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Forecasting cataract surgeries and intraocular lens implantation to 1990 using a model of population dynamics
Forecasting cataract surgeries and intraocular lens implantation to 1990 using a model of population dynamics Lewis W. Coopersmith, Ph. D. MaryAnne Carr, R. N. North Branch , New Jersey
ABSTRACT Extending the recently observed dramatic growth rates of cataract surgel'y and intraocular lens implantation into the future is not necessarily valid because of changes in population size, new incidence of cataracts, and rates of treatment for patients diagnosed in cUlTent as well as in previous years, Accelel'ated treatment of the pool of previously diagnosed patients caused a sharp growth in cataract surgery since 1980, but at the same time reduced patients and thus the potential for continued high growth rates, This paper de 'cribes a model that produces forecasts through explicit consideration of the many aspects of population dynamics. It provides an opportunity to examine how forecasts might vary under different assumptions about advances in medical technology. Key Words: cataract pre alenc , cataract surg ry, forecasting, intraocular lens implantation
Since 1982, Health Products Research, Inc. , has been monitoring the number of cataract surgeries and intraocular lens (IOL) implan tations for the IOL industry through the IOL Market Surljey. From 1983 to 1984, cataract surgery grew at an accelerating rate, as shown in Table 1, but now shows signs ofleveling off. Intraocular lens implantation also grew rapidly during this time because of changes in technology and more surgeons implanting lenses (Tables 2 and 3). The convers ion rate, defined as the percentage of cataract surgeries in which IOLs are implanted, grew from 68% in 1982 to 96% in 1986 as shown in Table 4. In 1986, between 1.2 and 1.3 million cataract surgeries and IOL implantations were perform ed. Extending recently observed trends, while intuitively appealing, may not be realistic, especially in light of the apparent leveling of rapid growth in 1985.
The 1986 figures were released just prior to p ublication and represent a deviation from this leveling. However, most of the 1986 increase was observed in the second half of 1986, suggesting that this increase might be related to anticipated changes in reimburs ement policies in 1987. We have included the 1986 figures in this paper for completeness. Analysis of what-they might imply for the future is a subject of current research to be released later in 1987 . It is clear from historical data that a wide range of forecasts of cataract surgeries can be obtained , depending on what one assum es regarding future new incidence and advances in technology that could affect the interval behveen diagnosis and surgery. NEED FOR A FORECASTING MODEL Because of the uncertainty of the future res ulting
From Rider College , Lawrenceville, New Jersey (Coopersmith ), and Health Products Research , Inc., North Branch, Nell; Jersey. Presented in part at the Symposium on Cataract , IOL and Refra ctive Surgery, Los Angeles , April 1986. Reprint requests to Lewis W Coopersmith, Ph.D., Vice President and Director, Health Products Research , Inc .. 3520 U.S. Ruute 22, P.O Box 5178, North Branch , New J ersey 08876-5178. 302
J CATARACT
REFRACT SURG- VOL 13, MAY 1987
Table 1. U.S. cataract surgeries, 1982-1986.
