Fresnel Prisms & Lenses

1mm

how thick are Fresnel prisms?

BO

for cosmesis, if you want to improve an outward eye turn with Fresnel prisms, what base direction do you give?

base L OU

if you want to tx a nystagmus with the slow phase to the right, what Fresnel prism direction do you give?

15-30^ BD

if you want to give a pt that cannot sit up Fresnel prisms, what do you give them?

base R OU

if you want to tx a pt with right homonymous hemianopsia w/ Fresnel prisms, what do you give them?

right angle

the base direction is at ______ to direction of visible lines on a Fresnel prism

thin, lightweight, immediate application to existing lenses, in-house application, sectoral applications, easy to change, reduce mag differences

list some advantages of Fresnel prisms

decreased VA & contrast, poor cosmesis, reflections, harder to clean, distortions

list some disadvantages of Fresnel prisms

chromatic aberrations, distortion, reflections

what are some reasons why there is decreased VA w/ Fresnel prisms?

1. high amounts of prism

2. temporary prism

3. sectoral prism application (muscle palsy, vertical imbalance, horizontal prism at near)

4. VF defects

5. BF only prism

6. cosmetic improvement of blind turning eye

7. tx of nystagmus

8. pt who cannot sit up in bed

9. partial occluder for amblyopia tx

what are some clinical applications of Fresnel prisms?

same

when working w/ homonoymous hemianopia defects, prism is applied in one section of the lens w/ the base direction in the _____ direction of the defect

closer

when a Fresnel prism is applied for a pt w/ a homonymous hemianopia defect, the image appears ______ to the center & is seen w/o moving the head

base to apex in horizontal (lines vertical), BO

how are Eli-Peli’s high powered prism segments oriented?

prism nomograph/rotation guide

kit that assists you in achieving a combined horizontal & vertical deviation by a single prism with its apex in an oblique position, assists in aligning press-on prism on the pt’s lens when rotation is required

Eli Peli’s high powered prism segment

two prism segment areas w/ base-apex in horizontal position placed on the lens of the eye w/ a temporal VF loss, placed base out, creates diplopia

20deg

how much does Eli Peli’s high powered prism segment expand the visual field?

Fresnel lens

similar to a series of concentric prisms, each w/ a slightly higher prismatic effect

projectors, railroad lights, windows, lighthouses

what are some non-spectacle uses of Fresnel lenses?

thin lens, temporary lenses (VT, post-op, unstable refraction in diabetes), swimming goggles, sector application, trial bifocals

what are some clinical applications of Fresnel lenses?

rinse under warm water, use a soft brush to clean the grooves, blot dry w/ a soft cloth, use hard CL cleaning sol

what are some ways to clean Fresnel lenses/prisms?

T

T/F: a disadvantage of a Fresnel prism is that they are more noticed by others because they look different than conventional lenses

F

T/F: a disadvantage of a Fresnel prism is that it is thick & very heavy

high

Fresnel prisms are especially useful for a patient with _______ amount of prism

left

Fresnel prisms are used in the tx of nystagmus. If the examiner sees that movement slows when the person looks to the right, equal amount of prism may be applied to both lenses. The correct base direction would be to the ______

toward

a person w/ homonymous hemianopia should have prism applied to spectacles w/ the base of the prism ______ the defect

nasal, temporal, 24-26mm from the temporal edge of their glasses

you are going to use sectorial prism for homonymous hemianopia. to find the location of the prism, first occlude the eye with the _______ field loss. start moving the card from the _______ side of the patient’s glasses in front of the non-occluded eye. the patient reports seeing the card after you have moved it 29mm. you should then place the apex of the prism ________________

T

T/F: Eli Peli’s high powered prism segments are an alternate method for helping people w/ homonymous hemianopia

therapy

Fresnel lenses can be especially handy during vision _______ or when lens powers may need to be changed frequently

hard

_____ CL cleaning solutions have been used to clean Fresnel optics

towards

Fresnel prisms should be oriented ______ the strabismic eye if using for that

quick

Fresnel prisms should be oriented with the base towards the ______ nystagmus if using for that

down

if a patient needs Fresnel prism because they cannot sit up, what base direction is given?

good eye

Fresnel prisms should be placed over the _______ in amblyopia tx

one on upper & one on lower limbus

where are the Eli-Peli’s high powered segments placed?

temporal

Eli-Peli’s high powered segments are placed on the eye with the _____ VF defect

vertically

if fresnel prisms are to be placed base out, in what direction do the lines appear?

perpendicular to 45 degrees

to mount a fresnel prim at base 45, how should the visible lines be oriented?

F

T/F: VA is better w/ Fresnel prisms than conventional

F

T/F: when high powered Fresnel prims is added to a regular refractive powered carrier lens, there is a decrease in VA, but when conventional prism is ground into a regular refractive powered lens, there is no decrease in VA

yes

are Fresnel prims & lenses reusable

apical scotoma

what defect does a yoked sector prism create?

apical scotoma, diplopia

what defect does a unilateral sector prism create?

allow the viewer to see what is in the central section of the nonseeing area

what is the primary reason for using peripherally placed oblique prism instead of just horizontal prism?

base L OU

if the nystagmus slows when the individual turns their head to the left while still looking straight, how should the Fresnel prism be applied?

back, towards the

Fresnel prims & lenses are applied to the _____ of the lens with the smooth side _____ lens

use running water

what is the best way to physically apply a Fresnel prism to the carrier lens?