Sensitivities in Older Eyes With Good Acuity: Cross-Sectional Norms

Alvin Eisner,*f Susan A. Fleming,*! Michael L. Kleins and W. Manning Mauldinf

We measured several indices of foveal visual function for a large group of people aged 60 and older. The data reported in this paper are from individuals who had good acuity in each eye and met a number of other criteria for good ocular health. For each index, we described the rate of cross-sectional change with age using linear regression statistics. We found age-related change for eyes having 20/20 or better acuity to exist for several different indices. Sensitivity mediated by the -sensitive cones decreased with age, as expected. However, the rate of decrease was faster for females than for males. At least part of the difference was associated with different rates of lenticular change. Absolute sensitivity at long wavelengths also decreased with age, but at the same rate for each sex. Rayleigh matches changed with age in a manner consistent with underlying age-related decreases of effective foveal cone photopigment density. However, not all indices showed age-dependent changes. For instance, the time constant describing the rate of photopic dark adaptation did not appear to change with age. Invest Ophthalmol Vis Sci 28:1824-1831, 1987

Human visual function changes with age. Cross- criteria for good ocular health in each eye. In particu- sectional age-related changes have been reported for lar, we have tested people having good acuity in each Snellen acuity,1 spatial2"4 and temporal4 contrast sen- eye. Macular change that can be observed fundu- sitivity, short-term adaptational dynamics,5-6 sensitiv- scopically is limited to the presence of drusen and/or ity at absolute threshold,7-8 color discrimination910 pigmentary change. and many other functions. However, few studies doc- The functional tests that we chose to use were umenting age-related functional change have tested among those likely to be especially sensitive to the many individuals older than age 60. Typically, only integrity of both the retinal pigment epithelium enough older individuals are tested to demonstrate (RPE) itself and the RPE/photoreceptor interface. that young and old people differ statistically for a We measured blue-sensitive ("S") cone mediated sen- given visual function." Thus, age-related functional sitivities, rates of photopic dark adaptation, and Ray- changes within the older age group remain largely leigh color matches. We measured S cone sensitivities unknown. For this reason, we have measured several because, in accordance with Kollner's rule, S cones different kinds of foveal sensitivity in a large popula- may be especially vulnerable to retinal insult, particu- tion of people aged 60 and older. larly at the level of the RPE.12 We calculated time By measuring different kinds of sensitivity in a constants of photopic dark adaptation rates because large older population, we have attempted to estab- those rates depend on the rate of photopigment re- lish sets of cross-sectional norms. Because many peo- generation,13 which in turn depends on the health of ple older than age 60 have ocular pathology, we have the RPE.1415 In calculating time constants, we mea- tested only people meeting a number of necessary sured absolute threshold at long wavelengths, where preretinal absorption is minimal.1617 We measured Rayleigh color matches for both small and large fields because Rayleigh matches depend on the ratio of L to From the *Neurological Sciences Institute and the tDepartment M cone quantum absorption, which varies systemati- of Ophthalmology, Good Samaritan Hospital and Medical Center, 1819 Portland, Oregon, and the ^Department of Ophthalmology, Ore- cally with retinal locus. In measuring color gon Health Sciences University, Portland, Oregon. matches, we also obtained an index of / color Supported by National Institutes of Health grant EY-05047 and discrimination. by the Oregon Lions Sight and Hearing Foundation. In the following paper20 we show that most of these Submitted for publication: November 4, 1986. Reprint requests: Alvin Eisner, PhD, Neurological Sciences Insti- functional indices can be affected by RPE compro- tute, Good Samaritan Hospital and Medical Center, 1120 N. W. mise which has not yet caused acuity to decrease to 20th Avenue, Portland, OR 97209. worse than 20/20.

