Objective and subjective assessment of accommodative insufficiency

SIGNIFICANCE

A variety of subjective and objective procedures are available to measure the amplitude of accommodation. However, it is unclear whether the standard criterion of Hofstetter's minimum minus 2 D can be used to diagnose accommodative insufficiency with each of these techniques.

PURPOSE

The use of objective dynamic retinoscopy and three subjective techniques to diagnosis accommodative insufficiency was examined.

METHODS

A total of 632 subjects between 8 and 19 years of age were enrolled. Accommodative lag, monocular accommodative facility, and subjective (push-up, modified push-down, and minus lens) and objective (dynamic retinoscopy) amplitude of accommodation were quantified. Accommodative insufficiency was diagnosed based on Hofstetter's minimum minus 2 D for each subjective method, as well as adding an additional subjective criterion (either accommodative lag exceeding 0.75 D or monocular accommodative facility falling below the age-expected norms).

RESULTS

The prevalence of accommodative insufficiency was lowest and highest with the push-up (7.9 and 1%) and dynamic retinoscopy (94 and 12%) procedures when measured without and with the additional subjective criteria, respectively. Comparing the validity of dynamic retinoscopy against the traditional criterion, moderate to low sensitivity and high specificity were found. However, adding the additional subjective criteria improved the findings with moderate to high sensitivity and high specificity. Using a cutoff for dynamic retinoscopy of 7.50 D showed moderate diagnostic accuracy based on likelihood ratios.

CONCLUSIONS

It is clear that a revised definition of accommodative insufficiency is required, which must include the method of assessing accommodation. The various objective and subjective methods for quantifying the amplitude of accommodation are not interchangeable, and subjective assessment does not provide a valid measure of the accommodative response.

Validation of the DYOP visual acuity test

PURPOSE

The dynamic optotype (DYOP) visual acuity (VA) test is based on motion detection rather than element resolution and has been proposed for routine clinical assessment. This investigation examined the validity, inter- and intra-session repeatability and subjective preference for the DYOP versus a static letter chart and examined its utility in detecting astigmatic defocus.

METHODS

VA of 103 participants was measured three times with the letter and DYOP charts and repeated within two weeks in 75 participants who also rated their subjective experience. The VA of 29 participants was measured using DYOP, letter, Landolt C, and Tumbling E charts, with habitual correction and astigmatism induced with +1.00, +2.00 or +3.00 cylinders at 45, 60, 90 and 180°.

RESULTS

The charts differed by a mean of 0.02 logMAR, with 81% of the measurements within one line of acuity. Inter-session, intraclass correlation coefficients, within-subject SD and repeatability were 0.03 logMAR, 0.95, 0.11 and 0.30 versus 0.01 logMAR, 0.92, 0.15 and 0.42 for the DYOP and letter charts, respectively. The DYOP was significantly more frustrating (1.79 vs.1.36), with 59% preferring the letter chart. The DYOP was least affected by induced astigmatism.

CONCLUSIONS

The DYOP and letter charts differed significantly in their mean values with wide limits of agreement. DYOP had better within-subject SD and narrower limits of agreement between sessions, though clinically insignificant, and performed significantly worse for the detection of uncorrected astigmatism. Thus, it is difficult to recommend this test for the clinical determination of refractive error.

Blue-blocking filters do not alleviate signs and symptoms of digital eye strain

CLINICAL RELEVANCE

There is some controversy about the utility of prescribing blue-blocking filters to mitigate digital eye strain. We found that using commercially available blue-blocking filters was ineffective in reducing orbicularis oculi muscle activity and visual symptomatology during a 30-min reading task from a computer screen.

BACKGROUND

There are some claims that blue-blocking (B-B) filters may be effective in reducing symptoms and signs of digital eye strain. However, recent studies have suggested that there is no sufficient evidence to support their use. This study assessed the short-term effects of a commercially available, B-B filter on orbicularis oculi (OO) muscle activity and symptoms of digital eye strain during the execution of a 30-min reading tas.

METHODS

Twenty-three healthy young adults (22.9 ± 3.2 years of age) performed two reading tasks from a computer screen with or without a B-B filter on two different days. OO muscle activity was recorded by surface electromyography 4-5, 9-10, 14-15, 19-20, 24-25 and 29-30 min into the trial. Participants reported their perceived levels of visual discomfort and activation before and after completing the reading task.

