European Journal of Cardiovascular Medicine

The differences between cycloplegic and noncycloplegic automated refraction are due to the accommodative response of the individual. In younger persons, accommodation can greatly influence refractive error measurement. Studies in children have found that autorefraction estimates without pharmacologic cycloplegia are more myopic than autorefraction estimates obtained after cycloplegia, particularly among children with hyperopia. ^[1] Due to the magnitude of these differences, methods of refraction without cycloplegia are often considered inappropriate for measuring refractive error in children. An autorefractometer can predict the accommodative system activation in children and young adults, and it is less time consuming & comfortable to the patients. ^[2] Latent refractive errors cannot be accurately diagnosed in youngsters due to accommodation. With the advent of handheld AR machines (Retinomax), AR is being considered as screening tool to evaluate refractive error among children. It may be useful in young adults as well. ^[3]

Refractive error is a global health concern affecting a huge number of people and is associated with various ocular morbidities, overall prevalence of refractive errors was found to be 29%. A refractive error study in children (RESC) in India showed, hyperopia present in 7.7% of children & myopia in 7.4%. Correction of significant refractive errors in childhood helps in preventing amblyopia & strabismus. ^[4]

Cycloplegic refraction is considered as the gold standard for measuring refractive errors in epidemiologic studies in children and adolescents. It has been well-established that generally myopia could be overestimated and hyperopia be underestimated if refraction was performed without cycloplegia, but to which extent the prevalence of refractive errors is overestimated or underestimated in different populations is different as the prevalence of refractive errors seems to be a major determinant for the difference between cycloplegic and non-cycloplegic refractive error. ^[5] Purpose of our study is to compare noncycloplegic refractive error with cycloplegic refractive error using autorefractometer among patients between the age group of 5-30 years.

Automated refraction (AR) is a computer-controlled machine to provide an objective measurement of a person's refractive status. It is quick, simple, user friendly, and independent of examiner.

Sixty-three patients in the age group of 5-25 years were included in the study. The study period was six months. The study was approved by the institutional ethics committee. Informed consent of the patient obtained. Uncooperative patients, patients with history of ocular trauma and patients outside the specified age group were excluded from the study. Age, gender, socioeconomic status, area of residence and occupation were recorded. The distant visual acuity was assessed uniocularly by using snellen’s visual acuity chart at a distance of 6 meters. Automated refraction was done using Shin Nippon Accurate K 9001refractometer before and after putting homatropine bromide 2% eye drops three times at an interval of ten minutes. Complete cycloplegia was confirmed by making the patient to read near vision chart. A decrease in visual acuity corresponding to doubling of visual angle for both distance and near were ensured. 

Three readings were taken for each eye and the average of these values were calculated. Cycloplegic retinoscopy was done after dilated AR by another observer and compared. Spherical equivalent was derived after correcting for distance and drug. Statistical analysis was performed with PASW version 18. Chi square test was used for univariate analysis. One way Anova was used to measure variance

In our study included 48.9% of males and 51.1% female patients, with maximum patients 30 (33.3%) in age group of 16-20years.

Table 1: Gender distribution of sample population

Table 2: Age distribution of sample population

Table 3: Comparison of pre and post score of Cycloplegic AR values in hypermetropia for right eye

Table 4: Comparison of pre and post score of Cycloplegic AR values in hypermetropia for left eye

Comparison of pre & post cycloplegic values of Autorefactrometer values in 23 & 24 right and left eyes of hypermetropia patients respectively, there was a significant increase in number of patient from dioptric range (+0.25 to +1.25) to (+2.75 to +3.75), which was 12 to 28 and 20 to 31 right and left eyes respectively, with (p- value= 0.0001) in right eye and (p-value = <0.001) in left eyes, which is significant.

Comparison of pre & post cycloplegic values of autorefactometer values in 36 & 34 right and left eyes of myopic patients respectively, there was decrease in number of patients in dioptric range (-2.75 to -3.75) from 22 to 1 in right eyes and decrease in number of patients in dioptric range (4.00 to 5.00) from 18 to 0 after cycloplegia in left eyes, with (p-value for the table= 0.0003140) for the right & (p = 0.0003234) for the left eyes, which is significant.

There was no significant shift in number of patients pre and post dilation in both eyes of patients of myopic astigmatism, with (p-value = 0.6484) and (p-value = 0.3868) for right and left eyes respectively, which are not significant. All patients accepted post cycloplegic autorefractometer values without any complications with good visual acuity and relief in asthenopic symptoms.

Table 5: Comparison of pre and post score of Cycloplegic AR values (minus) in myopia for right eye

Table 6: Comparison of pre and post score of Cycloplegic AR values (minus) in myopia for left eye

Table 7: Comparison of pre and post score of Cycloplegic myopic astigmatism for right eye

Table 8: Comparison of pre and post score of Cycloplegic myopic astigmatism for left eye

Objective determination of refractive status is a prerequisite for the subjective adjustment of refraction prior to prescription of glasses. Refractometry finds wide use in current ophthalmic practices, and is being used extensively for objective determination of refraction. During the last few years automated refractometry has gained tremendous popularity. This trend is supported by the possibility of delegating automated refractometry to assistant medical personnel.

Topcon KR8800 autorefractometer, which was used in present study, can measure, hyperopia of 0 to + 22D with a 0.25D step display, switchable to 0.12D, and myopia of 0 to -25D, with a 0.25D step display which is switchable to 0.12D. With respect to corneal features, it measures astigmatism of 0 to 10D with a 0.25D step display, which is switchable to 0.12D. Axial angle can be measured from 0 to 180°, with 1° step display which is switchable to 5° step display. In retinoscopy, the range depends on the available lenses in the trial set.

