Effect of Instructions on Conventional Automated Perimetry

Abstract

purpose. To investigate the effect of perimetrists’ instructions on automated perimetry thresholds.

methods. Eighteen volunteers in two age groups participated in a series of three test sessions. Each session consisted of a Humphrey Field Analyzer 30-2 test, a questionnaire, and a customized test program using a Humphrey perimeter to construct frequency of seeing (FOS) curves from which thresholds were calculated, and a descriptive measure of response criterion was derived. The FOS curves were obtained at a central and a peripheral test location within the same test session. The three test sessions differed only by the instructions given. The instructions were adapted from those listed in the manufacturer’s instruction manual and were designed to influence participants to respond to the stimuli in a conservative, liberal, or neutral manner.

results. For the 30-2 threshold test, a significant difference in mean deviation was found among the three instruction types (P = 0.001) and between the two age groups (P = 0.001). Although differences were small in the younger subjects (2.04 dB), the means for the responses from liberal to conservative differed by 6.57 dB in the older subjects. Thresholds obtained in a peripheral location by the customized threshold test were found to differ significantly between the age groups (younger group mean, 31.0 dB; older group mean, 27.2 dB) and among the instruction types (liberal mean, 30.9 dB; conservative mean, 28.1 dB; and neutral mean, 30.3 dB; P < 0.001). The descriptive measurement of response criterion suggests that a difference in criteria occurred as a result of the instructions in both peripheral and central locations for both age groups (P = 0.0001). In addition, according to self-reports, liberal instructions caused participants to be more likely to respond, whereas the conservative instructions caused them to be more reluctant to respond.

conclusions. Perimetrists’ instructions can significantly affect obtained automated perimetry thresholds.

Conventional automated perimetry measures a subject’s differential light sensitivity in locations within the central 30° of the visual field. Because perimetry is a psychophysical measure, the thresholds obtained are not dependent on the functional architecture of the visual system alone but also on a variety of physical and cognitive factors. For example, lens rim artifact, improper refraction, excessive pupillary constriction, or dilatation and blepharoptosis all affect luminance thresholds. In addition, cognitive factors including subject attention, motivation, fatigue, and response bias can influence the obtained thresholds. 

Although cognitive factors such as response biases (i.e., a participant’s willingness to report detection of a stimulus) can affect threshold measurements, there is no reliable method to quantify or describe the effects of these response biases on measurements of visual sensitivity in automated perimetry. In the field of psychophysics an attempt to quantify the effects of response bias lead to the development of signal detection theory. The main assumption of signal detection theory is that all stimuli are embedded in noise (both internal and external to the system). Thresholds are at best momentary and are not merely a function of the sensitivity of the system detecting the stimuli. Consequently, any attempt to measure the sensitivity of a detection system with a threshold, according to the theory, may be confounded by response biases. The criterion measure c was developed by psychophysicists as a method to measure and quantify these nonstimulus factors (including response biases, attention, motivation) that affect responding to the stimuli. ^{1 2}  

It is proposed, by signal detection theory, that response biases can result in responses from participants or decision makers that range from very liberal (responding when uncertain that a stimulus has been presented) to very conservative (responding only when certain a stimulus has been presented). This response criterion, which varies among individuals, can easily be changed in response to the demands of a specific situation and is defined automatically each time a response to a perimetric stimulus is required. ² This suggests that changes in a response criterion during or between testing sessions can influence sensitivity measurements and therefore the predictive value of perimetry testing. 

In clinical vision testing, the impact on visual sensitivity created by response bias has been studied for high-pass resolution perimetry (ring test) and contrast sensitivity testing. ^{3 4 5 6 7 8} However, although response bias may account for a portion of perimetric variability, the topic has received limited attention in perimetry literature. In a typical testing situation, there is uncertainty about how much response biases are affecting the observer. According to the principals of signal detection theory, it can be predicted that, with differential light sensitivity, automated perimetry adopting a conservative criterion would result in a constricted visual field or abnormally low sensitivity in the absence of visual system damage. A liberal response criterion, therefore, would result in abnormally high visual sensitivity that would not be truly indicative of visual system function. In both situations, the reliability of the visual field test would be reduced. 

