Objective Refraction Technique: Retinoscopy
Although autorefractors are easily accessible, retinoscopy remains an important skill and tool for the ophthalmologist to objectively determine the spherocylindrical refractive error of the eye. A retinoscope can also help the examiner detect optical aberrations, irregularities, and opacities, even through small pupils. Retinoscopy is especially useful for examinations of infants, children, and adults unable to communicate.
Most retinoscopes in current use employ the streak projection system developed by Copeland. The illumination of the retinoscope is provided by a bulb with a straight filament that forms a streak in its projection, or by means of a slit-shaped aperture. The light is reflected from a mirror that is either half silvered (Welch Allyn, Heine models) or totally silvered around a small circular aperture (Copeland instrument) (Fig 4-1). The filament light source (or the slit aperture) can be moved in relation to a convex lens in the system using the sleeve of the retinoscope. If the light is slightly divergent, it appears to come from a point behind the retinoscope, as if the light were reflected off a flat mirror (ie, a plane mirror setting) (Fig 4-2).
Alternatively, when the distance between the convex lens and the filament is increased by moving the sleeve on the handle, convergent light is emitted. In this situation, the image of the filament appears between the examiner and the patient, as if the light were reflected off a concave mirror (Fig 4-3).
Retinoscopy may be performed with either a concave mirror setting or a plane mirror setting, determined by the sleeve of the scope. Retinoscopy is usually performed using the plane mirror setting so that light is parallel (or slightly divergent) as it enters the pupil of the patient’s eye. We restrict our discussion to the plane mirror effect; in the concave mirror effect, the direction of motion is opposite that of the plane mirror effect. One use of the concave setting is to sharpen the reflex while determining the axis of astigmatism. Using the concave setting during power determination (of sphere or cylinder) may lead to false end points (neutrality). Not all retinoscopes employ the same sleeve position for the plane mirror setting. For example, the original Copeland retinoscope is in plane position with the sleeve up; the Welch Allyn (or Heine) instrument is in plane position with the sleeve down. The axis of the streak is rotated with the sleeve.
Figure 4-1 Retinoscope: Illumination system: Light path from light source through patient’s pupil to retina. Observation system: Light path from patient’s pupil, through mirror to observer’s retina.
(Illustration by C. H. Wooley.)
Figure 4-2 Illumination system: position of source (S) with plane mirror (M) effect.
Figure 4-3 Illumination system: position of source with concave mirror effect.
Positioning and Alignment
Ordinarily, the examiner uses his or her right eye to perform retinoscopy on the patient’s right eye, and the left eye for the patient’s left eye. Doing so prevents the examiner’s head from moving into the patient’s line of sight and thus inadvertently stimulating accommodation. If the examiner looks directly through the optical centers of the trial lenses while performing retinoscopy, reflections from the lenses may interfere. In general, if the examiner is too far off-axis, unwanted spherical and cylindrical errors may occur. The optimal alignment is just off center, where the lens reflections can still be seen between the center of the pupil and the lateral edge of the lens. Video 4-1 demonstrates the basics of retinoscopy.
Animation developed by Thomas F. Mauger, MD.
Access all Section 3 videos at www.aao.org/bcscvideo_section03.
Excerpted from BCSC 2020-2021 series : Section 3 - Clinical Optics. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.