September 2011
Volume 52, Issue 10
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Visual Neuroscience  |   September 2011
Efficacy of a Computerized Optokinetic Nystagmus Test in Prediction of Visual Acuity of Better Than 20/200
Author Affiliations & Notes
  • Sang Beom Han
    From the Department of Ophthalmology, Seoul National University Bundang Hospital, Seongnam, Korea;
    the Department of Ophthalmology, Seoul National University College of Medicine, Seoul, Korea;
  • Hee Kyung Yang
    From the Department of Ophthalmology, Seoul National University Bundang Hospital, Seongnam, Korea;
    the Department of Ophthalmology, Seoul National University College of Medicine, Seoul, Korea;
  • Joon Young Hyon
    From the Department of Ophthalmology, Seoul National University Bundang Hospital, Seongnam, Korea;
    the Department of Ophthalmology, Seoul National University College of Medicine, Seoul, Korea;
  • Jong-Mo Seo
    the School of Electrical Engineering, Seoul National University, Seoul, Korea; and
  • Jin Hak Lee
    From the Department of Ophthalmology, Seoul National University Bundang Hospital, Seongnam, Korea;
    the Department of Ophthalmology, Seoul National University College of Medicine, Seoul, Korea;
  • In Bum Lee
    the Electronics and Telecommunications Research Institute, Daejeon, Korea.
  • Jeong-Min Hwang
    From the Department of Ophthalmology, Seoul National University Bundang Hospital, Seongnam, Korea;
    the Department of Ophthalmology, Seoul National University College of Medicine, Seoul, Korea;
  • Corresponding author: Jeong-Min Hwang, Department of Ophthalmology, Seoul National University Bundang Hospital, 166 Gumiro, Bundang-gu, Seongnam, Gyeonggi-do 463-707, Korea; hjm@snu.ac.kr
Investigative Ophthalmology & Visual Science September 2011, Vol.52, 7492-7497. doi:10.1167/iovs.11-7663
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      Sang Beom Han, Hee Kyung Yang, Joon Young Hyon, Jong-Mo Seo, Jin Hak Lee, In Bum Lee, Jeong-Min Hwang; Efficacy of a Computerized Optokinetic Nystagmus Test in Prediction of Visual Acuity of Better Than 20/200. Invest. Ophthalmol. Vis. Sci. 2011;52(10):7492-7497. doi: 10.1167/iovs.11-7663.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose.: To evaluate the efficacy of a computerized optokinetic nystagmus (OKN) test in detecting visual acuity (VA) of >20/200.

Methods.: This was a combined retrospective and prospective, noninterventional study. In phase I of the study, data from 168 eyes of 154 subjects who underwent the computerized objective VA test using OKN responses at Seoul National University Bundang Hospital were reviewed and reanalyzed, and a table for predicting the range of subjective VA for each step of objective VA was made. From the table, the cutoff value for detecting VA of >20/200 was determined. In phase II of the study, the distribution of subjective VA according to each objective VA step was determined for 80 eyes of 40 subjects at Seoul Veteran's Hospital. The sensitivity and the specificity of our cutoff value were evaluated in the two groups.

Results.: No significant difference was found in the distribution of subjective VA according to objective VA steps between the two groups. For the subjects in phase I of the study, the sensitivity of our cutoff value was 91.7% and the specificity was 88.3%. For patients in phase II of the study, the sensitivity of our cutoff was 86% and the specificity was 96.7%.

Conclusions.: This study shows that an objective VA test using OKN responses can be effective in predicting real VA and detecting VA of >20/200.

