Abstract
AIM
To compare noncycloplegic and cycloplegic results of Retinomax measurements with findings achieved after cycloplegia using table-top autorefractor and retinoscopy.
METHODS
The study included 127 patients (mean age 96.7mo, range 21 to 221). Retinomax (Rmax) (Nikon Inc., Japan) was used to obtain noncycloplegic refraction. Under cycloplegia, refraction was measured with Rmax, table-top autorefractor (TTR) (Nikon NRK 8000, Inc., Japan) and retinoscopy. The values of sphere, spherical equivalent, cylinder and axis of cylinder were recorded for Rmax, TTR and retinoscopy in each eye. All results were analyzed statistically.
RESULTS
The mean spheric values (SV), spherical equivalent values (SEV) and cylindrical values (CV) of the noncycloplegic Rmax (SV: 0.64 D, SEV: 0.65 D and CV: 0.03 D, respectively) were found to be significantly lower than cycloplegic TTR (1.43 D, 1.38 D and 0.3 D; P=0.012, P=0.011 and P=0.04, respectively) and retinoscopy (1.34 D, 1.45 D and 0.23 D; P=0.04, P=0.002 and P=0.045, respectively). Mean cycloplegic SV, SEV, CV were not significantly different between Rmax and TTR, Rmax and retinoscopy, TTR and retinoscopy. Cycloplegic or noncycloplegic axis values were not different between any method.
CONCLUSION
Rmax may be used successfully as a screening tool but may not be accurate enough for actual spectacle prescription. Cycloplegic Rmax measurements may be able to identify refractive error in children because of approximate results to retinoscopy.
Keywords: autorefractor, hand-held refractors, retinoscopy, Retinomax
INTRODUCTION
Abnormal refractive errors in childhood may lead to amblyopia[1],[2]. Early detection and prompt treatment of refractive errors can prevent amblyopia and strabismus[1],[3]. For this reasons, to identify and correct the refractive errors as early as possible is crucial. The traditional method for identify refractive errors in children includes noncycloplegic and cycloplegic retinoscopy which performed by skilled experienced ophthalmologist. Conventional retinoscopy requires long training for examiners and cooperative patients. Therefore, there has been an effort to develop techniques and instruments that permit detection of refractive errors with minimal requirement of cooperation in children. Autorefractors have been used for some years but may not be suitable for use in small children becuse of their immobility[4]–[8]. Currently, hand held autorefractors (HHR) allow refractive errors to be estimated rapidly. Several authors have already studied its accuracy and reproducibility as a screening device[7]–[11].
The aim of this study was to investigate the accuracy of the Retinomax, to compare results of Retinomax measurement in children under noncycloplegic condition with findings achieved after cycloplegia using table-top autorefractor and retinoscopic results of an experienced pediatric ophthalmologist and to asses the agreement between these results.
SUBJECTS AND METHODS
One hundred and twenty-seven consecutive patients were evaluated for ophthalmological assesment. Written informed consent was obtained from parents of all children. The conduct of the study followed the tenets of the Declaration of Helsinki. This study was conducted in accordance with ethical guidelines. Visual acuities were obtained with Snellen letters, Allen pictures or Teller acuity card according to children ages. After initial ocular and systemic history visual acuities recorded, the full ophthalmic examination includes cover test, TNO stereotest and anterior segment examination. We excluded subjects with squint, media opacity, amblyopia or any cause of decreased vision before the study. Retinomax (Rmax) (Nikon Inc., Japan) was used to obtain noncycloplegic refraction. Cycloplegia was achieved by instillation of one drop of 1% cyclopentolate and one drop 1% tropicamid 5min apart. Refraction was measured with Rmax and table-top autorefractor (TTR) (Nikon NRK 8000, Inc., Japan) 45min after the last instillation. Subsequently, the child was manually refracted and refined by an experienced pediatric ophthalmologist who was masked to previous autorefractor's results. The refined refraction was accepted as the ‘gold standard’. All measurements were made during same consultation. The values of sphere, spherical equivalent, cylinder and axis of cylinder were recorded for Rmax, TTR and retinoscopy in each eye. The spherical equivalent values (SEV) was calculated as the sum of the sphere plus half the cylindrical power. The pateints who could not be refracted by autorefractor because of poor compliance or whose measurements' reliability was under <8 were excluded. Moreover, in cycloplegic retinoscopic examination, the refraction results of -1.00 D or greater, +2.50 D or greater, and +1.00 D or greater were defined as myopia, hyperopia and astigmatism, respectively. The diagnostic accuracy of refractive errors was assessed by sensitivity and specificity.
