12 - Fresnel Prisms & Aniseikonia

Question 1

What is fresnel Prism? 3

Answer 1

-A “tower” of small, wide prisms
-equally powered prisms and gluing them, one above the other, onto a thin piece of plastic
-1mm thick.

Question 2

What are 6 advantages of Fresnel Prism?

Answer 2

-Very thin
-Extremely lightweight
-Flexible
-Can be applied in house
-Can be cut into any shape
-Reduce magnification differences

Question 3

What are 3 disadvantages of Fresnel Prism?

Answer 3

-Cosmetically different
-Harder to clean
-Slight loss of visual acuity caused by the reflections

Question 4

What are 4 steps to applying Fresnel Prism?

Answer 4

-Check Base direction desired
-Cut the shape to match the lens with base direction in mind
-Peel the backside away
-Using backside of fresnel + warm soapy water adhere fresnel to lens. (Make sure their is no air bubbles).

Question 5

When is fresnel used? 7

Answer 5

-High Prism Amounts
-Temporary prism to test the amount
-Sectional application
-Visual field defects
Prism in bifocal
-Cosemetic improvement(blind/turnt eye)
-Prism Bifocal areas only
-Treatment of nystagmus

Question 6

What is Anisometropia?

Answer 6

Having two eyes have a different refractive power, so there is unequal focus between the two eye,
(slightly different shapes and sizes)

Question 7

What is the relationship between spectacle lenses and anisometropia? 4

Answer 7

even if anisometropia is corrected with specs, problems arent always over
-spec lenses can create difficulties
-spec lenses worn at a distance from the eye will + or - objects viewed
-different lens powers magnify different amounts.

Question 8

What is happening when the two lenses in a pair of glasses are of differing powers?2

Answer 8

The image viewed will not be the same size if the lens are of differing powers.
The brain tries to fuse these images into a single object

Question 9

What is Aniseikonia?

Answer 9

A relative difference in the size/shape of the images seen by the right and the left eyes

Question 10

Name the 6 types of Aniseikonia? (Name the subcategories)

Answer 10

-Physiologic - Natural/Anomalous
-Symmetrical- classic symmetrical/meridional
-Asymmetrical
-Anatomic
-Optical
-Relative spectacle Magnification

Question 11

What is Physiologic Aniseikonia? 2 subcategories

Answer 11

Natural Aniseikonia occurs in all eyes regardless of rx and is dependant on the distance the object is from each eye.

Clinically significant aniseikonia = anomalous

Question 12

What is Symmetrical Aniseikonia? 2 subcategories

Answer 12

-Symmetrical Aniseikonia -1 eye sees an image equally larger in all meridians than the other
-Meridional Aniseikonia - occurs when their is a size difference in a meridian of one eye compared with the other eye (found in any meridian)

Question 13

What is Asymmetrical Aniseikonia?

Answer 13

Progressive increase/decrease across the visual field
Image gets progressively larger across the visual field

Question 14

What is Anatomic Aniseikonia ?

Answer 14

Caused by unequal distrubution of rods and cones in one eye vs the other

Question 15

What is Optical Aniseikonia? 2 subcategories

Answer 15

Inherent optical aniseikonia - aniseikonia because of optics of the eye
Induced Aniseikonia - because of outside source (correcting ophthalmic lenses)

Question 16

What is Relative Spectacle Magnification Aniseikonia? 2

Answer 16

The amount of magnifcation produced by the eye relative to a standard eye.
Compares a corrected ametropic eye with a standard emmetropic eye.

Question 17

How do we determine if it’s present in a px? Step 1

Answer 17

you are concerned but no clear evidence = First Pass Method

Question 18

How do we determine if it’s present in a px? Step 2

Answer 18

Fairly certain A is present, want to address but cant measure it = directionally correct magnification changes to each lens individually.

Question 19

How do we determine if it’s present in a px? Step 3

Answer 19

Estimate percent magnificationdifferences based on refractive prescription and change lens parameters accordingly

Question 20

How do we determine if it’s present in a px? Step 4

Answer 20

Measure the percent magnification differences between the two eyes and change the lens parameters accordingly

Question 21

What is the First Pass Method? 4

Answer 21

-Use a frame with a short vertex distance
-use a framer with a small eye size
-use an aspheric lens design-flattens base curve
-use high-index lens material-thins plus lens center thickness

Question 22

What are the 3 categories Aniseikonia?

Answer 22

-Anisohyperopia - requires hyperopic corrective lenses
-Anisomyopia-requires myopic corrective lenses
-Antimetropia - One eye requires a myopic correction and a hyperopic correction.

Question 23

How do we reduce the effects of Anisohyperopia?
2 then Higher+lower +rx lenses (3 points each)

Answer 23

-small vertex distance
-eyesize small
Higher Plus lens:
-flatten BC
-thin
-decrease vertex distance
Lower Plus lens:
-steepen the BC
-Increase centre thickness(not thicker than high plsu lens)
-move bevel towards the back of the lens, moves lens forward which increases magnifcaiton.

Question 24

How do we reduce the effects of Anisomyopia?
3 then Higher+lower +rx lenses (2 points each)

Answer 24

-small vertex distance
-eyesize small
-avoid BC changes especially if over -2.00D
Higher Minus Lens:
-Move bevel towards front of lens decrease the vertex distance
-If BC needs to be changes the center thickness may need to be thickened
Lower Minus Lens:
-Edge the bevel back (increasing vertex distance)
- Do not thin the lens

Question 25

How do we reduce the effects of Antimetropia? 2 then Plus (3 points) + Minus (2 points)

Answer 25

-small vertex distance
-eyesize small
Plus Lens:
-Flatten the BC
-Thin the lens
-Decrease the vertex distance
Minus Lens:
-Do not thin
-Decrease the vertex distance by moving bevel to front of the lens.