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Materials and Methods fundus photographs were taken of the macula. These photographs are evaluated in the following paper.20 Criteria For Subject Eligibility Written informed consent was obtained from all sub- Individuals of age 60 or older were eligible for in- jects. clusion into the study if they met the following set of criteria: Numbers of Subjects a) best corrected acuity of no worse than 20/30 in A total of 122 subjects with 20/20 or better best either eye (however data are reported only for eyes corrected acuity in at least one eye were tested; 53 having 20/20 or better best corrected acuity; see females and 27 males in their sixties, 29 females and 8 "Statistical Considerations" below). males in their seventies, and 2 females and 3 males in b) < 22 mm Hg in each eye. their eighties. Sixteen of these individuals had 20/20 c) no history or evidence of , macular or better acuity in one eye and 20/25 acuity in the lesions, , diabetes, or ocular surgery. other. Five of these individuals had 20/20 or better d) no abnormal macular changes other than mac- acuity in one eye and 20/30 in the other. Out of 86 ular drusen or pigmentary changes. females, 25 took unspecified doses of estrogen. Eigh- e) no > 5 diopters. teen of these 25 were in their sixties, six were in their f) not taking digitalis or chloroquine derivatives.21 seventies, and one was in her eighties. g) no congenital or color anomaly. Visual Function Testing Subject Recruitment Instrumentation: Two apparatuses were used for testing. Subjects were recruited from the following sources: through a newspaper article in which volunteers aged All threshold measurements were obtained using a 60 or older having normal vision were requested, by two channel Maxwellian view testing device having word of mouth from those who had already been an exit of 1.23 mm. For each subject, the stop tested, from a retirement home for active living, which defined the test field was translated along the through recruitment letters at doctors' offices, at a optical path to the position which corresponded to hospital health fair, from among individuals accom- the subject's "mideye" spherically equivalent correc- panying someone else to the Eye Clinic, through ad- tion. (We define the mideye value for a given index as vertisements in newsletters for senior citizens, and the average of that index's values over a subject's two from patients attending the Eye Clinic for routine eyes.) Subjects positioned themselves by placing their examination. The sources are listed in order of de- brow and cheekbone against an eyepiece so that an creasing frequency. Subjects were paid $ 10 for partic- adapting field or an annular fixation aid appeared ipating in the study. maximally bright. For about 80% of the subjects tested, a chin rest was available. Subjects responded with a buzzer when the test spot appeared to reach Subject Screening criterion. Upon arriving at the Eye Clinic, potential subjects Rayleigh matches (primaries of peak wavelengths had histories taken by one of two certified ophthal- 546 nm, 588 nm and 649 nm with half height band- mic technicians. These same technicians then mea- widths of about 10 nm) were made on a free viewing sured potential subjects' distance Snellen acuities in anomaloscope in deutan mode with the field at opti- each eye separately by using a standard projection cal infinity. The proportion of 546 nm (G) and 649 system. If subjects read at least half the letters on the nm (R) was controlled by varying the linear po- 20/20 line correctly using their own glasses, then they sition of a stage that carried two interference filters were not refracted. If potential subjects had poorer and a neutral density filter. The stage could be trans- acuity on initial testing, then they were manifest re- lated in a plane adjacent to a fixed square aperture fracted to their best corrected acuity. The acuities through which passed collimated light. The linear reported in this paper are defined using the criteria of position of the stage depended upon the setting of a at least half the letters on a line correct. Following micrometer, thus allowing adjustment of R/G ratios acuity testing, potential subjects were examined by a reliably and precisely to within about ±0.0005 log screening ophthalmologist (usually WMM). The unit. The luminance of the 588 nm (Y) light was fundus was viewed using a direct ophthalmoscope controlled using a neutral density wedge. The R/G with the pupil undilated. After psychophysical test- mixture and Y matching were directed into ing, the pupil was dilated and stereoscopic color separate integrating spheres, thereby producing uni-