Current methods of measuring visual acuity (VA) depend completely on subjective statements from the patient, and thus the cooperation of the patient is crucial for the reliability of the VA tests. 1 3 However, the creditability of the subjective VA tests declines sharply in patients with poor cooperation, including those with functional visual loss (FVL). 1 3  
Optokinetic nystagmus (OKN) is the physiologic response induced by a series of displays moving across the visual field. 1,3 As the reflex is known to be almost impossible to inhibit voluntarily, many researchers have attempted to evaluate visual function using OKN with stimuli of various sizes, velocities, and presentation modes. 4 16 Although these studies demonstrated that OKN test results correlated with VA, they failed to present the reference value used for predicting “real VA.” 
Previously, we developed an objective VA test device using OKN elicited by a computerized display combined with a recording system using infrared oculography. With this device, we measured the VA of normal subjects and patients with various ocular diseases and showed the close correlation of our objective VA test results with subjective VA. 1 3 Moreover, we recently revealed significant differences in subjective VA among various objective VA points, suggesting the possibility of quantification of objective VA test results according to the corresponding subjective VA. 1,3 However, probably due to the small sample size, the precision of the estimate of real VA based on our previous study results is still limited, which is an obstacle to clinical application of our objective VA test in evaluating exact VA. Nonetheless, by setting the cutoff of the objective VA test at a certain subjective VA, we assumed that we could determine whether a subject has a specific VA (i.e., >20/200). In the present study, we determined the distribution of subjective VAs corresponding to various steps of objective VAs, to develop a cutoff value for detecting VA of >20/200, using the data obtained in our previous studies. 1,3 Then, we evaluated the efficacy of our objective VA test in detecting VA of >20/200 in another group of patients, as well as in patients included in the previous studies. 1,3  
Patients and Methods
Subjects
This study was approved by the Institutional Review Board (IRB) of Seoul National University Bundang Hospital and conformed to the tenets of the Declaration of Helsinki. Informed consent was obtained from all patients. 
The study subjects comprised a total of 248 eyes of 194 subjects (91 male and 103 female), including 168 eyes of 154 subjects from Seoul National University Bundang Hospital and 80 eyes of 40 subjects from Seoul Veteran's Hospital. The patients' mean age was 59.0 ± 15.4 (range, 7–91) years. 
The first phase (phase I) of the study was conducted retrospectively. Data of 168 eyes of 154 subjects (83 eyes of 83 normal subjects and 85 eyes of 71 patients with ocular diseases) who underwent the objective VA test at Seoul National University Bundang Hospital were reviewed and reanalyzed. 1,3 The details of the ocular diseases are as follows: (1) 39 eyes of 30 patients with central vision impairment caused by age-related macular degeneration, central serous chorioretinopathy, macular hole, epiretinal membrane, or optic neuropathy; (2) 24 eyes of 20 patients with peripheral visual defect including glaucoma and retinitis pigmentosa; and (3) 22 eyes of 21 patients with media opacity, such as cataract, corneal opacity, and vitreous opacity. 3 Based on the subjective and objective VAs obtained from these subjects, a table for predicting the range of subjective VAs at each step of objective VA was generated. From the table, the cutoff value for detecting a VA of >20/200 was developed. 
The second phase (phase II) of this study was performed prospectively. For validation of the cutoff value, a second independent sample of 80 eyes of 40 patients (16 eyes of 8 patients with refractive error, 26 eyes of 13 patients with central visual impairment, 18 eyes of 9 patients with peripheral visual defect, and 20 eyes of 10 patients with media opacity) was recruited at Seoul Veteran's Hospital. Exclusion criteria were as follows: (1) physical or psychological disability preventing completion of the test; (2) ocular motility disorders such as nystagmus or strabismus; (3) a history of binocular disruption in early stages of visual development to rule out the influence of monocular OKN asymmetry; (4) the presence of any neurologic diseases that can affect the control of eye movements; (5) any possibility of malingering; or (6) two or more vision-disturbing ocular pathologies. 1,3 Objective and subjective VAs were measured for each subject, and the distribution of subjective VA according to each objective VA point was determined. The sensitivity and specificity of our cutoff value were also evaluated. 
Subjective and Object VA Tests
For each subject, subjective and objective VAs were measured in the same way as in our previous studies. 1 3 Subjective VA was measured either with the Early Treatment Diabetic Retinopathy Study (ETDRS) chart in subjects with VA >20/200 or with the Feinbloom chart in those with VA ≤20/200. Objective VA was determined using the computerized OKN test performed by one trained examiner who used the same method as was used in our previous studies. 1 3 The OKN test was performed under monocular viewing conditions. Briefly, horizontal OKN stimuli were projected with a laser beam projector (CP-X300; Hitachi, Tokyo, Japan) on a 127-inch white screen located 10 feet from the subject in a dark room. A head rest and chin cup were used to immobilize the patient's head position and minimize head movement. Each subject was instructed to stare at the center of the screen and stay attentive to the OKN stimuli during the examination. Eye movements were captured with an infrared camera (30 frames/s) attached to the headrest frame and imported into oculography software for image analysis, to determine the presence of OKN. 
In the induction method, alternating black-and-white vertical stripes (contrast, 85%) were used to elicit OKN. The stripe width varied from 0.6° (0.833 cyc/deg) to 0.2° (2.5 cyc/deg) with a decrement of 0.1° in each step. The stimuli were moved from right to left at a velocity of 10 deg/s. The smallest size of the stripes that induced OKN was defined as the objective VA by the induction method. In the suppression method, stripes wide enough to elicit OKN (20°) were presented as the background stimuli, to induce an OKN response, and then a suppression stimulus (a white dot), with a size increase from 0.036° (step 1) to 0.36° (step 8) in eight steps, were superimposed on the center of the moving background stripes for 10 seconds. The earliest step (stimulus of the smallest size) that suppressed OKN was defined as the objective VA by the suppression methods. Step 9 was defined when the largest stimulus failed to suppress OKN. Each subject underwent three sets of induction and suppression procedures, and if there were any repeated values among the three measurements, those were taken as the result. If there were no repeated values, the median values were taken as the result. 
Statistical Analysis
Subjects were categorized according to their objective VA points presented as the combination of the results of the induction and the suppression methods. 
In phase I, the mean subjective VA and its 95% confidence interval (CI) were calculated for each step of objective VA. From the distribution of the subjective VA, the cutoff value for detecting legal blindness was determined using the receiver operating characteristic (ROC) curve. 17 19 The χ2 test was used to evaluate the sensitivity and specificity of the cutoff for the subjects included in phase I. 
The distribution of the subjective VA according to each objective VA point was also determined for the patients included in phase II and was compared with that of the subjects in phase I by Student's t-test and Mann-Whitney U test, as appropriate. For validation of the cutoff developed in phase I, Fisher's exact test was used to determine its sensitivity and specificity in the patients included in phase II (SPSS software for Windows, ver. 15.0; SPSS Inc., Chicago, IL). 
Results
The distribution of subjective VA scores at each objective VA step is summarized in Table 1. These results show that subjects with an objective VA of ≥7 in the suppression and ≥0.3 in the induction testing methods or those with objective VA of 8 in the suppression and 0.2 in the induction testing methods have a high probability of having subjective VA >20/200. Based on these data, we identified three candidate sets of criteria for determining a cutoff value of objective VA that corresponds to subjective VA >20/200: (1) ≥7 in the suppression and ≥0.3 in the induction methods; (2) ≥8 in the suppression and ≥0.3 in the induction methods; (3) ≥7 in the suppression method and ≥0.3 in the induction method or ≥8 in the suppression method and ≥0.2 in the induction method. We compared the diagnostic value of each candidate by using the ROC curve, and candidate 1 had the highest diagnostic accuracy, with the largest area under the ROC curve (Fig. 1).Therefore, we set the cutoff value for objective VA as ≥7 in the suppression and ≥0.3 in the induction methods for the prediction of subjective VA of >20/200. 
Table 1.
 
