Imaging and investigations of the eye Flashcards
How far does a patient stand from a snellen chart?
6m
What does a snellen result of 6/18 mean?
The patient at 6m is only able to read to a line that a normal person would be able to read at 18m
What is myopia and how is it corrected?
This is shortsightedness meaning that light is converging infront of the retina.
This is corrected by divergent lenses
What is hypermetropia and how is it corrected?
Hypermetropia is far sightedness meaning that light is converging behind the retina.
This is corrected by divergent lenses
What should be assessed during opthalmoscopy?
The red reflex followed by the lens
Then the retina is examined
The optic disc should be pink, cup to disc ratio, contour, formation of any new vessels
Diameter of vessels should be assessed, arteries are lighter and thinner
What is a slit lamp biomicroscope and what is it used for?
It is a machine that is used to shine a thin sheet of light onto the eye so it can be observed. This allows the anterior eye to be examined, used in conjunction with a lens the posterior eye can be examined.
What are the three main ways to test a patients visual field?
Testing visual fields to confrontation e.g. cranial nerve examination
Humphrey visual field exam, this is an automatic test that introduces a light into the patients visual field and they indicate when they can see it
Goldmann visual field test is similar but requires an examiner and is often used for people with cognitive problems
What is fundus fluorescein angiography (FFA)
This is a method to observe the choroid and retinal circulations of the fundus. Patient is given an IV injection of fluorescein dye which then enters the retinal circulations
When is FFA indicated?
It is indicated in diagnosis of choroidal vascular disease (wet AMD, Diabetic retinopathy) and in planning retinal laser procedures
What is OCT and how does it work?
This is optical coherence tomography and is used to look at the retina. It uses light beams in a similar way to ultrasound to visualise a coronal section through the retina.
When is OCT used?
It is commonly used in disease monitoring patients with glaucoma, macular degeneration, chorioretinal vascular diseases and inflammatory conditions.
What information can OCT give?
It allows measurement of retinal and macular thickness. This allows atrophy and exudate deposits to be measured.
What is electrodiagnostic testing and why is it used?
This is a way of accessing the visual pathway by looking at the electrical activity in the eye generated by neurones
When is electrodiagnostic testing used?
Commonly used in diagnosis of hereditary eye disorders when function is hard to evaluate if the patient is uncooperative
What are the three main forms of electrodiagnostic testing?
There are visual-evoked potentials (VEP) that assess the optic nerve function
There is electro-retinography which assesses the retina and macula
There is electro-oculography which assesses the electrical activity between the cornea and the back of the eye
