Ophthalmoscopy Flashcards
what is the cornea, its function and structure?
highly specialised tissue
main function is refraction and transmission of light
structure is an outer epithelium, and avascular hypocellular stroma and replicating endothelial monolayer
the endothelium pumps water out of the stroma into the anterior chamber; failure leads to loss of transparency
what is the uvea composed of?
choroid
ciliary body
iris
where is the choroid and what is its function?
consists of blood vessels, connective tissue and pigment cells and is between the retina and sclera
it provides oxygen and nutrition to the outer retinal layers
what is Bruch’s membrane?
formed by the basement membrane of the uvea along with the retinal pigment epithelium
what is the function of Bruch’s membrane?
acts as a diffusion barrier between choroid and retina
what is the ciliary body?
made up of the ciliary muscles and ciliary processes
the 3 sets of ciliary muscles are the longitudinal, radial and circular muscles, and they are responsible for altering the shape of the lens in accommodation, they attach to the lens by the zonules of Zinn
what is the iris?
lies on the anterior surface of the lens, it is a thin diaphragm made up of the sphincter and dilator papillae which constrict and dilate the central aperture (the pupil)
what is the retina?
composed of several layers, divided into the optic component mad e up of the neural light receptive layer, and pigment layer and the non visual component, which is the anterior continuation of the pigment layer, spanning the ciliary body and posterior surface of the iris
what do photoreceptors do?
convert light energy into electrical, transmit it to the ganglion cells via connector neurones
where do ganglion cells go?
gangion cell axons pass across the surface of the retina and leave the eye at the optic disc
where are cone receptors concentrated?
macula for high quality colour vision
name the extra-occular muscles?
- superior oblique
- levator palpebrae superioris
- superior rectus
- lateral rectus
- inferior oblique
- inferior rectus
- medial rectus
what does the superior oblique do?
depress and abducts, conjugation with the inferior rectus to move the eyeball inferiorly, receives innervation from CNIV
what does the levator palpebrae superioris do?
elevates the superior eyelid, deep layer is innervated by sympathetic fibres
what does the superior rectus do?
elevated and adducts, innerated by CN III
what does the lateral rectus do?
adducts eyeball CN VI
what does the inferior oblique do?
elevates and abducts the eye, works in conjugation with superior rectus to move the eyeball superiorly, innervated by CN III
what does the inferior rectus do?
depresses and adducts, innervated by CNIII
what does the medial rectus do?
adducts the eyeball, innervated by CN III
what is accommodation?
the ability of the eye to maintain focus on an object regardless of the distant by increasing/decreasing the power of the lens
describe the process of accommodation with near objects?
as the object comes closer the image would focus behind the retina.
to prevent this the ciliary muscles contract and the zonules of zinn and allowing the lens to return to a rounder more convex shape and focusing the image on the retina
describe the process of accommodation with far objects?
as the object goes further the image would focus in front of the retina
to prevent this the ciliary muscles relax and place the zonulas of zinn under tension and pulling the lens into a flatter more concave shape and focussing the image on the retina
what is myopia?
the eye is too long and the retina is not in focus without correction
concave (minus) lenses bring the retina into focus
what is hypermetropia?
the eye is too short and the retina is not in focus without correction
convex lenses bring the retina into focus
what is the red reflex and what is the pathological significance of it being absent?
red-orange reflection observed at the centre of the pupil elicited with the opthalmoscope
the absence can suggest severe cataracts or retinoblastoma which show leukocoria (white discoloration of the eye)
what is the fundus?
the interior surface of the eye, opposite the lens, it includes the macula, the optic disc, fovea and posterior pole
what does direct opthalmoscopy involve?
visualisation of the structures of the funds with an ophthalmoscope
describe the process of examining with direct ophthalmoscope?
