First thing’s first: What is retinoscopy and why do we do it?
Retinoscopy is an “objective refraction.” Objective, as we know, means there is no input required from the patient; it is performed to obtain data based on what the examiner sees. This will be the same camp as your auto-refractor and both of these require patient cooperation. Retinoscopy is the refractive test of choice for pediatric patients and is helpful in circumstances in which verbal communication may be difficult (as with patients who do not speak the same language that you do or those with developmental delays), or when an auto-refractor is not available for use. Although this technique is not something you will be doing on every patient, it is a critical skill to have in your back pocket.
- “With motion” = the light reflex is traveling in the same direction as the retinoscope beam. You need to add more plus to the prescription.
- “Against motion” = the light reflex is traveling in the opposite direction of the retinoscope beam. You need to add more minus to the prescription.
(Helpful Hint: against motion (AM) = add minus (AM))
- “No motion” = the light reflex is neutral and is seen across the entire width of the pupil
- THE GOAL: Neutral reflex across the entire width of pupil (aka no motion)
- THE SETUP: Phoropter at plano, 20/400 letter with red/green filter, lights off. Make sure your beam is fully expanded (for many retinoscopes, this means making sure your beam adjustment is sleeve-down) and, of course, make sure your phoropter is level and that the patient’s pupils are centered. When scanning, you should be able to see the entire pupil while maintaining a position roughly 15 degrees temporal from the line of sight. If you can’t see the patient’s pupil, you may need to do a slight twist of the phoroptor to better face you. Just be sure the patient can still see the chart (albeit blurry) with each eye. It is also important to make sure the patient knows to maintain fixation on the chart behind you and not to look at your light. The patient should also tell you if at any point the view is obstructed (aka if your head gets in the way). Otherwise, you may be performing retinoscopy on a patient that is accommodating, leaving your results skewed to be more minus.
- THE CHASE: Always “find the good (+) in everyone” first!
- THE COUPLE: The spherical power and the axis are found together
Detailed Retinoscopy Procedure
The Chase: When working towards the goal of a neutral reflex, begin by scanning for the presence of cylinder. First, establish whether the patient’s reflex indicates a spherical cornea or an astigmatic one. Most clinicians will start scanning back and forth at the 90 or 180 meridian before rotating the beam by 90 degrees to scan the second meridian. This is because the majority of your patients that have astigmatism will be WTR (with the rule) or ATR (against the rule).
If you find a difference in the magnitude of motion when doing your initial scanning, you know you are dealing with astigmatism. The magnitude difference will be apparent based on the thickness of the beam when you scan across the pupil. As optometrists and optometry students, we work predominantly in minus cylinder. For finding the prescription, you want to scan one of the meridians to a neutral reflex (this will be your spherical power) and the other meridian to have against motion (indicating minus, which will be your cylinder power). In other words, the starting point in the retinoscopy prescription is the meridian that has the most plus/least minus.
To neutralize a meridian, you will be adding or subtracting power in your dials for sphere until the reflex appears to “blink red” at you when you scan across the pupil. Even if both of your starting reflexes have against motion, choose one meridian and add minus lenses until you hit a neutral reflex. This meridian is confirmed as the spherical power by rotating your scope 90 degrees away to the other meridian and seeing against-motion. Even if you are adding minus lenses to get your sphere, this is still the most plus meridian. Therefore, if you want to find your spherical power, I say to first “find the good (+) in everyone.”
Once you have neutralized one meridian and have confirmed against-motion in the second, you are ready for the next step: finding cylinder power. This step is similar to finding spherical power in that you continually add lenses as you scan for neutral motion, except using your front knobs for cylinder power.
Once this meridian is neutralized, narrow your retinoscope beam and hone in on the cylinder axis, which you can read directly off the knob. This part can be confusing, so it important to note that this method of making the beam as narrow as possible while in the “cylinder power position” is telling you the axis at which the spherical power is located. So, if you have the beam lined up in a position that crosses the 180 (left to right), then you are scoping the 90. This is because the orientation of the beam and the scanning motion are always perpendicular to one another. If you are scoping the 90 (so again, beam is oriented along the 180) and you neutralize the reflex, and you turn the beam by 90 degrees to find against motion, then your axis is 90. Think of one of those push brooms that have a wide base and tall bristles; the direction you are sweeping is always perpendicular to the broom, much like the scoping action and light orientation during retinoscopy. Once this is complete, you’re ready to move on to the other eye! **Note: it is a good idea to get in the habit of going back over to the first eye you neutralized so that you can verify it is still showing a neutral reflex. The first eye you neutralize may be slightly off, especially if the patient has a large prescription.
When you finish neutralizing each eye, you must remember that you are not done yet! There are two things you still need to do:
- Subtract your working distance. You must subtract the dioptric equivalent of your working distance from the prescription you find after ret. The dioptric power (D) can be calculated by taking the inverse of your working distance in meters (m).For example, a 50 cm working distance would lead to: (1/0.50 m) = 2.00 D. In this case, you would subtract 2.00 D from your ret. Let’s say you found +3.00-1.50×180 after ret. You would then subtract 2 D from the sphere to yield +1.00-1.50×180 as your final prescription.
- Check vision. What’s the point of doing a refraction if we can’t assess how well the patient sees afterwards? I would consider anything within a line or two of 20/20 a “win.” You can then refine the prescription with manifest refraction.
- Practice. With practice comes confidence, and with confidence comes speed. It’s that simple.
- If you can, make it a party. Our class held a couple of “practice parties” to get lots of students together to practice mastering retinoscopy. This was helpful because we could switch roles as “patients” and “doctors,” as well as ask each other questions.
- Get a schematic eye. These can be purchased online if your school doesn’t provide any to practice on. Many optometry school provide them for students to use before practicing on each other. Just remember: if you are working with a schematic eye through the phoropter, your prescription will be the opposite sign of your lenses! Putting a +3.00 D trial lens in the schematic eye will result in a -3.00 D neutralization in the phoropter. The same goes for cylinder power, too!
- Know your working distance and stick to it! You can tie a string to the end of your retinoscope and quickly check the distance from the phoropter to your retinoscope before starting. The key is consistency, so check yourself often when doing ret to get a feel for your working distance.
- It’s okay to scope the wrong meridian first. If you see with motion when you neutralize the second meridian instead of against motion, this means that your sphere and cylinder powers are 90 degrees off. Continue to neutralize the with motion reflex with spherical lenses, then switch to the other meridian and you should see against motion. Neutralize this with cylinder lenses, and remember to adjust your axis so that it is 90 degrees away from the meridian you are scoping (in other words, adjust the axis to line up with your beam).
Remember, these are just recommendations. Once you find a way that works for you, stick with it! You want retinoscopy to be a skill that you can master and perform in just a few minutes! Good luck, and happy retting!
Check out this interactive retinoscopy simulator to see the reflexes with different refractive errors, axes, and working distances.