Dear Editor:

We read with interest the recent article by Ho and colleagues [1]. The authors present a study of teenagers who underwent visual acuity testing, noncycloplegic autorefraction, and habitual refraction. The authors define myopia as a spherical equivalent (SE) of at least -1.00 diopters (D).

It has been reported that autorefraction (AR) can overestimate myopia in noncycloplegic pediatric patients [2]. Recently we saw a 17 year old girl with visual acuity of 20/40 in each eye without correction. A noncycloplegic autorefraction (AR) using a Topcon Elite KR-7000P (Topcon, Paramus, NJ) revealed -7.75 + 0.50 x 011 in the right eye and -8.75 + 0.75 x156 in the left eye. Subjective refraction (SR) starting from the AR results showed 20/20 acuity in each eye. Her SR did not change with fogging. After cycloplegia, her SR and AR were -1.25 + 1.00 x 015 (20/20) in the right eye and -1.25 + 0.25 x 152 (20/20) in the left eye. This patient's spherical equivalent was -0.75 diopters and -1.00 diopters in the right and left eye respectively. Her noncycloplegic AR overestimated her myopia by 6.75 diopters (D) in the right eye and 7.25 D in the left eye, but acuities were 20/20 in each eye.

In the discussion Ho et al state that their uncorrected refractive error rate of 22.3% is more than double the rates seen in several other countries. They suggest the difference could be attributed to the high refractive error rates in the Singapore population. Most likely the authors began their refractions using the results of the AR which likely overestimated myopia and then performed SR without cycloplegia. Although the authors acknowledge that the lack of cycloplegia was a limitation in their study, it likely affects the results significantly.

Sincerely, Michael S Lee, MD Andrew R Harrison, MD Minneapolis, MN

References

1.Ho CSD, Ng CBC, Chan E, et al. Uncorrected refractive error in Singapore teenagers. Br J Ophthalmol 2006;90:202-07.

2.Choong YF, Chen AH, Goh PP. A comparison of autorefraction and subjective refraction with and without cycloplegia in primary school children. Am J Ophthalmol 2006;142:68-74.