A novel and cheap method to correlate subjective and objective visual acuity by using the optokinetic response

Automated visual acuity estimation by optokinetic nystagmus using a stepped sweep stimulus

PURPOSE

To describe an automatic system for objective measurement of visual acuity (VA) using optokinetic nystagmus (OKN). This pilot study tested the system's sensitivity and specificity for detecting reduced VA in healthy adults by comparing VA-OKN to VA with an Early Treatment of Diabetic Retinopathy Study (ETDRS) chart (VA-ETDRS).

METHODS

Adult participants (age 30 ± 12 years) with either reduced VA (n = 11, VA-ETDRS > 0.20 logMAR) or normal VA (n = 12, VA-ETDRS ≤ 0.20 logMAR) completed monocular VA-OKN measurements in each eye. The VA-OKN stimulus was an array of drifting (5°/s) vanishing discs presented in descending/ascending size order (0.00-1.00 logMAR in 0.10 steps). The stimulus was stepped every 2 s, and 10 sweeps were shown per eye (five ascending and five descending). Eye-tracking data determined when OKN activity ceased (descending sweep) or began (ascending sweep), which was used to determine VA-OKN for each sweep. The estimates were averaged across sweeps to produce an automated VA-OKN. The automated sweeps were then provided in randomised order to a reviewer blinded to the VA-ETDRS findings who determined a final VA-OKN for an eye.

RESULTS

A single randomly selected eye from each observer was used for analysis. The sensitivity and specificity of VA-OKN using the same 0.20 logMAR threshold as VA-ETDRS was 100%. Comparisons between the VA-OKN and VA-ETDRS measures were made for participants in the reduced VA group. There was no significant difference between VA-OKN and VA-ETDRS (p = 0.55) and the two measures produced comparable values (r2 = 0.84, 95% limits of agreement = 0.19 logMAR, intra-class correlation coefficient = 0.90 [95% CI:0.68-0.97]).

CONCLUSIONS

Visual acuity using optokinetic nystagmus correctly identified a VA deficit in adults and for those with a VA deficit, VA-OKN was strongly correlated with the gold-standard clinical measure of VA. OKN is a promising method which has the potential for use in cognitively impaired adults and pre-verbal children.

Preliminary study on the computer-based optokinetic nystagmus analyzer to detect the visual acuity of preschool children

The purpose of this study is to examine the viability, precision, and consistency of a computer-based optokinetic nystagmus analyzer (nystagmus meter) for diagnosing eyesight in preschoolers. A total of 59 subjects who could pass the log of minimum angle of resolution (LogMAR) visual acuity chart were divided into three groups by age, 4-, 5-, and 6-year-old groups, and their visual acuity was tested with nystagmus meter. The percentage of children in each age group that could be detected by nystagmus was recorded along with the differences between these groups. The correlation between the test results from the two methods was found for each age group using the correlation coefficient method. Repeated measurements were used to assess the two visual acuity values of the measured nystagmus, and the repeatability of the two measurement techniques for different age groups was compared. The overall measurability of the visual acuity detected by nystagmus was 93.22%, and the measurability of the 4-, 5-, and 6-year-old groups was 90%, 95%, and 94.74%, respectively. There was no statistically significant difference in the measurability of subjects among all age groups (P = 1.0). The outcomes of the LogMAR visual acuity chart had a negative correlation with the visual acuity measured by the nystagmus meter. The overall correlation coefficient R value was -0.80, and the correlation coefficient R value of the 4-, 5-, and 6-year-old groups was -0.79, -0.76, and -0.87, respectively. The nystagmus meter has good feasibility, accuracy, and stability in visual acuity testing and can be used for visual acuity testing in children.

