8.2 Streak Retinoscopy: With Motion, Against Motion, Neutralisation & Working Distance
Key Takeaways
- With motion means the reflex moves in the same direction as the streak and is neutralised with plus power.
- Against motion means the reflex moves opposite to the streak and is neutralised with minus power.
- The working distance lens must be subtracted from the gross result: 1.50 D at 67 cm, 2.00 D at 50 cm.
- A brighter, faster, wider reflex means you are close to neutrality.
- Scissoring of the reflex indicates irregular astigmatism, most commonly keratoconus.
What the retinoscope does
A streak retinoscope projects a linear band of light into the eye and lets you observe the reflex — the light returning from the retina through the pupil. By watching how that reflex moves as you sweep the streak, you determine whether the eye's far point lies in front of, behind, or at your own eye.
The sleeve controls the vergence of the projected streak:
- Plane mirror effect (sleeve typically down on a Welch Allyn instrument, up on some others) — diverging beam; this is the standard working position.
- Concave mirror effect — converging beam; the motion rules reverse, which is a classic source of confusion. Learn one instrument and keep the sleeve in the same position.
Rotating the sleeve rotates the streak so you can sweep along any meridian.
The motion rules
Sweep the streak across the pupil and watch the reflex.
| Reflex behaviour | Meaning | Correction |
|---|---|---|
| With motion — reflex moves the same direction as the streak | The far point is behind your eye; the eye is less minus (or more plus) than the working distance lens accounts for | Add plus |
| Against motion — reflex moves opposite to the streak | The far point is in front of your eye | Add minus |
| Neutral — the whole pupil fills and flashes with no directional movement | The far point is at your eye | Stop; record the gross value |
A useful mnemonic pair: "With — add plus. Against — add minus."
Characteristics as you approach neutrality:
| Distance from neutrality | Reflex brightness | Reflex speed | Reflex width |
|---|---|---|---|
| Far from neutral | Dim | Slow | Narrow |
| Approaching neutral | Brighter | Faster | Wider |
| At neutral | Brightest flash, fills the pupil | Instantaneous | Fills the pupil |
This is why you always work toward brighter, faster, wider. If the reflex is getting dimmer and slower, you are moving in the wrong direction.
Technique
- Dim the room. A dilated or at least a naturally larger pupil gives a better reflex.
- Sit at your working distance — 67 cm (about arm's length, corresponding to 1.50 D) or 50 cm (2.00 D). Be consistent; the whole result depends on it.
- Have the patient fixate a distance target with the fellow eye — a large letter, or a light — so accommodation is relaxed. Never let the patient fixate your retinoscope or your face.
- Work off-axis: examine the patient's right eye with your right eye, holding the retinoscope slightly temporally so your head does not block the patient's fixation.
- Sweep the streak across the pupil in one meridian and read the motion.
- Find the principal meridians. Rotate the streak and look for the orientation in which the reflex band is brightest, narrowest and exactly parallel to the streak. That is one principal meridian; the other is 90 degrees away. The break phenomenon (the reflex inside the pupil is discontinuous with the light outside it) disappears when you are on axis.
- Neutralise each meridian separately with sphere and cylinder, or with spheres and then convert.
- Subtract the working distance.
Subtracting the working distance
Because you sit at a finite distance, the eye must be focused at your eye rather than at infinity to appear neutral. The dioptric value of that distance must be removed from the gross finding.
Working distance in dioptres = 1 ÷ distance in metres
| Working distance | Dioptres to subtract |
|---|---|
| 100 cm | 1.00 D |
| 67 cm | 1.50 D |
| 50 cm | 2.00 D |
| 40 cm | 2.50 D |
Worked example 1. At 67 cm, neutrality is reached at +2.00 D. Net = +2.00 − 1.50 = +0.50 D.
Worked example 2. At 67 cm, neutrality at −3.00 D. Net = −3.00 − 1.50 = −4.50 D.
Worked example 3. At 50 cm, the 180 meridian neutralises at −1.00 and the 090 meridian at −3.00. Subtract 2.00 from each: 180 → −3.00, 090 → −5.00. In minus cylinder the sphere is the less minus meridian power with its own axis: −3.00 −2.00 × 180.
An alternative to subtracting is placing a working distance lens (+1.50 D at 67 cm) in the trial frame or using the phoropter's built-in retinoscopy lens (marked R or +1.50). If you use it, the reading at neutrality is the net result already — but you must remove it before subjective refinement, and forgetting to do so is one of the most common technique errors.
Reflex appearances that carry information
| Appearance | Meaning |
|---|---|
| Scissoring — two reflex blades moving toward and away from each other | Irregular astigmatism, classically keratoconus; also post-surgical ectasia, large pupils with spherical aberration |
| Dull, dark, no reflex | Media opacity — dense cataract, corneal scar, vitreous haemorrhage |
| Dark central zone with a peripheral reflex (oil droplet) | Nuclear cataract; also seen in lenticonus |
| Bright reflex that varies with the cardiac pulse | Normal, from the choroidal circulation |
| Reflex neutralises at very different powers in different parts of the pupil | Irregular cornea or lens; spectacles will not fully correct |
| Reflex constantly changing in a young patient | Accommodative fluctuation — fog better or cycloplege |
Practical pitfalls
- Patient accommodating on the retinoscope light. The single commonest error. Maintain distance fixation with the fellow eye, keep the room dim, and work off-axis.
- Forgetting to subtract or remove the working distance lens. Produces an error exactly equal to the working distance.
- Inconsistent working distance. Drifting from 67 cm to 50 cm mid-examination corrupts the result by 0.50 D.
- Neutralising on an oblique meridian believed to be principal. Confirm by checking that the reflex is parallel, narrow and bright with no break.
- Small undilated pupil — accept that accuracy falls; consider dilating.
- Reversing the motion rules with the sleeve in the concave position. Keep the sleeve in one position for all routine work.
- Reading the reflex in the pupil periphery rather than the centre, where spherical aberration distorts the motion.
During retinoscopy at 67 cm the reflex shows with motion. What should the technologist do?
At a 50 cm working distance, neutrality is reached at −4.25 D. What is the net refractive error?
A scissoring reflex is observed during retinoscopy on a 19-year-old with progressive blur and against-the-rule astigmatism. What does this most likely indicate?
Why should the patient fixate a distance target with the fellow eye during retinoscopy?
As you approach neutrality during retinoscopy, how does the reflex change?