Homework Help

[keagles2]

I AM PREPARING TO SIT FOR MY WRITTEN AND BOARDS THIS NOV. AND DEC.
I AM HAVING A HARD TIME INTIGRATING CHAPTERS 17 AND 18 OF THE BROOKS AND BORISH 2ND EDITION. IS THERE ANY ONE AVAILABLE TO POSSIBLY MEET AND STUDY WITH OR IS ANYONE SIGHNED UP TO YAHOO?:) ANY HELP WOULD BE APPRECIATED. EXAMPLE QUESTION IS AS FOLLOWS:IF A PT W/ AN RX OF +11.00 WERE GIVEN THIS RX AT 13 MM VERTEX BUT FITTED FOR A FRAME W/ A 19 MM VERTEX WHAT WOULD THE CORRECTED RX BE? HOW WAS THIS ACHIEVED?
I HAVE MANAGED TO MAKE IT THROUGH THE FIRST 2 SEMESTERS AND THIS IS THE LAST SEMESTER.

[Alvaro Cordova]

This problem shouldn't be too hard.
You should know what direction you are going in. In this case the glasses (19) are further than the Rx was taken at (13). Which is a difference of 6mm or 0.006 meters.

Plus lenses are effectively stronger the further away from the patient's eye it gets. So to compensate for this, you must make the lens weaker.

1 / Diopter = Focal Length
1 / +11.00 = 0.0909 meters

A larger focal length means weaker lenses. So we want to add the difference we got in exam vs. fitting to the lens power

0.0909 + 0.006 = 0.0969

1 / FL = Diopter
1 / 0.0969 = 10.3199 which would round up to +10.37 in 1/8ths

remeber the opposite is true of minus lenses. If minus lenses are fit further than the exam length, than the lens is effectively weaker and so must be made stronger to compensate for this.

Rules of thumb:
Lenses fit closer than exam
+ Lenses must be made stronger because they get weaker
- Lenses must be made weaker because they get stronger

Lenses fit further than exam
+ Lenses must be made weaker because they get stronger
- Lenses must be made stronger because they get weaker

[keagles2]

THANK YOU FOR THE SPEEDY REPLY.I UNDERSTAND THE COMMENSURATE DESIGN OF THE QUESTION, HOWEVER I DID NOT HAVE ALGEBRA WHEN I WENT TO SCHOOL SO I AM RELYING SOLEY ON BOOKS ! AN ABSOLUTE NO FUNNY HAHA

[Alvaro Cordova]

yeah, a little algebra would be good to have under your belt. Did you understand the solution? If not, let me know.