RESULTS

A Bayesian analysis favoured the null hypothesis that there was no change in OO muscle activity with or without using the B-B filter (Bayes Factor01 [BF01] = 7.08). Regarding symptomatology, the analysis favoured the time model that reading increased visual fatigue and discomfort but reduced activation levels (BF01 < 0.33 in all cases). However, our data did not support the alternative model that using B-B filter affected these visual symptoms.

CONCLUSIONS

The B-B filter did not alter OO muscle activity or visual symptomatology significantly during the execution of a 30-min reading task in asymptomatic subjects. These findings support the idea that B-B filters do not attenuate signs and symptoms of digital eye strain.

Digital Eyestrain and the Critical Fusion Frequency

SIGNIFICANCE

Although the high prevalence of digital eyestrain has been well established, to date, there is no objective measurement of this condition. Previous studies have suggested that digital eyestrain may be associated with decreased critical fusion frequency, but the published evidence to support this association is sparse.

PURPOSE

This study sought to determine whether symptoms of digital eyestrain after a sustained computer task are indeed associated with changes in critical fusion frequency.

METHODS

The experiment was performed on 30 young visual-normal subjects. They attended two sessions, during which they undertook a 20-minute reading task. This comprised either reading random words from a tablet computer or a story from a printed children's book. Critical fusion frequency was measured both before and immediately after each of the reading tasks. In addition, the level of digital eyestrain was assessed by subjects completing a questionnaire regarding ocular and visual symptoms experienced during each of the reading trials.

RESULTS

The mean increase in digital eyestrain symptoms after the digital and printed conditions was 11.37 (standard error of the mean [SEM], 2.23) and 4.40 (SEM, 1.34), respectively. Both the post-task symptom change (P < .001) and the difference between the two reading conditions (P = .004) were significant. The mean change in critical fusion frequency after the digital and printed conditions was -0.42 (SEM, 0.25) and -0.72 (SEM, 0.26), respectively. Neither the post-task change nor the difference between the two reading conditions was significant. In addition, when considering the digital condition only, no significant correlation was observed between the changes in critical fusion frequency and reported symptoms.

CONCLUSIONS

These results do not support the proposal that changes in critical fusion frequency can be used as an objective measure of eyestrain or other symptoms of digital eyestrain.

Computer-related visual symptoms in office workers

PURPOSE

Many individuals report visual symptoms during office work and specifically computer use. This study determined the prevalence of symptoms in a population of office workers, and examined the association between these symptoms and both dry eye disease and other demographic factors.

METHOD

A written questionnaire was used to quantify the prevalence of symptoms in 520 New York City office workers, and to determine the effect of risk factors including gender, ethnicity, age, smoking, type of refractive correction and hours spent doing computer work. The questionnaire also examined the prevalence of ocular surface disease.

RESULTS

A significant positive correlation was observed between the symptom score and the number of hours spent working on a computer in a typical day. The most prevalent symptom was tired eyes, which was reported by approximately 40% of subjects as occurring 'at least half the time'. 32% and 31% of subjects reported symptoms of dry eye and eye discomfort, respectively. Symptoms varied significantly with gender (being greater in females), ethnicity (being greater in Hispanics) and the use of rewetting drops. A significant positive correlation was observed between computer-related visual symptoms and the Ocular Surface Disease Index (OSDI), a measure of dry eye.

CONCLUSIONS

Visual symptoms associated with computer use occur frequently in the general population producing discomfort for extended periods of time. They are strongly associated with ocular surface disease. Therapeutic regimens need to be developed for this widespread condition.

The effects of induced oblique astigmatism on symptoms and reading performance while viewing a computer screen

INTRODUCTION

Computer vision syndrome (CVS) is a complex of eye and vision problems related to computer use which has been reported in up to 90% of computer users. Ocular symptoms may include asthenopia, accommodative and vergence difficulties and dry eye. Previous studies have reported that uncorrected astigmatism may have a significant impact on symptoms of CVS. However, its effect on task performance is unclear.

METHODS

This study recorded symptoms after a 10 min period of reading from a computer monitor either through the habitual distance refractive correction or with a supplementary -1.00 or -2.00D oblique cylinder added over these lenses in 12 young, visually-normal subjects. Additionally, the distance correction condition was repeated to assess the repeatability of the symptom questionnaire. Subjects' reading speed and accuracy were monitored during the course of the 10 min trial.

RESULTS

There was no significant difference in reading rate or the number of errors between the three astigmatic conditions. However, a significant change in symptoms was reported with the median total symptom scores for the 0, 1 and 2D astigmatic conditions being 2.0, 6.5 and 40.0, respectively (p < 0.0001). Further, the repeatability coefficient of the total symptom score following the repeated zero astigmatism condition was ± 13.46.