SPSS statistical software, version 16.0 (SPSS Inc., Chicago, IL, USA) was used for statistical analysis. Refraction techniques were compared by analysis of variance test (ANOVA). A variance ratio (F) was calculated to determine overall statistical differences. Paired t-test was then used to investigate individual statistical differences between the methods. A P-value of <0.05 was considered statistically significant.
RESULTS
One hundred and twenty-seven patients (254 eyes) were evaluated as a study group. The mean age of patients was ranged from 21-221mo (mean 96.7mo). Sixty-two of patients (48.8%) were female, 65 of patients (51.2%) male.
In noncycloplegic children, using the Rmax, the mean spherical value (SV) was 0.64 D (range -10.50 to 14.00), mean cylindrical value (CV) was 0.03 D (range -3.50 to 5.00) and mean axis measurement was 71.9° (range 0 to 180). The mean SEV was 0.65 D (range -11.75 to 15.88). According to SEV, 82 (32.3%) of eyes were myopic, 111 (43.7%) were hyperopic and 61 (24%) were plano. Astigmatism was found in 91 (35.8%) of eyes, 67 (73.6%) of these eyes had a CV more than 1.00 D.
In cycloplegic measurements, using the Rmax, the mean SV was 1.27 D (range -10.00 to 15.00), mean CV was 0.18 D (range -3.75 to 5.00) and mean axis measurement was 74.9° (range 0 to 180). The mean SEV was 1.36 D (range -11.75 to 15.88). According to SEV, 49 (19.3%) of eyes were myopic, 153 (60.3%) were hyperopic and 52 (20.4%) were plano. Astigmatism was found in 81 (33.1%) of eyes, 70 (83.3%) of these eyes had a CV more than 1.00 D.
The mean SV recorded with TTR was 1.28 D (range -10.75 to 14.00), mean CV was 0.3 D (range -3.00 to 4.75) and mean axis measurement was 81.4° (range 0 to 180). The mean SEV was 1.43 D (range -12.63 to 14.75). A myopic SEV was found in 45 (17.7%) of the eyes, 153 (60.2%) were hyperopic and 56 (22.1%) plano. Astigmatism was diagnosed in 78 (30.7%) of eyes, 54 (69.2%) of these eyes had a CV more than 1.00 D.
The mean SV recorded using retinoscopy was 1.34 D (range -9.00 to 13.00), mean CV was 0.23 D (range -3.50 to 5.00 ) and mean axis measurement was 75.9° (range 0 to 180). The mean SEV was 1.45 D (range -10.00 to 14.00). According to SEV, 38 (15.0%) of eyes were myopic, 168 (66.1%) were hyperopic and 48 (18.9%) were plano. Astigmatism was found in 83 (32.7%) of eyes, 33 (39.8% ) of these eyes had a CV more than 1.00 D. These findings were summarized in Table 1.
Table 1. The mean sphere, spherical equivalent, cylinder and axis values.
| Mean values | Rmax (NC) | Rmax (C) | TTR | R |
| Sphere | +0.64 | +1.27 | +1.28 | +1.34 |
| Spherical equivalent | +0.65 | +1.36 | +1.43 | +1.45 |
| Cylinder | +0.03 | +0.18 | +0.3 | +0.23 |
| Axis | 71.9° | 74.9° | 81.4° | 75.9° |
Rmax: Retinomax; NC: Noncycloplegic; C: Cycloplegic; TTR: Table-Top Autorefractor; R: Retinopathy.
ANOVA testing of SV revealed an F ratio of 3.905 (P=0.009) which indicates an overall difference. Comparison of noncycloplegic Rmax with retinoscopy based on SV showed statisttically significant difference (P=0.040). Also, there was statistical difference between noncycloplegic Rmax and TTR results (P=0.012). The difference among cycloplegic Rmax, TTR and retinoscopy measurements was not statistically significant (P>0.05, for all) (Table 2).
Table 2. Statistical analysis of data for spherical values. Agreement between different techniques.
| ANOVA for sphere |
t-test for sphere |
|||||
| Rmax(NC) vs TTR | Rmax(NC) vs R | Rmax(C) vs TTR | Rmax(C) vs R | TTR vs R | ||
| F=3.905 | d | 0.65 | 0.71 | 0.11 | -0.07 | -0.06 |
| P=0.009 | P | 0.012 | 0.040 | 0.787 | 0.125 | 0.145 |
| 95%CI | 0.0146 to 1.153 | 0.224 to 1.204 | -0.068 to 0.089 | -0,173 to 0.212 | -0.152 to 0.227 | |
| Different | Different | Different | Similar | Similar | Similar | |
d: Mean difference between measurement technique; ANOVA: Analysis of variance test; CI: Confidence Interval; F: Variance ratio; Rmax: Retinomax; NC: Noncycloplegic; C: Cycloplegic; TTR: Table top autorefractor; R: Retinoscopy.
