Optical Cross Problems

1
Optical Cross Problems

• Review

2
Problem 1

• You get a prescription from the ophthalmologist
• you had referred your cataract patient to.
• After IOL surgery he has prescribed
• OD -0.25 0.75 X 093 OS 0.25 1.25 X
  085
• You only have minus cylinder lens blanks in your
  optical.
• What should you do?

3
Solution 1

• Transpose to MINUS CYLINDER form
• OD -0.25 0.75 X 093 OS 0.25 1.25 X
  085
• Add sphere and cylinder values
• 0.50 1.50
• Change sign of cylinder
• -0.75 -1.25
• Modify axis by 090 degrees
• 093 - 090 003 085 90 175
• Final prescription
• OD 0.50 -0.75 X 003 OS 1.50 -1.25 X
  175

4
Problem 2

• The patient's old rigid lenses measure as
  follows
• OD -2.50 _at_ 030 and -3.00 in the other meridian.
• OS -2.00 _at_ 165 and -3.00 in the other meridian.
• If there is no other error in the patient's eye
  and you ignore the vertex distance change, what
  do you expect the spectacle prescription to be?

5
Solution 2

• OD -2.50 -0.50 X 030
• OS -2.00 -1.00 X 165

6
Problem 3

• You hand neutralize the patients prescription
  with the following lenses from your lens rack.
• OD 1.00 _at_ 030 and -0.50 _at_ 120
• OS -1.00 _at_ 025 and 1.00 _at_ 115
• What is the patient's prescription?

7
Solution 3

• OD -1.00 _at_ 030 and 0.50 _at_ 120
• gives 0.50 -1.50 X 120
• OS 1.00 _at_ 025 and -1.00 _at_ 115
• gives 1.00 -2.00 X 025
• Note No working distance to adjust

8
Problem 4

• You are on a SVOSH trip to the jungles of
  Equador.
• You find a remote village where some of the
  population has never seen an optometry student.
• You want to impress them with your retinoscopy
  skills, but you only have a battery operated
  retinoscope (fully charged) and the sphere lens
  rack lenses in your posession.

9
Problem 4 Continued

• You scope at 67 cm and find the following
  neutrality points
• OD -1.00 _at_ 180 and -2.00 _at_ 090
• OS 1.00 _at_ 180 and 2.00 _at_ 090
• What glasses should you give for this patient?

10
Solution 4

• Without adjusting for your working distance,
• OD -1.00 -1.00 X 180 OS 2.00 -1.00 X 090
• Subtract your working lens of 1.50 for 67 cm
• OD -2.50 -1.00 X 180 OS 0.50 -1.00 X 090

11
Problem 5

• While on this same SVOSH trip, you drop your
  minus lens rack into the river while crossing by
  canoe.
• But, as luck would have it, the headhunters in
  the next village have vision needs as well.
• They have shrunk the heads of their enemies so
  small, that now they cannot locate them, but they
  have located you.
• You talk them into not taking your head if you
  can give them some glasses to find their old
  heads.

12
Problem 5 Continued

• You find the following creates neutrality with
  your retinoscope for the chief of the tribe
• OD 1.00 at 50 cm in the 180 meridian
• and 2.00 at 67 cm in the orthagonal meridian
  
• OS 3.00 at 33 cm in the 180
• and 1.00 at 50 cm
• What Rx would you give the chief?

13
Solution 5 (Right eye)

• For the first meridian
• 50 cm WD 2.00 _at_ 180
• Needs 1.00 more to create neutrality at 50 cm.
• Therefore, total need is 3.00 at 180,
• Rx needs -3.00 _at_ 180 to see to infinity

14
Solution 5 (Right eye)

• For the other meridian
• 67 cm 1.50 _at_ 090
• Needs 2.00 more to create neutrality at 67 cm.
• Therefore, total need is 3.50 at 090,
• Rx needs -3.50 _at_ 090 to see to infinity

15
Solution 5 OD

• Cross cylinders are
• -3.00 _at_ 180 and -3.50 _at_ 090
• So prescription would be
• OD -3.00 -0.50 X 180

16
Solution 5 (Left Eye)

• For the first meridian
• 33 cm WD 3.00 _at_ 180
• Needs 3.00 more to create neutrality at 33 cm.
• Therefore, total need it 6.00 _at_ 180
• Rx needs -6.00 _at_ 180 to see to infinity

17
Solution 5 (Left Eye)

• For the other meridian
• 50 cm 2.00 _at_ 090
• Needs 1.00 more to create neutrality at 50 cm.
• Therefore, total need is 3.00 at 090
• Rx needs -3.00 _at_ 090 to see to infinity

18
Solution 5 OS

• Cross cylinders are
• -6.00 _at_ 180 and -3.00 _at_ 090,
• So prescription would be
• OD -3.00 -3.00 X 090