To understand better the effects of response bias on perimetric thresholds, we manipulated the participant’s natural or neutral criterion by using specifically worded instructions to help set either a liberal or a conservative response criterion. In addition, to study the impact of response biases on age differences in automated perimetry outcomes, we included two groups of participants ranging from 24 to 35 and 62 to 71 years of age. 

Methods

Participants

Eighteen paid and unpaid participants were recruited from employees, friends, and family members of employees in the University of Iowa Ophthalmology Clinic, some of whom responded to local advertisements. The study was approved by the University of Iowa Investigational Review Board and followed the tenets of the Declaration of Helsinki. 

Each participant met the following criteria for inclusion in the study: best corrected Snellen visual acuity of at least 20/20, refractive error no greater than 5 D sphere and 3 D cylinder, undilated pupil size of at least 3 mm, and no history of eye disease other than refractive error in the selected eye. Potential participants who were experienced with automated perimetry were excluded. The age of the participants in the younger group ranged from 24 to 35 years (mean, 29.7 years) and in the older group from 62 to 71 years (mean, 67.5 years). There were 12 participants in the younger group and 6 in the older group and an equal number of men and women in each age group. 

All participants had an ophthalmic examination consisting of a confrontation visual field examination and a direct ophthalmoscopic examination. Potential participants were asked to complete a vision and health history questionnaire to exclude volunteers with visual dysfunction. We did not inform study participants of the nature of the study before participation. Participants were told only that they were to follow the specific instructions given each day to the best of their ability. After the final test session, participants were debriefed about the intent of the study. Each participant was given a full-field threshold test (Humphrey 30-2; Humphrey Instruments, San Leandro, CA) using the test instructions we defined as neutral, found in the owner’s manual. ⁹ This practice test was intended to screen for visual field defects and to decrease the effects of perimetric learning. 

Apparatus and Stimuli

Humphrey Full-Field Threshold Test.

We used the full-field threshold test of the field analyzer (model 640, program 30-2; Humphrey) with a white Goldmann size III stimulus varying over a 4-log-unit range. This white background was calibrated to 31.5 apostlib (asb). Each participant’s appropriate near correction was used with an additional refraction performed at the perimeter. Threshold values at test locations throughout the central 30° field were determined with a 4 dB–2 dB staircase procedure. For each participant, the number of false-positive responses (responses when no stimuli were presented), false-negative responses (no response to a 9-dB brighter stimulus than had previously been seen), fixation losses, and short-term fluctuation at selected test locations were calculated by the test instrument. After completion of the full-field threshold test, each participant was given a minimum of 10 minutes’ rest before the second threshold test. 

Customized Threshold Test.

After the rest period, two additional thresholds were obtained to confirm the effect of instructions with a customized threshold test program using the method of limits. An IBM-compatible personal computer (486/66 mHz; Hewlett–Packard, Palo Alto, CA) was used to control the field analyzer externally. FOS curves were obtained for two predetermined locations chosen to represent central and peripheral locations. ¹⁰ White Goldmann size III stimuli, varying in intensity from 40 to 20 dB (in 2-dB increments) were presented 20 times each in random order on a background of 31.5 asb at two locations (−27°, 3° and 3°, −3°). Eighty-eight catch trials (17% of the total number of trials), in which no stimulus was presented, were included as a false-positive response measure. The technician monitored the participant’s fixation, and the appropriate near correction was used. If the participant did not respond within 2 seconds, the stimulus was considered not seen. 

FOS curves were then constructed to obtain a threshold for each subject by calculating cumulative gaussian functions and a least-squares fit by computer (Excel solver function; Microsoft, Redmond, WA; the FOS curves were fitted with a cumulative gaussian function). This function changed the mean ± SD of the curve fit until the R ² value was maximized. The resultant mean of the fitted distribution corresponds to the 50% correct threshold for the test location (defined as the stimulus intensity corresponding to the 50% FOS point of the fitted curve). The SD of the cumulative gaussian function (an index of the maximum slope of the FOS function) and the coefficient of determination or goodness of fit (R ²) were calculated for each FOS curve. 

Questionnaire.

We designed a survey to ascertain how and to what degree several factors influenced participants’ responses while taking the full-field threshold test. Participants were instructed to rate the extent to which anxiety, the test instructions, and their desire to follow the instructions correctly affected test performance by choosing a number on the scale between 0 (strongly disagree) and 10 (strongly agree). The specific wording of the questionnaire items can be found in Table 1 . 

