When the practitioner shines the light of a retinoscope into an eye, they see the light reflected from the retina. This reflected light is called the retinoscopic reflex, or ‘ret reflex’; it looks like a red light inside the pupil. Depending on the person’s refractive error, when the practitioner moves the retinoscope, the ret reflex will move in a certain way inside the pupil. Trial lenses can be used to measure the amount of movement that a ret reflex has so that the refractive error can be estimated accurately.
Types of Retinoscopy :
- rotated to any axis position (by rotating the sleeve)
- made wider or narrower in width (by moving sleeve up or down)
- changed from convergent to divergent light (by moving the sleeve up or down). It is normally used in the ‘down’ position.
- made larger or smaller in diameter (by moving the sleeve up or down)
- changed from convergent to divergent light (by moving the sleeve up or down).
- Plus lenses neutralize a ‘with’ movement.
- Minus lenses neutralise an ‘against’ movement.
- Spherical lenses, with a wide range of powers, both positive and negative, generally 0.12 D, 0.25 D, and then in steps of 0.25 D up to a certain point, then in steps of 0.50 D, and then finally in steps of 1.00 D. At least two of each power are included.
- Cylindrical lenses in a variety of powers, often both positive and negative, mostly in steps of 0.25 D
- Accessory lenses used for special tests: prisms, filters, occluders, pinhole, and others.
- Do you get a streak of uniform brightness when the instrument is turned on?
- Does the brightness of the streak vary when the brightness control is turned?
- Does the sleeve in the instrument slide up and down freely and vary the length when it is moved?
- Does the patch of light or the streak rotate when the bulb is turned using the sleeve?
- Wipe lenses with a lens cleaning cloth if stained or smudged.
- Keep the lenses in the case after use.
- Wipe the trial frame’s nose rest with an alcohol wipe after each patient.