VA According to Each Step of Induction and Suppression in Objective VA Testing in Patients in Phase I of the Study
Table 1.
 
VA According to Each Step of Induction and Suppression in Objective VA Testing in Patients in Phase I of the Study
Induction Method Suppression Method Total
1 2 3 4 5 6 7 8 9
0.2 n = 27 n = 11 n = 17 n = 16 n = 6 n = 6 n = 4 n = 3 n = 90
20/26 20/48 20/65 20/53 20/108 20/108 20/300 20/586 20/57
(20/32–20/21) (20/135–20/17) (20/100–20/42) (20/84–20/33) (20/287–20/40) (20/191–20/61) (20/1270–20/70) (N/A*) (20/72–20/45)
0.3 n = 1 n = 3 n = 11 n = 1 n = 7 n = 6 n = 8 n = 37
20/100 20/85 20/83 20/200 20/125 20/271 20/411 20/159
(N/A*) (N/A*) (20/116–20/59) (N/A*) (20/193–20/82) (20/972–20/76) (20/1000–20/167) (20/222–20/114)
0.4 n = 7 n = 13 n = 20
20/373 20/1135 20/769
(20/653–20/213) (20/2010–20/640) (20/1220–20/484)
0.5 n = 1 n = 2 n = 8 n = 11
20/125 20/1000 20/2750 20/1730
(N/A*) (N/A*) (20/6650–20/1130) (20/4190–20/711)
0.6 n = 1 n = 9 n = 10
20/500 20/2580 20/2240
(N/A*) (20/5510–20/1210) (20/4690–20/1070)
Total n = 28 n = 11 n = 20 n = 28 n = 7 n = 14 n = 19 n = 41 n = 168
20/28 20/48 20/68 20/69 20/118 20/118 20/358 20/1260 20/151
(20/35–20/22) (20/135–20/17) (20/100–20/46) (20/97–20/49) (20/266–20/52) (20/154–20/90) (20/557–20/229) (20/863–20/1840) (20/195–20/117)
Figure 1.
 
Area under the ROC curve based on different candidates for the cutoff value. Candidate 1, ≥7 in the suppression and ≥0.3 in the induction methods; candidate 2, ≥8 in the suppression and ≥0.3 in the induction methods; and candidate 3, ≥7 in the suppression and ≥0.3 in the induction methods or ≥8 in the suppression and ≥0.2 in the induction methods.
Figure 1.
 
Area under the ROC curve based on different candidates for the cutoff value. Candidate 1, ≥7 in the suppression and ≥0.3 in the induction methods; candidate 2, ≥8 in the suppression and ≥0.3 in the induction methods; and candidate 3, ≥7 in the suppression and ≥0.3 in the induction methods or ≥8 in the suppression and ≥0.2 in the induction methods.
The results of validation of the cutoff for the subjects in phase I are shown in Table 2. The sensitivity of our cutoff was 91.7% (99/108) and the specificity was 88.3% (53/60). The false-positive and -negative rates were 11.7% (7/60) and 8.3% (9/108), respectively. The positive and negative predictive values were 93.4% (99/106) and 85.5% (53/62), respectively. 
Table 2.
 
Validation of the Cutoff Value of Objective VA in Patients in Phase I of the Study
Table 2.
 
Validation of the Cutoff Value of Objective VA in Patients in Phase I of the Study
Subjective VA Objective VA Total (%) Odds Ratio (95% CI) P *
≥Cutoff Value (n, eyes) <Cutoff Value (n, eyes)
>20/200 99 9 108 (64.3) 83.3 <0.001
≤20/200 7 53 60 (35.7) (29.4–237)
Total 106 (63.1%) 62 (36.9%) 168 (100)
No significant difference was found in the distribution of subjective VA according to objective VA values between the patients in phase I and those in phase II (Table 3). There was no significant difference in the mean subjective VA between the two groups. In patients in phase II, the sensitivity of the cutoff determined in phase I was 86% (43/50) and the specificity was 96.7% (29/30). The false-positive and -negative rates were 3.3% (1/30) and 14% (7/50), respectively. The positive and negative predictive values were 97.7% (43/44) and 80.6% (29/36), respectively (Table 4). 
Table 3.
 
Distribution of VA According to each Step of Induction and Suppression in Objective VA Testing at Distance in the Patients in Phase II of the Study
Table 3.
 