Year
(000)
IntracaEsular % Change Per Year
1982 1983
402 305
-24
1984 1985 1986
245 133 95
-20 -46 -29
Extracapsular %
(000)
Total
55 39
325 488
24 12
762 974 1,166
8
Total
% Change
%
Per Year
Total
(000)
+28 +20
%
Per Year
Total
+9 +27 +10 +14
100 100 100 100 100
727
45 61 76 88 92
+50 +,56
% Change
793 1,007 1,107 1,261
From IOL Market Survey, Health Products Research, Inc. Table 2. U.S. intraocular lens implants, 1982-1986. Anterior Chamber IOL
Posterior Chamber IOL
Iris-Fixated IOL
% Change
%
% Change
%
%
Per Year
Total
Per Year
Total
(000)
% Change
Per Year
Total
(000)
48
23 ,5
-78 -80
5 1 <1
513 6,52
Year
(000)
1982 1983 1984 198,5
242 223 239 186
1986
140
17
248 424 703 888
+71 +66 +26
11
1,110
+25
47 34 2,5
-8 +7 -22 -25
(000)
65 75 83 89
1
Total % Change
%
Per Year
Total
100 100 100 100
+27 +44 +14 +16
942 1,073 1,250
100
From IOL Market Sun;ey, Health Products Research, Inc. Table 3. U.S. intraocular lens implants, 1982-1986. Primary % Change Per Year
Year
(000)
1982 1983
493 625
+27
1984 1985 1986
912 1,045 1,210
+46 +15 +16
Secondary %
Total
% Change
%
Per Year
Total
(000)
4 4 3 3 3
513 652 942 1,073 1,250
Total
(000)
96 96 97 97 97
20 27
+35
30 28 40
+11 -7 +43
% Change
%
Per Year
Total
100 +27 +44 +14 +16
100 100 100 100
From IOL Market Survey, Health Products Research, Inc.
from mixed signals from past observed growth, a structured modeling approach is needed to obtain desired accuracy in forecasts and evaluate how forecasts might change under varying assumptions related to diagnosis and treatment. Accurate forecasts are needed by (1) physicians-to help plan the direction of their practices; (2) industryto properly meet the need for devices, pharmaceuticals, and related services; and (3) government and other third parties-to assure the availability of financial support for insured patients. A model is needed to evaluate the cause of past observed rapid growth and to determine whether or not similar trends can be expected in the future. The model should contain enough detail to answer quesJ CATARACT REFRACT
Table 4. Use of IOLs during cataract surgeries (OOOs).
Year
IOLs in Primary Surgery
1982 1983 1984
493 625 912
1985 1986
1,045 1,210
Cataract Surgeries
Percent Conversion
727 793 1,007 1,107 1,261
68 79 91 94 96
From IOL Market Survey, Health Products Research, Inc.
tions such as the following: Was accelerated growth due to more new patients or earlier treatment of the pool of previously diagnosed eyes? With the incidence of biSURG-VOL 13, MAY 1987
303
lateral cataracts, what if the time to surgery for the second eye is decreased? What if more patients can be encouraged to have their eyes examined, therefore increasing the recorded prevalence of cataracts?
Table 6. Percent prevalence of senile lens changes by age group.
DATA Building a usable and reliable model requires consideration of both available and obtainable data, as well as appropriate methodology (which is considered in the next section). The most reliable population data is from the u.s. Bureau of the Census. l Table 5 shows population growth for the five age groups that we feel will allow the proper level of analytical detail. From now until 1990, this shows less than 2% growth in the 45to 64-year-old group, with decelerating growth in the upper age groups. Death rates are also provided. Prevalence of cataracts is reported for a number of sources in an NIH publication. 2 Combining reported figures provides the data in Table 6. Measurable prevalence begins at 5% for ages 45 to 64, increases to 23% for ages 65 to 74, and reaches a maximum of 50% for persons 75 and older. One reported source had prevalence for the 65 to 74 age group as high as 28.5%. Government reports on vital health statistics 3 provide information on the distribution of cataract surgeries over the age groups under study. This, plus Health Products Research, Inc.'s, IOL Market Survey data on cataract surgeries and IOL implantation, provides a basis for determining current numbers of aphakic eyes. Key information that was missing when this research project was begun were rates of treatment for diagnosed patients. To obtain this information, questions were sent to 300 ophthalmologists to determine the following: (1) For all patients who are newly diagnosed as having cataracts, what percentage come to surgery within various time frames? (2) At the time only one eye was treated surgically, what percentage came to surgery for the second eye within various time frames? The survey was administered by having 150 randomly
Age (Years)
Percent Prevalence
Under 25
0.1
25 - 44
0.4
45 - 64
5.0
65 - 74
23.0
75 and Over
50.0
From U.S. Department of Health and Human Services 2
selected ophthalmologists answer the first question, and a separate random sample of 150 answer the second. Results of the two surveys are displayed in Tables 7 and 8, respectively. As one would expect, time to surgery decreases with increasing age. It should be noted that "Never" could reflect the responding physician's never treating the patients, not necessarily the patient's never receiving treatment. Also of interest in Table 8 is the percentage of second eyes that are treated within six months of surgery on the first eye. Results in Tables 7 and 8 allow derivation of useful data for the forecasting model, which are displayed in Table 7. Results of time frame survey. Question: For all patients who are newly diagnosed as having cataract(s), what percentage come to surgery within the time frame indicated? Age (years)
Up to 1 Mo.
