# Retinoscopy Basics > Retinoscopy basics for Optometry exams: streak reflex movements, with and against rules, neutralisation, working distance subtraction and cycloplegic choices. - Canonical URL: https://prepelephant.com/topics/allied/optometry/retinoscopy-basics - Exam / course: Allied Health · Subject: Optometry - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Retinoscopy Basics", PrepElephant, https://prepelephant.com/topics/allied/optometry/retinoscopy-basics ## Direct answer Watch the reflex, not the chart: retinoscopy reads the direction the pupillary light reflex moves as the streak sweeps the pupil, and the rule is two words long — "with, add plus; against, add minus" — power is added until the pupil fills instantly with light at neutrality. The neutral values are then corrected for working distance: at 67 cm subtract 1.50 D, at 1 metre subtract 1.00 D, at 50 cm subtract 2.00 D. Because it asks nothing of the patient, retinoscopy is the objective foundation of every subjective refraction and the only reliable refraction in children and non-communicative patients. ## What you must remember - Streak retinoscope, plane-mirror setting: sweep each meridian and compare reflex movement with streak movement — "with" (same direction) means the far point lies behind, add plus; "against" means relative myopia, add minus. - Neutrality: the reflex becomes instantly bright, fills the whole pupil and appears motionless; beyond it movement reverses, so bracket through and come back. - Working distance correction: net retinoscopy value minus the dioptric equivalent of the working distance (67 cm → 1.50 D) gives the true refractive error. - Astigmatism: sweep 360 degrees; the break (reflex and streak misalign), width (narrower in the more ametropic meridian) and skew cues locate the principal meridians before any lens is dialed. - Neutralise each principal meridian separately — sphere for one, plus cylinder at the perpendicular axis for the other with a plus-cylinder technique. - Fog or occlude the fellow eye and direct fixation past your ear to a distant target so accommodation relaxes instead of fixing on the retinoscope light. - Cycloplegic retinoscopy: atropine 1 per cent over the preceding days for young children and suspected high hypermetropia or strabismus; cyclopentolate 1 per cent is the routine office cycloplegic; tropicamide gives mydriasis but inadequate cycloplegia in children. - An irregular, scissor-like or dancing reflex suggests keratoconus until corneal topography says otherwise. ## A worked neutralisation with numbers Sit at 67 cm from a young adult, streak horizontal first. In the 180-degree meridian the reflex moves with the streak; plus sphere is added until +3.00 D gives neutrality. Rotate the streak vertical; in the 90-degree meridian the reflex still moves with, but narrower and slower — a second, more hypermetropic meridian. Adding more sphere would break the first meridian, so hold 180 neutral and neutralise 90 with plus cylinder at axis 90: +1.00 DC × 90 achieves neutrality in both. Now the arithmetic. Gross retinoscopy: +3.00 DS with +1.00 DC × 90. Subtract the working distance from the sphere: 1.50 D. Objective result: +1.50 DS/+1.00 DC × 90 — compound hypermetropic astigmatism, or in minus-cylinder form +2.50 DS/−1.00 DC × 180. The patient reads 6/9 or better through these trial lenses on the subjective run, confirming the objective result before prescribing. Had the examiner sat at 50 cm and forgotten the subtraction, the same eye would walk out with +2.50 more plus than it needs — the commonest numerical error in refraction. ## Where students slip Four confusions recur. Reversing the rule under stress — chant it: with means plus, against means minus, in the plane-mirror setting. Forgetting the working distance, or applying it to the cylinder (it comes off the sphere only). Mixing axes when neutralising with a plus cylinder in the frame — the cylinder axis must match the meridian being corrected; mixing them creates a power that exists in no eye. And the cycloplegic questions: which drug for an infant with suspected high hypermetropia (atropine, over two to three days, with parents warned of flush and fever), and why not tropicamide (mydriasis without adequate cycloplegia — the ciliary muscle still works). The scissor reflex deserves respect too: an irregular reflex in a young adult with one-line acuity loss means keratoconus and topography, not "more cylinder". ## Frequently asked questions ### Why is 1.50 D subtracted from the retinoscopy finding? The examiner works at 67 cm — itself a 1.50 D vergence; neutralisation includes that distance, which must be removed to leave the patient's true error. ### What defines the point of neutralisation? The pupil fills instantly with a bright, motionless reflex as the streak sweeps — movement disappears because the far point coincides exactly with the retinoscope sight hole. ### What does "with movement" signify, and what is added? With movement (plane mirror) means the far point lies behind the examiner, so plus lenses are added; against movement means relative myopia and minus lenses are added. ### Which cycloplegic is preferred in young children? Atropine 1 per cent over two to three days for infants and suspected high hypermetropia or strabismus; cyclopentolate 1 per cent serves older children. ### What is the significance of a scissor or irregular reflex? Irregular astigmatism, classically keratoconus — confirmed by corneal topography rather than by adding trial cylinders. ### How is the axis of astigmatism located before neutralising? By the break phenomenon — the meridian where reflex and streak misalign — together with reflex width and skew, which mark the principal meridians for separate neutralisation.