Distribution of VA According to each Step of Induction and Suppression in Objective VA Testing at Distance in the Patients in Phase II of the Study
Induction Method Suppression Method Total
3 4 5 6 7 8 9
0.2 n = 4 n = 8 n = 8 n = 9 n = 8 n = 2 n = 13 n = 52
20/27 20/35 20/71 20/66 20/65 20/200 20/231 20/80
(20/42–20/16) (20/49–20/24) (20/107–20/47) (20/116–20/38) (20/84–20/50) (N/A*) (20/413–20/129) (20/104–20/62)
    P 0.469 0.315 0.614 0.272 0.272 0.800 0.239 0.075
0.3 n = 3 n = 2 n = 2 n = 2 n = 6 n = 15
20/50 20/80 20/100 20/158 20/483 20/169
(N/A*) (N/A*) (N/A*) (N/A*) (20/1760–20/133) (20/339–20/84)
    P 0.400 0.667 0.222 0.262 0.955 0.935
0.4 3 3 n = 6
20/293 20/200 20/242
(N/A*) (N/A*) (20/905–20/65)
    P 1.000 0.314 0.451
0.5 n = 4 n = 4
20/633 20/633
(20/4600–20/87) (20/4600–20/87)
P 0.516 0.516
0.6 n = 3 n = 3
20/1170 20/1170
(20/4380–20/312) (20/4380–20/312)
    P 0.371 0.371
Total n = 4 n = 11 n = 8 n = 11 n = 10 n = 7 n = 80
20/27 20/38 20/71 20/69 20/71 20/221 20/123
(20/42–20/16) (20/56–20/26) (20/107–20/47) (20/107–20/44) (20/89–20/55) (20/493–20/98) (20/162–20/93)
    P 0.469 0.319 0.614 0.179 0.151 0.254 0.214
Table 4.
 
Validation of the Cutoff Value of Objective VA in the Patients Included in Phase II of the Study
Table 4.
 
