NRA/ PRA

Question 1

What is the significance of NRA and PRA

Answer 1

positive and negative relative accommodation represents the changes in accomm. which are elicited while the stimulus for vergence is held constant

Question 2

for both NRA and PRA where is the endpoint taken

Answer 2

when pt resports FSSB

Question 3

what the the magnitude of relative accommodation

Answer 3

the amount of additional sph power added to the distance correction

Question 4

pt dist rx = -3.00 SPH
mesSure NRA: pt reports FSSB thru -1.00
What is their NRA

Answer 4

+2.00
think of it as a number line, going more +

Question 5

pt dist rx = -3.00 sph
mesSure PRA: pt reports FSSB thru -5.25
What is their PRA

Answer 5

• 2.25
  think of a number line, going more -

Question 6

when viewing through a lens and the image and object are on the same visual axis , then what happens to vergence ?

Answer 6

vergence doesnt change

Question 7

what are the expected values for NRA and PRA for a young pt ( < 30yr of age)

Answer 7

NRA +2.00 to +2.25
PRA -2.50 TO -2.75

Question 8

the increase in blur driven accomm will stimulate

Answer 8

increase in accomm convergence

Question 9

in PRA when an image doesn’t fall on the fovea, what do we expect

Answer 9

image appears double

Question 10

what is retinal disparity

Answer 10

when the images appear double bc it doesnt fall directly on fovea

Question 11

In PRA if the eye converged in more than needed, this can be fixed by

Answer 11

reducing disparity vergence or divergence, diverging the eyes back towards primary gaze

Question 12

In PRA the divergence places the image on fovea but will

Answer 12

reduct the convergent accomm (reduces power of the eye) .. unfavorable in PRA bc the goal is to increase F eye

Question 13

in PRA to compensate for reduced convergent accom we need to

Answer 13

increase blur driven accomm

Question 14

what is the PRA mecahnism

Answer 14

minus lenses under power > increases blur driven accommodation > increases accomm convergen > decreases disparity divergence (eliminating double) > decrease convergence accom > increase blur driven .. recycle

Question 15

What is the NRA mechanism

Answer 15

plus lenses under power > decreases blur driven accommodation > decreases accomm convergence > increases disparity convergence > increases convergence accom > decrease blur driven .. recycle

Question 16

what are the factors to low PRA

Answer 16

Inability to either
1. increases blur driven accomm (common for presbyopes) or
3. no ability to decreased disparity diveregence (continues to see double)

Question 17

for low PRA what are the common factors that lead to difficulty increasing blur accommodation

Answer 17

• presbyopia
• accommodative insufficiency

Question 18

for low PRA what are the common factors with disparity divergence

Answer 18

• esotropia
• convergence excess

Question 19

a low NRA finding is typically caused by

Answer 19

difficulty decreasing blur driven accomm. or difficulty with disparity convergence

Question 20

for low NRA what are the common factors that lead to difficulty decreasing blur accommodation

Answer 20

• accommodative excess
• pesudomyopia
• latent hyperopia (pt always accommodating, hard to remove)

Question 21

for low NRA what are the common factors with disparity convergence

Answer 21

• convergence insufficiency
• exotropia

Question 22

which two conditions are associated with low and high NRA

Answer 22

psuedomyopia and latent hyperopia

Question 23

if the patient is able to relax that AR then,

Answer 23

high NRA

Question 24

if the patient was not able to relax the AR then

Answer 24

low NRA

Question 25

what patient factor must be elimintated to ensure proper PRA measurement

Answer 25

supression

Question 26

What is crossed diplopia

Answer 26

when the image formed by an eye is seen on the other side
OS image is located infront of OD eye itself