Chua 5 Flashcards
How is visual acuity measured?
Uniocularly for near, distance
What to do when refracting nystagmus patient
Fog fellow eye with high plus lens
Complete occlusion worsens nystagmus
What is the purpose of fogging?
REduced or eliminates accommodation
Plus sphere to plus correction or reduce minus sphere in minus correction
End point is most plus power or least minus that gives best vision
How is accommodation reduced in objective refraction
Get patient to look at distance or using cycloplegia
When sleeve is placed in plane mirror position what movmeent is observed
With motion in hypermetropia
Against motion in myopia
What sleeve is placed in concave mirror position what movement is observed
Against motion in hypermetropia
With motion in myopia
How is working distance related to power of distance lens
Inversely proportional
What does use of minus cylinder inrefration cause in young vs older people
In young hypermetrope - repvents stimulation or accommodation
In elderly, may over correct the hypermetrope (and in cycloplegic refration)
Streak retinoscopy at x degrees
That is the axis - power is required at 90 degrees from this
Order of testing power/axis
SPH then axis then CYL
When can duochrome test be used
SPH is corrected within 1D or emmetropia
If red is clearer - myopic or overplussed
For a patient with accommodative esotropia what must be done to measure IPD
Both eyes in primary position - with correcting lens or using cover test
What can reduce exophoria?
Correction of myopia due to stimualtion of accommodation (convergence)
What happens to image if correcting lens is moved forward?
MOves forward irrespectiv eof concave or convex
How may a hypermetrope read in early presbyopia
Move glasses away from eyes
When is back vertex disrtance important?
If correcting lens is more than 5 D
What is relative spectacle magnification
Corrected ametropic image size/emmetropic image size
What happens if lens is placed at anterior focal point in axial ametropia?
RSM is 1
What ahppens if correcting lens is placed at anteiorr focal point in index ametropia
Hypermetropia - RSM >1
Myopia RSM<1
What is RSM in aphakia
1.33 (index hypermetropia
What can affect the IOL calculation
Velocity of US
Varies according to type/density of cataract
Important to set US to phakix/pseudophakix/aphakix
What is the SRK formula accurate for?
22mm - 2.5mm eyes
What should be used for axial length <21mm
Hoffer Q
What is the power of the crystalline lens? What does it contribute? What myopia can be corrected by aphakia?
+19D
Contributes +15D
IF extracted - can correct myopia of -18 to -20D
