The Nidek HandyRef-K is a closed-field handheld, portable, easy-to-use, monocular auto-refractometer that detects refractive errors in infants, any age of childhood, and adolescents sitting, standing, or supine position. A fogging mechanism is exerted to reduce accommodation. Its measurement range is -20.00 D to + 20.00 D sphere (0.12 D/0.25 D increments), cylinder 0 D to 12.00 D (0.12 D/0.25 D increments), and axis 0° to 180° (1°/5° increments) [5].
Topcon TRK-2P is a table-mounted instrument that assembles a refractor keratometer, non-contact tonometer, and pachymeter in one compact device. However, these devices are large, difficult to move, and not appropriate for bedridden patients, infants, or any patient who cannot sit down to get measurements. The refractive measurement range of Topcon TRK-2P is -30 D to + 25 D sphere (0.12 D/0.25 D increments), 0 D to 12 D cylinder (0.12 D/0.25 D increments), and 0° to 180° (1°/5° increments) astigmatic axis.[6] Topcon TRK-2P also uses a fogging mechanism to diminish accommodation.
Screening the refractive error in childhood and adolescence without cycloplegia is controversial. Because accommodation is more active at these ages, it is challenging to estimate myopia’s prevalence or latent hyperopia. The cycloplegic refraction is strongly recommended, especially in patients with strabismus or high refractive error [7, 8].
Cycloplegic agents have some side effects such as irritation, burning, photophobia. Some adverse reactions, such as concentration and memory problems, confusion, drowsiness, disorientation, and seizures, were reported [9, 10]. However, these side effects are temporary and well-tolerated. Although some studies have shown that a handheld auto-refractometer is useful for non-cycloplegic screening for refractive errors, cycloplegic refraction is recommended to avoid problems caused by accommodation and to determine latent refractions in childhood and adolescence [11].
The accuracy of varied auto-refractometers differs concerning Spwr, Cpwr, SE, and Cax, depending on cycloplegia. Mirzajani et al.[12] reported prominent variation in the Spwr, SE, and J45 vector between the Nidek table-mounted auto refractometer (Nidek ARK-510A; Gamagori, Japan) and Nidek ARK-30 handheld auto refractometer (NidekARK-30) in a multi-stage cluster sampling cross-sectional study. They found a strong positive correlation and fair agreement for Spwr, SE, J0, and J45 vectors. However, the patients’ mean age was 32.7 ± 18.72 years, ranged from 3 to 90 years, and refractive measurements were undertaken in non-cycloplegic conditions with both devices.
Akil et al.[13] compared outcomes of a handheld (Retinomax K-plus 3; Righton, Tokyo, Japan) and a table-mounted (Canon RK-F1; Canon USA Inc., Lake Success, NY, USA) auto-refractometer. They evaluated significantly hyperopic results for mean SE with Canon RK-F1 before cycloplegia. Good agreement and no significant difference was obtained for Spwr, Cpwr, J0, and J45 among Retinomax K-plus, Canon RK-F1, and cycloplegic retinoscopy after cycloplegia. However, their sample size was relatively small, and they did not compare the results in subgroups that were designed to measure Spwr and Cpwr.
In a cross-sectional study, Oral et al.[14] evaluated the cycloplegic results of a handheld autorefractor with cycloplegic retinoscopy and reported no significant difference in terms of mean Spwr, Cpwr, and SE, and a strong correlation with each other. Nevertheless, they also did not consider the results in subgroups that were designed for the Spwr and Cpwr.
Farook et al.[15] compared a handheld autorefractor (Retinomax K-plus 3; Righton, Tokyo, Japan) with a table-mounted autorefractor (Topcon RM8000B; Tokyo, Japan) and subjective refraction. They found that the Retinomax measured more myopia than the Topcon RM8000B and subjective refraction. However, their measurements were in non-cycloplegic condition and included adult participants.
Seymen et al.[16] compared three handheld autorefractors (HandyRef-K, Retinomax, and Plusoptix). They reported no significant difference among three handheld devices for mean Spwr and Cax. However, the mean SE measured with Plusoptix was significantly more myopic compared to HandyRef-K and Retinomax. The authors also found that the mean Cpwr measured by HandyRef-K was considerably higher compared to Plusoptix and Retinomax. In their study, refractive measurements with Plusoptix were undertaken in non-cycloplegic conditions, while those with HandyRef-K and Retinomax were in cycloplegic states. Moreover, they did not compare the mean J0 and J45 values.
This current study was designed as an observational cross-sectional study in pediatric patients whose ages ranged from 5 to 16 years in cycloplegic conditions. We found that the Nidek HandyRef-K handheld autorefractor measured more astigmatism and myopia in terms of mean Cpwr, SE, and showed more prominent Cax compared to Topcon TRK-2P. Nidek HandyRef-K showed significantly myopic results in subgroups with Spwr between + 1.50 D and + 4.50 D hyperopia, more than + 4.50 D hyperopia, and − 3.00 D myopia. Nidek HandyRef-K also showed more prominent astigmatism and axes in the subgroup with Cpwr less than − 1.00 D compared to the Topcon TRK-2P. Clinically, there was a good agreement for Spw, Cpwr, SE, J0, and J45. There was also a strong correspondence for Spwr, Cpwr, SE; a moderate positive correlation for J0; and a weak positive correlation for J45 between two devices.
This study had some limitations. The primary flaw was not comparing the results with cycloplegic retinoscopy. We could not measure cycloplegic retinoscopy from all the patients due to technical problems with the device when the study continued. Therefore we did not reach enough cycloplegic retinoscopy results for the comparison. We also did not compare the repeatability of Spw and Cpwr with both devices.
In conclusion, the two autorefractors showed clinically suitable agreement intervals and reliability for Spwr, Cpwr, SE, J0, and J45 in cycloplegic conditions, although Nidek HandyRef-K measured more astigmatism and myopia. Nidek HandyRef-K showed significantly myopic results in patients whose Spwr was more than + 1.50 D hyperopia and − 3.00 D myopia and more prominent astigmatism in patients whose Cpwr was less than − 1.00 D compared to Topcon TRK-2P. These differences should be kept in mind in clinical practice to correct the refractive error in pediatric age.