Procedures

After completing the initial screening, both groups participated in a series of three test sessions separated by a minimum of 24 hours between sessions. During the first session, each participant was given a Humphrey 30-2 test for practice, and then, after a 10-minute minimum rest break, a second Humphrey 30-2 test was administered. The second visual field test was followed by a second 10-minute rest break during which participants responded to the questionnaire. Finally, the customized threshold test was administered. To decrease the effect of fatigue, a 1-minute break was given after approximately every 7 minutes of testing or when requested by the participant. The test instructions were repeated before beginning the threshold tests and were paraphrased again during breaks. These procedures, with the exception of the Humphrey 30-2 practice test, were each repeated for sessions 2 and 3. Each session lasted approximately 70 minutes, with all threshold tests performed on the same eye. 

During the first testing session, the standard instructions recommended by the manufacturer’s instruction manual were used to allow participants to respond according to their natural or neutral response criterion. ⁹ The verbatim instructions used are listed in Table 2 . All participants received the neutral instructions for the first session, whereas the remaining two sessions were counterbalanced between liberal and conservative instructions. The instructions were read from cue cards by a single experienced technician (KEK) before each threshold test to ensure that the same instructions were given to each participant. It is important to note that the only instructions given before and during test sessions were those listed in Table 2 . A shortened version of the initial instructions was repeated during the short intratest breaks to remind participants of the instructions or in the event of poor test performance. 

Statistical Analysis: Customized Threshold Test

The measures for threshold (visual sensitivity) and descriptive measures of response criterion were obtained in the following manner with data from the customized test. For the descriptive measure of response criterion, a true-positive rate (H) was obtained for each intensity at both locations by dividing the total number of yes (stimulus was detected) responses by the number of repetitions (n = 20) of each intensity. A false-positive rate (F) was calculated by dividing the number of yes responses to catch trials by the total number of catch trials (n = 88). To obtain a measure of sensitivity (d′), the H and F proportions were transformed to z values, where z is the inverse of the standard normal distribution function: d′ = z(H) − z(F). ¹ An independent measure of the participant’s willingness to say yes or response criterion proposed by signal detection theory was calculated using H and F rates: c = −0.5[ z(H) + z(F)]. ² Infinite values were avoided by adding a correction factor of 0.028[ 1/(2N)] to proportions of zero and subtracting it from a proportion of one. ² In addition, the resultant value was limited to two decimal places. The c value was calculated for each of the 11 stimulus intensities at both locations and averaged to calculate a final c value to be used in further analysis. 

To obtain thresholds, FOS curves were derived by plotting the proportion of correct responses as a function of each stimulus intensity for each test location separately from the calculations used to measure response criterion. Threshold was defined as the stimulus intensity corresponding to the 50%-seen point of the fitted curve. 

Results from the customized threshold test (threshold and separate criterion calculations), questionnaires and Humphrey 30-2 (mean deviation [MD], false-negative responses, false-positive responses, fixation losses, and short-term fluctuations) were analyzed using analysis of variance (ANOVA) with a 2 (age) × 3 (test instructions) split plot design. Student–Newman–Keuls was used for post hoc test analyses. Statistical significance was set at P < 0.05. All statistical analyses were performed by computer (SAS ver. 6.12 software; SAS, Cary, NC). 

Results

Humphrey 30-2 Threshold Test

The effect of instructions can be seen by viewing the gray scale representations of two participants. Figure 1 shows the decrease in visual sensitivity for a 35-year-old man corresponding to going from liberal (a), to neutral (b), to conservative (c) response instructions. A more dramatic effect is evident from the visual field results of a 71-year-old woman (Fig. 2) . Note the large generalized effect of the conservative instructions. 

Table 3 shows the MDs obtained by participants in each of the two age groups. For the younger group (aged 24–35) the conservative instructions led to greater MD’s than either the liberal (2.14-dB difference) or neutral (1.25-dB difference). However, only a small difference in MD (0.66 dB) was found between the liberal and neutral instruction conditions. For the older participants (aged 62–71 years) conservative instructions also led to greater MD’s than either the liberal (4.27-dB difference) or neutral (2.41-dB difference) instructions. For these older participants there was also a significant difference in MD (1.86 dB) between the liberal and neutral conditions. A difference between the age groups (P = 0.001) was also found for all instruction types, with the older participants (mean, −2.26 dB) obtaining lower visual sensitivity (P = 0.001) than the younger group (mean, −0.46 dB). 

