Unit 4 Flashcards
Steps to determine BVS
-Right eye is refracted first (OC the left)
-Fog OD VA to a 20/40 to 20/60 by adding +1.00
-Display full chart with 20/20 line at the bottom
-Reduce plus (add minus) in 0.25 steps
-Check VA and encourage px to read the next smallest line each time you change power
-Add minus power until the best line can be resolved
questions to ask during BVS
Whats the smallest line you can read
let me know when you can read the top line
Can you read the second line
How about the bottom line
What is an important question to ask during BVS refractin
IS the bottom line clearer or just smaller and darker/more bold?
Steps to determine cyl axis
-Align the handle with the current lens axis
-Advice the px that neither option will be completely clear but ask which one is best
-Flip the JCC - if the px prefers one option over the other, rotate the cyl lens axis towards the minus axis (red dot) on the JCC by 15
-Repeat the question
-If the response is in the opposite direction, move the axis back by 10 degrees
-continue until the px notices no difference
Steps to determine cyl power
-Rotate the JCC so the P lies along the axis line
-Flip the JCC (one lens will be one, other will be 2)
-If the px prefers red add -0.25
-If px prefers white remove 0.25
Spherical equivalent
Give +0.25 for every -0.50 you add
Give -0.25 for every -0.50 you remove
Refine the best sphere
-Show the full chart with 20-20 at the bottom
-Fog the vision by adding +0.75 of sphere (acknowledge the chart will be blurry)
-Slowly add minus power in 0.25 steps, checking VA each time
-Stop when VA no longer improves
when do we do Binocular balancing
Occurs after a subjective refraction under monocular conditions has been preformed
Why is it important to do binocular balancing
Neccessary to equalize the accomodative effort between the two eyes
What happens if you dont preform binocular balancing
if the right and left prescription are not balanced the eyes accomodate by the least amount possible to produce a clear retinal image in one yee
-the other eye may be slightly blurred and asthenopia could result
Steps to binocular balancing
-Add +0.75 or +1.00 over each eye
-display the 20/30 line (or 2 lines about the best VA)
-Occulde each eye alternatly and ask the px which eye is clearer (add +0.25 to the clearer eye)
-If the px says they are the same leave power as is
-If px keeps switching between R and L, leave the dominnant eye slightly clearer
-display the full VA chart to 20/20
-Reducce the plus power binoculalry by 0.25 steps while checking VA
-Continue until 20/20 is acheived
-Conclude w duochrome test
How else can binocular balancing be done?
Risley prism
A line of the chart is split horizontolly or vertically into seperate images
-Apply 3 prism base up in front of OD and 3 prism base down in front of OS
-this will result in the OD seeing the lower image and OS seeing the upper image
-Fog px with +1.00
-Present the 20/40 line
-Ask px which image is clearer, add +0.25 to the clearer eye to fog it futher
-Ask again, add +0.25 to the clearer eye
-Endpoint is reached when both sets of letters look the same
-The prisms are now removed and the chart is shown with 20/20 linem, reduce your plus power in 0.25 till best VA
Duochrome test - color explanation
Red light (620nm) focuses 0.25 behind the retina
Green light (535nm) focuses 0.25 in front of the retina
It is estimated yellow light (570nm) is preferred by the eye
Duochrome when to add minus or plus
If the letter on the red side are blacker - add minus
If the letter on the green side are blacker - add plus
Duochrome - if a -025 sphere is placed before the eye what happens
Both the red and green foci would move to the right by 0.25
The px would report the targets on the green t appear blacker and the red appear blurred
