Card Set Information
intro Sph rx changes ret va charts
Normal visual perception tasks?
- Light perception
- Discrimination of figures
- Form recognition
- High order tasks
Symptoms of refractive error?
- Blurred vision
- Double vision
- Reading or learning problems
Objective tests to determine
- retinoscopy (subjective cos results rely on decisions made my examiner)
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
- 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
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?
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
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
variables in refractive errors
axial length- 50%
crystalline lens- 25%
cornea at birth
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?
: problems that a patient notices or feels
: 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?
: vert line lies posterior
: 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?
- 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
- 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?
: 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?