The measures of false-negative responses, fixation losses, and short-term fluctuation obtained using the Humphrey Field Analyzer 30-2 threshold program showed no significant differences among the three instruction types for either age group. However, both young and older participants had, on average, significantly more false-positive responses when given liberal instructions (mean, 4.6%) than when given conservative ones (mean, 0%; P = 0.023). Only 3 of the 72 program 30-2 threshold tests given were marked for low reliability: one in the young group and two in the older group. In each case, however, this was due to an excessive score for fixation losses. Although fixation was monitored by the perimetry technician and centered throughout the test, if a head tilt occurs after the blind spot location procedure, fixation losses may occur in correctly fixating patients. ¹¹  

Differences were found between the two age groups regardless of instruction type in the number of false-negative response errors calculated by the Humphrey 30-2 test. The Humphrey Field Analyzer includes trials 9 dB brighter than a previously seen stimulus as its normal testing procedure for false-positive catch trials. The average number of these false-negative responses for the older group was 11 but only 5 for the younger group (P = 0.026). There was also a difference between the older and younger groups for the short-term fluctuation measure (P = 0.002), with the older group (1.74 dB) having a slightly higher value than the younger group (1.27 dB). The younger group had a greater number of false-positive response errors for both the neutral (young, three errors; old, two errors) and liberal (young, seven errors; old, five errors) instruction sets, but these differences in the number of errors failed to reach statistical significance when the two age groups were compared (P = 0.86). 

The Glaucoma Hemifield Test (GHT) classified Humphrey Field Analyzer 30-2 test results as abnormal for three of the six older participants for the conservative instruction set and three as abnormal with the neutral set. In addition, four of the neutral instruction program 30-2 results were classified as borderline according to the GHT. None of the tests for the younger group, for any instruction type, was classified by the GHT as either borderline or abnormal. As shown in Table 3 the older participants for the conservative and neutral instruction types had MD, pattern standard deviation (PSD), and corrected pattern standard deviation (CPSD) indices flagged with P values of less than 10% more frequently than the younger group. 

Customized Threshold Test

In the peripheral test location (−27°, 3°) significant differences in threshold (50% seen intensity) were obtained among instruction types (P = 0.0001) and between the two age groups (P = 0.0001). The fits (R ²) for the cumulative gaussian functions used to calculate the thresholds ranged from 0.94 to 1.0 (Table 4) . Liberal instructions led to the highest visual sensitivity (mean, 30.9 ± 3.05 dB), whereas conservative instructions (mean, 28.1 ± 2.49 dB) led to the lowest. The older adults overall averaged lower visual sensitivity (mean, 27.2 ± 1.92 dB) than the young participants (mean, 31.0 ± 2.29 dB). Figure 3 shows the mean threshold values for each participant in both the older and younger age group at the both the central and peripheral test locations for all three instruction types. 

In the central location (3°, −3°), no significant differences in threshold were found among the instruction types (P = 0.06). The central location results followed the same general pattern as those in the peripheral location, with conservative instructions leading to lower sensitivity (mean, 34.5 dB) and liberal instructions resulting in higher visual sensitivity (mean, 35.5 dB). As in the peripheral location, a significant difference at the central location was found between the two age groups (P = 0.0001), with the older group having consistently lower visual sensitivity (mean, 33.6 ± 1.33 dB), regardless of the instruction type, than the younger group (mean, 35.7 ± 1.24 dB). 

The descriptive measurement of response criterion suggested differences in the degree of response biases affecting participants in both the peripheral and central locations for all instruction types and between age groups (Fig. 4) . In the peripheral location a significant difference was found between the conservative (mean, 1.3 c) and both neutral (mean, 1.0 c) and liberal (mean, 0.87 c) instructions (P = 0.0001). Centrally, however, only differences in criterion between the conservative and liberal instructions were significant (P = 0.039). At both test locations, the older group responded more conservatively than the younger participants regardless, of instruction type (P = 0.0001, Fig. 4 ). 

