C7 Problem Set

Q39. The full ametropic correction for a patient's right eye is -3.00 -5.00 axis 15. However, the patient can only tolerate 2.00 DC, so you decide to make up a partial astigmatic correction. The power for the partial astigmatic correction should be: (A) -1.50 -2.00 axis 15 (B) -3.00 -2.00 axis 15 (C) -4.50 -2.00 axis 15 (D) -6.00 -2.00 axis 15

(C) -4.50 -2.00 axis 15 With -3.00 -5.00 x 15 we remove -3.00 DC, we must compensate by adding -1.50 DS to keep the COLC on the retina

Q9. True or false (C) Toward the finish of a JCC phoropter refraction, the COLC is on the retina and a -0.25 D cylinder increase is indicated. It is better to add +0.25 D sphere (smallest increment on the phoropter) than leave the patient "overminused" for the next JCC presentation.

(C) False. Better to have the COLC 0.125 D behind the retina and allow minimal accommodation to bring it forward to the retina. If the COLC is set 0.125 D in front of the retina, the patient cannot bring it "back" to the retina.

Q12. Trial lens combination: +2.00 -2.00 x 55. JCC handle at 10 degrees First view with negative JCC axis at 145. Patient prefers second view. What next? (MC) (A) +2.00 -2.00 x 45 (B) +2.00 -2.00 x 65 (C) +1.75 -1.50 x 55 (D) +2.25 -2.50 x 55

(D) +2.25 -2.50 x 55 2nd option is with negative JCC axis (red) at axis 55, red on red" meaning they want more negative cylinder

Q26. At one stage in a subjective refraction you have a +3.25 DS in the trial frame and a -2.25 DC x 50. Total power of this lens combination in the 10 meridian is: (A) +0.41 D (B) +1.00 D (C) +1.93 D (D) +2.32 D

(D) +2.32 D F(10) = (-2.25 DC) sin^2(50-10) F(10) = -0.93 F(total at 10) = -0.93 + 3.25 = +2.32 D

Q5. A patient requires a full astigmatic correction of +4.50 -5.50 x 30 (left eye). However, only 3 diopters of cylinder can be tolerated. The partial astigmatic correction should be (A) +5.75 -3.00 x 30 (B) +4.50 -3.00 x 30 (C) +4.00 -3.00 x 30 (D) +3.25 -3.00 x 30

(D) +3.25 -3.00 x 30 +4.50 -5.00 x 30 *we remove -2.00 DC to make +4.50 -3.00 x 30 *now we have to compensate by adding -1.00 to sphere

Q35. A patient's left eye has +2 D refractive hyperopia in the 75 principal meridian and 4 D (regular) with-the-rule astigmatism. The eye has +2 D axial hyperopia. BVS for this eye would be: (A) +1.0 DS (B) +2.0 DS (C) +4.0 DS (D) +6.0 DS

(D) +6.0 DS If eye has +2 D axial hyperopia, the power needed for emmetropia is +62 D (the eye is +58). With WTR astigmatism, the vertical meridian is more positive.

Q41. A patient's full ametropic correction is +1.50 -1.50 × 90. You currently have a trial lens combination +1.25 -1.00 × 90 in front of the eye. With the ±0.25 D Jackson Cross cylinder aligned with handle at 45, what dioptric change occurs in the Interval of Sturm between "first" and "second" views? (A) 0.00 D (B) 0.25 D (C) 0.50 D (D) 1.00 D

(D) 1.00 D There is -0.50 residual astigmatism. A +/- 25 D JCC has a dioptic change of -0.50 assuming the COLC is on the retina. The residual astigmatism added produces a total change of 1.00 D in 1 view and 0.00 D in the second view

Q8. During a JCC subjective refraction, the clinician has not paid very careful attention to maintaining sphere while adding cylinder. At this stage, there is -1.50 DC trial cylinder in the trial frame (along with the BVS + 0.50 DS) and the clinician is at the power refinement stage. The patient is a 20-year-old with-the-rule astigmat. Our clinician is also picking out letters at random on the 20/40 line of the VA chart for the patient to look at during "first/second" presentations. What would be the worst possible letter to have the patient view during the final stages of cylinder power refinement (if the trial cylinder power is currently less than the correcting cylinder power)? (Multiple Choice): (A) O (B) E (mainly horizontal) (C) H (mainly vertical) (D) Either E or H (E) W (mainly oblique).

