PC - Binocular Vision 1 Accommodation - Week 2 Flashcards
By what age is accommodation thought to be fully developed?
6 months of age.
Name the 4 major stimulators of accommodation in order of strength.
Blur - primary driver
Proximal awareness
Vergence
Tonic accommodation
Name 6 factors that influence accommodation.
Blur Luminance Proximity Chromatic aberration Convergence of eyes Age
What are 5 features of accommodation that can be measured clinically?
Posture (lag/lead) Amplitude (NPA) Accommodative facility Relative accommodation (NRA/PRA) Convergence accommodation (A/AC)
Describe Monocular Estimate Method - Near Retinoscopy for measuring accommodation.
The target and observer are at the same distance, so the reflex is a measure of the stability and accuracy of the accommodative response.
What are two advantages of doing MEM?
Objective and can be done in free space
What are the expected values for a MEM finding, and keeping this in mind, what value would raise suspicion?
Expected - +0.25 - 0.50
Minus findings, or above +0.75 should raise suspicion
Consider binocular cross cylinder. Is it subjective or objective?
Subjective
Can the binocular cross cylinder be done in free space?
No, requires a phoropter.
Name a disadvantage of the binocular cross cylinder.
Not close enough to a reeal life near task, and can be influenced by a lack of proximal cues.
What are the expected values for the binocular cross cylinder?
+0.50 with a standard deviation of +0.50.
Describe the pushup method to measure amplitude of accommodation. Is it subjective or objective?
What are the expected values?
Near point accommodation technique. Is a subjective test. Amplitude = 18 - (age/3) or Minimum amplitude = 15 - (age/4) SD = +/-2.00D
Consider the reverse pushup method. Explain why this method overestimates the accommodative amplitude.
Due to the magnification effect of bringing the target closer and improving VA.
Describe the refractor head and portable near point rule.
A variation of the monocular pushup method, allowing you to measure blur using the refractor head attachment.
Name a disadvantage of doing the pushup method when the patient is behind a phoropter.
It interferes with proximal cues and may give a different result.
Describe the minus lens to blur technique.
Minus lens are added to a target at 33cm until it can no longer be seen.
Compare the expected results of the pushup method to minus lens to blur, and explain why the difference, if any.
Minus lens to blur typically less than pushup method by 2.00D. This is due to the lack of the magnification effect of moving the target closer to the patient.
Define accommodative facility.
The speed and efficiency at which accommodation takes place.
How is accommodative facility measured?
Using near accommodative facility flippers.
Describe how accommodative facility is performed.
The patient is given a near fixation target. The flippers are + and - lenses. Beginning with the + side, the lenses are flipped, and the patient is timed on how long it takes for them to regain focus.
What is accommodative facility measured in, and what are the expected adult values?
Cycles per minute
Average is 8 cycles per minute
Define 3 characteristic signs of accommodative insufficiency.
High lag
Low amplitude
Poor facility
Define 3 characteristic signs of accommodative excess.
Variable VA
No lag/lead
Fails + facility
Define 2 characteristic signs of accommodative spasm.
Reduced VA
Reduced lead
Fails + facility
Define 2 characteristic signs of ill-sustained accommodation.
High variable lag
Slow facility
Define 2 characteristic signs of in-facility accommodation.
Slow facility + and -
