Midterm II Flashcards
When are refractive errors considered as combinations of refractive and axial issues?
When are refractive errors considered as almost completely axial in nature?
> +/-4.00D
What is the dioptric difference between the far and near points of accommodation called?
amplitude of accommodation
Is the amplitude of accommodation underestimated or overestimated for a hyperope?
underestimated
When hyperopes wear contact lenses do they accommodate more or less than without?
less
Is the amplitude of accommodation underestimated or overestimated for a myope?
overestimated
Will myopes or hyperopes require presbyopic correction earlier?
hyperopes
Does an aphakic patient have an increased of decreased peripheral field of view? 1. macular FOV? 2
- decreased
2. decreased
When hyperopes wear contact lenses do they accommodate more or less than without?
less
What happens to the scotoma size for each of the following:
- increase lens power
- inc vertex distance
- inc lens size
- dec pupils size
- inc lens thickness
- inc base curve
- increase scotoma size
- dec scotoma size
- inc scotoma size
- inc scotoma size
- inc scotoma size
- inc scotoma size
What is the field of view for the moving eye, subtended at the center of rotation?
macular field of view
What is larger, the macular field of view or the peripheral field of view?
peripheral field of view
What is the prismatic effect that a high plus lens creates, having an angular gap in object space completely around the lens?
ring scotoma
What is the work eyes will have to do to see a single image (demand for fusional vergence)?
phoria
What kind of distortion do aphakic spectacle wearers experience?
pincushion distortion
What kind of distortion do high myopic spectacle wearers experience?
barrel distortion
What are methods to increase the field of view for an aphakic patient?
- dec vertex distance
2. inc lens size
What are the lenses designed to create a “bullseye” appearance and reduce cosmetic issues of aphakic lenses?
lenticular lenses
What is the work eyes will have to do to see a single image?
phoria
For aphakic patients, what is the movement necessary for each degree of pantoscopic tilt?
lower frame 0.5mm
For normal patients glasses, what is the movement necessary for each degree of pantoscopic tilt?
lower OC 0.5mm
What are methods to increase the field of view for an aphakic patient?
- dec vertex distance
2. inc lens size
How will unilateral aphakia patients achieve binocular vision with spectacle lenses?
not possible
What are ways to reduce minification in high myopes?
- dec vertex distance
2. fit CL
Which have larger retinal image sizes: refractive myopes or refractive hyperopes?
both the same
What lenticular lens is a small concave disk ground on the back surface of plano lenses called?
myodisc
What are methods to minimize edge reflections?
- edge coating
- edge painting
- semitransparent edge
- buffing edge
- tinting lens
- hide-a-bevel
What is the retinal image size directly proportional to?
- angle that the incident chief ray makes with optic axis
2. axial length of eye
What is the comparison of the size of the retinal image of the eye, with the correcting lens, to the size of the retinal image of the emmetropic eye?
relative spectacle magnification
What are each of the following labels for spectacle frame measurements:
- A
- B
- GC
- DBC
- DBL
- ED
- eye size, horizontal size
- vertical size
- geometric center
- distance between centers, frame PD
- distance between lenses, bridge size
- effective diameter
Which have larger retinal image sizes: corrected axial myopes or corrected axial hyperopes (assuming both at the primary focal plane)?
both the same
What is the equation for the minimum blank size?
MBS = ED+2(decentration)
What impacts the spectacle magnification?
- the power
2. the shape (form) of the lens
What is the comparison of the size of the retinal image of the eye, with the correcting lens, to the size of the retinal image of the emmetropic eye?
relative spectacle magnification
What does the frame PD equal?
DBC or A+DBL
What is the rule that states the prismatic effect at any point on a spherical lens is equal to the distance off the point from the pole of the lens (in cm) multiplied by the power of the lens?
Prentice’s Rule
What is the standard rule for obliquely crossed prisms? 1. What must be true for this to work? 2
- same base: add prisms; opposite base: subtract prisms
2. monocular
Where is light deviated towards in regard to the base of the prism?
to the base
What is one prism diopter equal to in terms of displacement at a certain distance?
1 cm at a distance of 1 m
Where is an image shifted to in terms of the base of the prism?
shifted towards apex
When are PRP and OC not the same?
prism present
What is the location on the lens where the desired prismatic effect should be verified?
prism reference point
What point on the lens should always be located directly in front of the patients pupils when looking in primary gaze?
PRP
What is the amount and direction of the displacement of the pole of the lens from the geometric center of the lens box?
decentration
What kind of prism would be used to fix an eso? 1. An exo? 2. A hyper? 3
- BO prism
- BI prism
- BD in front of hyper eye
When are PRP and OC not the same?
prism present
What happens to the prismatic effect as the vertex distance increases? 1. What distance of objects does this apply to? 2
- decreases
2. near objects
What type of lenses require more rotation to see in the periphery?
plus lenses
How great is the convergence demand for myopes in glasses compared to contacts?
decrease demand in glasses
What are the two methods to create prism?
- grinding
2. decentration
What are a series of identical small prisms lying adjacent to each other on a thin base called?
Fresnel prisms
What are the benefits of Fresnel prisms?
- thin
- lightweight
- in-office application
- easily changable
What are the disadvantages of Fresnel prisms?
- dec VA
- dec contrast
- striated appearance
What are the effects of excessive base down prism?
- floor and other horizontal expanse to seem concave
- people and vertical objects seem taller
- patient feels like walking uphill
What are the effects of excessive base up prism?
- floor and other horizontal expanse to seem convex
- people and vertical objects seem shorter
- patient feels like walking downhill