(D) Either E or H

Q9. True or false (D) If too much negative trial cylinder is added during refraction (but COLC maintained on the retina), the two focal lines will move farther apart for the patient's preferred JCC view (first/second) rather than closer together

(D) False. With the COLC on the retina, reducing the interval of Sturm will give better vision regardless of which side of the retina the focal lines are located

Q6. During a refraction, you have a trial lens combination +3.00 -1.00 x 80 in front of your patients right eye. You place the JCC in front of the patient's eye, first and second. Of the two views, the patient prefers second with the JCC negative cylinder axis at 35. What is your next move? (Multiple Choice): (A) Increase negative trial cylinder (B) Decrease negative trial cylinder (C) Rotate trial cylinder axis counterclockwise (toward 90) (D) Rotate trial cylinder axis clockwise (toward 180) (E) Not enough information to decide

(D) Rotate trial cylinder axis clockwise (toward 180) (we are doing axis refinement so the JCC handle is at TCA axis 80) -they want less axis so we rotate it clockwise towards 180

Q3. During a sphere-cylinder refraction, the trial lens combination -3.00 -1.00 x 90 is placed in front of the patient's eye. The cross cylinder is placed in front of the eye and "first" and "second" presentations are shown. As a result, a lens combination of -3.25 -0.50 x 90 is indicated. The patient's preferred view for the cross cylinder must have been with: (A) the negative cross cylinder axis at 45 (along the 45 principal meridian) (B) the negative cross cylinder axis at 90 (C) the negative cross cylinder axis at 135 (D) the negative cross cylinder axis at 180.

(D) the negative cross cylinder axis at 180. Patient wanted less cylinder, means that it was "black on red" so the black JCC is @ 90, meaning the negative cross axis is at 180.

Q4. A patient's full correction (right eye) is +2.00 -3.00 x 180. Retinoscopy (objective refraction) indicates a correction of +1.25 -2.50 x 180 to the clinician, who does not verify sphere subjectively prior to Jackson Cross Cylinder. Since the clinician is confident that the cylinder axis is correct, cylinder power is checked. The patient is instructed to view a letter 'T' on the VA chart (rather than a more appropriate circular letter or target). The initial "first" and "second" presentation will indicate that: (A) cylinder power should be decreased (B) cylinder power should be increased (C) cylinder power should remain the same (D) the patient may choose any one of the above (A, B or C).

(D) the patient may choose any one of the above (A, B or C). This is because a T has both horizontal and vertical biased lines.

Q9. True or false (E) A JCC of higher power would be more useful for the initial stages of subjective axis and subjective power determination, rather than the final stages.

(E) True. Higher power JCCs produce larger effective axis rotations for axis refinement. They are therefore more useful for the initial stages were larger axis changes are likely. Similarly for power refinement, larger changes are more likely initially and a higher power JCC will produce larger differences in IOS between views one and two.

Q18. When using a +/-0.50 D Jackson Cross Cylinder for cylinder power refinement, what is the change in the interval of Sturm between first and second views? (A) 0.50 D (B) 1.00 D (C) 2.00 D (D) 4.00 D

(c) 2.00 D (for a +/- 0.25 it would be 1.00 D change)

Q16. An astigmatic patient, who is wearing a partial astigmatic correction of power -3.00 -2.50 x 80, is now ready to be prescribed the full astigmatic correction for their 3.50 D spectacle astigmatism. The full astigmatic correction is: (A) -4.00 -3.50 x 80 (B) -3.50 -3.50 x 80 (C) -2.50 -3.50 x 80 (D) -2.00 -3.50 x 80

(C) -2.50 -3.50 x 80 Adding -1.00 DC means we have to add +0.50 DS to keep COLC on the retina

Q30. During the Jackson cross-cylinder (JCC) part of a refraction, a lens combination +2.00 -1.50 axis 50 is in place. The JCC is shown "first" with negative axis aligned along the 5 meridian; "second" with the negative JCC axis along 95. The patient prefers the "first view." This result indicates that the most appropriate trial lens combination to use next would be: (A) +2.00 -1.50 axis 40 (B) +1.75 -1.00 axis 50 (C) +2.25 -2.00 axis 50 (D) +2.00 -1.50 axis 60

(A) +2.00 -1.50 axis 40 This is axis refinement (power is not on power) Wants less axis so we turn clockwise

Q27. A patient's BVS power for the left eye is -2.50 DS. Reduced axial length is 24.24 mm and reduced surface power in the 20 meridian is +63 D. If the eye has regular astigmatism, reduced surface power in the 110 meridian will be: (A) +52.0 D (B) +57.5 D (C) +59.0 D (D) +60.5 D

(A) +52.0 D

Q34. A patient whose full ametropic correction is -1.75 -1.50 × 125 has a subjective refraction conducted at 2/3 meter (66.7 cm). At this test distance, what total sphere power would place the circle of least confusion on the retina? (A) -1.00 DS (B) -2.50 DS (C) -3.25 DS (D) -4.00 DS

(A) -1.00 DS For corrected distance vision, the BVS is -2.50 DS (pushing 2.50 D to the right) If a subjective refraction is conducted 66.7 m in front of the patient, the entering vergence is -1.50 D. This will move the COLC 1.50 D to the right. -leaving only -1.00 of the original BVS -2.50 needed to keep the COLC on the retina

Q36. During the Jackson cross-cylinder (JCC) part of a refraction, a lens combination -2.00 -1.50 axis 105 is in place. The JCC is shown "first" with negative axis aligned along the 150 meridian; "second" with the negative JCC axis along 60. The patient prefers the "second view." This result indicates that the most appropriate trial lens combination to use next would be: (A) -2.00 -1.50 axis 95 (B) -1.75 -2.00 axis 105 (C) -2.25 -1.00 axis 105 (D) -2.00 -1.50 axis 115

