Refraction / Keratometry Flashcards
In myopia, the image forms ______ the retina while in hyperopia, the image forms _____ the retina
myopia - front of retina
hyperopia - behind retina
The emmetropic eye focuses parallel light onto the retina when accommodation is _____
relaxed
In myopia, the power that the eye has has is ____ than what it needs. The discrepancy is ____ and the Rx is ____
In myopia, the power that the eye has has is more than what it needs. The discrepancy is plus and the Rx is minus
In hyperopia, the power that the eye has has is ____ than what it needs. The discrepancy is ____ and the Rx is ____
In hyperopia, the power that the eye has has is less than what it needs. The discrepancy is minus and the Rx is plus
The Rx is always ____ and ____ to the discrepancy
equal and opposite
Pinhole changes the ____ of each blur circle without changing the ____
Pinhole changes the size of each blur circle without changing the defocus (dioptric blur)
Whatever VA the patient has through pinhole, they should see ______ with refraction
at LEAST as well
What is Hofstetter’s formula for accommodation?
15 - 0.25(age)
Amplitude of accomodation peaks at age ___
14
accommodation is always ____
plus or 0
What do the values in B = LOAD stand for?
Blur Lens Object distance Accommodation Discrepancy
Define Fog
too much plus on purpose
What is the purpose of fog?
to relax accommodation
Why do young hyperopes often have perfect vision?
They can accommodate the difference
What are the three clouds of hyperopia?
- Asthenopia at near
- Earlier presbyopia
- Complete dependence on correction later in life
The range of clear vision is measured from the _____ to the _____
near point to the far point
What does beyond infinity mean optometrically?
no matter how far away the object is, the eye is always going to be TOO CLOSE for that eye to see it clearly
the axis of the cylinder corresponds to the principal meridian containing ________
plane power
What is the circle of least confusion?
the dioptric midpoint of the two line foci
What is the sphero equivalent?
the point that coincides with the circle of least confusion
a meridian forms an image of a line ____ to itself
perpendicular
Autorefractors give the ___ no the ___
Rx not the discrepancy
Autorefractors give the Rx in the _____ plane and use ____ to control accommodation
in spectacle plane
use fog to control accommodation
What does a Keratometer measure?
refractive power in the two principal meridians of the cornea
Keratometers provide information regarding _____ not ______
astigmatism, not spherical ametropia
Keratometer is also known as a/n ______
ophthalmometer
What are the applications of the Keratometer?
- Predict total astigmatism
- Contact lens fitting
- Evaluate integrity of cornea
- Calculate Estimated Lens Power before cataract surgery
A steep cornea has a ____ radius of curvature
short
What does with the rule mean?
more power in the vertical meridian
What does against the rule mean?
more power in the horizontal meridian
Oblique astigmatism has an axis that is not within ___ degrees of the 90 or 180 axis
30 degrees
Irregular astigmatism has two principal meridians that are what?
not 90 degrees apart from each other
What is Javal’s Rule?
1.25(corneal astig) + 0.50 AR
The problems with Javal’s Rule is that internal astigmatism is _____, _____ with age, and the 1.25 constant doesn’t take ____ into consideration
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
If there is significant refractive astigmatism, it probably comes from the ______
cornea
What can corneal topography identify? (4 things)
- Keratoconus
- Pellucid marginal degeneration
- Pre and Post LASIK measurements
- Irregular astigmatism
