O2A-b

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Author:
sookylala
ID:
148141
Filename:
O2A-b
Updated:
2012-07-22 01:00:09
Tags:
intro Sph rx changes ret va charts
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  1. Normal visual perception tasks?
    • - Light perception
    • - Discrimination of figures
    • - Localisation/projection
    • - Form recognition
    • - High order tasks
  2. Symptoms of refractive error?
    • - Blurred vision
    • - Double vision
    • - Asthenopia
    • - Reading or learning problems
  3. Objective tests to determine refractive error?
    • - autorefraction
    • - retinoscopy (subjective cos results rely on decisions made my examiner)
    • - photorefraction
    • - keratometry
  4. 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
  5. Disadvantages of objective testing?
    • - subjected to examiner bias
    • - poor repeatability
    • - qualitative rather than quantitative
    • - does not monitor accomodation
  6. Objective tests for VA?
    • - preferential looking
    • - visual evoked response
    • - optokinetic nystagmus
  7. 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
  8. Advantages of subjective testing?
    • - pt opinion is valuable
    • - whole field- holisitc approach
    • - patient security
  9. Disadvantages of subjective testing?
    • - can't be used on infants
    • - can't be used on poor communicators- deaf/mutes, immigrants
    • - malingerers
  10. What is the idea behind the duochrome chart
    • - longitudinal chromatic abberation
    • - shorter wavelength (green) is refracted more than longer ones (red)
  11. What are the disad/adv of duochorme chart
    • Adv
    • - quick and easy
    • - instructions are easy for pt to follow
    • - good for balancing amblyopes
    • - test is independent of colour vision status
    • Disadv
    • - 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
  12. Duochrome: red/green means?
    • red=reduce (-ve)
    • green= give (+ve)
  13. MPMVA?
    • maximum plus to maximum visual acuity
    • add +1.00D- should reduce by 4 lines
    • come back down
  14. how do you know you've reached BVS?
    Add +0.25 worsens, add -0.25, no change
  15. List a few different balancing techniques (using b/w charts)
    • rapid succesive comparison
    • simultaneous comparison
    • turville infinity balance
    • humphriss
  16. 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
  17. advantages and disadvantages of fan and block chart?
    • - ret has failed- mitotic pupils
    • - jcc failed
    • - patient has patchy ocular media

    • dis
    • - vision poorer than 6/18 (fan line thickness)
  18. blur circles in clinic- preferable size?
    • 2-5mm
    • less than 2: diffraction effects
    • greater than 5: spherical abberation effects
  19. What do these stand for: CF, HM, LP
    • count fingers
    • hand movements
    • light perception
  20. variables in refractive errors
    • cornea- 25%
    • axial length- 50%
    • crystalline lens- 25%
  21. cornea at birth
    55D
  22. axial length at birth/adult
    • - 16-19mm
    • - 24mm
  23. crystalline lens at adult?
    17.35mm
  24. Percentage of low/mod hyperopia?
    24%
  25. percentage of high hyperopia?
    1%
  26. Percentage of low myopia?
    15-25%
  27. Percentage of mod myopia?
    6%
  28. Percentage of low myopia?
    1%
  29. 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
  30. 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
  31. When adding a negative lens, if the px reports the letters are blacker and smaller, rather than sharper and clearer, what does this suggest?
    ACCOMMODATION FAGGGGGGSSSSSSSSSSSS
  32. In the +/-0.50 do the horizontal/vertical lines lie anteriorly/posteriorly
    • hoz=ant
    • verty=post
  33. In a +/-0.50 auxiliary lens, what happens in an underplussed/overplussed situation?
    • underplussed: vert line lies posterior
    • overplussed: horz line lies anterior
  34. 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
  35. 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
  36. 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
  37. 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
  38. How do you estimate Astig?
    VA/8
  39. What lens power is in place when you start fan chart?
    BVS+ast/2+0.50D
  40. Factors affecting rx?
    • hereditary
    • race
    • gender
    • environmental
    • age
    • health
  41. Limitng factors when measuring VAs?
    • - aberrations
    • - ocular media
    • - physiology and anatomy of the eye 
  42. 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 
  43. Pros/Cons Snellen?
    • Pros:
    • widely available, universally understood
    • Cons:
    • less repeatability than logMAR
    • less sensitive to amblyopia
    • do not contain lines of small letters and are truncated 
  44. Pros/Cons bailey lovie? 
    • Pros:
    • most reliables and discrimnative VA measurements
    • twice as repeatble as snellen
    • more sensitive to amblyopic changes
    • cons:
    • no as widely available
    • cant read bottom line 
  45. When is monocular pinhole used?
    When VA is worse tha 6/9
  46. What does static ret mean?
    • reveals distance rx
    • no accomdation taking place 
  47. Optical principles of plane mirror use in ret?
     
    • Parallel or diverging rays
    •  
  48. What does the endpoint look like in ret?
    very fast, wide and bright
  49. What are some factors affecting the refex?
    • clarity
    • intensity
    • 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
  50. Min of lines different of VA to be unusual?
    1 line

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