Vertical imbalance

Question 1

Anisometropia

Answer 1

-Imbalance in RX between OD and OS (could be + or -)
-Generally 1.5D or more in difference
-Can lead to amblyopia in children if undetected bc the brain will suppres the vision in the most blurry eye

Question 2

verticle imbalancec in the lensometer

Answer 2

-unwanted difference in OC when verifying the RX from OD to OS (without moving the table)

Question 3

vertical imbalance on the px

Answer 3

-when gaze drops below the optical center in lenses that are unequal value, particularly in an rx difference of 1.5D or more

Question 4

how does undesried prism occur?

Answer 4

-nothing being stiupulated on the rx
-caused by a lab error on the vertical line only
-a large difference in the RX between both eyes

Question 5

vertical imbalance can cause??

Answer 5

-headaches
-eyestrain
-diplopia
-dissatisfication w. eyewear

Question 6

ways to avoid vertical imbalance

Answer 6

-contact lenses (OC moves w their eyes)
-two pairs of glasses (distance and near)

Question 7

correcting vertical imbalance

Answer 7

-lowering the MRP height or OC
-raising the segment height
-dissimilar segs
-fresnel press on prism
-slab off

Question 8

Dissimilar segs

Answer 8

can correct for VI by using the prism induced by the segment and choosing 2 different styles-Round, ST28 or ST35. The seg OC will be diff for each style. The seg with the highest OC is placed on the most minus or least plus power lens

Question 9

Fresnel press on prism

Answer 9

-Cut to fit the lower half only. They are made of thin transparent flexible plastic that is cut and adhered to the back surface of the lens.
Not a permanent solution but a trial

Question 10

Slab off

Answer 10

-Most commonly used option by producing vertical prismatic effect to the lower half of 1 eye only
-placed on the most minus least plus powered rx
-it is visible on the lens
-hard to use w less than 1.5D of power
-biggest advantage is that it can be used for large amounts of necessary prism, splitting between the two lenses if necessary.

Question 11

slab of for progressives

Answer 11

calculated from the prism reference point - not the fitting cross

Question 12

prentices rule

Answer 12

P=cF
P= prism
C= decentration (cm)
F= power

Question 13

when calculating for vertical prism and the RX has an axis of 180 what do u do ?

Answer 13

we would need to transpose in order to get it to vertical because we are dealing with decentration being up or down

Question 14

direction of prism when the lens is decentered (way to remember it)

Answer 14

-Any minus lens the direction will be opposite from decentration
-plus lens the direction of decentration will be the same direction.