CONCLUSIONS

The presence of induced astigmatism produced a significant increase in post-task symptoms but did not affect reading rate or the number of reading errors. The correction of small astigmatic refractive errors may be important in optimizing patient comfort during computer operation.

Does the dynamic cross cylinder test measure the accommodative response accurately?

BACKGROUND

The dynamic cross cylinder (DCC) test is a standard clinical procedure used to assess the accommodative response (AR) subjectively. However, because of potential problems arising from the ambiguous stimulus conditions, it is unclear whether this test provides an accurate measure of the AR. The aim of this study was to compare clinical subjective findings with objective measurements of the AR.

METHODS

Subjective findings to a 2.50-diopter (D) accommodative stimulus obtained with the DCC test (without fogging lenses) were compared with objective measurements of the AR obtained with a Grand Seiko WAM 5500 optometer (RyuSyo Industrial Co. Ltd., Kagawa, Japan) in 25 young subjects. As spherical lenses were introduced to quantify the subjective finding, objective measures of the AR were also recorded through these lenses.

RESULTS

The mean AR recorded subjectively and objectively was 2.35 and 1.68 D, respectively (P < 0.0001). Of the 10 subjects who demonstrated a lead of accommodation subjectively, only 1 had a lead objectively. For the 8 subjects who showed a lag of accommodation subjectively, all had a lag objectively. Introducing lenses produced a significant change in the mean AR.

CONCLUSION

The subjective DCC test as performed here does not provide an accurate measurement of the AR to a near target in a young population. We recommend that alternative techniques such as using an objective, open-field optometer or Cross-Nott retinoscopy be adopted for determining the within-task AR.

Does prior instillation of a topical anaesthetic alter the pupillary mydriasis produced by tropicamide (0.5%)?

PURPOSE

It is common clinical practice to instill a topical anaesthetic prior to the instillation of a mydriatic agent into the eye. The main rationale for using the anaesthetic is to increase corneal permeability, so that more of the mydriatic agent reaches the receptor sites within the anterior chamber. It addition, as mydriatics generally cause stinging, prior use of an anaesthetic should reduce the degree of discomfort. The aim of the present study was to determine whether the efficacy of mydriasis produced by an antimuscarinic agent is enhanced by prior instillation of a topical anaesthetic.

METHOD

The study was performed using a double-masked protocol on 20 healthy young subjects. One drop of either proparacaine (proxymetacaine) (0.5%) or isotonic saline was instilled into the eye, followed by one drop of tropicamide (0.5%). Pupil diameter was measured using a customized photographic device at 0, 10, 20, 30 and 60 min following drug instillation. Additionally, subjects were asked to rate the degree of discomfort following the instillation of each drop on a scale from 0 (no discomfort) to 10 (agony).

RESULTS

There was no significant difference in either the rate of onset of mydriasis, or the maximum pupil diameter achieved between the two conditions. The mean change in pupil diameter produced by tropicamide after the instillation of saline or proparacaine was 2.31 and 2.28 mm, respectively. The mean discomfort scores following instillation of saline and proparacaine were 1.15 and 1.65, respectively, while mean discomfort scores following the instillation of tropicamide after saline or proparacaine were 4.00 and 0.85, respectively.

CONCLUSIONS

Instillation of a topical anaesthetic does significantly reduce the degree of discomfort produced by the instillation of tropicamide. However, it does not produce any significant increase in either the magnitude or rate of onset of mydriasis.

A combination solution for routine pupillary dilation

BACKGROUND

This study investigated the ability of a combination drop containing reduced concentrations of tropicamide and phenylephrine to produce pupillary dilation adequate for routine fundoscopy.

METHODS

One eye of each subject (N = 28; age range, 21 to 40 years; median, 23 years) was dilated with 1 drop of a solution containing 0.5% tropicamide and 2.5% phenylephrine (0.5T/2.5P). The other eye was dilated with 1 drop of either of 2 mixtures: 0.5% tropicamide and 1.25% phenylephrine (0.5T/1.25P, N = 15; median age, 23 years), or 0.25% tropicamide and 1.25% phenylephrine (0.25T/1.25P, N = 13; median age, 23 years). A topical anesthetic was administered before instilling the mydriatic agents. Pupil diameter was measured from a flash photograph taken every 15 minutes for 3 hours. There was no significant difference in pupil diameter between eyes dilated with the 0.5T/1.25P test solution and the 0.5T/2.5P control solution for the first 75 minutes after instillation (P = 0.41). All pupils reached their maximum diameter 60 minutes after drop instillation; where no significant difference was observed between the 3 mydriatic solutions (P = 0.81). All pupils were at least 7 mm in diameter 30 minutes after drop instillation, and this size was maintained for at least another 75 minutes for all solutions.