Questionnaire Data

Although we found no significant differences in anxiety level among the three instruction types or between the age groups, participants tended to report feeling less anxious with the neutral instructions. The older group participants were more likely to report that they were motivated to follow instructions correctly than participants in the younger group (P = 0.043). Also, the older participants were more than twice as likely to be very certain before responding than the younger group, regardless of instruction type (P = 0.01). Differences among all three instruction types were found with self-reported estimates of the percentage of time that the participant guessed when responding (P = 0.012). These average estimates for the liberal instructions were much higher (21%) compared with the neutral (13%) and conservative (5%) instructions. Participants also reported that the liberal instructions made them more likely to respond (P = 0.02), whereas the conservative instructions made them more reluctant to respond (P = 0.0001). 

Discussion

We found that the instructions given to participants during conventional automated perimetry influenced the threshold values obtained. Statistically significant effects were found in a group consisting of both young (24–35 years old) and older (60–72 years old) visually healthy adults. 

The impact of instructions on threshold values is of obvious interest for clinical perimetry, because the ability to detect generalized improvement or worsening of the visual field is limited by long-term or interest variability. This long-term variability has been partitioned into homogeneous and heterogeneous components ¹² resulting from the fluctuation of repeated measurements at the same test location at different times. The heterogeneous component refers to local fluctuations, whereas the homogeneous component refers to effects involving the entire visual field manifested by a change in total mean deviation. Our findings suggest that instructions given by a perimetrist are responsible for some of the homogeneous component of long-term variability. 

Overall, all participants had higher visual sensitivity values on both the Humphrey 30-2 threshold test and on the customized method of limits test when given liberal instructions and lower sensitivity with the conservative instructions. Although the differences in thresholds obtained from the younger group were statistically significant, from a clinical perspective, in most cases the results were not of the magnitude that commonly signals clinical change (liberal mean, 0.55 ± 0.98 dB; conservative mean, −1.55 ± 1.4 dB; and neutral mean, −0.34 ± 0.86 dB). However, a clinically significant change (Fig. 2) could easily be mistakenly concluded in some of our older healthy participants (liberal mean, −0.22 ± 1.2 dB; conservative mean, −4.49 ± 5.6 dB; and neutral mean,− 2.08 ± 2.7 dB) based on the instruction set used. 

The number of false-negative response errors obtained from the 30-2 threshold test were not significantly associated with instruction type. This may be due in part to our small sample size (n = 18). However, in both age groups, no false-positive response errors were recorded after the conservative instructions, a greater number for the neutral instructions, and the largest number for the liberal instructions. Consequently, none of the 18 participants was found to have abnormally high false-positive response rates on either the program 30-2 or the customized threshold test (5 false-positive responses for the neutral instructions and 12 for liberal instructions in both age groups combined). There are several possible implications for clinical perimetry from these findings: Based on the standard cutoff criteria for reliability, patients do not become unreliable, even when heavily encouraged to respond using liberal instructions; the number of false-positive responses is not a reliable indicator of response bias; liberal instructions given by perimetrists do not cause an excessive number of false-positive responses, but these responses may be the result of other psychological factors; and changes in threshold from response bias, especially in older subjects, can mimic visual field changes due to sensory visual system damage. 

The customized test allowed us to obtain a second more precise threshold at both peripheral and central locations along with a false-positive response rate. For the younger group at the central test location, the threshold differences between the neutral and liberal instructions were slight. This suggests that the response bias used by the younger participants tested was more liberal when the test instructions did not give specific cues as to when to respond to a stimulus. In contrast, the older participants were found to demonstrate a more conservative response bias than the younger group for the perimetric threshold task, regardless of instruction type or location within the visual field. It is important to note that even when participants were following liberal instructions, their false-alarm rate was not higher than the miss rate, as the true definition of liberal would indicate. Because our sample size was small, we cannot conclude that all older participants will respond in a conservative manner to a light stimulus. Inconsistent use of conservative criteria by older adults has been reported in the aging and psychology literature. ^{13 14 15}  

The methodology used for this study differs from that used in previous work, ³ in that response bias was not only measured but specifically manipulated. Although sensitivity is lower in the periphery, the descriptive measurement of c additionally showed that participants in both age groups responded in a more conservative manner in the periphery regardless of the instructions. Although at the central test locations, thresholds did not differ significantly between the neutral and liberal instructions in the younger group and between the neutral and conservative instructions in the older group, the quantified measure of response criterion used by the participants corresponded with the instructions that were given. The liberal instructions and conservative instructions were correlated with liberal and conservative response criterion, respectively. 

