Refraction
 Refractive Anomalies
o Simple hyperopic
 AFL is on the retina
 PFL behind the retina
 COLC behind the retina
o Simple myopic
 AFL is in front of the retina
 PFL is on the retina
 COLC in front of the retina
o Compound hyperopic
 AFL and PFL are behind the retina
 COLC behind the retina
o Compound myopic
 AFL and PFL are in front of the retina
 COLC in front of the retina
o Mixed
 AFL is in front; PFL is behind
 COLC is in front, behind, or on the retina
 COLC is always at the dioptric midpoint of the interval
o Defines the equivalent sphere (=sphere + ½ cyl)
 Identifies the best possible vision without cylinder
 Best vision is when the Interval of Sturm is collapsed to a point (AFL, PFL and
COLC are all one point)
o The point is on the retina
 Increasing minus lenses: shifts light away from the cornea
 Increasing plus lenses: shifts light toward the cornea
 Spheres affect all focal lines/points
 Cylinders affects only one focal line and the line is in the same direction as the axis
of the cylinder (opposite the power meridian)
o Minus cylinder phoropter moves the AFL
 Conclusion
o Sphere determines location of the PFL
o Cylinder determines location of the AFL and the size of the Interval
(determines size of and location of the COLC)
 Visual Acuities
o Expect 1 LOL decrease in VA for every -0.25DS or -0.50DC
o If cylinder is oblique, expect 1 extra LOL decrease in VA
 Monocular refraction
o Step 1: 1st Best Sphere=maximum plus for best VA
 Occlude eye not being refracted
 Fog to place the COLC in front of the retina (Note: Fogging first
relaxes accommodation)
 Use 3 or 4 LOL above BVA
 Add plus in 0.25D steps
o Each 0.25D should decrease 1 LOL
Decrease fog in 0.25D steps until no improvement in VA (stop at the
last decrease where there was improvement)
 Adding +0.25 decreases VA
 Adding -0.25 does not improve VA, VA remains the same or
makes VA worse
o Accommodation may be innervated
 If uncorrected astigmatism exists, COLC moves 0.125D with each
0.25D change
 End point is when the COLC is on or closest to the retina
 Patient will report clearer vision, not smaller and/or darker
 If the COLC cannot be placed on the retina, then it needs to be
slightly behind (-0.12D)
o Slightly over minus rather than over plus because patient
can accommodate
 Correct astigmatism: collapse the interval of Sturm and maintain
COLC on the retina
o Jackson Cross Cylinder
 JCC combines a +0.25DC and -0.25DC oriented 90° apart
 White dots= plus cylinder axis
 Red dots= minus cylinder axis
 Power position: alignment with the axis of the cylinder
 Straddle position: 45° off axis of cylinder bank axis
o Step 2: Power Search or Power Acceptance
 Use 3 or 4 LOL above the first best sphere
 Tell the patient “I am going to show you two choices, both of
which may be fuzzy, but of the 2 choices tell me which one is
the best or are they about the same”“1 or 2”
 Power Search Method 1: place -0.25 x 180 in the cylinder bank
 With the JCC in aligned position, flip
 If they accept the cylinder (red dots aligned to 180):
o Patient has at least -0.25DC close to 180
o Move on to axis refinement
 If they reject (white dots aligned to 180): repeat process with
axes 045, 090 and 135
 Power Search Method 2: leave the cylinder bank at plano
 With the JCC positioned x 090/180, flip
 If both are the same, no cylinder exists at either 090 or 180
o Repeat with JCC at 045/135
 If one view is better, patient has at least -0.125DC close to
where the red dots were located with better view
o Place -0.25DC where the red dots were located and
confirm that at least 0.25DC exists
 Power Acceptance: starts with cylinder in the bank
 Align the JCC to the axis of the cylinder
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Tidbits
o If rejection (white dots aligned with axis), remove
-0.25DC and repeat until accept or no cylinder remains
(maintain COLC)
 If all cylinder is rejected, change to power search
for the remaining 3 meridians
o If acceptance at any point (red dots aligned with axis),
move on to axis refinement
Step 3: Axis Refinement
 Place JCC in straddle position (45° to axis of cylinder in bank)
 Flip the JCC with instructions
 If one view is better, rotate the cylinder bank TOWARD the red
dots
o Initially rotate 15° (with some exceptions)
o Repeat until direction is reversed
o Once reversed, rotate back 7.5°
o When reversed again, rotate 3° to 4°
 End point is when the patient reports “the same” (or oscillates
between 1and 2 degrees)
o Move on to power refinement
Step 4: Power refinement
 Rotate the JCC to aligned position
 Flip JCC
 If acceptance (red dots aligned with axis), add -0.25DC and
repeat flipping JCC
o For every -0.50DC added, compensate with +0.25DS
 If rejection (white dots aligned with axis), take away -0.25DC
and repeat flipping JCC
o For every -0.50DC taken away, compensate with
-0.25DS
 Endpoint is when patient says “the same” or “equal”
o Move on to 2nd best sphere
nd
Step 5: 2 Best Sphere= maximum plus for best visual acuity
 Same criterion as first best sphere
o No improvement or gets worse with -0.25D
o Blurs with +0.25D
 For a presbyope, it will blur with -0.25 or +0.25
o COLC is maintained on the retina or as close as possible
o JCC always ends with power refinement
 If cylinder is present at the start: power acceptance axis
refinement power refinement
 If no cylinder present at the start: power search axis refinement
power refinement
o “Equal” is always an endpoint
o There is a difference of 1.00D between the flips
o “Darker” or “smaller” is NOT better VA
More letters, even 1 or 2, are better VA
Keep lens numbers low (1 or 2, 3 or 4, etc)
Control chart by giving limited LOLs
If you are lost in JCC, stop and redo best sphere, then go back to cylinder
On JCC, if adding -0.25DC after acceptance and then rejection on next flip,
remove the -0.25DC
 Better to undercorrect cylinder
 If you also added +0.25DS (to maintain COLC), you do not have to
remove the +0.25DS because your next step is fog before best sphere
o In JCC power refinement, redo axis for every 1.00DC change
o In JCC, redo best sphere if large cylinder axis or power change
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