CONCLUSIONS

Combination preparations of reduced concentrations of tropicamide and phenylephrine can produce clinically adequate mydriasis.

Effect of heterophoria measurement technique on the clinical accommodative convergence to accommodation ratio

BACKGROUND

Measurement of the stimulus accommodative convergence to accommodation (AC/A) ratio is a standard procedure in clinical optometric practice. Typically, heterophoria is assessed at several accommodative stimulus levels, and the gradient of the vergence to accommodation function computed. A number of procedures are available for the subjective measurement of heterophoria, but it is unclear whether the use of different vergence measurement techniques will alter the obtained AC/A value. Accordingly, the current study compared AC/A ratios measured using 3 clinical subjective heterophoria tests, namely the von Graefe (VG), Maddox Rod (MR), and Modified Thorington (MT) procedures.

METHODS

The AC/A ratio was measured in 60 visually normal subjects between 20 and 25 years of age using each of the 3 procedures listed above. The accommodative stimulus was varied by the introduction of +/-1.00 diopter (D) spherical lenses over the distance refractive correction while subjects viewed a target at a viewing distance of 40 cm. To examine the repeatability of each procedure, the AC/A ratio was measured on 2 separate occasions for each measurement technique, with the 2 sessions being separated by at least 24 hours.

RESULTS

Mean values of stimulus AC/A ratio measured using the VG, MR, and MT procedures were 3.47, 2.99, and 2.46Delta/D, respectively. These differences were significant (p=0.0001). In addition, the coefficient of repeatability for the 3 techniques was 2.22, 1.99, and 1.20 Delta/D, respectively.

CONCLUSIONS

Ratios obtained using the Modified Thorington technique with +/-1.00 D lenses showed the best repeatability, whereas the poorest repeatability was found with the von Graefe technique when only +1.00 D lenses were used to vary the accommodative stimulus. Accordingly, we recommend that that Modified Thorington procedure with +/-1.00 D lenses be used to quantify heterophoria during clinical measurement of the stimulus AC/A ratio.

Comparison of Subjective Heterophoria Testing With a Phoropter and Trial Frame

PURPOSE

Subjective measurement of the oculomotor deviation at both distance and near is a standard test in optometric practice. A number of procedures are available to the practitioner, and previous studies have demonstrated differences in the repeatability of many of the techniques. However, it is unclear whether testing the subject through a phoropter or in free space (trial frame) will alter the oculomotor deviation.

METHODS

Distance and near heterophoria was measured in 60 visually normal subjects between 20 and 34 years of age using the Von Graefe (VG), Maddox Rod (MR), and Modified Thorington (MT) procedures. The deviation was assessed for viewing distances of 6 m and 0.40 m using both a phoropter and trial frame. To examine the repeatability of each technique, the deviation was measured on two separate occasions for each procedure, with the two sessions being separated by at least 24 hours.

RESULTS

The mean vertical deviations at both distance and near were extremely close to orthophoria, and only minimal variation was observed. However, the MR procedure, when used with a trial frame, gave the best repeatability for measuring vertical deviations both at distance and near. Regarding horizontal deviations, the repeatability was better for all three procedures when using a trial frame compared with the phoropter. The best repeatability at distance and near was observed when the MT and MR techniques, respectively, were used with the trial frame. Consistent with previous reports, the VG procedure had poor repeatability, especially when used with the phoropter, and the mean findings showed a greater exo deviation when compared with the other two techniques.

CONCLUSIONS

Testing oculomotor deviations in free space provides a more repeatable response than when using a phoropter. Accordingly, we recommend that subjective measurements of heterophoria in the clinical setting can best be quantified using either the MR or MT techniques in free space.

