveal scleral outflow not a distinctive pathway

Answer 20

12-21 mmHg

Answer 21

Primary open angle glaucoma | Closed angle glaucoma

Answer 22

Commonest | Functional blockage of trabecular meshwork

Answer 23

relatively common acute or chronic forward displacement of iris/lens complex narrowing trabecular meshwork occurs in patients with small eyes (hypermetropic) Sudden painful red eye with acute drop in vision Treatment - peripheral laser iridotomy

Answer 24

Veins are thicker and darker

Answer 25

Sustained raised increased intraocular pressure gradual and accumulative damage to optic nerve Retinal ganglion cell death and ENLARGED optic disc cupping Untreated = loss of peripheral vision GRADUAL, eventual blindness

Answer 26

Where the optic nerve meets the retina there are no light sensitive cells

Answer 27

Fovea has highest concentration of cones but low conc. of rods (more sensitive to light hence everything in periphery brighter) Fovea is most central macula and most sensitive part of the retina

Answer 28

Central: detail day vision (fovea has highest cone) Reading, facial recognition Assessed by visual acuity assessment loss of foveal vision = poor visual acuity ``` Peripheral: shape, movement, night vision navigation vision assessed by visual field assessment With loss become unable to navigate in environment, patient may need white stick even with perfect visual acuity. ```

Answer 29

Outer layer: photoreceptors first order (detect light, point away from pupil and light bounces pack of pigmented epithelium of retina and is then detected) Light hitting different parts of retina gives spatial awareness Middle layer: bipolar cells = 2nd order = local signal processing to improve contrast sensitivity, regulates sensitivity Inner layer: retinal ganglion cells - signal from eye to brain

Answer 30

Fovea forms pit at centre of macula due to absence of overlying ganglion cell layer, can be assessed with OCT

Answer 31

Rod - longer outer segment with photosensitive pigment 100 times more sensitive than cones to light Slow response to light Night vision, 120 mill rods Cone - less sensitive to light, faster response, fine vision during day, 6 mill Photopigments are synthesised in inner photoreceptor segments and are transported to outer segment discs Distal discs with de-activated pigment are shredded from tips by phagacotytic retinal pigment epithelial cells and regenerated inner and bulk transfer

Answer 32

Dark - Increase in light sensitivity on dark. cone adaption in 7 mins and rod in 30 mins after regeneration of rhodopsin Light: dark to light, 5 mins, bleaching of photopigments, inhibition of rod/cone functoin pupil adaption - constriction of pupil with light

Answer 33

Perfect focusing Parallel rays converge exactly on fovea forming a clear image on the retina No accommodation needed Cornea - 2/3 lens - 1/3

Answer 34

Mismatch between axial length and refractive power | Dont fall on retina - myopia(near sight), hyperopia(far), presbyopia, astigmatism

Answer 35

Parallel rays converge at focal point ant. to the retina, etiology is not clear maybe genetic Cause: excessive long globe more common and excessive refractive power symptoms: blurred distance vision, headache, squinting CONCAVE LENSE

Answer 36

Parallel rays focus behind the retina blurred vision Not enough focusing power or short globe CONVEX LENS symptoms: visual acuity at near tends to be blurry, eyepain, headache in frontal region, burning sensation, blepharoconjunctivitis

Answer 37

cornea is OVAL rather than spherical so you get different refraction along one meridian parallel rays come to focus in 2 focal lines rather than a single focal point hereditary symptoms: astenopic symptoms (headache and eye pain) blurred vision distorted vision head tilting and turning treatment: cylindrical lenses, if irregular you need surgery

Answer 38

``` -Contraction of the Circular Ciliary Muscle inside the Ciliary Body – This relaxes the zonules that are normally stretched between the ciliary body attachment and the lens capsule attachment – Note that zonules are passive elastic bands with no active contractile muscle – In the absence of zonular tension, the lens returns to its natural convex shape due to its innate elasticity – This increases the refractive power of the lens • Mediated by the efferent Third Cranial Nerve ```

Answer 39

``` Adaptation for Near Vision • Near Response Triad – Pupillary Miosis (Sphincter Pupillae) to increase depth of field, maintain clear focus across range of distances without accommodation If shallow lose focus easily with movement of an object. – Convergence (medial recti from both eyes) to align both eyes towards a near object – Accommodation (Circular Ciliary Muscle) to increase the refractive power of lens for near vision, lens becomes thicker ```

Answer 40

Naturally occurring loss of accommodation onset from 40 distant vision intact corrected by reading glasses to increase refractive power of the eye