Tutorial: Optics for Optometric Instrumentation

Please answer this tutorial question;

How does the focimeter works in determining power of ophthalmic lenses? Please explain it in point form.

Due date: 12/ June/ 2011

Prismatic Effect Calculation

Assalamualaikum and Very Afternoon to all readers,

For 2nd year students, do you still remember the rule how to determine Prismatic Effect (base up, down, in out) that I've been taught in class last week. InsyaAllah, I'll share it the rule using video post with all of the readers in next time.

How to calculate the prismatic effect amount induced by decentration??? The formula is very simple.

P (prism power)=c (decentration, in cm, not in mm) x F (focal power, D)

Simple, right...most of us have difficulty to determine which base will be induced by the decentration (c- in, out, up, down) and focal power (F- plus, minus)...by using my rule, InsyaAllah it will be easier to determine it. As I said before, the video is under construction but I've explain it in 2nd year class..Thus, in this post I would to give a tutorial to all 2nd year regarding this topic.

Question: Calculate prismatic effect if the decentration and focal power as follow; 

Rules of Transposition

Do you know that we have simple rules to transpose minus (-ve negative) cylinder form to plus (+ve positive) cylinder form and vice versa? Just follow these rules below, InsyaAllah, you will always obtain a correct answer.

Rules of transposition

1.Add the sph and cyl, taking into account their sign

2.Change their sign of the cyl

3.Alter the axis by 90°

  a. if the original axis is 90° or less, add 90° to it

  b. if the original axis is over 90°, subtract 90° from it

Movement of Retinosope Reflex

There are two ways to explain how does movement of retinoscope reflex happens. 1) aerial image-blurred image orientation/ position on retinoscopist's retina, 2) Secondary Source-Far point location , MR. Always remember 1) the aerial image will be located either in front of or at  behind examiner's eye, and 2) the Far point, MR will be located either in front of or at  behind patient's eye.