Validation of the Cutoff Value of Objective VA in the Patients Included in Phase II of the Study
Subjective VA Objective VA Total (%) Odds Ratio (95% CI) P *
≥Cutoff Value (n, Eyes) <Cutoff Value (n, Eyes)
>20/200 43 7 50 (62.5%) 178 <0.001
≤20/200 1 29 30 (37.5%) (20.8–1530)
Total, n (%) 44 (55) 36 (45) 80 (100%)
Discussion
Since the idea of evaluating visual function using OKN first developed in the 1920s, several researchers have demonstrated a correlation between subjective VA and objective VA measured using the OKN response. 2,9,10,16,20,21 However, none of the studies have presented a method of estimating a subjective VA using the objective VA test results obtained with OKN responses. Recently, by dividing the OKN responses into various steps, we demonstrated that each step of the OKN response corresponded to a certain level Snellen VA and that there was a significant difference in the extent of Snellen VA among several steps. 1,3 As a follow-up study, by recruiting more patients and combining the data of induction and suppression methods, we created a table for estimation of Snellen VA using the objective test results (Table 1). As Snellen VAs are ordinal data rather than interval data and are not adequate for quantification and statistical analyses, we converted the Snellen VAs to logMAR VAs for statistical analyses. 22,23 Then, we converted the logMAR units to Snellen VAs to express the estimated VA in each objective VA step. Moreover, by analyzing the results, we established a cutoff value for detection of VA of >20/200. Validation of the cutoff revealed high reliability in both groups of patients. In particular, the false-positive rate of the cutoff was low (11.7% in phase I and 3.3% in phase II), and the positive predictive value was high (93.4% in phase I and 97.7% in phase II) in both groups. 
In the present study, we developed a cutoff of objective VA for a subjective VA of 20/200. A VA of 20/200 is one of the criteria for legal blindness in the United States and Europe as well as in Korea, where it is an important criterion for diagnosing visual disability. Patients who are diagnosed with legal blindness or visual disability can receive government disability benefits; therefore, malingerers usually feign a low vision of ≤20/200, although their real VAs are substantially higher. Detecting a VA of >20/200 would also be an effective way to uncover malingering; thus, our objective VA test device could be very helpful in the diagnosis of legal blindness, particularly in the detection of FVL, which is defined as any vision decrease with an origin that cannot be attributed to a pathologic or structural abnormality. 24  
There is a debate about the roles of the macula and the peripheral retina in the generation of OKN responses. Miyoshi 25 demonstrated the increased difficulty in eliciting an OKN response with narrowing of the central visual field (VF). By contrast, several researchers have revealed that patients with a central VF defect show an OKN gain similar to that in those who do not have a central VF defect. 26 29 Valmaggia and Gottlob 29 observed that, in patients with a central VF defect, OKN was suppressed when they fixated on the central scotoma, whereas OKN was elicited simultaneously with filling in of the scotoma. They postulated that the OKN response was triggered by activation of the visual cortical area corresponding to the scotoma through filling in—that is, expansion of receptive fields accompanied by feedback pathways. 29 In addition, the OKN response was shown to be suppressed through fixation to the central scotoma with central artificial scotomas where filling in is impossible, suggesting that the central retina is also important in the generation of the OKN response. 11,14,30,31 Therefore, our suppression method may be a useful tool that can specifically reflect the function of the central retina, as it can induce the patients to fixate on the center of the screen, whereas the induction method conceivably reflects both central and peripheral retinal function. 3 Fukai et al. 6 reported that the objective VA test result was worse than the subjective VA in patients with central scotoma due to the lesion of retina or optic nerve, supporting the assumption that the suppression method may be a good option for determining central visual function. We also believe that the suppression method is suitable for measurement of central visual function, and the combination of induction and suppression methods makes the estimation of objective VA more accurate, thus enabling clinical application of the objective VA test. 3  
