Accommodation Flashcards
(31 cards)
Where is the posterior chamber located?
Posterior to the iris and anterior to the lens and lens zonules.
Where does the primary innervation for increased accommodation originate?
The parasympathetic nervous system.
Why does stress interfere with accommodation?
Stress is indicative of sympathetic nervous system activation, which also decreases or inhibits accommodation.
What is the near triad?
It is an explanation of the relationship between accommodation between accommodation, convergence, and pupil diameter.
Increased accommodation increases convergence and decreases pupil diameter.
Increased convergence increases accommodation and decreases diameter.
Decreased pupil diameter does NOT affect accommodation or convergence.
Which factor of the near triad is the strongest?
Accommodation.
How big is the human lens?
About 9 mm in diameter and 3.6 mm thick.
During accommodation, how much thicker does the lens get?
About .5 mm.
What is presbyopia?
Normal age-related loss of ability to accommodate and thus see close targets clearly.
What are some common symptoms of accommodative dysfunction?
Reduced accommodative facility, blurry vision (especially with near targets), asthenopia.
How do added minus lenses affect accommodation?
They stimulate accommodation and increase accommodative demand. Minus lenses partially diverge the light, increasing the accommodative demand on the lens.
How do added plus lenses affect accommodation?
They relax accommodation. The plus lenses partially focus light, reducing the accommodative demand on the lens.
What three factors must be measured to accurately assess accommodation?
Amplitude, facility, and posture.
How can you measure accommodative amplitude?
You can increase accommodative demand by decreasing the target distance until the patient notices prolonged blur. This is called the Donders push-up test for NPA and is performed monocularly.
You can also add minus lenses of increasing magnitude to increase the accommodative demand until the patient notices prolonged blur.
What is Hofstetter’s equation for maximum amplitude?
25.0-(0.40 x age in years)
What is Hofstetter’s equation for average amplitude?
18.5-(0.33 x age in years)
What is Hofstetter’s equation for minimum amplitude?
15.0-(0.25 x age in years)
What is the primary stimulus to accommodation?
Retinal image blur.
What is PRA and how is it measured?
Positive Relative Accommodation. It is a test to measure the amount that accommodation can be increased (via the near triad) at a target distance of 40cm before vergence is affected.
What lenses would you use to measure PRA?
Minus lenses to stimulate the POSITIVE response in the eyes.
Why is PRA not a true measure of accommodative amplitude?
Since the test is performed binocularly, the vergence system is in play as well as accommodation.
What is NRA and how is it measured?
Negative Relative Accommodation. It is a test to measure the amount that accommodation can be decreased (via the near triad) at a target distance of 40cm before vergence is affected.
What lenses would you use to measure NRA?
Plus lenses to stimulate the NEGATIVE response in the eyes.
What is meant by the terms “accommodative lag” and “accommodative lead?”
They are the difference between the calculated accommodative demand of a given target distance and the amount of accommodation that the individual responds.
What two tests can be used to measure accommodative posture?
Cross grid technique (subjective test) and dynamic retinoscopy (objective).