- hold in right hand
- use right eye to examine patients right eye
- place top of ophthalmoscope against brow and place free hand against patient forehead
- elicit the red reflex whilst at arms length
- move In close as possible and adjust focus
- identify optic disc and 3cs
- examine vascular supply
- repeat with other eye
what is the red reflex and what does its absence suggest?
- the red orange reflection at the centre of the pupil elicited with opthalmascope
- when absent can suggest severe cataracts or retinoblastoma (show leukocoria-white discolouration of the eye)
what are the considerations when examining the funds?
- optic disc-cup, colour, contour
- macula and fovea
- retinal vessels
- abnormalities (haemorrhages or exudates)
- colour-red-purple
- clinical context
what are the 3 Cs?
- cup (cup-disc ratio <0.5)
- colour (yellow/orange-pink)
- contour (margins should be sharp)
what is papilloedema?
swelling of the first part of the optic nerve due to increased intracranial pressure
what can cause raised intracranial pressure?
cerebral oedema
malignant hypertension
optic nerve tumours
what is glaucoma?
increased pressure in the eye which can lead to vision loss
it can be primary or secondary
-primary acute (angle closure), chronic (open angle) glaucoma
-secondary
can present with increased cup:disc ratio
what is optic disc atrophy?
degeneration of the optic nerve, visible as pallor of the optic disc
what is the macula?
central point of vision
dark spot on retina surrounding greatest concentration of cones
no vessels
may be slightly pigmented
abnormalities-fluid, haemorrhage, exudates drusen (small round yellow deposits deep in retinal layer)
what is the fovea?
small depression in retina containing largest amount of cones therefore it is the point of greatest acuity
what abnormalities may be seen on the fovea?
changes in colour and contour
abnormalities such as cherry red spots
haemorrhages, drusen, laser scars, exudates, oedema
what abnormalities are looked for in the retinal vessels?
calibre -excessive narrowing of arteries as in arteriosclerosis -tortuous and dilated veins AV nipping -hypertension -arteriosclerosis abnormality -AV malformation -new vessel formation -sheathing
what are the characteristics of diabetic retinopathy?
- early disease - dot and blot haemorrhages and micro aneurysms
- as capillary non perfusion increases the signs of retinal ischaemia become visible including cotton wool spots, venous dilatation and angiogenesis
what are cotton wool spots?
superficial retinal deposits which occur around areas of infarcted retina
what are hard exudates?
well defined yellow/white deposits in the retina
caused by lipoproteins leaking from abnormally permeable blood vessels
what are micro aneurysms?
first lesions appearing in diabetic retinopathy
physical dilations of the smallest intra-retinal blood vessels
these lesions appear as small circular red dots having distinct margins and are no larger than a blood vessel width at disk margin
what are retinal haemorrhages?
represent actual bleeding within the retina as a result of MAs or when capillaries become leaky enough to let blood out of vessels
can be a variety of shape (dot, blot, flame shaped)
usually larger than MAs with unevenly indistinct edges and causes
what are the other causes of retinal haemorrhages?
hypertension trauma retinal breaks subarachnoid haemorrhage retinal vein occlusion sickle cell disease anticoagulants age related macular disease
what do proliferative lesions suggest?
advanced sign of diabetic retinopathy
require treatment
aim to reduce retinas need for oxygen and nutrients
what is hypertensive retinopathy?
chronic hypertension leads to diffuse or segmental narrowing of arterioles as the vessel walls thicken
thickened arterioles cause compression of veins
accelerated haemorrhage signs include flame haemorrhage, hard exudates and papilloedma
what is the grading for hypertensive retinopathy?
grade 1 - arteriolar narrowing
grade 2 - arterio-venous nipping
grade 3-exudates, haemorrhages, cotton wool spots
grade 4 - papilloedema
describe dot and blot haemorrhages of the retina?
lies deep in retina reflecting leakage of capillaries or venues
common in diabetic retinopathy
describe flame haemorrhages?
these lie within superficial nerve fibre layer, they reflect ischaemic leakage from arterioles or veins under high pressure