This study had the following limitations: (1) The sensitivity of our cutoff was 91.7% in phase I and 86% in phase II, suggesting that approximately 10% of patients with a VA of >20/200 can be diagnosed as having VA of ≤20/200, which can lead to the misdiagnosis of legal blindness. For more sensitive measurement of objective VA, further studies with adjusted velocity of visual stimuli and size of target are needed. Moreover, technical development, such as, the use of projectors with a higher refresh rate, can enable the use of faster velocity of stripe movement and thus can improve the sensitivity and reduce the false-positive rate of our objective VA test device. (2) The number of patients at each step of the objective VA scale is still not large enough to present a more specific range of corresponding Snellen VA. Therefore, further studies with a larger sample group to accumulate both objective and subjective VA data are needed for more precise and accurate predictions of subjective VA. (3) In its current state, our test device cannot be used in patients with spontaneous nystagmus. Although patients with nystagmus were excluded from this study, application of an objective VA test device in patients with spontaneous nystagmus is still necessary, considering that a substantial number of patients with low vision have spontaneous nystagmus. Upgrade of both hardware and software of the objective VA test device (i.e., development of a new algorithm that can analyze and offset the effect of spontaneous nystagmus—for instance, by quantifying the slow-phase eye velocity of the spontaneous nystagmus and subtracting that from the slow-phase velocity during optokinetic stimulation) can offer a solution. (4) There are some technical restrictions displaying moving stripes with liquid crystal display (LCD) beam projector or LCD/light-emitting diode (LED) flat panel display. The first one is the stroboscopic effect. Conventional LCD beam projector and LCD/LED flat panel display supports a 60-Hz refresh rate signal from the video card of the computer. This restrains the v max of the stripe movement up to 10 deg/s in the current experimental setting. If the moving speed were increased, then the narrow stripe would be shown as reversed, slow motion instead of running fast. We can experience this phenomenon in a rotating ceiling fan or a rotating wheel of a car. The fast-rotating fan or wheel may sometimes be perceived as still, and this phenomenon can occur in our experimental setting if we increase the velocity of stripe movement beyond 10 deg/s. With the development of an LCD/LED panel with a higher refresh rate (i.e., 120 Hz), we expect that the efficacy of our objective VA test device will be enhanced by overcoming the stroboscopic effect and enabling the use of the velocity of stripe movement beyond 10 deg/s. The second one is the moving direction of the stripes. All the television systems and the standard computer monitor make their image by assembling scanning lines that run from the right to the left, from the top to the bottom of the screen. This determines the direction of the smooth movement of the object on the screen. If the moving object is shown on the screen from left to right, then the horizontal image misalignment can be seen more easily than it can in with right to left movement of the target. We can observe this phenomenon when we watch a soccer game on digital television. If the player moves from the left to the right very fast, then the “block noise” usually occurs, which can be identified as blocked or mosaic patterned border of the player's body. This is why we always used a right-to-left moving target. However, considering that monocular OKN is nearly symmetrical for stimulus in the temporal-to-nasal and nasal-to-temporal directions in adults without any history of binocular disruption in early life, we believe that the fact that we used only one direction for the OKN stripes significantly limits the clinical importance of the study. 1,3 Third is the level of contrast. If we increase the contrast up to 100%, then the rainbow effect can be seen more easily in a moving target. That is, the moving white stripes will cause a rainbow-like color dispersion on the tail-side border, because the white signal is composed of red+green+blue cells, and each cell signal will be delivered sequentially, not simultaneously. This is inevitable in controlling liquid crystal in an LCD display and more severe in a digital light processing (DLP) projector, because the DLP projector uses a rotating red/green/blue filter. The 85% contrast is rather arbitrary; however, it appeared to be the optimal condition for our experiments. 
Despite these limitations, however, our results, especially the low false-positive rates, suggest that our objective VA test device could be an effective tool in detection of VA of >20/200 and has a possibility of clinical application (i.e., detection of FVL or diagnosis of legal blindness), even in its current state. 
In conclusion, this study showed that an objective VA test using OKN responses can be effective in the detection of VA of >20/200. Widespread clinical use could be possible through development of more precise steps for measurement of objective VA. Development of new technologies is also expected to enhance the efficacy of our objective test device. 
Footnotes
 Supported by Grant A080299 from the Korea Health 21 R&D Project, Korea Health Industry Development Institute, Republic of Korea.
Footnotes
 Disclosure: S.B. Han, None; H.K. Yang, None; J.Y. Hyon, None; J.-M. Seo, None; J.H. Lee, None; I.B. Lee, None; J.-M. Hwang, None
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Figure 1.
 