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formly illuminated fields. A mirror at 45° to the two upon a 1000 td, 480 nm background. The 20 Hz integrating sphere exit ports and an adjacent field flicker sensitivities were obtained following the S stop holder together served to produce bipartite fields cone sensitivities. Since 440 nm and 490 nm excite L of up to 6.5° diameter. Subjects viewed the bipartite and M cones in nearly equal proportion,24 S cones fields through a 200 mm focal length achromat . can be deduced to mediate sensitivity at 440 nm on An adjustable chin rest allowed subjects to position the 1000 td, 580 nm background if the difference in themselves comfortably so that the two halves of the sensitivity between 440 nm and 490 nm on that bipartite field appeared equally sized. When subjects background is greater than the difference in sensitiv- wore optical corrections for anomaloscope testing, ity to 20 Hz flicker between 440 nm and 490 nm on the corrections were untinted. Neither pupil size nor •the 480 nm background. The deduction that S cone chromatic aberration were controlled or monitored. response is isolated assumes that neither S cone25 nor Procedure: Subjects were tested on a battery of tests rod2627 response to the test stimulus significantly in- by either of two examiners (AE or SAF). Subjects fluences detection of 20 Hz flicker on a 1000 td, 480 were tested in each eye alternately. Before thresholds nm background. and anomaloscope color matches were obtained, b) Photopic dark adaptation and absolute thresh- subjects were tested for about 10 min with a series of old: Foveal sensitivity at absolute threshold was mea- plate and arrangement tests administered under sured using a 3°, 160 msec, 660 nm test stimulus. The Macbeth lamp illumination. The results of these plate test stimulus was presented at a rate of 1.0 Hz. It was and arrangement tests are not reported here. Some of centered within a 2 td, 580 nm, 8.6° I.D., 11.5° O.D. the results are reported elsewhere.22 annular surround. Before the examiner measured Following the initial plate and arrangement tests, sensitivity at absolute threshold for a given eye, that threshold measurements were obtained by having the eye had adapted to the dark for period of at least 7 examiner increase the light level of a test field step- min. Seven minutes corresponded to the minimal wise in increments of about 0.04 log unit until a crite- time elapsed since that eye had viewed the 1000 td rion of "just seen" was reached. Subjects' fixation 480 nm adapting field used for the 20 Hz flicker sen- was not monitored. Subjects were coached to fixate sitivities. Mean absolute thresholds were computed appropriately, especially if they reported the appear- from eight settings. Early settings for which there ance of the adapting field to change in a manner were systematic threshold decreases were not in- suggesting inappropriate fixation. cluded in the average. a) S cone thresholds: Foveal S cone sensitivity was Immediately after the absolute threshold measure- measured for each of two test diameters. The two ments were obtained for a given eye, that same eye diameters were 3° and 1 °, and were presented in that viewed a foveally centered 7.5°, 20,000 td, 580 nm order. The test stimuli were square wave modulated bleach for 3 min. At the conclusion of the bleach the at a rate of 1.5 Hz. Two test wavelengths, 440 and 490 examiner increased the light level of the test stimulus nm, were used for each test stimulus diameter. The until the subject responded that he or she saw the test test stimuli were all centered upon a 6°, 1000 td, 580 stimulus. The time and threshold value were re- nm adapting background field. Thresholds were ob- corded. This process was repeated until the thresholds tained after a minimum of 3 min adaptation. Mean had returned to within 0.3 log unit of the average threshold values were computed from four threshold absolute threshold. Time constants* of rate of recov- settings. If thresholds continued to decrease at the ery were computed by calculating the negative recip- outset of data collection, then more than four settings rocal of the slope of the least squares linear regression were obtained and the initial decreasing thresholds line which was fitted to the transformed data, were not included in the average. The background In ((D(t) - Df)/(D0 - Df)), where D(t) represents the illuminance was chosen to be 1000 td in order to (1) log threshold at time t after extinction of the bleach, effectively isolate S cone response at 440 nm in all Df represents the mean log threshold obtained before subjects while (2) minimizing the dependence of S the bleach, and Do represents the initial value of log cone mediated sensitivity on the precise retinal illu- threshold obtained after the bleach. To prevent ran- minance of the background.23 We found that S cones mediated sensitivity at 440 nm for all subjects tested. S cone isolation was veri- * The interpretation of the calculated value as a true time con fied by comparing the sensitivity difference between stant assumes that log threshold changes exponentially with time This is not true in all people,28 but the calculation still serves as « 440 nm and 490 nm on the 1000 td, 580 nm back- first order estimate upon which theoretically significant intersub ground with the sensitivity difference between the ject variability is added. The calculated value will be called "tim< same test wavelengths to 20 Hz square wave flicker constant" in the text.

