Spectacle Magnification and Unequal Refractive Errors Flashcards
What does the prefix “a” or “an” indicate?
Not, or without
What does the prefix “iso” indicate?
equal
A wildly fluctuating refraction is frequently caused by what?
Diabetes
Vertical imbalances are caused by anisometropia in which meridian?
90th
The problem of unequal retinal image sizes is called what?
aniseikonia
If the optical center of a minus lens is moved nasally, it creates prism whose base is in which direction?
Out
If the rx is OU +3.00 sphere, and both eyes deviate 10mm upward, what is the prismatic effect at that point?
Zero - there is no prismatic effect
In the rx pl +2.00 x180, what is the total power in the 30th meridian? Remember the Percentage Cylinder Power chart!
+0.50
In the rx -3.00 -3.00 x090, what is the total power in the 30th meridian? Remember the Percentage Cylinder Power chart!
-4.50
One of the common problems experienced by anisometropic spectacle wearers is what?
motility/diplopia
Anisometropia is almost always a problem with which type of patient?
Presbyope
Bicentric grinding (slab-off) in bifocals result in prism. Which direction does this prism go?
Base up
Slab-off should not be ordered for imbalance under what dioptric power?
1.5
Slab-off can be measured by using what device?
Lens clock
Slab-off is placed in which lens?
Most minus, least plus
In selecting frames for anisometropic presbyopic patients, what parameter should be followed? Symmetrical lens, small eye size, proper centration
All of these shapes
For large increments of rx change, increasing the power in gradual, temporary steps may be more economically feasible by using what?
Fresnel lenses
Anisometropic symptoms may include all of the following except for what? Headaches, pulling and drawing sensations, increased intraocular pressure, burning and itching
Increased intraocular pressure
The preferred method of prismatic compensation for patients who cannot tolerate looking below the optical centers is what?
Slab-off
The uncorrected anisometrope will generally learn to adjust by doing what?
Dropping the head to read
The following rx is an indication of what type of disorder?
OD: -5.00 -1.00 x180
OS: +2.00 -1.00 x180
Antimetropia
The following rx is an indication of what type of disorder?
OD: +5.00 -1.00 x180
OS: +2.00 -1.00 x180
Anisometropia
What is the name of the condition whereby two unequal images are sent by the eyes to the brain?
Aniseikonia. It can be sub-divided into two different conditions: Antimetropia, where one eye is myopic and the other eye is hyperopic; and Anisometropia, where both eyes are either myopic or hyperopic but there is a sizable difference in prescription.
What variables are used to produce iseikonic lenses?
base curve, center thickness, index of refraction, vertex distance
Left uncorrected, aniseikonia may result in what condition?
Amblyopia, or lazy eye
As a plus lens is moved further away from the eye, the effect on magnification is what?
Magnification increases
As a minus lens is moved further away from the eye, the effect on magnification is what?
Magnification increases
As a rule of thumb, differences in magnification over ___ from eye to eye are usually problematic to the wearer.
5%
In addition to magnification/minification problems, a wearer with unequal refractive errors may experience what visual disturbance?
Vertical imbalance
Correction for visual imbalance could include all of the following except: Slab-off, two pairs of eyewear, aniseikonic lenses, or dissimilar segments
Aniseikonic lenses
