ophthalmics

Question 1

Major Reference Point adjustment with pantoscopic tilt

Answer 1

2-for-1 rule: 2 degree pantoscopic tilt, move MRP down 1 mm

Question 2

bifocal type vs image jump or OC

Answer 2

FT 22 to 28 = 5mm below segment line
FT 35, Curved top, Panoptik, Ribbon = 4.5mm
Executive (Franklin), FT 40, FT 45 = 0 image jump, OC on segment line
Round = divide by 2 (ex. Round 22mm = 11mm image jump)

Question 3

segment height adjustment with prism

Answer 3

every 1 pd change = 0.3mm adjustment of seg height in direction of APEX

BU = subtract the change to original segment height
BD = add the change to original seg height

Question 4

write bifocal add Rx

Answer 4

Distance: +3.25 -1.00 x180;
Add = +2D
Near segment; +5.25 -1.00 x180

Question 5

Intermediate segment add

Answer 5

Add/2

Question 6

Intermediate power (with lensometry)

Answer 6

Add/2 + (distance sphere)

Question 7

Lens power equation with radius (r1, r2)

Answer 7

F = (n - 1) [(1/r1) - (1/r2)]
n = lens material

Question 8

Effective power

Answer 8

F/ 1 - dF

CAP = closer add plus = farther remove plus

Question 9

spectacles to contacts (Plus power)

Answer 9

more power

Question 10

spectacles to contacts (minus power)

Answer 10

Less power

Question 11

30-45-60 rule for estimating cyl power

Answer 11

30 deg -> 25% of cyl power
45 deg -> 50% of cyl power
60 deg -> 75% of cyl power

*Take the cyl power calculated and add that to the original sphere for answer

Question 12

F = (-)n/f

Answer 12

negative if location of the object or image is in front of the lens

Question 13

Vergence equation

Answer 13

L’ = L + F

Question 14

real object, minus lens

Answer 14

image is in front of lens so L’ = negative
ex. real object at 50cm away from -4D. how far from lens is image pt?
L’ = L + F -> 1/-0.50m + (-4) = -6D
l’ = n/L’ -> 1/-6 = -16.67cm in frotn of lens is where image is located

Question 15

Transpose Rx

Answer 15

• 2.00 -2.00 x180 can be written as:
• 2.00 @ 180, -4.00 @ 090
• 2.00 x090, -4.00 x 180

Question 16

finding cyl using 30-45-60 rule

Answer 16

what is the power of a pl. +2.00 x 030 cylinder in the 180 deg meridian?
30 deg -> 0.25 * +2 = +0.50D -> +0.50 + distance sphere (plano) = +0.50D

Question 17

Base Curve Facts to remember

Answer 17

BC ALWAYS at front surface–no matter what
Minus cyl form: BC is front sphere
Plus cyl form: BC is weakest, flattest pwr
Ex. +8D at 180, +6D at 090 -> BC is +6D
BC is always OPPOSITE from where CYLINDER is

Question 18

Measure with Lens clock

Answer 18

F(lens) = F(lens clock) x [(n lens - 1)/ (n lens clock - 1)]

Question 19

Lens clock features

Answer 19

if lens clock is 1.53 n then BC is exactly what the reading is
BC cannot be measured with lens clock for contacgts
only measures CL thickness with lens clock