Although perimetry is automated, interaction with the patient remains important. The criterion differences demonstrated between the instruction sets and their differential effect on the central and peripheral regions of the visual field for both age groups illustrates the need for perimetrists to give instructions that emphasize a liberal response criteria for the peripheral area. Failure to encourage a liberal type of response in the periphery may result in a constricted visual field, because of a conservative response criterion. Our formulation for criterion (c) resulted in a range of values with zero at the center; a criterion of c = 0 indicated that the proportion of false-positive responses would be equal to that of false-negative responses and thus no response bias. A criterion of c < 0 indicated a liberal response tendency—false-positive responses would exceed false negative ones; a criterion of c > 0 indicated a conservative response tendency—false-positive responses would be fewer than false negative ones. ² Although we obtained various criterion differences, examination of the c values indicates that most of our observers responded in a conservative manner, even when liberal test instructions were administered. Our results included only visually normal subjects of two age groups. The impact of response criterion on the visual fields of patients with visual field loss remains uncertain. 

In conclusion, our results show response bias can have a statistically and clinically significant effect on perimetric thresholds. A problem inherent in automated perimetry is that although there are recommended instructions, there is large interperimetrist variability in instructions used. There is no standardization of instructions. Our study suggests perimetrists should use a standard set of instructions to reduce the response bias effect. This will lessen the chance that changes in threshold from response bias will imitate visual field changes due to sensory visual system damage. 

³  Present address: Department of Epidemiology, University of Michigan, Ann Arbor.

 Supported by VA Merit Review, and an unrestricted grant to the Department of Ophthalmology, University of Iowa, from Research to Prevent Blindness (MW).

 Submitted for publication October 21, 1999; revised December 17, 1999; accepted January 11, 2000.

 Commercial relationships policy: N.

 

Table 1.

 

Questionnaire Items and Resultant Responses for Both Age Groups Combined

	Neutral	Conservative	Liberal
Of the number of times you responded that you saw a light, what percentage of the time were you guessing? 0%–100%	13.1 ± 9.3	5.4 ± 4.8	21.1 ± 14.3
How likely to respond to a light did these instructions make you? 0, Very likely to 10, not at all likely.	3.1 ± 2.6	4.4 ± 2.9	1.2 ± 1.6
How reluctant to respond to a light did these instructions make you? 0, Very likely to 10, not at all likely.	8.0 ± 1.9	4.6 ± 3.1	9.3 ± 1.0
Please choose the number that best describes how you are currently feeling. 0, Anxious to 10, calm.	6.3 ± 2.5	7.6 ± 2.2	7.1 ± 1.8
How motivated were you to follow the instructions correctly? 0, Very motivated to 10, not at all motivated.	0.8 ± 1.1	0.9 ± 0.8	0.8 ± 0.9
On average, how certain were you that you saw a light before pressing the buzzer? 0, Absolutely certain to 10, absolutely uncertain.	4.3 ± 2.4	2.8 ± 2.9	3.6 ± 1.8

 Data are mean percentage ± SD for first item and means response ± SD on a scale of 1 to 10 for the remaining items.

Table 2.

 

Instructions Given to Participants to Provide Neutral, Conservative, or Liberal Criteria

Neutral	Always look straight ahead at the steady yellow light. Other lights will flash, one at a time off to the side. Some will be bright, some dim. Press the button whenever you see one of these flashes. You are not expected to see all of them. The best time to blink is just as you press the button.
Conservative	On this test you will be able to see half of the stimuli that are presented. (This statement is recommended, by Humphrey Field Analyzer Manual to help combat false positive responses). We want you to be certain that you see a light before pressing the button. Do not respond if you are unsure. If you respond while there is no light presented, the test time will increase and an error will be recorded. Remember, you will not be able to see all of the lights that are presented. Make sure that you are certain a light was presented before pressing the button.
Liberal	On this test we are trying to find the dimmest light that you can see. The test will push you to see very dim targets. We want you to press the button as soon as you think you might see a light. There is no penalty for guessing. In fact, we encourage guessing. Remember the test is trying to push you to see very dim targets.