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dom error from producing spuriously large time con- of significance. Unless stated otherwise, all tests are stants, only values of D(t) such that D(t) was greater one sided and significance values are for eyes with than Df + 0.3 were used to calculate time constants, 20/20 or better acuity only. When each of an individ- c) Rayleigh matches—anomaloscope color- ual's two eyes had 20/20 or better acuity, only one match-area-effect: Rayleigh midmatchpoints and value, the "mideye" value, was used for statistical matching ranges were determined for large and small comparison or calculation (except when left versus bipartite fields, 5.8° and 1.1°, respectively. The ex- right eyes were being compared). When only one eye aminer set the red/green (R/G) ratio of the mixture had 20/20 or better acuity, that eye's data were used. hemifield in 0.005 log unit steps, and then asked the Although data are reported only from eyes having subject to attempt to match the two hemifields by. 20/20 or better acuity, none of the .mean intraindi- adjusting the luminance of the 588 nm hemifield. vidual differences between 20/25 eyes and 20/20 or The subject then reported if the two halves could or better eyes were significantly different from zero for could not be made to appear the same in color and any visual function indices that we have analyzed.t brightness simultaneously while looking at the cen- The mean ages and associated standard deviations of tral border. Fixation was not monitored. Subjects individuals with at least one 20/20 or better eye were were encouraged to fixate correctly, and to blink or 64.3 ± 2.7 years for females in their sixties, 65.0 ±2.8 glance away periodically in order to minimize time- years for males in their sixties, 72.3 ± 1.9 years for dependent widening of the matching range. For each females in their seventies, and 72.6 ± 1.9 years for eye, settings were made first for the large field and males in their seventies. Data from all eyes with then for the small field.Fiel d luminance was about 15 20/20 or better acuity are represented graphically. cd/m2. The end points of the R/G ratios for which a color match could be obtained were geometrically Results averaged and a midmatchpoint computed. The dif- ference of the logarithms of the midmatchpoints for S Cone Sensitivities large versus small fields defines the color-match- 1819 As expected, S cone sensitivities tended to decrease area-effect. with age (Fig. 1). Unexpectedly however, S cone sen- sitivities did not appear to decrease at the same rate Calibration for females as for males. The linear regression slopes of log sensitivity versus age were greater for females in Both apparatuses were calibrated with an EG&G their sixties or seventies than for males in their sixties (Salem, MA) model 550 radiometer. The test channel or seventies. These slopes for females and males were of the Maxwellian view device was typically cali- 0.42 and 0.12 log unit per decade respectively for 3° brated weekly. The greatest spread in measured lamp test stimuli, and 0.39 and 0.14 for 1° test stimuli. output ever noted for a given lamp was 0.06 log unit. Consequently, when S cone mediated sensitivities The light source (General Electric DDP; Cleveland, pooled over sex were age-corrected via linear regres- OH) was voltage underrun by 5% and lasted about sion, females were found to be less sensitive than 300 hr. New lamps were aligned so that the test fields males for both 3° and 1° test stimuli (P < 0.001 and P were uniform to within 0.02 log unit. Both channels < 0.002 respectively, 2-sided tests). The sex-depen- of the device were calibrated for all relevant wave- dent sensitivity differences did not appear to exist for lengths when a new lamp was positioned. The anom- people in their early sixties. The limited amount of aloscope, which also had a General Electric DDP data for people in their eighties suggests that S cone lamp underrun by 5% as a source, was calibrated at sensitivity may decrease precipitously for people in the beginning and towards the end of data collection, that age group. and was verified to be stable over time. A portion of the age-related S cone sensitivity loss Statistical Considerations for people aged 60 and older would be expected to be associated with age-related lens density change.17 We Linear regression and correlation statistics were used two methods to estimate the linear rate of evaluated for significance with t-tests; unless specified otherwise, all other statistics were evaluated with Mann-Whitney U tests. When significance values are t The mean intraindividual difference in log S cone sensitivity quoted for linear regression or correlation statistics, between 20/20 or better eyes and 20/25 eyes approached signifi- cance (2 sided t-test) for 1 °, but not for 3°, stimuli, with the 20/25 the distributions of residual errors from the regression eyes being more sensitive! Perhaps 20/25 eyes fixatedpoorly , thus lines appeared to meet the homogeneity of variance causing the 1° test stimulus to fall on a retinal region having a and/or normality assumptions required for the tests relatively high spatial density of S cones.2930

