Revision lecture notes Flashcards
(17 cards)
Contrast sensitivity
This is the ability of the visual system to distibguish an object from its background when both are of similar liminance.
Contrast sensitivity measures how faint or low-contrast an object can be for you to still detect it.
Pseudomyopia
is a condition where the eyes appear to be myopic, but htis is due to a spasm of the cilliary muscles rather then a true anatomical elongaion of the eyeball.
it is a functional and temporty condition that is pofen reversable.
Pseudomyopia Causes
extensive near work
emotional stress or fatigue
poor visual ygene and posture
accomaditive disorders such as spasms of accomodation
It can also be seen in convergence excessive problems
Night Myopia
This is when a person experiences a more myopic shift in low light conditions, resulting in more blurred vision at night, even though they see clearly durring the day
Questions to ask for a patient experiencing headaches
Location
Onset
Frequency
Type
Self treatment and its effectiveness
Effects on px
Associated symptoms
Structural changes that cause presbyopia
- Loss of capsule elasticity - meaning the capsule becomes less able to mold the lens into more complex shapes
- Stiffness of lens nucleus
- Growth of crystaline lens size throyghout life
- Growth (hypertrophy)
near addition: method 1
use the following chart for patients under 60 assuming their WD is 40
cm
- 45 years - +1.00 D
- 50 years - +1.50 D
- 55 years - +1.75 D
- 60 years - +2.00 D
Near addition: method 2
for over 60s, base the tentative near add soley on the working distance using:-
(100/WD)
and then allow and allowance of 0.25 for depth of focus.
Near addition: method 3
You can base the near add off the patients current symptoms
E.g if px is currently reading N6 then do bvs until they are able to read n 4
Near addition: method 4
Regardless of age using near add equation:-
NA = WD - (1/2 x accomadative amplitude)
Anisometropia
a condition where there is a sifgnificant difference in refractive power betweent he two eyes that leads to unequal retinal image sizes and therefore potential BV problems
Pathological causes of anisometropia
Unilateral congenital cataracts or lens opacities - may lead to amblyopia or refractive disparities
Unilateral high myopia or hyperopia - due to unequal eye growth or developmental abnormalities
Ectasia (keratoconus in 1 eye) - causes refractive irregularities and assymetry
surgical causes of anisometropua
Cataract surgery (IOL) only in 1 eye:- creates diff in retina images if refractive target isnt mathched to the other eye.
Refractive surgery done with assymetric outcomes:- can induce anosemetropia if correction level is significantly different.
Methods of dissociation
Cover test- best method
maddox rod
maddox wing
Von Grafes’
Supranuclear pathways that cause saccadic eye movements
Frontal eye fields (voluntary) & parietal cortex (reflex)
* Communicate via internal capsile
* Nerves pass down the pyramidal pathway
* Direct, or
* Via basal ganglie
* Brainstem Saccadic Pulse Generator
* Vertical saccades – rostral interstitial nucleus of the medial longitudinal fasciculus
* Horizontal saccades – paramedian pontine reticular formation
* Different types of neurons in these areas
* Excitatory burst neurons
* Inhibitory burst neurons
* Long-lead excitatory burst neurons
* Pause neurons
* These neurones send signals to the 3 cranial nerves controlling eye
movements
* Cerebellum has an important role co-ordinating the signals
Define a Horopter
A horopter is a locus of corresponding points in space
Physiolocal basis of a Horopter
based on:-
1. Chiasmal decussation
2. Striate (primary visual) cortex
3. Binocular corresponding cells
