The impact of off the visual axis retinoscopy on objective central refractive measurement in adult clinical practice: a prospective, randomized clinical study.

Purpose: The objective of this study was to examine the effect of the off axis retinoscopy on objective central refractive measurement in adult clinical practice.

Methods: In all, 40 subjects underwent undilated retinoscopy in a randomly selected eye both on and off the visual axis by a single masked examiner. Off axis retinoscopy was defined as retinoscopy performed with the testing eye of the examiner aligned with the contralateral (non-test) eye of the subject resulting in an off axis deviation in the nasal horizontal visual field. Retinoscopy was performed in negative cylinder only and spherocylindrical measurements were converted to power vectors for analysis. Paired t-test was used to assess differences in M, J(0) and J(45) power vectors including differences between mean aided and unaided LogMar acuities.

Results: In all, 14 subjects were myopic (SE≤-0.5 D), 13 subjects were emmetropic (SE between -0.49 and 1.0 D) and 13 subjects were hyperopic (SE >1.0 D). Mean angle of deviation was 5.58° in the nasal horizontal visual field. J(0) showed a significant negative shift in those with myopia (P<0.001) and emmetropia (P=0.049) following off axis retinoscopy. No significant differences in M, J(0) and J(45) were found in the hyperopes. Mean aided LogMar acuities after on and off axis retinoscopy were both significantly better than mean unaided LogMar VA (P<0.001 in both cases).

Conclusion: Small degrees of off axis retinoscopy encountered in everyday clinical practice can induce errors in objective central refractive measurement.