(A) -2.00 -1.50 axis 95 This is axis refinement, power is not on power Patient was less axis (turn towards 60)

Q40. A patient's full ametropic correction is -2.00 -1.00 × 180. You currently have a trial lens combination -2.25 -0.50 × 180 in front of the eye. With the ±0.25 D Jackson Cross cylinder aligned with handle at 180, what dioptric change occurs in the Interval of Sturm between "first" and "second" views? (A) 0.00 D (B) 0.25 D (C) 0.50 D (D) 1.00 D

(A) 0.00 D With handle at the TCA axis, this would be axis refinement, the JCC will not change the power/IOS

Q9. True or false (A) It should be easier to set cylinder axis accurately for a 4 D astigmat than for an 0.75 D astigmat

(A) True. The higher the cyl power, the more the image degrades for a given cyl axis rotation.

Q25. You are conducting a full subjective refraction on a patient. BVS power for the patient's left eye is -0.75 DS. Vision with BVS indicates 3.00 D of astigmatism. After initial axis determination, you decide that the starting cylinder axis should be 125. To begin the Jackson Cross Cylinder (JCC) axis refinement, you add a -3.00 D cylinder axis 125 to the phoropter. The new total sphere power in the phoropter as you commence the JCC cylinder axis refinement should be: (A) -2.25 DS (B) +0.75 DS (C) +1.50 DS (D) +2.25 DS

(B) +0.75 DS because you are adding -3.00 D, have to add +1.50 to -0.75 DS

Q33. The full ametropic correction for a patient's right eye is +3.00 -4.00 axis 85. However, the patient can only tolerate -2.50 DC, so you decide to make up a partial astigmatic correction. The power for the partial astigmatic correction should be: (A) +1.50 -2.50 axis 85 (B) +2.25 -2.50 axis 85 (C) +3.75 -2.50 axis 85 (D) +4.50 -2.50 axis 85

(B) +2.25 -2.50 axis 85 If we remove -1.50 DC, we must add -0.75 DS

Q10. A patient's required full correction is +4.00 -3.00 45. With the current trial cylinder in place (not the full correction), the patient's preference (first/second) with the JCC is with the negative JCC power meridian at 135. The most likely trial lens combination in the phoropter during this JCC comparison would be (Multiple Choice): (A) +4.25 -3.50 x 45 (B) +3.75 -2.50 x 45 (C) +4.00 -3.00 x 55 (D) +4.00 -3.00 x 35

(B) +3.75 -2.50 x 45 This means that patient wants more negative cylinder x 45, meaning that the trial cylinder in place is not negative enough

Q2. A patient's eye, represented in reduced eye form, has the following specifications: reduced axial length = 23.39 mm; Fe = +58 D in the 70 principal meridian and +61 D in the 160 principal meridian. The BVS for this eye would be (A) +0.50 DS (B) -2.50 DS (C) -3.00 DS (D) Plano

(B) -2.50 DS

Q9. True or false (B) JCC refraction only works with negative trial cylinders

(B) False. Either works fine.

Q19. The following trial lenses are used during cylinder axis refinement for a patient's right and left eyes respectively: -1.00 DC (OD) and -2.00 DC (OS). During cylinder axis refinement with the Jackson Cross Cylinder, in which eye will the greater "effective axis rotation" be obtained with each view (first and second)? (A) cannot be determined without being given Jackson Cross Cylinder power. (B) right eye (C) left eye (D) effective axis rotation will be the same for both eyes

(B) right eye effective axis rotation is always greater for a lower power trial cyl

Q24. A patient has 4.50 D of astigmatism, but was initially given a (balanced) partial astigmatic correction of +6.00 -3.00 x 20. Having adapted to the partial correction, the patient is now ready to be prescribed their full correction, which is: (A) +5.25 -4.50 x 20 (B) +6.00 -4.50 x 20 (C) +6.75 -4.50 x 20 (D) +7.50 -4.50 x 20

(C) +6.75 -4.50 x 20 Add -1.50 DC, will have to add +-0.75 DS

Q7. A patient comes in to your practice wearing their most recent distance correction -3.50 +2.00 x 25 (prescribed 2 years ago by an Ophthalmologist). The correction that the patient requires now (which you, as the clinician, do not know at this point) is -0.50 -2.50 x 105. You make up the Ophthalmologist's prescription in negative cylinder form and (because the patient is claustrophobic) place it in a trial frame instead of the phoropter. After any necessary sphere adjustment (not Multiple Choice): (A) For the initial comparison (first/second) step of cylinder axis refinement with the JCC, where is the minus JCC axis for the patient's preferred view? (B) For the initial comparison (first/second) step of cylinder power refinement with the JCC, where is the minus JCC axis for the patient's preferred view?

Must first convert plus cylinder to negative cylinder notation: -1.50 -2.00 x 115 (A) Axis refinement: JCC handle at 115, patient wants axis rotated toward 105. Therefore minus JCC axis 45 clockwise from handle = 70 (B) Power refinement (after refining axis to 105): JCC axes 105 and 15 (parallel and perpendicular to TCA). Patient wants more cylinder; therefore prefers minus JCC axis along 105.