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S Cone Sensitivity depends on the untested assumption that S cone re- sponse is isolated at 490 nm on the 580 nm back- 6.0 ground. We calculated lens density changes between 440 5.6 and 490 nm for males and females separately using each method. The two methods yielded identical 5.2 values for females, 0.11 log unit per decade. For * r -i! males, the rates of increase derived from the rapid 4.8 - flicker and S cone estimates respectively were 0.00 and -0.02 log unit per decade, values not signifi- 4.4 • cantly different from each other or from zero. These rates for males were significantly different from the 4.0 corresponding rates for females at the 0.05 and 0.02 levels. We used our values along with Pokorny, 3.6 - Smith, and Lutze's17 estimates of relative age-related lens density change as a function of wavelength to 3.2 compute values of absolute age-related lens density 60 64 68 72 76 80 84 88 change at 440 nm. For females, this calculation Age (years) yielded a value of 0.23 log unit per decade. For males, Fig. 1. S cone sensitivity (440 nm, 3°) versus age for all eyes the rate of lens density change would be appreciably having 20/20 or better best corrected acuity. Description of testing less than that for females. parameters are in Materials and Methods. Open circles, males; closed triangles, females. Photopic Dark Adaptation and Absolute Threshold Sensitivity at absolute threshold to a long wave- change of the lens density difference between 440 and length test decreased with age (P < 0.01), about 0.09 490 nm. First, we calculated the rate of change of the log unit per decade (Fig. 2). The rate of decrease was difference in 20 Hz flicker sensitivity between 440 the same for both males and females. Sensitivity at and 490 nm on a 480 nm background. Second, we absolute threshold tended to be less for females than calculated the rate of change of the difference in 1.5 for males, but the difference was not statistically sig- Hz sensitivity between 440 and 490 nm on a 1000 td nificant (2-sided test). 580 nm background for a 3° test stimulus. The two methods make different assumptions. The first The photopic dark adaptation time constant did method depends on the assumptions that 440 and not increase significantly with age; the linear regres- 490 nm are tritanopic metamers,24 and that sensitiv- sion slope was 2.6 sec per decade (Fig. 3). There was ity to rapid flicker does not depend on rod or S cone no indication of a sex difference. Three of the five response to the test stimulus.25"27 The second method eyes whose data lie off the top of Figure 3 had a fellow eye with 20/25 or 20/30 acuity.

Absolute Sensitivity (660nm) Color Matching Younger individuals were more likely than older 6.8 individuals to have a relatively large color-match- 6.6 area-effect (Fig. 4). The linear regression slope de- 6.4 scribing rate of change with age was —0.010 log unit 6.2 per decade.t This value was significantly less than 6.0 5.8 1.? 5.6 t A color-match-area-effect could not be obtained for eleven 5.4 individuals. The most common reason a color-match-area-effect 5.2 could not be obtained was rod intrusion and consequent inability 5.0 to make color matches. Several individuals could not make color 60 64 68 72 76 80 84 88 matches because the center of the field disappeared with fixation. Of the eleven individuals for whom a color-match-area-effect could Age (years) not be obtained, only seven had 20/20 or better acuity in each eye. Fig. 2. Sensitivity at absolute threshold to a 660 nm test versus For one individual with 20/20 or better acuity in each eye, a color- age. Other details as in Figure 1. match-area-effect could be measured in one eye only.

