Can U help on ABO questions?

[Lizzy D]

I am studing for my abo and not sure how to figure out the math on some of these questions. Is it possible to get help on this site?

[OPTIDONN]

Sure we can help but there is very little math on the ABO.

[GOS_Queen]

I am studing for my abo and not sure how to figure out the math on some of these questions. Is it possible to get help on this site?

Maybe if you post a specific question, we can help work it out :bbg:

[Lizzy D]

I really do not understand how to figure out the ones they ask. I have never worked in a lab as far as prisms and vertical imbalance and how to figure them out?? Like this one..

A lens which reads +2.00 +2.00 X 180 is decentered to much resulting in a PD which is 5 mm narrow. How much prism and what base direction is experienced by the wearer???

When verifying and add with a lens clock a +2.75 ADD would clock _______ in distance and _________ in segment....


I already have the answers I just want to know how to get the answers.. Not cheating just want to understand this and not have to take a quess at the answers.

Thank you so much..

Liz

[lensgrinder]

To find out the amount of prism, you use Prentice's Rule:

P = c X d

P is prism
c amount from OC in cm
d power

When dealing with PD use the power in the 180^th meridian which in this case is +2.00 and you know it is 5mm or 0.5 cm off.

P = 0.5 X 2.00
P = 1^ of prism

You know the PD is narrow so the base of a plus lens would be in. Look at the attachment.

1^ BI

A +2.75 add will clock 2.75 greater than the base of a lens. For example if the base is 6.00 and your add is 2.75 you will get 8.75 in the segment.

You may want to purchase a copy of "Optical Formulas Tutorial" by Stoner, Perkins, Furguson. It will help you to get a better understanding of the math principles.

[Audiyoda]

As I recall - and someone who's taken the ABO more recently may have better insight - but the ABO had all the mathematical formulas in the back of the exam booklet when I took it oh so many years ago. Of all of them the only one that came up on my exam was Prentice's Rule.

[HarryChiling]

Prentice's Rule was the only one I remember on the test. A simpler version to remember is:

Prism = (Dec * Power)/10

The divided by 10 part is so that you can work in mm instead of converting it to cm. I would brush up on the metric though, I seem to remember a few questions that had to be turned to mm or cm to work the problem out (that should be simple). I remember a few questions on pantascopic tilt, and a few question asking which way to adjust a temple if a particular side was out of alignment, I seem to remember a few decentration questions, know the speed of light.