What is the difference between with and against movement in retinoscopy?

With movement means the retinal reflex moves in the same direction as the retinoscope streak, indicating the eye needs more plus power. Against movement means the reflex moves in the opposite direction, indicating the eye needs more minus power. The clinician adds lenses until reaching neutralization, where the reflex fills the pupil with no directional movement.

Why do you subtract the working distance in retinoscopy?

The clinician works at a finite distance from the patient, which adds artificial plus power to the optical system. To find the patient's true refractive error, this artificial plus (working distance factor) must be subtracted from the neutralization finding. At a standard 67 cm working distance, subtract 1.50 D. At 50 cm, subtract 2.00 D.

When is retinoscopy preferred over an auto-refractor?

Retinoscopy is preferred for infants and young children who cannot use an auto-refractor, non-verbal patients, patients suspected of feigning poor vision, patients with significant media opacities (moderate cataracts), and any case where the auto-refractor provides inconsistent or questionable readings. The clinician has direct control over the measurement process.

What does a scissoring reflex in retinoscopy indicate?

A scissoring reflex (the reflex appears to split into two halves moving in opposite directions) typically indicates corneal irregularity. Common causes include keratoconus, corneal scarring, or significant corneal surface irregularity. When a scissoring reflex is observed, further corneal evaluation such as topography or slit lamp examination is warranted.

Retinoscope: Objective Refraction Through Retinal Reflex Observation

What Is a Retinoscope?

A retinoscope is an optical instrument used to perform objective refraction by observing the behavior of light reflected from the patient's retina. The clinician projects a streak of light into the patient's eye and observes how the retinal reflex (the reflected light seen in the pupil) moves as the streak is swept across the pupil. By adding lenses that change the behavior of this reflex, the clinician determines the patient's refractive error.

Retinoscopy is one of the most fundamental clinical skills in optometry and remains the gold standard for objective refraction, particularly for patients who cannot provide reliable subjective responses.

How Retinoscopy Works

The retinoscope projects a beam of light through the pupil onto the retina. The light reflects back out through the pupil, creating a visible reflex. The clinician sweeps the retinoscope beam and observes how the reflex moves:

"With" movement: The retinal reflex moves in the same direction as the retinoscope streak. This indicates the eye needs more plus power (or less minus) at the current working distance.
"Against" movement: The retinal reflex moves in the opposite direction from the streak. This indicates the eye needs more minus power (or less plus) at the current working distance.
Neutralization: The reflex fills the pupil simultaneously with a bright flash. No directional movement is seen. This is the endpoint.

The Neutralization Process

Project the retinoscope streak into the patient's eye
Sweep the streak horizontally and vertically, observing the reflex direction
Add plus or minus trial lenses to change the reflex behavior
Continue adding lenses until the reflex shows neutralization (bright flash filling the pupil with no directional movement)
The lens power at neutralization, minus the working distance compensation, equals the patient's refractive error in that meridian

At neutralization, the retinoscope beam, the patient's refractive error, and the trial lens power combine to focus the retinal image at the clinician's retinoscopy plane. The total lens power at this point must be adjusted by subtracting the working distance factor to get the true refractive error.

Working Distance Compensation

Because the clinician works at a finite distance from the patient (not at optical infinity), the retinoscope's light enters the eye at a convergent angle. This adds artificial plus to the system. To get the true refractive error, subtract the working distance factor:

Working distance factor = 1 / working distance (in meters)

Working Distance	Factor to Subtract
67 cm (2/3 meter)	-1.50 D
50 cm (1/2 meter)	-2.00 D
40 cm	-2.50 D

The most common working distance is 67 cm (arm's length), requiring subtraction of 1.50 D from the neutralization finding.

Forgetting to subtract the working distance factor. If neutralization is found at +3.00 D using trial lenses and the working distance is 67 cm, the patient's actual refractive error is +3.00 - 1.50 = +1.50 D, not +3.00 D. This error overestimates the hyperopia by the working distance factor.

Clinical Advantages

Retinoscopy has several advantages over automated objective refraction:

Does not require patient responses: Essential for infants, toddlers, and non-verbal patients
Detects media irregularities: The quality of the reflex provides information about corneal and lens clarity
Less affected by accommodation: The clinician can use fogging techniques or cycloplegic drops to control accommodation
Works through media opacities: Can often obtain a reading even with moderate cataracts
Detects simulation: Useful when a patient may be exaggerating or faking visual loss

The quality of the retinoscopy reflex provides clinical information beyond the refractive error. A dull, irregular reflex may indicate media opacity (cataract). A scissoring reflex (the reflex splits into two halves moving in opposite directions) may indicate keratoconus or corneal irregularity. Always note the reflex quality alongside the numerical findings.

Retinoscopy for Astigmatism

When the eye has astigmatism, the retinal reflex behaves differently in different meridians. The clinician sweeps the beam along each principal meridian separately:

Neutralize one meridian (e.g., the horizontal sweep)
Rotate the streak 90 degrees and neutralize the other meridian
The difference between the two neutralization powers equals the cylinder
The axis corresponds to the orientation of one of the principal meridians

Clinical Relevance

Retinoscopy remains a core clinical skill despite the availability of auto-refractors. It provides objective data that the clinician directly controls and interprets, making it more reliable in difficult cases (children, uncooperative patients, media opacities). The ABO exam tests knowledge of retinoscopy principles, particularly reflex behavior and working distance compensation.

Key Takeaways

The retinoscope provides objective refraction by observing the retinal reflex
"With" movement means more plus is needed; "against" movement means more minus is needed
Neutralization (bright flash, no movement) is the measurement endpoint
Always subtract the working distance factor from the neutralization finding
Standard working distance of 67 cm requires subtracting 1.50 D
Retinoscopy works for non-verbal patients, children, and cases where auto-refraction is unreliable