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Dark Adaptation Time Constant Color Match Area Effect

350 • 0.14 • 300 - 0.12 • 250 • 5 0.10 • U 200 • cr 8 ft, m 0.08 • 150 • '«8 ,« A ' 0.06 • 100 0.04 • 50 H 0.02 - 0 60 64 68 72 76 80 84 88 0.00

Age (years) -0.02 Fig. 3. Dark adaptation time constant versus age. Data adjacent 60 64 68 72 76 80 84 88 to or between upward arrows would lie off the top of the graph. Age (years) Other details as in Figure 1. Fig. 4. Color-match-area-effect versus age. Other details as in Figures 1 and 3. zero (P < 0.05). The linear trend is not obvious in the graph because the correlation coefficient is only gression analysis may not have been appropriate, for -0.17. The negative linear regression slope is consis- small-field matching ranges of less than about 0.05 tent with an underlying age-related decrease of the 1819 log unit appeared to become progressively rarer with quantum catching ability of the foveal cones. increasing age (Fig. 5). Large-field matching ranges Interestingly, the color-match-area-effect and log tended to increase slightly with age; the linear regres- sensitivity at absolute threshold appeared to be un- sion slope was 0.006 log unit per decade. Because correlated (r = —0.01). However, the correlation coef- about 15-20% of the female population is heterozy- ficient increased to 0.18 when 28 individuals having gous for congenital color deficiency,33 females might possibly inflated color-match-area-effects due to large 31 be expected to have poorer color discrimination than small-field matching ranges (>0.15 log unit) or else males. This expectation was borne out for small fields outlying absolute thresholds (log sensitivity < 5.40) in (P < 0.05), but not for large. either eye were excluded from the calculation. The correlation of 0.18 is significantly greater than zero, Discussion although only marginally so (P = 0.05). The fact that the correlation is small suggests that (1) individual The results of this study pertain to eyes with good differences in effective cone photopigment density acuity. However, with increasing age, eyes with good play a relatively minor role in determining individual differences in sensitivity; (2) effective photopigment density is much influenced by pupil size32 for the test Table 1. Left vs. right eye correlation coefficient conditions under which we measured the color- Intereye match-area-effect; or (3) other factors may serve to correlation increase color-match-area-effect variance. The last Visual function coefficient N possibility is a likely one, for the left versus right eye 3° log S cone sensitivity 0.89 101 intereye color-match-area-effect correlation coeffi- 1 ° log S cone sensitivity 0.83 100 cients across individuals with two 20/20 or better eyes Log absolute sensitivity 0.79 101 Time constant 0.48 101 were relatively small compared to the corresponding Color-match-area-effect 0.47 93 correlation coefficients for several other functions (Small-field matching range 0.51 72 (Table 1). Small-field matching range 0.59 93 The linear regression slope describing small-field (£0.15) 0.51 72 matching ranges was only negligibly different from Left versus right eye intereye correlation coefficients across individuals zero, -0.001 log unit per decade. However, despite with 20/20 or better acuity in each eye. N represents the number of such individuals for whom the correlation coefficients are computed. The entries the negligible linear regression slope, an age-depen- in parentheses define criteria which are met by each of an individuals two dent effect may have existed. In essence, linear re- eyes.

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Anomaloscope Small Field Matching Range pendent differences in S cone spatial density underlie sex-dependent differences in S cone sensitivity.

