Subjective Refraction Flashcards
When would it be appropriate to perform subjective refraction
- To determine a prescription through which the patient can see comfortably.
- To assess the patient’s blur discrimination
- When you cannot perform objective testing
e.g., due to media opacities or pinhole pupils.
the vertical focal line is formed at the point where the
horizontal rays focus
the horizontal focal line is formed at the point where the
vertical rays focus
the dioptric midpoint between the 2 focal lines is called
COLC
plus lenses move focal lines ___ towards the retina
anteriorly
hyperopes MR is posterior to R thus moves forward
minus lenses move focal lines __ towards the retina
posteriorly
myopes MR is anterior to R thus move back
we can estimate the potential change in spherical refinement error in the following patients except ?
a. myopia
b. non accommodating hyperopia
c. absolute hyperopia
d. accommodating hyperopia
D
on JCC, the red and white denotes which cylinder axis respectively ?
minus, plus cyl axis
The cylinder axis is where the power is not. given the minus cyl axis lies at 180, while the plus cyl axis lies at 90, where are the respective cyl powers ?
minus cyl power = 90
plus cyl power = 180
given the cylinder axis found during retinoscopy is 90, which two axis would you bracket during JCC cyl axis refinement ?
(90 + 45) and 90-45
what is the order of subjective refraction ?
initial sph refinement OD
initial cyl axis refinement OD
cyl power refinement OD
second sph refinement OD
- repeat all steps for OS
binocular balance
binocular sph refinement
When increasing the cyling by -0.50D, the sph power adjustment is ___ to keep the COLC on the retina
+ 0.25D
when changing cyl power, which focal line are we moving
front focal line
if a patient has a VA of 20/40 after best sphere, what is the estimated uncorrected astigmatism ?
1.50 D
when using a fan chart, what components of the prescription are used to start the procedure
sph equivalent, no cyl
during axis refinement the patient mentions all lines of the fan chart are equally dark, whats the finding
no astigmatism or COLC is on the retina (unfavorable)
if a pt is 0.50D myope along 30M and 2.50 myope along 120M, which focal line is closest to retina
30M has lowest refractive error, the equivalent focal line is 120 FL, thus closest to R
when performing axis refinement, the doctor sees an angle of 45, the patient will see an angle of ?
180-45 = 135
given from dr perspective the 120 FL is closest to the retina, then the focal line nearest R for pt perspective is ?
(180-120) =60 FL
the orientation of the clearest line on the fan chart (from pt perspective) is the same as the orientation of focal line nearest the retina (from pt perspective)
pt perspective: 70 FL is nearest retina
doctor perspective: (180- 70) = 110 FL nearest retina
what is the meridian nearest retina from dr perspective ?
110-90 = 20
The meridian nearest the retina from dr perspective represents
cyl axis
if the pt says the clearest line is at 30, what is the meridian from doctors perspective
dr perspective FL = 180-30 = 150
dr perspective meridian = 150- 90 = 60M
60M
After cyl axis refinement, to correct cyl power, decreased the number of choice by providing 2 blocks that are _______ to achieve equal appearance of clear and dark
90 degrees apart
what are two instances when 2 blocks appear equal to the pt:
- succesfully corrected astig
- COLC is on the retina, uncorrected astigmatism is still present
if block appear equal, how can you confirm the astigmatism is fully corrected ?
place additional +1.00SPH to move the entire IOS, if equal pt voices equal blur
if block appear equal, how do you know if COLC was left uncorrected ?
place additional +1.00 SPH and pt voices one block clearer than another > recheck cyl power
when undergoing second sph refinement, what line VA should you stop at if pt can go to 20/20
beyond 20/20 until they reach best VA
under duochrome tests, a hyperopic patient would report which target as clearest and dark
green, shorter AL
under duochrome tests, a myopic patient would report which target as clearest and dark
red , longer AL
would you perform binocular balance on a presbyopic pt?
yes, to ensure equal ADD OU
does the eye accommodate more or less under binocular conditions
more
what is exophoria
under converged eye under monocular conditions (outward turn), require more convergence when testing binocularly
what is esophoria
the eye turns inwards under monocular conditions
which of the binocular balancing techniques are the least reliable in represent daily encounters?
a. succesive alternate occlusion
b. vertical prism dissociation
c. septum techniques
d. polaroid techniques
e. A and b
E
successive alt occlusion
occluding an eye leads to convergence of the open eye and this is a false reality as the pupil isn’t in that position during primary gaze
VPD is the same as occluding one eye without actually doing it
Given then prism is base up, where is the image
image appears down
when performing humphriss binocular balancing technique, the blurred eye under a +1.00D lens has a central retinal blur of how many degrees ?
2-3
during polaroid techniques, if a filter blocks transmission of the light reflecting from a letter, what color with the letter be?
black letter against white background
during polaroid techniques, if a filter allows transmission of the light reflecting from a letter, what color with the letter be?
white letter on white background
when a letter appears black, what does this represent
the absence of light, blocked light transmission
which technique doesn’t require fogging lenses
polarized duochrome
