3 Chapter 3: The Flow of Refraction

3A. General Flow of Refraction

[1.] Background 

When we consider the overall possible lens combinations that make up a final prescription, there are tens of thousands of possible options.  It is foolhardy and impracticable to try each possible combination on each patient.  Over the past 100 years, methods have been developed to shorten the time it takes to determine a final glasses or contact lens prescription.  There are multiple methods of refraction (we will get into alternative methods later in the course), but all follow some variant of this general flow.  The over arching point to the flow is to take all the possible lens conditions, distill it down to a few options, and then test those options while controlling accommodation to reach best visual acuity. 

[2.] The overall flow of refraction 

[3.] Modify, Remove, and/or Add Steps Based upon the patient, the findings, and the chief complaint.

These steps are there for the worse case condition that walks into an office 1-2 times a week.  That condition is a patient with significant prescription but has lost their glasses and you have no other information.  The majority of patients coming into your office will have a more focused refraction that does not require all the steps needed in refraction.

A simple example is a 20 year old coming in for glasses.  They are NOT presbyopic, so it would be silly to measure them for an add.

Another straight forward example, during the JCC test, you change neither the power nor the axis.  Due to this, the second MPMVA is completely redundant.

For the purposes of most of this class, we will expect you to run through all steps of this flow chart to prove you understand how to perform the tests.  Having said that, always keep in mind when and where each step is needed.

[4.] Astigmatism Steps

The JCC astigmatism step has 3 potential steps depending upon the situation.  The are the following:

1. Axis Check – to find the correct axis

2. Power Check – to find the correct power

3. Probe for Astigmatism – to find astigmatism (also caused elicit cylinder)

See the figure below to help understand when and where to apply them.  

Axis check is always performed FIRST in all situations if astigmatism is found in the starting lens over 0.50 D.  If it is less than 0.50 D, there is a significant chance that the astigmatism is not there.  In the case of low astigmatism, first perform a power check to confirm the presence of astigmatism.  If it is there, proceed to the axis check.  If it is not there, the JCC test is complete.  

The final situation is eliciting or probing for cylinder.  This is performed when there is NO astigmatism in the starting lens but you suspect there is based upon acuities and chief complaint.  In that case, you will probe for astigmatism and then start the axis check if astigmatism is found.