O2A-b

• - Light perception
• - Discrimination of figures
• - Localisation/projection
• - Form recognition
• - High order tasks

• - Blurred vision
• - Double vision
• - Asthenopia
• - Reading or learning problems

• - autorefraction
• - retinoscopy (subjective cos results rely on decisions made my examiner)
• - photorefraction
• - keratometry

• - Remove pt bias
• - remove language difficulties
• - good starting pt for subj testing
• - provide ind confirmation
• - can measure ametropia, va, corneal curvature

• - subjected to examiner bias
• - poor repeatability
• - qualitative rather than quantitative
• - does not monitor accomodation

• - preferential looking
• - visual evoked response
• - optokinetic nystagmus

• - 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

• - pt opinion is valuable
• - whole field- holisitc approach
• - patient security

• - can't be used on infants
• - can't be used on poor communicators- deaf/mutes, immigrants
• - malingerers

• - longitudinal chromatic abberation
• - shorter wavelength (green) is refracted more than longer ones (red)

• 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

• red=reduce (-ve)
• green= give (+ve)

• maximum plus to maximum visual acuity
• add +1.00D- should reduce by 4 lines
• come back down

Add +0.25 worsens, add -0.25, no change

• rapid succesive comparison
• simultaneous comparison
• turville infinity balance
• humphriss

• - b/w useless, crowding phenomenon can only read 2 or 3 words from each line
• - doesnt rely on VA

• - ret has failed- mitotic pupils
• - jcc failed
• - patient has patchy ocular media

• dis
• - vision poorer than 6/18 (fan line thickness)

• 2-5mm
• less than 2: diffraction effects
• greater than 5: spherical abberation effects

• count fingers
• hand movements
• light perception

• cornea- 25%
• axial length- 50%
• crystalline lens- 25%

55D

• - 16-19mm
• - 24mm

17.35mm

24%

1%

15-25%

6%

1%

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

• Symptoms: problems that a patient notices or feels
• Signs: whatever a physician can objectively detect or measure

ACCOMMODATION FAGGGGGGSSSSSSSSSSSS

• hoz=ant
• verty=post

• underplussed: vert line lies posterior
• overplussed: horz line lies anterior

• - ret/ objective rx reveals the need for cyls
• - bvs is not as good as expected
• - erratic vision on successive lines of the chart

condition where dimness or blurring of eyesight due to a fault in transmission of signatls to the brain from an otherwise healthy eye

• 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

• - 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

VA/8

BVS+ast/2+0.50D

• hereditary
• race
• gender
• environmental
• age
• health

• - aberrations
• - ocular media
• - physiology and anatomy of the eye 

• - 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 

• Pros:
• widely available, universally understood
• Cons:
• less repeatability than logMAR
• less sensitive to amblyopia
• do not contain lines of small letters and are truncated 

• 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 

When VA is worse tha 6/9

• reveals distance rx
• no accomdation taking place 

• Parallel or diverging rays
•  

very fast, wide and bright

• 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

1 line