Optics of Retinoscopy

What is retinoscopy used for?

Measuring refractive error objectively

Retinoscopy is closely related to which optical principle?

The Foucault knife-edge principle

What limits the accuracy of retinoscopy?

The wave-like nature of light

What is the “red reflex”?

The red glow seen in the pupil when light enters the eye.

What are the three possible movements of the reflex?

With movement, against movement, or neutral (no movement).

What are the two main types of retinoscopes?

Streak and spot.

What creates the streak in a streak retinoscope?

A single filament strand in the light source.

What can rotating the filament determine?

Refractive error in different meridians (used for astigmatism).

What happens with divergent or parallel light when the mirror is rotated?

The image on the retina moves in the same direction

What happens with strongly convergent light when the mirror is rotated?

The image on the retina moves in the opposite direction.

What occurs if the light source is imaged into the pupil or at the mirror?

Neutral reflex (no movement).

What acts as the aperture stop in retinoscopy?

The smallest aperture near the examiner’s eye (observation stop).

In emmetropia, hyperopia, or low myopia, how does the reflex move?

In the same direction as the retinal patch

In high myopia (far point between eye & stop), how does the reflex move?

In the opposite direction.

What is seen when the far point is at the observation stop?

Neutral reflex (no movement).

What determines the speed of the reflex movement?

Distance of the far point from the observation stop.

What happens to reflex speed at the neutral point?

It becomes infinitely fast (no visible movement).

How do divergent and convergent light conditions relate to reflex direction?

Rules invert (with ↔ against) when changing from diverging to converging light.

At the neutral point, does reflex depend on illumination type?

No, reflex is neutral regardless of illumination.

What is the main difference between streak and spot retinoscopy?

Streak has an orientation axis (to measure astigmatism), spot does not.