? + 2.00X180.

The ? of course is the sphere power, but that is easy enough to find with “better one, or two”. Of course you will also need to confirm and refine the cylinder power and axis.

If you have an autorefractor that is also an auto-keratometer, I recommend that you always use it in the combined mode. That way you can use the autoK to double-check the auto-refraction readings. A discrepancy may mean there is a problem with the optical media of the eye.

I have found auto-K readings to be generally accurate with a healthy cornea. If you have a choice, always buy an auto-refractor that has autoK.

The disadvantage of keratometry is that it is an extra step, and it may require moving the patient to a keratometer.


Current or old glasses

This is a much used starting point for refractometry. After all, you probably won’t find much refractive change if the patient is seeing 20/20 with his current glasses Rx, and many people have little change in their cylinder and axis over the years.

You can, however, get into trouble with this starting point if the patient has a cataract, or has had eye surgery within the past year. In these cases, I like to have more information than just the current glasses Rx, even if the patient is seeing well. Many times the patient will see just as well, or better, with a reduced cylinder correction that is revealed by the auto-refractor, keratometer, or retinoscopy.

Adjust the leveling knob so that the bubble on the level aligns with the dot. With the phoropter level you will be able to tell if your patient is level. If not, try to get her to cock her head to a level position. This is important for cylinder axis orientation. A patient may not physically be able to level her head. In this case adjust the phoropter at an angle to match the angle of her face.  This means that the bubble will not be level, but as long as the phoropter is aligned with the angle of the head tilt, you will still get an accurate axis reading.

Next, adjust the forehead rest and the forward tilt of the patient’s head so that the eyelids are not touching the back of the phoropter. This is very important.

Any pressure on the eyeballs from the lids pressing against the case will change your refraction, then the poor optician will have to push the eyeglasses against the patient’s face to duplicate the effect.

Make sure the patient is squarely facing the eye chart. You may have to move behind the patient and the phoropter to view the chart from the patient’s angle.

Of course, if you were performing manual retinoscopy,  this is where you would begin, but we will assume that this has already been done, or you are using other information.

Just before starting refractometry, check to see that the auxiliary lens wheel is set to “open” on the eye that you are checking, and “occlude” on the opposite eye. It’s frustrating to go through all the steps of refractometry and discover that both eyes were “open” all the while, because you will have to begin again unless the vision is poor in the opposite eye.

While performing refractometry, periodically check that your patient has not been sinking down under the phoropter. This is common with the older folks. They usually don’t realize what is happening. A minute ago they were seeing 20/30 and now they can’t see anything, and it’s your fault. A quick adjustment will get them seeing through the eye ports again.  Pictured below: that sinking feeling.

Pay attention to details. It will pay off in accuracy and efficiency.
 

Better One, or, Better Two (Testing Procedures)


If you talk to ten different technicians about how to do refractometry, you are likely to get ten variations concerning procedure. There is not a single “right” way, or “best” way to perform refractometry. However, some procedures are better than others in terms of efficiency and final results. As a former evaluator for the technician level skill evaluations, I had the opportunity to observe many techniques and procedures that don’t work very well, and some that do.  Also, the procedures presented here are based on the "EDTRS" procedures, which are the standard refractive protocols for research studies.

At this point we have our patient lined up behind the phoropter, the opposite eye is occluded (OC), the eye being tested has no aux. lens (0), and we have our starting Rx (from retinoscopy, autorefraction, or the current glasses Rx) in place.

I can’t emphasize enough the importance of a good starting point Rx. The closer you are at the beginning to what the final Rx will be, the faster your refractometry will go and the more accurate you will be. The best refractionists know retinoscopy.

With retinoscopy you get visual confirmation of the sphere, cylinder amount, and the cylinder axis. You know where you are going before you start. Conditions that may affect the final result, such as a cataract or an opaque capsule, are visible with retinoscopy. You do not get this information from an autorefractor.

Lights on, or lights off?

Some refract with the room lights on, some with the room lights off, and some with the lights dimmed. I like to refract with the room lights on to some degree. Isn’t it nice to be able to see what you are doing? I also think it is preferable to have the patient’s pupil size as close to normal as possible. Projected eye charts usually have plenty of contrast without the help of dim room lights.

The visual target

In order for our patient to give us feedback (this is a subjective test) she needs to be looking at something that offers her the opportunity to discriminate between some visual choices. So we project something on the screen in her field of view. But what do we put on the screen? Having watched and having been the “patient” for many refractometry skill evaluations, I can tell you what not to put on the screen.