 Adapted from the owner’s manual for the Humphrey Field Analyzer, San Leandro, CA with permission from Zeiss Humphrey Systems.

Figure 1.

 

Humphrey 30-2 threshold test results in a 35-year-old participant: (a) after liberal instructions (MD, 0.12 dB), (b) after neutral instructions (MD, −1.73 dB), and (c) after conservative instructions (MD, −4.10 dB). Note the superior defect on the conservative field.

Figure 2.

 

Humphrey 30-2 threshold test from 71-year-old participant: (a) after liberal instructions (−1.56 dB), (b) after neutral instructions (MD, −4.76 dB), and (c) after conservative instructions (−15.63 dB).

Table 3.

 

Mean Deviation of the Humphrey Program 30-2 Test by Age and Instruction Type

Participant	Neutral	Conservative	Liberal	Test Order
Young Group
1	−1.74	−0.87	−0.42	N, L, C
2	0.19	0.62	1.67	N, L, C
3	0.00	−2.60	0.25	N, L, C
4	0.33	−1.36	0.14	N, L, C
5	−0.53	−3.48* , † , §	−0.06	N, L, C
6	−0.38	−2.39, §	0.80	N, L, C
7	0.95	−1.17	2.56	N, C, L
8	0.68	−0.22	1.94	N, C, L
9	−0.32	−2.56	−0.42	N, C, L
10	−1.10	−0.59	−0.16	N, C, L
11	−0.45	−0.33	0.23	N, C, L
12	−1.73	−4.10* , † , §	0.12	N, C, L
Average	−0.34	−1.59	0.55
Older Group
1	1.16	0.58	1.97	N, C, L
2	0.35	−2.42, † , §	−0.52	N, C, L
3	−4.76* , † , §	−15.63* , † , §	−1.56	N, L, C
4	−1.38	−3.03*	−1.08	N, C, L
5	−5.78* , † , ‡ , §	−3.23* , † , §	−0.13	N, L, C
6	−2.04, † , §	−3.21* , † , §	−0.02, † , §	N, L, C
Average	−2.08	−4.49	−0.22
Overall Average	−0.92	−2.56	0.30

 N, neutral; C, conservative; L, liberal.

*  MD (mean deviation) flagged <10%.

†  PSD (pattern standard deviation) flagged <10%.

‡  SF (short-term fluctuation) flagged <10%.

§  CPSD (corrected pattern standard deviation) flagged <10%.

Table 4.

 

R ² of FOS Curves by Age, Location, and Instruction Type

Participant	Neutral Central	Conservative Central	Liberal Central	Neutral Peripheral	Conservative Peripheral	Liberal Peripheral
Young Group
1	0.99	0.98	0.99	1	1	1
2	1	1	1	1	1	0.99
3	1	0.99	0.99	1	1	1
4	0.96	0.99	0.99	1	1	1
5	1	0.99	0.99	0.99	0.99	1
6	0.99	0.97	0.99	1	1	1
7	0.98	0.99	0.93	0.99	1	0.99
8	1	1	0.89	0.98	0.99	0.90
9	0.98	0.99	0.99	1	1	1
10	1	0.98	0.99	1	1	0.99
11	1	0.97	1	0.99	1	1
12	1	1	1	1	1	0.97
Older Group
1	1	0.99	0.97	1	1	1
2	1	0.99	0.98	0.98	0.99	0.97
3	1	0.99	0.94	1	1	1
4	0.97	0.98	1	0.95	0.99	0.99
5	0.99	0.97	0.94	0.98	1	0.99
6	*	*	0.97	0.98	1	1

*  Unable to calculate value.

Figure 3.

 

Thresholds as measured by FOS curves for the (a) younger participants and (b) older subjects at their central test location. Results from the peripheral location for the younger group (c) and older group (d). Note the pattern of higher visual sensitivity with the liberal instruction set and the lower visual sensitivity with the conservative set.

Figure 4.

 

Measure of participants criterion (c) for both young and old participants by instruction type in the (a) central test location in younger subjects, (b) central test location in older subjects, (c) peripheral test location in younger subjects, and (d) peripheral test location in older subjects. Note that the older subjects consistently had a greater c value, demonstrating that they responded more conservatively. Also note the different pattern of results from those in Figure 3 , showing the effect of the false-positive rate used in the calculation of c.