What is the difference between retinoscopy and autorefraction?

Both measure refractive error objectively without relying on patient responses. Retinoscopy is performed manually by a clinician using a streak retinoscope to observe light reflex movement in the pupil. Autorefraction is automated, using infrared light and computer analysis to measure refraction quickly. Retinoscopy requires skill and interpretation; autorefraction is faster but can be affected by accommodation. Both provide starting points for subjective refinement.

What does 'with movement' mean in retinoscopy?

In retinoscopy, 'with movement' means the light reflex in the pupil moves in the same direction as the examiner sweeps the streak. This indicates the eye needs more plus power (or is undercorrected hyperopia). The examiner adds plus lenses until the reflex neutralizes (fills the whole pupil with no movement), which represents the endpoint corrected for the working distance.

Why should autorefraction not be used as a final glasses prescription?

Autorefraction is an objective starting point that may differ from the true best-corrected refraction by ±0.50 D or more. It tends to over-minus young patients due to accommodative spasm during testing. It cannot assess binocular balance, account for patient preference, or detect subtle monocular differences the way subjective refraction can. The physician always refines autorefraction results with subjective testing.

Retinoscopy and Autorefraction: CPO Exam Guide

Objective vs. Subjective Refraction

Objective refraction determines a patient's refractive error without relying on their verbal responses. This is the foundation of the refraction process and is especially valuable for young children, cognitively impaired patients, or anyone who cannot reliably respond to subjective questions. Two main techniques exist: retinoscopy and autorefraction. As a CPO, you will routinely perform autorefraction and may observe or assist with retinoscopy.

Retinoscopy

Retinoscopy is a technique performed by the physician or skilled clinician using a streak retinoscope, an instrument that projects a streak of light into the patient's eye. By observing the movement of the light reflex in the pupil as the streak is swept across different meridians, the examiner can determine the direction and amount of refractive error.

With vs. Against Movement

With movement: the reflex moves in the same direction as the streak sweep, indicating undercorrected hyperopia or insufficient plus power. Add plus lens power to neutralize.
Against movement: the reflex moves opposite to the streak sweep, indicating myopia or excess plus power. Add minus lens power to neutralize.
Neutralization: when the reflex fills the entire pupil with no discernible movement, the working distance correction has neutralized the refractive error.

Retinoscopy is performed at a working distance (usually 67 cm or 1 meter). The examiner must subtract the working distance lens equivalent from the final finding. At 67 cm, subtract -1.50 D; at 1 meter, subtract -1.00 D from the sphere.

Autorefraction

An autorefractor is an automated instrument that measures refractive error objectively using infrared light. The patient rests their chin in the instrument and fixates on an internal target (often a balloon or house image on a road) while the device analyzes the reflected light pattern from the retina.

How to Perform Autorefraction

Position the patient comfortably at the chin and forehead rest
Align the instrument using the joystick until the pupil is centered
Ask the patient to keep both eyes open and blink normally
Capture 3-5 measurements per eye; the instrument averages them
Print or record the result: sphere, cylinder, axis, and pupil size

Instruct the patient to look at the image inside the machine without squinting or straining. Squinting causes accommodation spasm that skews the result toward more minus. Tell patients to pretend the image is far away, which relaxes accommodation and provides a more accurate reading.

Interpreting the Autorefractor Printout

The autorefractor printout typically shows:

S: sphere power (D)
C: cylinder power (D)
A: axis (degrees)
PD: pupillary distance (mm)
SE: spherical equivalent (sphere + half the cylinder)

The result is a starting point for subjective refraction, not a final prescription. Autorefraction can vary by ±0.50 D from the true refraction. It should always be refined subjectively.

Giving a patient their glasses prescription directly from the autorefractor reading. Autorefraction is an objective starting point only. It tends to over-minus young patients due to accommodation, and it may not accurately represent the optical axis, particularly in patients with high astigmatism or irregular corneas.

Keratometry Data

Many autorefractors also measure keratometry (corneal curvature) and report it alongside the refraction data. The K readings (flat and steep meridians) are useful for contact lens fitting and surgical planning.

Key Takeaways

Objective refraction (retinoscopy or autorefraction) does not require patient responses
Retinoscopy: with movement = add plus; against movement = add minus; neutralization = endpoint
Subtract working distance lens (−1.50 at 67 cm, −1.00 at 1 m) from retinoscopy findings
Autorefraction: 3-5 measurements averaged per eye; instruct patient not to squint
Autorefraction is a starting point for subjective refraction, never a final prescription