Don’t isolate individual letters. Don’t use parts of large letters. Don’t put up one line of letters and leave it up for the entire procedure. Don’t put up letters that are too small for your patient to read. Don’t use those little pictures that make up the Allen children’s chart.

My recommendation is to initially put up an entire screen of letters, with the 20/20 line at the bottom. Ask the patient to read the lowest line they can read on the chart. Now isolate the line of letters just above the line that the patient had a little trouble reading. For instance, if our patient missed two letters on the 20/30 line, isolate the 20/40 line.

As you proceed with your refraction work your way down the chart as the patient’s vision improves. An exception to this would be with the patient who can initially read 20/20. I would keep this patient on the 20/30 or 20/25 line for the first checks of the sphere and cylinder power, and the initial axis check.


Communicating with the patient

You are going to be presenting your patient with a choice between two different lens powers (or axis). Explain that to your patient. Explain to her that you want to know which choice gives the better vision. Give the choices names to aid communication. Many refractionists say “tell me which way is better, one, or two” (just prior to saying “two” the lens power or axis is changed). For the next series they may use “three, or four” to avoid confusion with the previous choice.

If your patient is deaf, a touch system can be used. For instance, you can touch his left hand for one choice and the right for the other. The patient then indicates his preference by moving the appropriate hand.

Order of Testing

The standard order of testing for refractometry is as follows:

1. Initial sphere power check

2. Cylinder axis check

3. Cylinder power check

4. Sphere power refinement

There are some refractionists who check the cylinder power first and then the cylinder axis.  I believe it is most efficient to check the axis first, and most "experts" agree with this.  If tested on this point, make sure you list axis first, then power.

The initial sphere check

Ok, we have the room lights on, and our patient is viewing FZBDE (20/40) because she messed up a little on OFLCT (20/30).

The first check we are going to do is the sphere power. Remember that the sphere power is changed by rotating that big wheel on the side of the phoropter (those of you familiar with this can skip to the next paragraph). Each click of the wheel changes the sphere power by .25 diopter. If your hand is going down, you are traveling in the plus direction. If your hand is going up, you are traveling in the minus direction. Tip: If you want to make big changes in the sphere power (3 diopters at a time), such as when setting up the initial Rx, use the wheel on the auxiliary lens knob.

On this initial sphere check, present the patient with a choice of powers at least .50 diopters apart (two clicks on the sphere wheel). It is very difficult for most people to discriminate between .25 diopter changes. If the initial vision check was not good (e.g. 20/50 to 20/80), you might use .75 diopter changes, or even 1.00 diopter changes if the patient's vision was worse than 20/80.

Remember to “push plus”. You want the most plus, or the least minus, for the best vision. If you leave someone underplused or overminused, then they have to use some of their accommodative power constantly even to see clearly in the distance. This may cause symptoms of eye fatigue and will make it more difficult for them to read.

Because you are going to "push plus", you will always want to start with a change in the plus direction.  This will save you time.  If the patient likes the change in the plus direction, you will not have to do a check in the minus direction.

For this first check, if two choices seem about the same to the patient, leave the lens on the most plus or least minus choice.

Cross-cylinder axis refinement

We have done an initial check of the sphere power and we are now ready to refine the cylinder axis and power. Although there are some other methods available, the cross-cylinder is the most widely used for this purpose. The cross-cylinder is quick and accurate in most situations. Like most refractometric techniques, it works best when we are reasonably close to the endpoint. Again we are reminded of the importance of a good starting point.

Just as you did when checking the sphere power, have the patient view a line of letters that can be read, but is one line above the line the patient has trouble reading. But don’t go below the 20/30 line.

Rotate the cross-cylinder into place.




Begin by lining up the “A”s with your starting axis position. In the example below the starting axis position is 90 degrees.





In this position the dots on the cross-cylinder will straddle the axis and will change positions when the wheel is “flipped”. Ask the patient which view gives the better vision as you flip from one position to the other. Just as you did when checking the sphere, identify each position with a number such as “one” or “two”.

Let’s say that our patient sees better on flip two, with the red dot to the left. If we are using a plus cylinder phoropter we will rotate the axis and cross-cylinder in the clockwise direction, toward the white dot. This is called "chasing the white dot". If we are using a minus cylinder phoropter we will rotate the axis and cross-cylinder clockwise, toward the red dot.  This is called "chasing the red dot". 