The effect of refractive error on optokinetic nystagmus

Subjective refraction is the gold-standard for prescribing refractive correction, but its accuracy is limited by patient’s subjective judgment about their clarity of vision. We asked if an involuntary eye movement, optokinetic nystagmus (OKN), could serve as an objective measure of visual-clarity, specifically measuring the dependence of OKN—elicited by drifting spatial-frequency filtered noise—on mean spherical equivalent (MSE) refractive error. In Experiment 1 we quantified OKN score—a measure of consistency with stimulus-direction—for participants with different MSEs. Estimates of MSE based on OKN scores correlate well with estimates of MSE made using autorefraction (r = 0.878, p < 0.001, Bland–Altman analysis: mean difference of 0.00D (95% limits of agreement: − 0.85 to + 0.85D). In Experiment 2, we quantified the relationship between OKN gain (ratio of tracking eye-movement velocity to stimulus velocity) and MSEs (− 2.00, − 1.00, − 0.50, 0.00 and + 1.00D) induced with contact lenses for each participant. The mean difference between measures of MSE based on autorefraction or on OKN gain was + 0.05D (− 0.90 to + 1.01D), and the correlation of these measures across participants was r = 0.976, p < 0.001. Results indicate that MSE attenuates OKN gain so that OKN can be used as an objective proxy for patient response to select the best corrective lens.

Objective measurement of visual acuity by optokinetic nystagmus suppression in children and adult patients

PURPOSE

To investigate the correlation between subjective and objective visual acuity as elicited with a new computerized optokinetic nystagmus (OKN) suppression test ("SpeedWheel") in adults and school-aged children.

METHODS

Fifteen children (6-12 years) and 27 adults with refractive errors, amblyopia, cataract, age-related macular degeneration, and thyroid-associated orbitopathy underwent testing of subjective visual acuity with E- and Landolt-C symbols (Freiburg Acuity and Contrast Test [FrACT]) and visual acuity as estimated with the SpeedWheel on an LCD screen.

STATISTICAL ANALYSIS

linear regression, Spearman correlation, and Bland-Altman plots.

RESULTS

Mean difference against the mean was -0.01 when SpeedWheel was compared to Landolt C, but -0.15 when compared to E-symbols. Overall, SpeedWheel correlated very strongly to FrACT ("E": r = 0.85; P < 0.001; Landolt-C: r = 0.81; P < 0.001). This also held true in children ("E": r = 0.74; P < 0.003; Landolt-C: r = 0.69; P < 0.005).

CONCLUSIONS

SpeedWheel enables estimation of visual acuity in a variety of conditions in both adults and school-aged children.

The optokinetic response is effective to assess objective visual acuity in patients with cataract and age-related macular degeneration

PURPOSE

To estimate objective visual acuity in subjects suffering from cataract and age-related macular degeneration via the optokinetic response evoked by a non-conventional induction method (oktotype); in addition, to compare such objective outcome with the subjective acuity based on the ETDRS charts.

METHODS

Patients were presented with 13 sequences of symbols arranged horizontally to form a serial pattern, moving from left to right at a constant rate. In each sequence, the size of the stimuli was reduced progressively, while the operator checked for the disappearance of the optokinetic response via a small video camera mounted on the test lens frame. The minimum angular size of the serial pattern able to evoke the optokinetic response (MAER) was referred to as the objective visual acuity of the subject.

RESULTS

Correlation between logMAER and logMAR was significant in the cataract and macular degeneration group ([Formula: see text] = 0.70, p < .0001; [Formula: see text] = 0.63, p < .0007). In the two samples, the correspondence between subjective and objective visual acuity (as, respectively, decimal units and arbitrary decimal units) was satisfactory (concordance correlation coefficient: cataract group = 0.91 and AMD group = 0.93). Test-retest reliability of the oktotype was good for the cataract group and moderate for the AMD sample (Κ 0.81 and 0.59, respectively).

CONCLUSION

The oktotype seems a promising tool to objectively assess visual acuity in noncooperating subjects with cataract or macular degeneration. Further research on other clinical conditions is needed to clarify the suitability of the procedure in the clinical setting.