Keratometry and Rx

Question 1

Determine Spherical equivalent:
-1.00 +1.00 x090
-2.00 -1.00 x180
+1.00+1.00 x090
-5.50+2.00 x090
+1.00-1.00x 180

Answer 1

0.50
-2.50
+1.50
-4.50
+0.50

Question 2

Determine Base Curve:

43. 00/41.00@090 fit on K
44. 00/44.00@090 fit on K
45. 00/44.00@090 fit 1/2 D steeper
46. 00/41.00@090 fit 1/2 D flatter

Answer 2

41. 00
42. 00
43. 50

40.50

Question 3

Convert D to mm:

41. 00
42. 00
43. 50
44. 50

Answer 3

337. 5/41.00= 8.23mm
338. 04
339. 94
340. 33

Question 4

To determine the diameter for an Intrapalpebral fit:

Answer 4

Diameter = Vertical lid aperature (VLD)-0.2mm
Iris visable between open lids up and down

Question 5

To determine the diameter for an Upper lid attachment (corneal alignment)

Answer 5

Diameter = Visable Iris Diameter - 2.3mm
(whole size of iris) side to side.

Question 6

What is the vertex distance adjustment formula?

Answer 6

Fc= Fs/1-dFs

Question 7

WITH the Rule:

Answer 7

Horizontal 180 is flatter (lower#) Minus cylinder in 180 deg

(160) - 180 - (020)

Question 8

AGAINST the Rule:

Answer 8

Vertical 90 flatter, Minus cylinder in 90 deg

(070) - 090 - (110)

Question 9

Determine base curve:
K 42.75/44.25@090
Lens diameter = 9.2mm (use chart)

Answer 9

Flat K = 42.75
Delta K = 44.25-42.75=1.50D
1.50D @ 9.2mm =0.25 Steeper
BC= 42.75 + 0.25 = 43.00D

Question 10

Determine Power:
K 42.75/44.25@090
-6.00+1.00 x090
BC = 43.00
Diam=9.2mm

Answer 10

-5.00-1.00x180
-5.00 @ 12mm = -4.75 corrected for vertex
Adjust for tear lens: BC is steeper than Flat K, plus tear film, compensate for this Add Minus Power SAM Flat K 42.75 BC 43.00 Tear comp = 0.25
Adjusted power-5.00

Question 11

Rx +3.00+1.00x090
Contact Diameter 8.7mm
K 43.00/44.50 @090
Calculate final parameters for order

Answer 11

BC 43.50D
Diam 8.7mm
+3.50D

Question 12

Calculate Residual Astigmatism:
+2.00-2.50x090
45.50/44.00@090

Answer 12

Delta K = 1.50 (Corneal)
Refracted 2.50
Residual 1.00
Correct with Front toric

Question 13

With a Back toric what are you correcting:

Answer 13

Corneal Astigmatism of 2.50D or higher

Question 14

With a Front toric what are you correcting:

Answer 14

Residual Astigmatism of 0.75 or higher

Question 15

For a Bitoric lens what are you correcting:

Answer 15

Corneal astig of 2.50D AND Residual astig of 0.75 or more.

Question 16

To properly adjust the eyepiece, turn the knob all the way _______. Slowly turn the knob ______ until proper focus is achieved.

Answer 16

counterclockwise
clockwise

Question 17

range of 44.00 D, 42.50 and 40.75. The central ball, equivalent to a ___ corneal refracting power, is the one generally used for basic calibration tests.

Answer 17

42.50 D

Question 18

Remember that if the cornea is _____, it will be _____ to get the plus and minus signs, (both principal meridians) in focus at one time. For greater accuracy, focus the plus or horizontal mires sharply then ____ for the minus or vertical readings.

Answer 18

astigmatic
impossible
refocus