Residency · Residency · Ophthalmology
Objective and Subjective Refraction Techniques
Retinoscopy Principles
Retinoscopy is the primary objective method for determining a patient's refractive error. The examiner observes the reflex of light returning from the retina and adds lenses to neutralize the movement of that reflex. The technique requires accounting for the working distance; for instance, at a typical 67 cm working distance, the examiner must subtract 1.50 D of plus power from the final result. At the point of neutralization, light fills the pupil instantaneously with no discernible directional movement.
Streak vs. Spot Retinoscopes
The streak retinoscope, exemplified by the Copeland model, projects a line of light that allows simultaneous assessment of both axis and power, making it the standard instrument in most training programs. The spot retinoscope, such as the Welch Allyn model, projects a round spot and is simpler to use but less precise for determining the cylinder axis. During retinoscopy, the streak is rotated to align with each principal meridian in order to separately evaluate the astigmatic components.
Retinoscopy Technique
The examination is performed in a dimly lit room with the examiner positioned at arm's length, approximately 67 cm from the patient. The streak is swept across the pupil perpendicular to its orientation. "With" motion, in which the reflex moves in the same direction as the streak, indicates that plus power should be added (or that the eye is relatively hyperopic at that working distance). "Against" motion, in which the reflex moves opposite to the streak, calls for minus power. Each meridian is neutralized independently to determine the spherical and cylindrical components of the correction. A scissors reflex, in which the light appears to split, suggests irregular astigmatism and should prompt consideration of keratoconus.
Autorefraction and Aberrometry
Autorefractors use infrared light to provide a rapid objective estimate of sphere, cylinder, and axis. While convenient, they may overestimate minus power in young patients because of instrument-induced accommodation. Wavefront aberrometers, such as those based on the Hartmann-Shack sensor, go further by measuring higher-order aberrations in addition to the standard refractive error. Cycloplegic autorefraction is essential in children to unmask latent hyperopia that voluntary accommodation would otherwise conceal.
Subjective Refraction
Subjective refraction refines the objective starting point by incorporating patient responses. The overarching goal is to determine the maximum plus (or minimum minus) lens that provides the best corrected visual acuity.
Fogging Technique
The fogging technique involves adding plus power to deliberately blur the patient's vision past their best acuity, which relaxes accommodation by placing the focal point in front of the retina. Plus power is then gradually reduced until the patient reports the clearest vision. This approach is particularly valuable in young patients whose active accommodation might otherwise lead to over-minusing.
Jackson Cross-Cylinder (JCC) Technique
The Jackson cross-cylinder is a lens with equal and opposite powers in perpendicular meridians (for example, +0.25/-0.50) and is used to refine both the axis and the power of the cylinder correction. For axis refinement, the handle of the JCC is aligned along the correcting cylinder axis, and the lens is flipped while the patient reports which position gives better vision. For power refinement, one axis of the JCC is aligned with the correcting cylinder axis, and flipping determines whether more or less cylinder is needed. The endpoint should always be bracketed to ensure accuracy.
Duochrome (Red-Green) Test
The duochrome test exploits chromatic aberration, since red light focuses behind green light in the eye. If the patient reports that the red side is clearer, the eye is under-minused or over-plussed. If the green side is clearer, the eye is over-minused. Equal clarity on both sides indicates the appropriate endpoint. This test is unreliable in patients with color vision deficiency.
Binocular Balancing
Binocular balancing ensures that both eyes are exerting equal accommodative effort at the final prescription. Methods include alternate occlusion with fogging, prism dissociation, and the Humphriss immediate contrast technique. The goal is for both eyes to be equally fogged or equally clear.
Cycloplegic Refraction
Cycloplegic refraction is essential in children, young hyperopes, and patients with accommodative esotropia. Cyclopentolate 1% is the standard agent, reaching full effect in 30 to 45 minutes and lasting 12 to 24 hours. For maximum cycloplegia in heavily pigmented irides or when cyclopentolate is insufficient, atropine 1% is used, though it takes 1 to 3 days for onset and its effects persist for 7 to 14 days. Comparing the cycloplegic refraction to the manifest refraction reveals the amount of latent hyperopia.
| Cycloplegic Agent | Concentration | Onset | Peak Effect | Duration | Primary Use |
|---|---|---|---|---|---|
| Tropicamide | 1% | 20 min | 20-35 min | 4-6 hr | Mydriasis (weak cycloplegia) |
| Cyclopentolate | 1% | 30 min | 30-45 min | 12-24 hr | Standard cycloplegic refraction |
| Atropine | 1% | 60-180 min | 1-3 days | 7-14 days | Maximum cycloplegia; heavily pigmented irides |
| Retinoscopy Reflex | Meaning | Action |
|---|---|---|
| "With" motion | Eye is hyperopic relative to working distance | Add plus power |
| "Against" motion | Eye is myopic relative to working distance | Add minus power |
| Neutralization | Reflex fills pupil instantly | Subtract working distance lens |
| Scissors reflex | Irregular astigmatism | Evaluate for keratoconus |
<image>Illustration showing the retinoscopy setup: examiner at 67 cm working distance, holding a streak retinoscope in the right hand and a lens rack in the left. Show the retinoscope beam projecting into the patient's pupil and the reflex emerging. Two panels: left panel shows "with" motion (reflex moving in the same direction as the streak sweep, with arrows), right panel shows "against" motion (reflex moving opposite to the streak, with arrows). Label the working distance and the retinal reflex.</image>
<image>Diagram of the Jackson cross-cylinder technique for axis refinement. Show a phoropter view with the cross-cylinder lens positioned with its handle aligned along the correcting cylinder axis. Two flip positions labeled "Position 1" and "Position 2" with the plus and minus axes of the JCC straddling the cylinder axis at 45 degrees. Arrows indicate the direction of axis rotation based on patient preference.</image>
<image>Schematic of the fogging technique: cross-section of an eye with three scenarios. (1) Correct refraction: focal point on retina. (2) Fogged state: excess plus power moves focal point anterior to retina, relaxing accommodation. (3) Gradual reduction of plus until the focal point returns to the retina. Label the retina, lens, and focal points in each scenario.</image>
Clinical Pearls
Retinoscopy should always precede subjective refraction because it provides an essential objective starting point, particularly in children and nonverbal patients. The guiding principle of manifest refraction is "maximum plus to maximum visual acuity," which prevents over-minusing. A scissors reflex on retinoscopy should immediately prompt evaluation for keratoconus or other forms of irregular astigmatism. Cycloplegic refraction is mandatory in any child presenting with esotropia in order to rule out an accommodative component. The working distance must always be subtracted from the retinoscopy result, and placing a +1.50 D working distance lens in the phoropter simplifies this calculation. Autorefractors are useful screening tools but should never serve as definitive prescriptions; subjective refraction must always confirm the findings.
References
- American Academy of Ophthalmology. BCSC Section 3: Clinical Optics. 2023-2024.
- Corboy JM. The Retinoscopy Book: An Introductory Manual for Eye Care Professionals. 5th ed. SLACK; 2003.
- Michaels DD. Visual Optics and Refraction: A Clinical Approach. 3rd ed. Mosby; 1985.
