Ophthalmology Part 1 Flashcards
What is the most common from of visual impairment?
Uncorrected refractive error of which; presbyopia is the most common.
What is Myopia and what is the correction for it??
Common eye condition which causes distant objects to appear blurred while close object appear clearly. (short-sightedness) Occurs if eye is bigger
Concave lens is needed for correction.
What is hypermetropia?
Close objects appear out of focus/blurred whereas distant objects appear clear. (long-sightedness) Occurs if the eye is smaller and you need a convex lens
What is emmetropia?
Normal vision
What are the different photoreceptors in the eye?
Rods and Cones
What are the features of cone cells?
6 Million in retina. They have low convergence onto ganglion cells. There are three types; red, blue and green. Responding from different wave lengths. Concentrated in macula and have narrow spectral sensitivity.
Describe features of rod cells
120million in retina. High convergence to ganglion cells. One type (vision in grey scale only respond to one wavelength), they are very light sensitive so important in night vision, have widespread distribution in retina and broad spectral sensitivity. (found in periphery),
What is the process of light hitting the photoreceptors and then traveling out?
Light hits photoreceptor cells which are at the back of the retina (closest to blood supply) causing excitation. They then converge onto bipolar cells which synapse onto ganglion cells, sending the excitation along the axons. It is the axons of these ganglion cells with then pass via the optic nerve and chiasm to the lateral geniculate body
What lies beneath the retina?
Choroid layer
Where is the blind spot?
Where the optic nerve is, collection of axons. In the centre is a pale central cup which is just empty space
What occurs in glaucoma?
The cup becomes larger which suggests the axons are dying. SO when completing an ophthalmic exam you want to comment on the margin between neuro-retinal rim and retina, the colour of the neuro-retinal rim and size of cup.
Describe the normal visual pathway
The information from one eye travels along the optic nerve till it reaches the chiasm. Here the information from the half of the visual feild closes to the nasal crosses over whereas the half closest to the temple stay on the same side. Therefore one nerve will carry information about both left visual feilds, and the other about both right visual feilds. Nerves continue to travel posteriorly with half of the information travel up through parietal and half down through temporal till it reaches the primary visual cortex in the occipital lobe.
The motor fibres that are delivered to the eyes travel to both eyes. So sensory goes to one side but motor fibres from one side travels to both eye
What occurs if their is a lesion at the chaism?
Leads to loss of nasal retinal information. So bitemporal hemianopia. (lose outside halves of both eyes). Can occur when their is a pituitary tumour.
What would lead to a superior quadrantanopia?
If the visual information running in the temporal lobe was damaged. (it would either be left or right superior quadrant, dependant on what temporal lobe was damaged)
Why would you get a superior quadrantanopia?
This is because information coming from the superior visual world is sent to inferior part of retina and therefore travels down to the tract running in temporal lobe where as if the parietal lobe was damaged then you would get an inferior quadrantanopia as even though the tract is higher than the tract running in the temporal lobe, it recieves information from top part of the retina which sees the inferior visual world.
