Physiological Optics 1.1

Question 1

Indirect vs Direct Ophthalmoscope

• FOV
• Image Type
• Magnification
• Depth of focus

Answer 1

Indirect has larger DEPTH OF FOCUS and FOV
Direct has larger MAGNIFICATION
BIO/Indirect image is real and inverted; Direct image is virtual and upright

Question 2

How to solve for power in a DO

Answer 2

Pt RX + Doc Rx

Question 3

How does a lensometer work?

Answer 3

Move a target so that light from a standard lens converges at the primary focal point of the test lens so parallel light leaves the device

• measures back vertex power
• target moving away = MINUS lens; towards = PLUS lens

Question 4

Lensometry Equation

Answer 4

Back Vertex Power = distance target moves / standard lens focal length ^2
-both in meters

Question 5

Motion seen in hand neutralizaton

Answer 5

Minus Lens: with motion

Plus Lens: against motion

Question 6

How does a radiuscope work

Answer 6

Forms two clear images- one at the surface of the lens and one at the CENTER of curvature. The distance b/t these two is the base curve/RADIUS of curvature

Question 7

How does a keratometer work

Answer 7

Provides the radius of curvature of the cornea by measuring the size of the reflected image (K acts as a mirror)

Question 8

What does a lens clock measure and how can you adjust it’s measurement for different n

Answer 8

Sag

Power = [(goal - 1) / (calibrated - 1)] x False Power

Question 9

Power in a Hruby lens and image formed

Answer 9

-55D, magnified, upright

Question 10

Components of a slit lamp

Answer 10

Keplerian telescope eye piece
Inverting prism and objective lens (add) for Keplerian telescope
Galilean telescope for magnification

Question 11

Equation for magnification through a fundus lens

Answer 11

Creates a telescope so M = - F (eye) / F (lens)

• more power in lens gives less mag and bigger FOV
• Equation indicates minification but overall magnification is seen due to the slit lamp optics

Question 12

ANSI: Sphere tolerance

Answer 12

0. 13D

- if its more than +/- 6.50D then 2% of sph. power

Question 13

ANSI: Cylinder tolerance

Answer 13

0.13 for < 2.00
0.15 for 2.00 - 4.50
4% of cyl for > 4.50

Question 14

ANSI: Axis tolerance

Answer 14

14 for 0.25 
7 for 0.50
5 for 0.75
3 for 1.50 
2 for more than 1.50
(all are for the range below value until next threshold)

Question 15

ANSI: Prism tolerance

Answer 15

VERTICAL: 0.33 PD for sphere power < 3.375
HORIZONTAL: 0.67 PD for sphere power < 2.75

Question 16

ANSI: Thickness

Answer 16

0.3mm

Question 17

ANSI: warpage

Answer 17

1.00D

Question 18

ANSI: Base Curve

Answer 18

0.75D

Question 19

ANSI: Impact Resistance

Answer 19

Resists 5/8 in. steel ball dropped from 50 in.

Question 20

ANSI: Safety Standards for Impact

Answer 20

High Mass: 500g dropped from 50 in.

High Velocity: steel ball 0.25 in. fired at 150 ft/sec.

Question 21

ANSI: requirements for safety eyewear

Answer 21

Organized by HAZARD type
Minimum coverage: ellipse of 40mm by 33mm on geometric center (34 x 28 for small head with “H” marking)
Markings: manufacturer logo, + (impact rating), Z87-2

Question 22

Toric lens form

Answer 22

one toric surface and one sphere surface

Question 23

Equiconcave/Equiconvex

Answer 23

Both sides are equally convex/concave thus providing 1/2 total power of the lens

Question 24

Label the curves on a typical minus cylinder lens

-What is different in plus cyl

Answer 24

Front is Base curve, on the back is the flatter Toric BC and steeper cross curve
-In a plus cyl lens base curve is the flatter curve on the front with cross curve being the steeper, the curve on the back called the sphere curve