0.45 n Men and women take different medications, which could lead to differences in S cone sensitivity. How- 0.40 ever, the difference in S cone sensitivity between the 0.35 women who took estrogen and the women who did not appeared to be too small to explain the difference 0.30 in S cone sensitivity between men and women. Possi-

0.25 bly, the men who met the eligibility criteria of this study represented a progressively more select group 0.20 with increasing age than the women who met the same eligibility criteria. 0.15 The sensitivity loss at long test wavelengths asso- 0.10 ciated with increasing age may be due to increased intraocular light scatter or to physiological compro- 0.05 mise at or central to the photoreceptor level.35"37 : '. 0.00 These same factors may, of course, cause S cone sen- 60 64 68 72 76 80 84 88 sitivity loss. Age (years) The age-related in variance of the rate of sensitivity recovery during dark adaptation confirms Birren and Fig. 5. Small field (1.1°) Rayleigh matching range versus age. 8 Other details as in Figure 1. Shock's findings of more than 30 years ago. Birren and Shock, however, measured recovery at 7.5° from fixation. acuity become increasingly atypical.1 Thus, our find- The decrease of the color-match-area-effect with ings and estimates cannot be generalized to eyes age may be related to the age-related photopigment which are more representative for their age, especially density differences found by van Norren and van for people in their seventies or older. Similarly, our Meel,38 and by Kilbride et al39 using densitometric results need not apply to longitudinal comparisons techniques. If so, the significant but low correlation and cannot be generalized to eyes which fail to meet between color-match-area-effect and age which we the other inclusion criteria required for entry into this find may support Kilbride et al's supposition that study. The companion paper20 demonstrates that their failure to find a significant correlation between good acuity alone does not suffice to define nor- anomaloscope midmatchpoint and age was due to mality. the limited number of subjects whom they tested. Probably the most unexpected finding of this study However, the densitometric measurements may re- was the difference in the rate of cross-sectional S cone flect photoreceptor dropout only, rather than a de- sensitivity loss between men and women having crease of effective photopigment density.39 In that 20/20 or better acuity. Part of the difference is due to case, our anomaloscopic measurements may reflect different rates of lens density change; the rate for systematic age-related change in pupil size32 rather women is greater than the rate for men, which may be than photoreceptoral change. zero. The sex-dependent lens density difference may With one exception, the linear regression slopes be related to the difference in proportions of men and derived from within the older population were con- women diagnosed as having .34 sistent with the differences which we previously Part of the sex-dependent difference in the rate of S found to exist between people in their twenties and cone sensitivity loss may be retinal, for deMonasterio people in their sixties or seventies.31 The one excep- et al29 have shown that a sex-dependent difference in tion was the anomaloscope matching range. We the retinal distribution of S cones exists for old, but found that people in their twenties tend to have better probably not for young, macaque monkeys. deMon- small-field red/green color discrimination than peo- asterio et al found that the spatial density of S cones ple over age sixty, whereas we find no linear age-re- in the fovea was least for old female monkeys. Con- lated increase in small-field matching range within versely, the spatial density of S cones outside the the older age group itself. The linear regression statis- fovea was less for old male than for old female mon- tic, however, probably masks both a real trend to- keys. This converse finding suggests an obvious psy- wards poorer color discrimination and a selection chophysical experiment to perform using human bias associated with strict eligibility criteria for the subjects in order to test the hypothesis that sex-de- older individuals whom we tested. We emphasize

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again that our findings from within the older age 16. van Norren D and Vos JJ: Spectral transmission of the human group are cross-sectional rather than longitudinal, ocular media. Vision Res 14:1237, 1974. 17. Pokorny J, Smith VC, and Lutze M: Aging of the human lens. and are applicable only to eyes which have retained Appl. Opt 26:1437, 1987. good acuity. 18. Pokorny J and Smith VC: Effect of field size on red-green color mixture equations. J Opt Soc Am 66:705, 1976. Key words: aging, dark adaptation, blue-sensitive cones, 19. Burns SA and Eisner AE: Color matching at high illuminances: lens density, photopigment density The color-match-area effect and photopigment bleaching. J Opt Soc Am A 2:698, 1985. 20. Eisner A, Fleming SA, Klein ML, and Mauldin WM: Sensitivi- Acknowledgments ties in older eyes with good acuity: Eyes whose fellow eye has exudative AMD. Invest Ophthalmol Vis Sci 28:1832, 1987. The authors wish to thank Julie Arends, COMT, Jim 21. 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