Lupine Publishers | Trends in Ophthalmology Open Access Journal
Abstract
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.
Keywords:Mohindra retinoscopy; accommodative excess;
monocular subjective refraction; refractive state; university students
Abbreviations:Accommodative Excess (AE);
Visual Acuity (VA); diopters (D); Monocular Estimation Method retinoscopy
(MEM); Autorefractor (AR); Mohindra Retinoscopy (MR); Monocular Subjective
(MS); Monocular Accommodative Facility (MAF); Early Treatment Diabetic
Retinopathy Study (ETDRS); Minnesota Low Vision Reading Test (MNREAD);
spherical equivalent (SE)
Introduction
The
accommodative excess (AE) is the most prevalent dysfunction among the
university students [1]. In this dysfunction, the patient hyper-accommodates,
which implies an excessive accommodative convergence [2]. The excessive use of
accommodative convergence will result in a pseudomyopia, what means a temporary
transition from refraction towards myopia [3- 7]. As such, in individuals with
accommodative excess, due to hyperaccommodation, there is a tendency to obtain
more myopic results in the techniques of subjective refraction, which are the
techniques usually used in clinic [2,8]. Other clinical signs found in subjects
with AE are low astigmatisms against the rule, variable visual acuity (VA),
failure or difficulty in relaxation of accommodation and low values on
Monocular Estimation Method retinoscopy (MEM) (accommodative response without
delay or with advance) [2,8]. In order to obtain a correct ocular refraction
without the influence of 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 [9-11].
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 [9,14-17]. 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 [9,17-19]. The
aim of this study was to compare the results of three non-cycloplegics
refractive techniques: Autorefractor (AR), Mohindra Retinoscopy (MR) and
Monocular Subjective refraction (MS), in university students. The purpose of
this study was to evaluate the results of MR and the results of MS technique,
to understand if the accommodation is being compensated, in addition to
patients ametropia.
Methods
The
data acquisition was performed between October 2017 and January 2018, at the
Optometry Laboratory and the Clinical and Experimental Center of Vision
Sciences. The project complied with the directives of the Helsinki Declaration
and was approved by the Ethics Committee (CE-UBI-Pj-2018-002). Participants signed
a free and informed consent, after knowing the nature of the study. A total of
85 university students’ volunteers (37 women and 48 men), aged between 18 and
30 years (mean age of 22.3±2.4 years), were evaluated. None of the subjects had
strabismus, amblyopia, previous history of refractive surgery or pregnancy.
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.
b)
Mohindra Retinoscopy (MR), using test glasses, loose lenses, and esquiascopia
rules.
c)
Monocular Subjective Refraction (MS), using a CSO LCD monitor, in logMAR scale,
test glasses and loose lenses. and
d)
Autorefractor (AR), using the Grand Seiko WAM-5500 open-field autorefractor
(Japan) with visual stimulus at far of 1.0 logMAR.
The following clinical tests
were performed for the study of the accommodative function:
a)
Monocular Accommodative Facility (MAF), performed on the habitual compensation
of the subjects, using lens flippers of ±2.00 D and MNREAD chart with a
stimulus of 0.2 logMAR; and
b)
MEM, using an accommodative stimulus of 0.2 logMAR and spherical lenses.
The
MR and the MS were performed by different researchers, to guarantee a greater
veracity of the results, since the researchers didn’t know the value of one of
the refractive techniques. MR was performed in a completely dark room after the
volunteer had his eyes closed for five minutes to allow relaxation of
accommodation. The measurement was taken in the right eye over the test glasses
and it was used a combination of spherical and cylindrical loose lenses, with
the left eye occluded. The volunteers were instructed to look right into the
light of retinoscope, that was 50 centimeters away. After de procedure of
retinoscopy, a value of +1.25 D was withdrawn from the final result.
