Keratometry

Question 1

gullstrand eye

Answer 1

2 lens optical system

Question 2

what is the rough average of all the RIs of the components of the eye?

Answer 2

about 1.33

Question 3

What is the optical power of the first surface of the cornea?

Answer 3

+48.83D

Question 4

What does keratometry measure?

Answer 4

the anterior surface of the cornea

-radius of the different meridians

Question 5

what is the radius of curvature of the cornea?

Answer 5

7.7mm

Question 6

radius of curvature

Answer 6

• units: m
• larger the radius, smaller the curvature
• same algebraic sign as curvature

Question 7

curvature

Answer 7

• diopters
• larger the curvature, smaller the radius
• same algebraic sign as radius

Question 8

What is the largest contributor to ocular optical power?

Answer 8

cornea, mainly attributed to the anterior surface of curvature

Question 9

What is there power of an emmetropic eye?

Answer 9

60D

Question 10

astigmatism

Answer 10

• no point imaging
• distinct meridians with more and less power
• not spherical, shaped like a watermelon

Question 11

sturm conoid

Answer 11

• circle of least confusion

- directly related to 2 different radius of curvatures along two different principal meridians

Question 12

With the rule astigmatism

Answer 12

steeper vertical

Question 13

against the rule astigmatism

Answer 13

steeper on horizontal

can shift with age

Question 14

is the cornea a mirror?

Answer 14

yes, it also reflects

Question 15

What is the light actually reflecting off of on the cornea?

Answer 15

the tear film

Question 16

image from the cornea as a mirror

Answer 16

virtual, upright, demagnified

Question 17

What kind of mirror is the cornea?

Answer 17

convex mirror

Question 18

the smaller then radius of curvature…

Answer 18

the larger the curvature, the smaller the image

Question 19

different types of keratometers

Answer 19

• the fixed doubling technique
• javal-schiotz keratometer
• ziess
• baush + Lomb

Question 20

@180: radius of curvature 7.8mm, Power 43.25 D,

@90: radius of curvature 7.8mm, power 43.25 D

Answer 20

the cornea is spherical because the powers are equal at different meridians

Question 21

@180: radius of curvature 7.8mm, Power 43.25 D,

@90: radius of curvature 7.6mm, power 44.50 D

Answer 21

WTR astig, steeper meridian is vertical

Question 22

@180: radius of curvature 7.8mm, Power 43.25 D,

@90: radius of curvature 8.2mm, power 41.15 D

Answer 22

ATR astig, steeper meridian in the horizontal

Question 23

keratometry limitations

Answer 23

• primary data taken from 4 points on the center 3mm
• assumes a lot. paraxial app only, low order aberrations only
• assumes rotationally symmetric cornea (spherocylindrical)
• assumes some symmetry, such as corneal apex, visual axis, and the axis of the instrument to coincide
• assumes normal astig
• keratocones may be challenging
• cannot measure asphericity
• tear film

Question 24

keratometry vs topography

Answer 24

topography is present and future

Question 25

topography

Answer 25

- multitude of info such as CL - applicable to any corneal abnormality - curvature and optical power on any meridian we select. not limited to just two - easy to use

Question 26

keratometry in comparison to topography

Answer 26

- measurement only at 3mm - curvature and optical power only for two meridians - manual alignment

Question 27

topography features

Answer 27

- still subject to tear film stability - Dx tool for corneal abnormalities - learning curve-a multitude of info needs to assessed and evaluated - high precision measurement of distribution of corneal curvature

Question 28

why is topo an indispensable tool for dr

Answer 28

- indispensable in planning and f/u in laser vision correction - helps select a CL - can monitor and document changes in corneal surface - can measure peripheral as well!

Question 29

placido topo

Answer 29

- lasted till early 90s - projects concentric rings on the cornea and records digitally the mires - auromated computer based data processing

Question 30

if the mires are closer together...

Answer 30

steeper cornea

Question 31

if the mires are spread out

Answer 31

flatter cornea

Question 32

if the mires look elongated

Answer 32

astig

Question 33

if the mires look wavy in weird spots

Answer 33

irregular astig probably

Question 34

curvature map green

Answer 34

good

Question 35

keratometric equation

Answer 35

RxP=337.5

Question 36

corneal asphericity reading

Answer 36

good for fitting CL

Question 37

elevation/altimetric map

Answer 37

essential for surgery | measured in microns

Question 38

simulated abberometry

Answer 38

dependent on pupil size

Question 39

color at the edge of healthy cornea

Answer 39

blue

Question 40

corneal asphericity

Answer 40

- not exactly sphere | - helps compensate spherical aberration

Question 41

what would cause a flatter central cornea?

Answer 41

abnormalities or surgery