Subjective Refraction Flashcards
What is the purpose of subjective refraction?
To determine the refractive state of the eye subjectively by combining lenses to place the far point of the eye at infinity, with accommodation relaxed
Why do we fog?
To ensure that accommodation is relaxed
How do we fog?
Create an artificially myopic eye by placing plus lenses in front and ensuring the image formed is in front of the retina
What is a stimulus for accommodation?
Blur
2 consequences if fogging is not done
Subjective refraction results in insufficient plus or excessive minus power
Asthenopia with extended near work
Asthenopia
Eye strain
End point criterion
Maximum plus power for maximum acuity
Circle of least confusion
Center of the conoid of Sturm located at the dioptric midpoint between the horizontal and vertical focal lines
When/why do you use astigmatic charts
To determine cylindrical component of refractive error when 20/25 or better cannot be achieved with net retinoscopic findings, another subjective test under monocular conditions
What are the two types of astigmatic chart?
Fixed and rotating
What kind of chart is the clock dial?
Fixed
What kind of chart is the paraboline chart?
Rotating
What is the rule of 30?
The smaller of the two clock hours reported by the patient is multiplied by 30 to determine the cylinder axis
How would WTR astigmatism respond to clock dial test?
12 and 6 o’clock would be sharpest
How do you find the power of cyl using clock dial?
Collapse the conoid of Sturm which makes the opposite spokes become clearer
What is the end point goal of clock dial?
When the patient reports that all of the spokes are equally distinct
What are the 3 reasons to do JCC?
Refine axis and cyl subjectively
Refine objectively determined astigmatic corrections from keratometry/ret
Refine subjectively determined astigmatic corrections from charts
What is the JCC lens?
Minus cyl on one side and plus cyl on the other with axes 90 degrees apart in powers of +-0.25
What must be done prior to JCC testing?
The spherical lens power that gives the best VA is placed in front of the eye and remains there throughout
True or False: JCC can be tested under fogged conditions
False, never (lol)
What are the 4 functions of JCC?
Analysis, diagnosis, treatment, prognosis
9 factors that influence subjective refraction
Case history Intelligence Discrimination Accommodative status Personality Health Age Past experience Interaction with doctor
Purpose of monocular subjective refraction
To determine monocular best sphere and to refine axis and cylinder
Three basic steps of monocular subjective refraction
Sphere check (MPMA)
JCC
Second sphere check
Which dots are the minus cylinder part of the JCC?
Red
Two basic steps of binocular subjective refraction
Balance the accommodative stimulus and finalize the sphere power binocularly
When is prism dissociated blur balance not performed?
When the patient is presbyopic
In which eye do you add +0.25D to during the prism dissociated blur balance test?
The eye they report to be least blurry
What is the purpose for the prism blur balance test?
To prevent unequal or excessive accommodative effort between the eye’s to prevent asthenopia
What is the end point of the prism blur balance test?
Equally blurry lines