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 (SE) and the
astigmatic components in horizontal/vertical (J0) and oblique (J45) directions
were calculated according to the expressions:
SE = S + c/2
J0 = − c/2 × cos(2×axis)
J45 = −C/2 × sin(2 ×
axis)
The
graphs of (Figure 1) show the distribution of the values for the SE (part A),
J0 (part B) and J45 (part C) components, obtained by each of the refractive
techniques: AR, MS and MR. With respect to the SE component, it can be observed
that of the three refractive techniques used, the open field AR was the method
that presented more myopic values. The MR presented median results very similar
to those of MS, although with slightly more positive values. Regarding the J0
component, it is observed that the median is slightly more positive in MR. The
MS test presented median values very similar to the open field AR, for the J0
component. With respect to J45 component, the results are similar in all three
refractive techniques. (Table 1) reports the mean and standard deviation of the
SE, J0 and J45 components of the three refractive techniques. It is possible to
observe that the mean differences between the techniques are around ±0.25 D,
and MR presents slightly more positive values and the AR the more negative for
the SE component. The comparison of the results of the three refractive
techniques shows that for the SE component, the AR provides more myopic values,
whereas the MR gives more hypermetropy values, and for the J0 and J45
components the techniques provide similar results. The differences found
through the Friedman test, for the SE component are statistically significant,
(2,85=42.771, p<0.0001) and the multiple mean comparisons reveals that there
are statistically significant differences between all pairs of techniques. For
the J0 component, the interpretation of the statistically test result
(2,85=6.607, p=0.037) indicates that this component also presents significant
differences, however through the multiple mean comparison test it is verified
that there is no statistical evidence to state that there are differences
between any pair of techniques. For the J45 component the differences between
the techniques are not significant (2,85=5.801, p=0.055).
In
order to analyze the relationship between the accommodative state and
refraction, the sample was stratified according to the accommodative state in
the following categories: normal accommodation, definite accommodative excess,
suspected accommodative excess, and other types of accommodative alterations.
To carry out this division, the MAF and MEM test standards were used and are
summarized in (Table 2). In this analysis, only the categories of normal
accommodation, suspected accommodative excess and definite accommodative excess
were considered, excluding subjects who presented other types of accommodative
alterations. In order to compare the results of the refractive techniques, as a
function of the accommodative state, two new variables, ΔSE and ΔJ0, were
created, characterized by the difference between MR results and the MS results,
for the SE component and for the J0 component, respectively. Only the SE and J0
components were studied since they are the parameters mentioned in the
literature as those that can be associated with the accommodative excess that
is, pseudomyopia and low astigmatism against the rule. (Table 3) shows the mean
difference and the level of statistical significance among refractive
techniques.
In
order to graphically analyze these small differences between accommodative
groups, the box plots of the SE and J0 components are shown in (Figures 2 &
3), respectively. The comparison of the results of the MR and MS techniques, as
a function of the accommodative state, shows that for the SE component (ΔSE =
MR-MS) the subjects with definite AE are those with higher mean values, meaning
that the value obtained by the MS tends to be more myopic than the one obtained
by MR. for the component J0 (ΔJ0 = MR-MS), the subjects with definite AE
present lower average values, meaning that the results obtained by the MS tend to
be more positive (presence of astigmatism against the rule) than those obtained
by MR. Despite the differences observed graphically, there was no statistical
evidence that those differences were statistically significant, for none of the
components, SE (H2,74=1.785, p=0.410) and J0 (F2,74=0.948, p=0.392).
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 [25-28]. 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- 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 D, with the open field AR presenting the
most negative values [35]. The results of this work showed that MR was the
technique that provided less myopic results. Even in subjects with normal
accommodation, the differences between MR and MS were around ±0.18 D. MR
provided less myopic values than the MS, which coincides with the mentioned by
Natarajan et al. This author concludes that although the values are similar, MR
provides slightly higher values, possibly due to the accommodative tone of
+0.75 D [36]. A single accommodative tonus value may not be advisable for all
age groups and further studies should be conducted in relation to this. The
results of this present study showed that for the age group of university
students, the accommodative tone value of +0.75 D may not be the most adequate,
since more hypermetropic values were obtained with the MR, compared to MS.
Regarding the astigmatic components, no statistically significant differences
were found between the refractive techniques. This means that all the
techniques used provided similar results in relation to astigmatism, which is
in line with found by Mohindra [37].
These
results show that there are statistically significant differences for the SE
component throughout the sample, with MR providing more positive results for
all individuals, around ±0.25 D, regardless of the accommodative state.
Although the findings are statistically significant, clinical routine may be
interpreted as having little significance. However, the results of this study
showed 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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