Area under the ROC curve based on different candidates for the cutoff value. Candidate 1, ≥7 in the suppression and ≥0.3 in the induction methods; candidate 2, ≥8 in the suppression and ≥0.3 in the induction methods; and candidate 3, ≥7 in the suppression and ≥0.3 in the induction methods or ≥8 in the suppression and ≥0.2 in the induction methods.
Figure 1.
 
Area under the ROC curve based on different candidates for the cutoff value. Candidate 1, ≥7 in the suppression and ≥0.3 in the induction methods; candidate 2, ≥8 in the suppression and ≥0.3 in the induction methods; and candidate 3, ≥7 in the suppression and ≥0.3 in the induction methods or ≥8 in the suppression and ≥0.2 in the induction methods.
Table 1.
 
VA According to Each Step of Induction and Suppression in Objective VA Testing in Patients in Phase I of the Study
Table 1.
 
VA According to Each Step of Induction and Suppression in Objective VA Testing in Patients in Phase I of the Study
Induction Method Suppression Method Total
1 2 3 4 5 6 7 8 9
0.2 n = 27 n = 11 n = 17 n = 16 n = 6 n = 6 n = 4 n = 3 n = 90
20/26 20/48 20/65 20/53 20/108 20/108 20/300 20/586 20/57
(20/32–20/21) (20/135–20/17) (20/100–20/42) (20/84–20/33) (20/287–20/40) (20/191–20/61) (20/1270–20/70) (N/A*) (20/72–20/45)
0.3 n = 1 n = 3 n = 11 n = 1 n = 7 n = 6 n = 8 n = 37
20/100 20/85 20/83 20/200 20/125 20/271 20/411 20/159
(N/A*) (N/A*) (20/116–20/59) (N/A*) (20/193–20/82) (20/972–20/76) (20/1000–20/167) (20/222–20/114)
0.4 n = 7 n = 13 n = 20
20/373 20/1135 20/769
(20/653–20/213) (20/2010–20/640) (20/1220–20/484)
0.5 n = 1 n = 2 n = 8 n = 11
20/125 20/1000 20/2750 20/1730
(N/A*) (N/A*) (20/6650–20/1130) (20/4190–20/711)
0.6 n = 1 n = 9 n = 10
20/500 20/2580 20/2240
(N/A*) (20/5510–20/1210) (20/4690–20/1070)
Total n = 28 n = 11 n = 20 n = 28 n = 7 n = 14 n = 19 n = 41 n = 168
20/28 20/48 20/68 20/69 20/118 20/118 20/358 20/1260 20/151
(20/35–20/22) (20/135–20/17) (20/100–20/46) (20/97–20/49) (20/266–20/52) (20/154–20/90) (20/557–20/229) (20/863–20/1840) (20/195–20/117)
Table 2.
 
