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Normal visual perception tasks?
- - Light perception
- - Discrimination of figures
- - Localisation/projection
- - Form recognition
- - High order tasks
Symptoms of refractive error?
- - Blurred vision
- - Double vision
- - Asthenopia
- - Reading or learning problems
Objective tests to determine refractive error?
- - autorefraction
- - retinoscopy (subjective cos results rely on decisions made my examiner)
- - photorefraction
- - keratometry
Advantages of objective testing?
- - Remove pt bias
- - remove language difficulties
- - good starting pt for subj testing
- - provide ind confirmation
- - can measure ametropia, va, corneal curvature
Disadvantages of objective testing?
- - subjected to examiner bias
- - poor repeatability
- - qualitative rather than quantitative
- - does not monitor accomodation
Objective tests for VA?
- - preferential looking
- - visual evoked response
- - optokinetic nystagmus
How does photorefraction work?
- - screens for rx, strabismus and anisometropia
- - used on uncooperative pts and children
- - bigger the lunular the greater the rx
- - lunular above lens= myope
- - lunular below lens = hyperope
- - no lunular = no rx
Advantages of subjective testing?
- - pt opinion is valuable
- - whole field- holisitc approach
- - patient security
Disadvantages of subjective testing?
- - can't be used on infants
- - can't be used on poor communicators- deaf/mutes, immigrants
- - malingerers
What is the idea behind the duochrome chart
- - longitudinal chromatic abberation
- - shorter wavelength (green) is refracted more than longer ones (red)
What are the disad/adv of duochorme chart
- - quick and easy
- - instructions are easy for pt to follow
- - good for balancing amblyopes
- - test is independent of colour vision status
- - psychological preference for one colour
- - elderly crystalline lens, red bias
- - colour defective patient must be told to ignore luminace difference
- - duochrome refinement within the 1D range
Duochrome: red/green means?
- red=reduce (-ve)
- green= give (+ve)
- maximum plus to maximum visual acuity
- add +1.00D- should reduce by 4 lines
- come back down
how do you know you've reached BVS?
Add +0.25 worsens, add -0.25, no change
List a few different balancing techniques (using b/w charts)
- rapid succesive comparison
- simultaneous comparison
- turville infinity balance
Why are amblyopes suited to the duochrome for balancing?
- - b/w useless, crowding phenomenon can only read 2 or 3 words from each line
- - doesnt rely on VA
advantages and disadvantages of fan and block chart?
- - ret has failed- mitotic pupils
- - jcc failed
- - patient has patchy ocular media
- - vision poorer than 6/18 (fan line thickness)
blur circles in clinic- preferable size?
- less than 2: diffraction effects
- greater than 5: spherical abberation effects
What do these stand for: CF, HM, LP
- count fingers
- hand movements
- light perception
variables in refractive errors
- cornea- 25%
- axial length- 50%
- crystalline lens- 25%
axial length at birth/adult
crystalline lens at adult?
Percentage of low/mod hyperopia?
percentage of high hyperopia?
Percentage of low myopia?
Percentage of mod myopia?
Percentage of low myopia?
What is a malingerer?
A medical term that refers to fabricating or exaggerating the symptoms of mental or physical disorders for a variety of "secondary gain" motives, which may include financial compensation
What is the difference between a symptom and a sign?
- Symptoms: problems that a patient notices or feels
- Signs: whatever a physician can objectively detect or measure
When adding a negative lens, if the px reports the letters are blacker and smaller, rather than sharper and clearer, what does this suggest?
In the +/-0.50 do the horizontal/vertical lines lie anteriorly/posteriorly
In a +/-0.50 auxiliary lens, what happens in an underplussed/overplussed situation?
- underplussed: vert line lies posterior
- overplussed: horz line lies anterior
How do you that astigmatism exists?
- - ret/ objective rx reveals the need for cyls
- - bvs is not as good as expected
- - erratic vision on successive lines of the chart
What is amblyopia?
condition where dimness or blurring of eyesight due to a fault in transmission of signatls to the brain from an otherwise healthy eye
What is HIC?
- Humphriss Immediate Contrast
- - balancing test using prisms/ endpoint of sphere
- - eye not under test is fogged by +0.75DS
- - refines sphere by bracketing +/-0.25DS
HOw is the HIC chart set out? What does the fogging do and problems with the test?
- - Blackened strip down the middle- peripheral parts of the mirror acts as a fusion lock
- - fogging relaxes accommodation and suppresses central vision while maintaining peripheral fusion
- - difficult to fog the dominant eye if suppression occurs- perform suppression tests if this occurs
How do you estimate Astig?
What lens power is in place when you start fan chart?
Factors affecting rx?
Limitng factors when measuring VAs?
- - aberrations
- - ocular media
- - physiology and anatomy of the eye
What are some factors that affect VA resolution?
- - retinal receptor size and spacing- size and location: 1 diameter pr
- - optical factors: (blur circles), homogeneity of media, pupil size, aberrations of refracting surfaces
- - blur circles: pupil size, state of focus
- - illumination
- - uncorrected Rx
- widely available, universally understood
- less repeatability than logMAR
- less sensitive to amblyopia
- do not contain lines of small letters and are truncated
Pros/Cons bailey lovie?
- most reliables and discrimnative VA measurements
- twice as repeatble as snellen
- more sensitive to amblyopic changes
- no as widely available
- cant read bottom line
When is monocular pinhole used?
When VA is worse tha 6/9
What does static ret mean?
- reveals distance rx
- no accomdation taking place
Optical principles of plane mirror use in ret?
- Parallel or diverging rays
What does the endpoint look like in ret?
very fast, wide and bright
What are some factors affecting the refex?
- pupil size
- pupil colour: more easier to see in dark
- size of retinal patch illuminated with increase of rx- larger blur circles
- speed- faster as neutrality is approached
Min of lines different of VA to be unusual?