Refraction / Keratometry Flashcards Preview

PPO Final 1 > Refraction / Keratometry > Flashcards

Flashcards in Refraction / Keratometry Deck (36)
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1
Q

In myopia, the image forms ______ the retina while in hyperopia, the image forms _____ the retina

A

myopia - front of retina

hyperopia - behind retina

2
Q

The emmetropic eye focuses parallel light onto the retina when accommodation is _____

A

relaxed

3
Q

In myopia, the power that the eye has has is ____ than what it needs. The discrepancy is ____ and the Rx is ____

A

In myopia, the power that the eye has has is more than what it needs. The discrepancy is plus and the Rx is minus

4
Q

In hyperopia, the power that the eye has has is ____ than what it needs. The discrepancy is ____ and the Rx is ____

A

In hyperopia, the power that the eye has has is less than what it needs. The discrepancy is minus and the Rx is plus

5
Q

The Rx is always ____ and ____ to the discrepancy

A

equal and opposite

6
Q

Pinhole changes the ____ of each blur circle without changing the ____

A

Pinhole changes the size of each blur circle without changing the defocus (dioptric blur)

7
Q

Whatever VA the patient has through pinhole, they should see ______ with refraction

A

at LEAST as well

8
Q

What is Hofstetter’s formula for accommodation?

A

15 - 0.25(age)

9
Q

Amplitude of accomodation peaks at age ___

A

14

10
Q

accommodation is always ____

A

plus or 0

11
Q

What do the values in B = LOAD stand for?

A
Blur
Lens
Object distance
Accommodation
Discrepancy
12
Q

Define Fog

A

too much plus on purpose

13
Q

What is the purpose of fog?

A

to relax accommodation

14
Q

Why do young hyperopes often have perfect vision?

A

They can accommodate the difference

15
Q

What are the three clouds of hyperopia?

A
  1. Asthenopia at near
  2. Earlier presbyopia
  3. Complete dependence on correction later in life
16
Q

The range of clear vision is measured from the _____ to the _____

A

near point to the far point

17
Q

What does beyond infinity mean optometrically?

A

no matter how far away the object is, the eye is always going to be TOO CLOSE for that eye to see it clearly

18
Q

the axis of the cylinder corresponds to the principal meridian containing ________

A

plane power

19
Q

What is the circle of least confusion?

A

the dioptric midpoint of the two line foci

20
Q

What is the sphero equivalent?

A

the point that coincides with the circle of least confusion

21
Q

a meridian forms an image of a line ____ to itself

A

perpendicular

22
Q

Autorefractors give the ___ no the ___

A

Rx not the discrepancy

23
Q

Autorefractors give the Rx in the _____ plane and use ____ to control accommodation

A

in spectacle plane

use fog to control accommodation

24
Q

What does a Keratometer measure?

A

refractive power in the two principal meridians of the cornea

25
Q

Keratometers provide information regarding _____ not ______

A

astigmatism, not spherical ametropia

26
Q

Keratometer is also known as a/n ______

A

ophthalmometer

27
Q

What are the applications of the Keratometer?

A
  1. Predict total astigmatism
  2. Contact lens fitting
  3. Evaluate integrity of cornea
  4. Calculate Estimated Lens Power before cataract surgery
28
Q

A steep cornea has a ____ radius of curvature

A

short

29
Q

What does with the rule mean?

A

more power in the vertical meridian

30
Q

What does against the rule mean?

A

more power in the horizontal meridian

31
Q

Oblique astigmatism has an axis that is not within ___ degrees of the 90 or 180 axis

A

30 degrees

32
Q

Irregular astigmatism has two principal meridians that are what?

A

not 90 degrees apart from each other

33
Q

What is Javal’s Rule?

A

1.25(corneal astig) + 0.50 AR

34
Q

The problems with Javal’s Rule is that internal astigmatism is _____, _____ with age, and the 1.25 constant doesn’t take ____ into consideration

A

The problems with Javal’s Rule is that internal astigmatism is variable, increases with age, and the 1.25 constant doesn’t take ametropia into consideration

35
Q

If there is significant refractive astigmatism, it probably comes from the ______

A

cornea

36
Q

What can corneal topography identify? (4 things)

A
  1. Keratoconus
  2. Pellucid marginal degeneration
  3. Pre and Post LASIK measurements
  4. Irregular astigmatism