ANOVA testing for CV did not show any statistical differences (F=1.866, P=0.136). Statistically significance between the noncycloplegic Rmax versus TTR and noncycloplegic Rmax versus retinoscopy were demonstrated (P=0.040 and P=0.045, respectively). The difference among cycloplegic Rmax, TTR and retinoscopy measurements was not statistically significant (P>0.05, for all) (Table 3).
Table 3. Statistical analysis of data for cylinder values. Agreement between different techniques.
| ANOVA for cylinder |
t-test for cylinder |
|||||
| Rmax(NC) vs TTR | Rmax(NC) vs R | Rmax(C) vs TTR | Rmax(C) vs R | TTR vs R | ||
| F=1.866 | d | 0.27 | 0.20 | 0.12 | -0.04 | 0.06 |
| P=0.136 | P | 0.040 | 0.045 | 0.178 | 0.420 | 0.470 |
| 95%CI | 0.078 to 0.329 | 0.005 to 0.404 | -0.051 to 0.275 | -0.165 to 0.692 | -0.111 to 0.239 | |
| Similar | Different | Different | Similar | Similar | Similar | |
d: Mean difference between measurement technique; ANOVA: Analysis of variance test; CI: Confidence Interval; F: Variance ratio; Rmax: Retinomax; NC: Noncycloplegic; C: Cycloplegic; TTR: Table top autorefractor; R: Retinoscopy.
ANOVA testing for SEV indicated an overall statistical difference (F=7.489,P=0.01). Comparison of noncycloplegic Rmax versus TTR and noncycloplegic Rmax versus retinoscopy was statistically different (P=0.011 and P=0.002, respectively). The difference between cycloplegic Rmax, TTR and retinoscopy measurements was not statistically significant (P>0.05, for all) (Table 4).
Table 4. Statistical analysis of data for spherical equivalent values. Agreement between different techniques.
| ANOVA for spherical equivalent |
t-test for spherical equivalent |
|||||
| Rmax(NC) vs TTR | Rmax(NC) vs R | Rmax(C) vs TTR | Rmax(C) vs R | TTR vs R | ||
| F=7.489 | d | 0.73 | 0.85 | 0.14 | -0.14 | -0.13 |
| P=0.01 | P | 0.011 | 0.002 | 0.736 | 0.625 | 0.657 |
| 95%CI | 0.165 to 1.29 | 0.313 to 1.387 | -0.068 to 0.096 | -0.239 to -0.034 | -0.220 to -0.024 | |
| Different | Different | Different | Similar | Similar | Similar | |
d: Mean difference between measurement technique; ANOVA: Analysis of variance test; CI: Confidence Interval; F: Variance ratio; Rmax: Retinomax; NC: Noncycloplegic; C: Cycloplegic; TTR: Table top autorefractor; R: Retinoscopy.
ANOVA testing for axis values did not show any statistical differences (F=1.721, P=0.161). Also, there was no statistical difference between any method in t-test in term of axis values (Table 5).
Table 5. Statistical analysis of data for axis values. Agreement between different techniques.
| ANOVA for axis |
t-test for axis |
|||||
| Rmax(NC) vs TTR | Rmax(NC) vs R | Rmax(C) vs TTR | Rmax(C) vs R | TTR vs R | ||
| F=1.721 | d | 9.56 | 4,03 | 6.44 | 9.13 | -5.53 |
| P=0.161 | P | 0.06 | 0.260 | 0.190 | 0.792 | 0.114 |
| 95%CI | -0.24 to 19.35 | -2.98 to 11.03 | -3.20 to 16.09 | -5.88 to 7.71 | -12.39 to 1.33 | |
| Different | Similar | Similar | Similar | Similar | Similar | |
d: Mean difference between measurement tecnique; ANOVA: Analysis of variance test; CI: Confidence Interval; F: Variance ratio; Rmax: Retinomax; NC: Noncycloplegic; C: Cycloplegic; TTR: Table top autorefractor; R: Retinoscopy.
The sensitivity and specificity are shown for cycloplegic Rmax and TTR (Table 6).
