Optical instruments 3 Flashcards by sheima derdour

What does fundus imaging do?

Its a camera which takes a picture of the retina at the back of the eye

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What is fundus imaging useful for?

diagnosing certain eye conditions

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How does a normal eye appear in a fundus image?

Orange/red background - which comes from light being directly reflected from choroidal blood vessels and light reflected from sclera and transmitted through choroidal blood vessels.

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What is the fundus and what does it include?

The back portion of the interior of the eyeball which includes retina, optic disc, vessels

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What determines the amount of light that is directly reflected from the choroidal blood vessels?

Degree of pigmentation of retina
Degree of pigmentation of choroid.
(varies from eye to eye- variations of normal)

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What do the degree of pigmentation of the retina and the choroid depend on?

Age
Race
Hereditary
Metabolic factors

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What is tesselated or tigroid fundus?

the background of the image appaears with a marble affect

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What is the optic disc and how does it vary?

optic nerve head

-varies in shape, size and colour and the margins (end of it)

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What is cupping?

optic disc has a dip

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How is the optic disc measured?

In a C:D ratio - the vertical diameter of the cup expressed as a fraction of the vertical diameter of the optic disc.

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What decimal notation is used for the C:D ratio?

goes from 0.1-0.9 being the largest C:D ratio.

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What are the optic disc features?

Choroidal crescent

Scleral crescent

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What is choroidal crescent?

c shape hugging the edge of the optic disc
common form of hyper-pigmentation
- choroid (not RPE) extends to the optic nerve head- allowing the choroid to be visible as a dark region.

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What is a scleral crescent?

Neither RPE or choroid extend to the optic nerve head. The sclera is visible as a relatively pale region.
c shape at edge of optic disc

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What are the the blood vessels?

central retinal artery
central retinal vein
- they branch from the ophthalmic artery and come into the eye through the optic nerve head.
-Each then branches from the optic nerve head to serve 4 main quadrants of the retina
- provide the blood supply for the inner 2/3rds of the retina

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What does it mean if there is a high C:D ratio?

the more cupping there is, the greater risk the eye has of damage (if there has been a change of the C:D ratio size otherwise its normal)

How do the arteries and veins appear in the eye?

small diameter arteries
veins are thicker than arteries
arteries light red=more oxygen
Veins are dark red
arteries and veins have crossing points

What is another feature of the back of the eye?

the macula - area where there are no major blood vessel, at its centre there is a fovea

What is the fovea?

fine detail viewing
light falls on fovea so you can see detail
avascular zone- doesnt impede vision with no blood vessels

What are the problems with imaging?

Small pupils- hard to allow light in eye to take image
Cataracts- the misty lens, makes lens hazy
Blinking

How to resolve a poor view/image?

Eye drops to dilate the pupil (mydriasis)

What intrument can examine the back of the eye in more detail than just the fundus imaging?

Direct Opthalmoscope- hand held instrument - which examines the back of the eye,/retina looking at the external eye, optic media and the fundus

What are the features of the ophthalmoscope?

Sight hole
Auxilliary lenses- bunch of different lenses with diff powers
Power Window- different powers of the lens
Power Wheel
Rheostat- light control (make bright or dim)

What is a red reflex?

reflection from the retina

when you shine light from ophthalmoscope

What can you detect from using direct ophthalmoscope?

Detect: - cataract - Retinoblastoma - hypertension - diabetes - macular disease - optic nerve inflammation

How can you detect cataracts from using an ophthalmoscope?

gives you info about the state of the crystalline lens e.g cataract, as the misty lens stops the reflection of the red light, so you get shadows

What is OCT?- Optical Coherence Tomography

Imaging device which allows to image the retinal lens

What does OCT allow you to see?

Able to get a cross section of the retina and visualise an image of the retina and see its layers

How does the OCT work?

-Non-invasive imaging technology -Infrared light (830nm) directed in patients eye -The reflection size of the light is picked by the machine and produces an image. -Image is based on the optical properties of the microstructure of the tissue -A scan- machine picks up reflections at each image point - B-scan- as the scanning beam moves across it forms a cross sectional image - A 3D cube is a collection of tightly packed B-scans

What does it mean if there are more A scans?

higher resolution of image

What is the foveal dip?

where light is maximised and hits the photoreceptors to get that fine detail view

What else does the OCT do?

tells you the thickness of the retina and shows whether treatment works by using numbers.

What is retinoscopy?

- An objective technique to determine refractive error of the eye (myopia, hyperopia, astigmatism) - shine light (determine rf from the reflections and their sizes) and change lenses

What is an advantage of the retinosocopy?

quick easy accurate requires minimal co-operation from the patient.

What patient is the retinosocopy useful for?

Kids- more reliable as its objective

Summarise how the retinoscopy works?

Shine a light on the pupil Watch the reflection from the fundus The reflection tells us whether our light is focused on the fundus or not. Depending on the direction of the light across the pupil, gives info about what lenses to put infront of the eye.

What is RPE?

retinal pigment epithelium