Validation of the Cutoff Value of Objective VA in Patients in Phase I of the Study
Table 2.
 
Validation of the Cutoff Value of Objective VA in Patients in Phase I of the Study
Subjective VA Objective VA Total (%) Odds Ratio (95% CI) P *
≥Cutoff Value (n, eyes) <Cutoff Value (n, eyes)
>20/200 99 9 108 (64.3) 83.3 <0.001
≤20/200 7 53 60 (35.7) (29.4–237)
Total 106 (63.1%) 62 (36.9%) 168 (100)
Table 3.
 
Distribution of VA According to each Step of Induction and Suppression in Objective VA Testing at Distance in the Patients in Phase II of the Study
Table 3.
 
Distribution of VA According to each Step of Induction and Suppression in Objective VA Testing at Distance in the Patients in Phase II of the Study
Induction Method Suppression Method Total
3 4 5 6 7 8 9
0.2 n = 4 n = 8 n = 8 n = 9 n = 8 n = 2 n = 13 n = 52
20/27 20/35 20/71 20/66 20/65 20/200 20/231 20/80
(20/42–20/16) (20/49–20/24) (20/107–20/47) (20/116–20/38) (20/84–20/50) (N/A*) (20/413–20/129) (20/104–20/62)
    P 0.469 0.315 0.614 0.272 0.272 0.800 0.239 0.075
0.3 n = 3 n = 2 n = 2 n = 2 n = 6 n = 15
20/50 20/80 20/100 20/158 20/483 20/169
(N/A*) (N/A*) (N/A*) (N/A*) (20/1760–20/133) (20/339–20/84)
    P 0.400 0.667 0.222 0.262 0.955 0.935
0.4 3 3 n = 6
20/293 20/200 20/242
(N/A*) (N/A*) (20/905–20/65)
    P 1.000 0.314 0.451
0.5 n = 4 n = 4
20/633 20/633
(20/4600–20/87) (20/4600–20/87)
P 0.516 0.516
0.6 n = 3 n = 3
20/1170 20/1170
(20/4380–20/312) (20/4380–20/312)
    P 0.371 0.371
Total n = 4 n = 11 n = 8 n = 11 n = 10 n = 7 n = 80
20/27 20/38 20/71 20/69 20/71 20/221 20/123
(20/42–20/16) (20/56–20/26) (20/107–20/47) (20/107–20/44) (20/89–20/55) (20/493–20/98) (20/162–20/93)
    P 0.469 0.319 0.614 0.179 0.151 0.254 0.214
Table 4.
 
Validation of the Cutoff Value of Objective VA in the Patients Included in Phase II of the Study
Table 4.
 
Validation of the Cutoff Value of Objective VA in the Patients Included in Phase II of the Study
Subjective VA Objective VA Total (%) Odds Ratio (95% CI) P *
≥Cutoff Value (n, Eyes) <Cutoff Value (n, Eyes)
>20/200 43 7 50 (62.5%) 178 <0.001
≤20/200 1 29 30 (37.5%) (20.8–1530)
Total, n (%) 44 (55) 36 (45) 80 (100%)
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