Table 6. The sensitivity and specificity for cycloplegic Retinomax (Rmax) and Table-Top Autorefractor (TTR).
| Parameters | Sensitivity (Rmax) | Specificity (Rmax) | Sensitivity (TTR) | Specificity (TTR) |
| Hyperopia | 93 | 79 | 92 | 72 |
| Myopia | 68 | 100 | 75 | 100 |
| Astigmatism | 72 | 86 | 70 | 88 |
%
DISCUSSION
Screening of amblyopia is difficult because visual acuity cannot be easily measured in children. Acuity cards are not accurate for the diagnosis of amblyopia and are difficult to use in the community screening situation where testing conditions are often less than ideal. Screening of children might best be carried out by detecting the risk factors for amblyopia such as strabismus and abnormal refractive errors rather than directly measuring visual acuity. HHR would be useful for screening for abnormal refractive errors, in addition to its possible use in clinical management[12]–[14].
The Rmax is a hand held instrument designed to provide a rapid estimate of refractive error. The portability and ease of use of the Rmax suggest that it might be a useful tool for providing definitive measurements of refractive error under cycloplegic conditions for use in research studies, and may be useful for screening young children for high refractive errors under noncycloplegic conditions[4]. But some studies showed that screening with the Rmax under noncycloplegic conditions resulted in overcorrection and too many false-positive referrals[15].
El-Defrawy et al[5] reported that the results of Rmax and retinoscopy under cycloplegia were similar for SV but the difference between the mean CV obtained by two methods was statistically significant, on the other hand this difference was clinically insignificant (0.23 D). And results using the Rmax without cycloplegic were grossly inaccurate. Kallay et al [16] reported high agreement of three refractive measurements (sphere, cylinder and axis) between the on table autorefractor and Rmax under cycloplegia. Liang et al[8] reported the difference of SV under the cycloplegic condition was significantly different from that under noncycloplegic condition by Rmax and TTR (0.59 D). Although this difference is within a clinical acceptable range, SV in the cycloplegic eyes measured by the 2 types of autorefractors were almost identical. Difference of cylinder and axis was not significantly in either cycloplegic or noncycloplegic condition.
Prabakaran coworkers[11] stated that mean SEV obtained from Rmax with cycloplegia (0.8 D) was significantly less than retinoscopy (1.09 D) while no significant difference was noted between TTR and retinoscopy. Astigmatism measured with Rmax (-0.89 D) and TTR (-0.83 D) were significantly greater than that retinoscopy (-0.58 D).
In present study, the mean SEV with cycloplegic Rmax 0.09 D more myopic than retinoscopy, but this diffrence was not statistically significant. Also, the difference of mean SV, SEV, CV and axis values under cycloplegia were not statistically significant between any methods (Rmax, TTR and retinoscopy).
Previous studies demonstrated Rmax measurements without cycloplegy were grossly inaccurate[5],[15]. Similarly, the current study showed that noncycloplegic Rmax measurements (SV, SEV and CV) were significantly lower than all cycloplegic measurement methods.
A few studies involving cyclopleged children where little difference was noted in spherical, cylinder or axis measurements for Rmax, TTR and retinoscopy[15]–[17]. In addition, Rmax, TTR and retinoscopy measurement with cycloplegic were revealed likely results most of studies in literature[5],[8],[11],[16],[18],[19].
Refractive errors definition differs between studies, there are wide ranges for sensitivity and specificity ratios were shown in these studies. Choong et al[15] reported the sensitivity and specificity in detecting myopia greater than 0.50 D was 100% and 51%, whereas that for hyperopia greater than 0.50 D was 84% and 82%, respectively. The Vision In Preschool study group reported a sensitivity of 66% for significant refractive errors with Rmax[20]. In our study, sensitivity and specificity for the Rmax were 68% and 100% for myopia, 93% and 79% for hyperopia and 72% and 86% for astigmatism, respectively. Similar to other studies we found that, the Rmax had slightly lower sensitivity for detecting myopia[9],[21]–[23].
In conclusion, noncycloplegic Rmax values were significantly ‘minus’. This difference was 0.80 D. This support the argument that, Rmax might be used successfully as a screening tool but may not be accurate enough for actual spectacle prescription. The accuracy of the Rmax and TTR when compared with retinoscopy were similar under cycloplegic condition. Because of the reliable results of measurements and easier to use in detection of refractive errors, cycloplegic Rmax can be used as an alternative method to cycloplegic retinoscopy in children.
Acknowledgments
Conflicts of Interest: Tuncer I, None; Zengin MO, None; Karahan E, None
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