Blur Adaptation in Myopes

It has been suggested that when subjects with myopia remove their refractive correction, blur adaptation develops to produce an improvement in their visual resolution. The present study measured visual acuity (VA) using high contrast letters and gratings with contrast levels between 2.5% and 40% at 30-minute intervals over the course of a 3-h period during which the subjects remained uncorrected. Twenty-two young subjects with moderate degrees of myopia (mean refractive error, -185 D) participated in the study. Immediately after a 1-h period of full correction, subjects spent 3 h without any refractive correction, during which time they watched television and videos at a viewing distance of 5 m. A significant change in letter and grating VA was observed during the course of the 3-h period of sustained blur, with the mean uncorrected letter VA improving from 0.76 (SD, +/-0.26) to 0.53 (SD, +/-0.23) logarithm of the minimum angle of resolution (logMAR). The Snellen equivalent to this change is from 6/35 to 6/20. A significant improvement in grating acuity was also observed. However, no significant change in refractive error, measured using noncycloplegic autorefraction, was found. These results demonstrate significant blur adaptation in subjects with uncorrected myopia, which does not result from a change in refractive state. We hypothesize that the improvement in visual resolution results from perceptual adaptation to the blurred image, which may occur at central sites within the visual cortex.

Blur Adaptation and Myopia

Previous studies have demonstrated a significant improvement in visual resolution during sustained periods of retinal defocus. This appears to result from perceptual adaptation designed to restore the perceived contrast of the degraded image. However, it is unclear whether perceptual adaptation to sustained blur is present in all individuals or only in certain subgroups, such as those who have been chronically exposed to sustained periods of blur due to uncorrected ametropia. Accordingly, the present study examined the effects of sustained retinal defocus on both high-and low-contrast visual acuity in emmetropes (n = 13) and myopes (n = 18). Subjects were required to view through +2.50-D spherical lenses worn over their distance refractive correction for a continuous 2-hour period. A significant improvement in both Landolt C and grating visual acuity measured through the fogging lenses was observed in both refractive groups. Although the mean change in grating visual acuity was significantly greater for the myopic subjects, the improvements in Landolt C acuity observed in the emmetropes and myopes were statistically equivalent. We hypothesize that the improvement in visual acuity results from perceptual adaptation to the blurred images, which may occur at central sites within the visual cortex.

Do progressing myopes show reduced accommodative responses?

Refractive error and accommodative responsivity were monitored at 4-month intervals over a 1-year period to determine whether an increased lag of accommodation either precedes or accompanies the development of myopia. Accommodation was measured for stimulus levels of 2.5, 3, 4, and 5 D, and both the slope of the stimulus-response function and accommodative error were computed. Almost all subjects exhibited accommodative stimulus-response gradients close to unity, although a lower gradient was observed in subjects who were myopic upon entry into the study and whose ametropia remained stable. These stable myopes also exhibited the largest lag of accommodation. These findings do not support the proposal that the development of myopia in young adults is accompanied by a reduced accommodative response during nearwork.

Vergence adaptation in children and its clinical significance

BACKGROUND AND PURPOSE

Vergence adaptation has not been well investigated in children even though it may contribute to binocular dysfunction and near work induced asthenopia.

METHODS

We compared vergence adaptation in 18 children and 18 young adult subjects by assessing tonic vergence (TV) before and immediately after a period of sustained near fixation, by measuring heterophoria with a synoptophore through 0.5 mm binocular pinholes. Adaptation was induced by a reading task at 15 cm for a continuous 5 minute period.

RESULTS

Mean pre-task TV values of 0.70 MA (Meter Angles) and 0.20 MA were observed for the children and young adults, respectively (p = 0.08). The initial mean vergence adaptation for children and adults was +0.45 MA and +0.11 MA, respectively (p = 0.001).

CONCLUSION

The greater vergence adaptation observed in children may impact upon the clinical assessment of their binocular vision, especially heterophoria measurement which may require longer periods of dissociation than previously recommended, and might also ultimately be partly responsible for the predominant development of esodeviations during childhood

Effect of near-vision addition lenses on the accuracy of the accommodative response

BACKGROUND

Addition lenses (adds) are frequently used to increase the accuracy of the near-vision focusing response, and may also play a role in the prevention or retardation of refractive error development. However, following the introduction of such a lens, if the accommodative response is reduced by an amount equal to the magnitude of the near add, then the resulting accommodative error (and degree of retinal defocus) would remain unchanged.

METHODS

This study measured the accommodative response in 28 subjects while they viewed a near target binocularly, either through their distance refractive correction alone or this correction combined with a +0.75 D, +1.50 D, +2.00 D, or +2.50 D near add.

RESULTS

The mean findings demonstrated a small (0.03 D) lead of accommodation to the near target through the distance correction, and monotonically increasing leads of accommodation with larger adds. Further, the additional lens power required to reduce the accommodative error to zero correlated significantly with the initial accommodative error.

CONCLUSIONS

Near addition lenses may actually increase the degree of retinai defocus for individuals who manifest small accommodative errors.