How far do we rotate the axis? That depends on our starting cylinder power. The larger the cylinder power is, the smaller your axis changes should be.  For example, if the starting cylinder power is only .25 or .5 D, then initially rotate the dial 15 degrees.  If the starting cylinder power is .75  to 1.25 D, initially rotate the dial 10 degrees.  If the starting cylinder power is above 1.25 D, then only rotate the dial 5 degrees.  There is nothing magic about these numbers.  The idea is to be efficient and to arrive at the final result in as few "trails" as possible.

Once we have a new axis position, we repeat the process. The idea is to zero in on the axis that provides the sharpest vision by "bracketing". The endpoint is reached when the sharpness on each flip seems about the same to the patient, or when the patient bounces you back and forth between two axis positions five degrees apart.
 

If the end-point axis is significantly different from the starting axis, you can double check your work by rotating off-axis in each direction and testing again.  For example, suppose your end-point is axis 90 (refer to the axis diagram above).  Rotate the axis dial to 80 and re-test (better one, or better two).  The patient should choose the flip that leads you back toward 90.  Now move the axis to 100 and test again.  Again, the patient's response should lead you back toward 90.

All modern phoropters have what is called a "coordinated" cross cylinder, which means that the cross cylinder automatically rotates when the axis dial is rotated.  Be aware that there are some older phoropters that do not have this feature.  In other words, you have to rotate the cross-cylinder separately from the axis dial, and this is a real pain in the rear.  I mention this in case you are ever in the market for a used phoropter.  Never buy a used phoropter that does not have a coordinated cross-cylinder.  You can test for this by simply rotating the axis dial and observing the cross-cylinder, which should rotate with the axis dial.

For instance, if the starting point is -1.50 (cylinder power), give the patient a choice between -1.75 and -1.25 by flipping between the powers with the cylinder power knob. If -1.25 gives the better vision, then present a choice between -1.00 and -1.50, and so on. Again, it is difficult for many patients to discriminate between choices .25 D apart, so give the patient choices .50 D apart most of the time.

The endpoint is reached when you find the lowest cylinder power that provides the best vision, as compared to it’s neighbors.

Using the cylinder power knob instead of the cross-cylinder to check cylinder power is particularly useful if your patient does not have good vision (<20/40).  Most phoropters are equipped with a .25 D cross-cylinder, which only gives the patient a .5 D power difference when the wheel is flipped.  When using the cylinder power knob, you can increase the diopter difference to whatever you find effective (e.g. 1 D compared to 2 D).

If you are making relatively large changes in the cylinder power, it is a good idea to recheck the sphere power in the middle of the process.  This is called "maintaining spherical equivalency".  The idea is that you may be moving the "circle of least confusion" off of the retinal plane.  For more information on this, see Modules 3 and 19.  For example, if you have made more than a .5 D change in the cylinder power, make a quick recheck of the sphere power before proceeding with cylinder power testing.  If you are using a plus cylinder phoropter, you will need to check the sphere power in the minus direction.  If you are using a minus cylinder phoropter, you will need to check the sphere power in the plus direction.  Some instructors advise you to automatically make a .25 D change in the sphere power for every .5 D change in the cylinder power.  I believe it is better to ask the patient which is better, the present sphere power, or the adjustment for the spherical equivalent, because you might not have the ratio between cylinder power and sphere power correct at this point.

Once you know the basics the actual operation will become much clearer once you see it in practice. Have someone demonstrate it for you, or order the cross-cylinder videotape from the American Academy of Ophthalmology (type "cross-cylinder" into the search field at the top of the homepage). Better yet, set yourself up as the patient as someone refines your axis.

Refine the Sphere Power

When you are finished with cylinder power refinement you are almost finished with the basic refractometric process.

You will now want to got back and re-check the sphere power using the same procedure you used with the initial check of the sphere power. If the patient sees well you may want to use .25 diopter steps instead of .50 diopter steps in this final check.

There are three more techniques that can be used for final “tweaking” of the prescription; the red-green test, binocular balancing, and checking cylinder power by spherical equivalent comparisons.

I find the red-green test to be the least useful because of inconsistent results, but it can be useful for the monocular patient or the patient who only sees well with one eye.  Binocular balancing (instead of the red/green test) should be used on everyone with good vision in each eye. Everyone with cylinder power over 1.00 D should be checked with spherical equivalent comparisons (see Module 3).