Comparative Study between Mohindra Retinoscopy and Subjective Refraction, in Young Adults with Accommodative Excess

Purpose: The aim of this study was to compare the results of three refractive techniques: Autorefractor (AR), Mohindra Retinoscopy (MR) and Monocular Subjective (MS) and study the differences between the results of Mohindra Retinoscopy and Monocular Subjective test, in subjects with accommodative excess. Methods: The refractive measurements were taken with the open field AR (Grand Seiko WAM-5500), the monocular subjective refraction and MR, and measures of accommodative flexibility and Monocular Estimated Method (MEM) were also taken, in 85 right eyes of 85 healthy university students. (22.3±2.4 years). Results: Statistically significant differences were found on the spherical equivalent for the three techniques, with the Friedman statistical test (N=85; χ_F^2=42.771; p<0.0001). The MR is the technique that provide more positive results and the AR the most negative. Regarding astigmatic components there was no statistically significant differences found between the techniques, with de Friedman statistical test. Data were also analyzed based on accommodation function and there were no statistically significant differences found between subjects with accommodative excess and subjects with normal accommodation, for the spherical equivalent (N=74; H=1.785; p=0.410), and for J0 component (N=74; F=0.948; p=0.392), with the Kruskal-Wallis statistical test. Conclusion: These results revealed significant differences between the three refractive techniques in young adults, independently of accommodative state. The open field AR overestimated some degree of accommodation during the refractive measurements and the MR was the technique that presented more positive results, even in subjects with normal accommodative function. Regarding astigmatic components, all the techniques provide similar results.

accommodation, cycloplegic refraction should be used. The active principle of the drugs used is to relax and paralyze accommodation [2,3]. Cycloplegic retinoscopy, in addition to Subjective refraction, is a technique considered standard in the measurement of the refractive state [9]. However, it is associated with temporary symptoms of blurred vision, photophobia and discomfort due to paralysis of the accommodation. In addition, Cycloplegic Retinoscopy is contraindicated in people with heart problems, primary glaucoma, people prone to glaucoma (narrow anterior chamber angle), and hypersensitivity to any of the excipients of the drug [9][10][11].
According to Mohindra, the Mohindra Retinoscopy is a good substitute technique for Cycloplegic Retinoscopy and provides similar results when used the correct correction factor, without the disadvantages indicated, a fact supported by other authors [9,12,13]. Recently, the use of open field autorefractor has become a widely used technique for measuring refractive state [9]. There is scientific evidence showing that the use of the autorefractor, without cycloplegics, has a reasonable precision when compared to the values obtained by Cycloplegic Retinoscopy and Subjective Refraction [9,[14][15][16][17]. However, there are also studies that show that the autorefractors without cycloplegics, fails to completely neutralize patients accommodation. In these studies, the results obtained by open field autorefractor leaded to a reduction in the accuracy of measurements between 0.01 and 0.38 diopters (D) towards myopia. This fact is especially relevant in people with large accommodative reserves [9,[17][18][19]. Participants were also excluded from taking medication that would interfere with accommodative function. Inclusion factors were the achievement of usual visual acuity better or equal to 0.1 logMAR and presentation for optometric evaluation without contact lenses.
Refractive and accommodative measures were taken. In order to study the refractive function.
The following acquisitions were made: a) Refractive and accommodative measures were taken. In order to study the refractive function, the following acquisitions were made: Monocular habitual VA at 4 meters, using wellcontrasted ETDRS charts for far vision.

Results
Considering the usual refraction of the volunteers who participated in this study, 44.7% had myopia, 52.9% were emmetropic, and 2.4% had hyperopia. The spherical equivalent of the usual refraction was divided according to criteria provided by the American Academy of Optometry [20,21]. The usual refractive error of the sample ranged from -7.75 to +2.25 spherical diopters.
The maximum magnitude of astigmatism was -3.75 cylindrical diopters. For the comparative study between the results of the different refractive techniques used in this work, the powers obtained in sphero-cylindrical form were converted to their vector components according to Thibos [22]. The spherical equivalent The graphs of ( Figure 1)

Discussion
The most prevalent spherical ametropia found in this study was myopia, with the low magnitude being the most frequent, which agrees with what is reported in the literature, for the same classification criteria for ametropia [23,24]. In relation to astigmatism, there was a greater predominance of astigmatism with the rule, a fact that has also been announced by other authors in young populations [25][26][27][28]. Regarding the accommodative state, the sample was divided according to the accommodative state in normal accommodation, definite accommodative excess, suspected accommodative excess and other accommodative alterations.
Of the 85 volunteers, 11.8% were classified as having definite accommodative excess, 28.2% with suspected accommodative excess, 47.1% with normal accommodation and 12.9% with other accommodative alterations. The frequency rate found has a value within the same order of magnitude as those indicated by Porker et al, although slightly higher, a situation that is expected, as reported in the literature, due to the change in visual habits derived from the increasing use of new technologies and the increase of hours of intensive study that a higher education requires [1,29]. The main objective of this study was to determine if subjects with an accommodative excess presented differences between the refractive results obtained by an objective technique and a subjective one, performed routinely in clinical practice. As a subjective technique, we used the subjective test because it was considered the standard refractive examination and as objective technique, we used the MR because it is considered the objective refractive technique that presents values closer to those of the Cycloplegic Retinoscopy [9,15,30]. The identification of subjects with accommodative excess was based on the interpretation of the results of the MEM test and the MAF test, following the criteria suggested by other authors [31][32][33].
The results revealed significant differences in SE component between three refractive techniques, and these differences were found to be identical in all groups, regardless of the accommodative state of the volunteers. The open-field AR tends to overestimate some degree of accommodation during refractive measurements, in university students, providing slightly more myopic values than the other techniques, which is also found by other authors and is well documented in the scientific literature [9,17,34,35]. Comparing the open field AR and MS techniques, although statistically significant differences were found through the Friedman test and the multiple mean comparison, these differences present a mean variation of ±0.11 D. These results are in line with those reported by Sheppard and others, who found differences between these two techniques ranging from 0.01 to 0. 38  that the prescription of university students may be overvaluing myopia. Since myopia is the refractive error most prevalent globally, it is strongly related to the excessive use of the near vision [24,38,39]. University students make use of near vision because of the intensive study hours a high education requires. As such, this greater accommodative effort may influence refractive outcomes.
The accommodation factor is quite controlled in children, however, there doesn't seem to be much interest in being controlled in older age groups. Given the changes in lifestyles, increased use of near vision, and increased rates of myopia, university students are expected to present accommodative reserves that may interfere with manual refraction, if they are not controlled. More studies within this area are needed to study the effect of accommodation on refraction in young adults using cycloplegic refraction. As future work, one aspect that deserves attention is to verify if the correction factor of +1.25 D proposed by Mohindra, in this age group, is updated, considering that this study happened in the year of 1977, and until the date there are not studies that verify if it is a good correction factor, in order to minimize the influence of working distance and tonic accommodation. Another aspect that should by studied is the effect of accommodation on refraction in young adults and students, because of the great use of the near work.

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