In the present study, the spherical power estimated by retinoscopy was subjectively accepted by 87.6% of the eyes while 12.4% of the eyes didn’t accept it. The cylindrical power on the other hand, as estimated by retinoscopy was accepted by 57% of the eyes and the axis on retinoscopy was accepted by 60.6% of the eyes. The retinoscopy estimation of cylinder power and axis was not accepted by 43% and 39.4% of the eyes respectively.

The spherical power as estimated by AR was accepted as it is subjectively by 43.4% of the eyes while 56.6% of the eyes didn’t accept it. The cylindrical power on the other hand estimated by AR was accepted by 78.6% of the eyes and axis on AR was accepted by 72.8% of the eyes. The AR estimation of cylinder power and axis was not accepted by 21.4% and 27.2% of the eyes respectively.

Consistent with the results of our study, in a study by Vilaseca et al where differences in Spherical Equivalent between the double-pass system and the other techniques were studied, retinoscopy was found to give more hypermetropic values than the double-pass system -0.51 ± 0.50D and also the subjective refraction -0.23 ± 0.50D while, more myopic values were yielded by means of autorefraction- 0.24 ± 0.49D. ^[6-10]

Similar to the results of our study, in a study by Jorge et al, the results obtained for the value of the spherical equivalent revealed that the values obtained by autorefractometer were more negative in the myopia and less positive in the hypermetropia as compared to retinoscopy and subjective refraction. ^[11]

Similar to the results of our study, a multitude of other studies in which different models of autorefractor were evaluated, also showed the same tendency of the autorefractor to underestimate the value of the refractive error in relation to the other two methods. Also in the study by Jorge et al, the retinoscopy and subjective refraction confidence interval was one-half that of the autorefractor and subjective refraction, and they concluded that, retinoscopy could be half a dioptre more precise than autorefraction, in the estimation of an objective start point for noncycloplegic refraction. ^[12] In our study, the mean SE with retinoscopy was 1.64 ± 1.26 (95% CI -0.88 to 4.16 D), with AR was 1.84 ± 1.36 (95% CI -0.88 to 4.56 D) and subjectively, it was 1.70 ± 1.29 (95% CI -0.88 to 4.28 D). In the study by Jorge et al, 44.3% accepted the sphere power obtained by AR and 74.5% accepted the retinoscopy estimates better. Regarding cylinder power 89.6% accepted AR values, while 96.9% accepted retinoscopy values. Also, with reference to cylinder axis, 55.2% accepted AR while, 65.6% accepted retinoscopy values. In this study, the spherical power acceptance correlates with our study, but the cylindrical power acceptance and axis of cylinder acceptance does not correlate with our study. ^[13]

In another study conducted on astigmatic powers in adults, prior to refractive surgery, it was concluded that noncycloplegic retinoscopy was the least reliable method with respect to cylindrical refractive powers as well as their axis.8 Our study was done with cycloplegia, and it revealed that retinoscopy is a relatively less reliable modality for estimating cylinder axis as well as power.

In our study, out of the tested eyes, 375 eyes i.e. 75% improved to 6/6, 76 eyes i.e. 15.2% to 6/9, 35 eyes i.e.7% to 6/12 and only 14 eyes i.e. 2.8% were able to read the 6/18 line on the Snellen’s chart on testing vision with a pin hole. In our study, it was observed that 450 eyes i.e. 90% of eyes improved visual acuity to 6/6, 20 eyes i.e. 4% improved to 6/9 and 6/18 and only 10 eyes i.e. 2% improved to 6/12.

Though AR produces a fast, repeatable measurement of refractive error, its validity is as important as its efficiency. Thus, it is important to assess its agreement with correction accepted by the patient. In present day ophthalmic practice, ARs are also widely used in optometric and ophthalmic research e.g., to examine refractive error development, accommodative responses, and comparison of pre- to- postoperative condition.

Guirao and Williams suggested that the possible source of disagreement between the various methods of refraction like retinoscopy, autorefractometer and subjective refraction is the presence of higher- order aberrations in the human eye. An important reason for this is that the pupil size may be larger while performing retinoscopy or AR, as compared to the size of the pupil during subjective correction. The larger the amount of higher- order aberrations present, the greater will be the amount of disagreement between various methods of refraction. ^[14]

Consistent with the results of our study, Uras R et al study results showed that for the mean spherical equivalent (M), the autorefractor yields more negative values. The result also showed that when performed by an experienced clinician, retinoscopy was more accurate than automatic refraction. Retinoscopy gives a better starting point to noncycloplegic refraction. ^[15]            

Thus, our study revealed that the agreement displayed by both retinoscopy and AR with respect to acceptance by patients, is similar. However, higher agreement was found with retinoscopy for the spherical power component, while AR was slightly better for cylindrical component of refractive error as well as axis of cylinder.

Retinoscopy is a reliable starting point for refraction; however, autorefraction values are important in order to accurately prescribe cylindrical correction. Autorefractometer is an invaluable aid for screening large number of cases in busy ophthalmological clinics. But it should not replace the art of clinical refraction testing and should be used with great caution especially in younger patients in whom accommodation is more active because of which true extent of hypermetropia may be unrevealed. Manual retinoscopy is still the most accurate technique to estimate refractive status especially in children and gives better starting point for refraction.

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