First things first: What is retinoscopy and why do we do it? Retinoscopy is an “objective refraction” Objective means there is no input required from the patient. Retinoscopy is the refraction test of choice for pediatric patients, and is helpful in circumstances with patients in which verbal communication may be difficult (such as with patients who do not speak your language or have developmental disabilities), or when an autorefractor 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.
- “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. (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).
- THE CHASE: “Find the good (+) in everyone”
- 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 cylinder. First, establish whether the patient’s reflex indicates a spherical cornea or astigmatism (more power in one meridian than another). Most clinicians start scanning at the 90 degree or 180 degree meridian a few times before rotating the beam by 90 degrees to scan the second meridian, noting the motion of the reflex along both axes. As optometrists and optometry students, we work predominantly in minus cylinder. This means that if you find a difference in the magnitude of the motion of the light reflexes between two meridians, you want to use the technique to scan the first meridian to a neutral reflex (indicating spherical power) and the second meridian to have a reflex of against motion (indicating minus cylinder power). In other words, the starting point in your retinoscopy evaluation is the meridian that has the most plus/least minus. Therefore, I say to “find the good (+) in everyone.”
Once you have against motion in the second meridian, 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 the 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. Once this is complete, you’re ready to move on to the other eye!
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 50cm working distance would lead to: (1 / 0.50m) = 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 2D 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? 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.