1-6 7-12 Mos. Mos.
1-2 Yrs.
>2 Yrs.
Never
Sample Size
Under 25
<1
9
5
3
21
61
54
25 - 44
<1
9
5
10
36
39
53
45 - 64
<1
13
14
25
24
23
59
65 - 74
<1
25
28
23
14
9
51
75 and Over
<1
28
27
16
10
18
59
From IOL Market Sun;ey, Health Products Research, Inc.
Table 5. U.S. population by age group showing year-to-year percentage change. Under 25 % Change
45 - 64 (000)
75,806
+2.7
44,764
-0.3
77,511
+2.2
-0.3
78,795
+ 1.7
90,200
-0.3
80,182
90,130
-0.1
81,376
(000)
1985
91,578
1986
91,022
-0.6
1987
90,707
1988
90,428
1989 1990 Death Rate (%)
25 - 44
% Change
Year
(000)
(000)
+0.3
44,942 45,552
+ 1.8
46,001
+ 1.5
46,453
73,792
0.11
65 - 74
% Change
(000)
17,128
+ 1.6
12,136
+3.2
+0.4
17,408
+ 1.6
12,517
+3.1
+1.4
17,627
+ 1.3
12,900
+3.1
+ 1.0
17,835
+ 1.2
13,280
+2.9
+2.0
18,035
+ 1.1
13,663
+2.9
44,652
0.16
16,855
0.9
From U.S. Bureau of the Census 1 304
J CATARACT REFRACT
75 and Older
% Change
SURG-VOL 13, MAY 1987
2.5
% Change
11,754
8.1
Table 8. Results of time frame survey.
PATIENTS WHO NEVER HAD
Question: Consider all cataract patients at the time only one eye was treated surgically. What percentage came to surgery for the second eye within the time frame indicated? Age (years)
Up to 1 Mo.
1-6 7-12 Mos. Mos.
1-2 Yrs.
CATARACTS
>2 Sample Yrs. Never Size
Under 25
9
11
5
2
31
41
65
25 - 44
4
9
11
16
40
20
68
45 - 64
8
14
18
20
29
11
73
65 - 74
10
24
20
22
17
7
73
75 and Over
16
24
16
18
13
13
73
NEW INCIDENCE NEWLY DIAGNOSED CATARACT PATIENTS CATARACT EYES
From IOL Market Survey, Health Products Research, Inc .
(
NONCATARACT EYES
Table 9. Model data derived from physician time frame survey. % Newly Diagnosed
Eyes Treated in First Year
% Patients with Two Eyes Diagnosed in First Year
Under 25
14
20
Age (Years) 25 - 44
14
13
45 - 64
28
20
65 - 74
53
33
75 and Over
55
40
Table 9. The percentage of newly diagnosed eyes treated in the first year is applied to new incidence to determine one source of cataract surgery. The percentage of patients with two eyes diagnosed is a measure of bilateral treatment within a year of diagnosis.
MODEL STRUCTURE AND METHODOLOGY The forecasting model considers the population that contributes to the need for treatment and the various rates of treatment resulting in surgery. For a given year, Figure 1 shows the population divided into groups in which cataracts are and are not prevalent. Some prevalent patients have been diagnosed in the current year (new incidence) and some have been diagnosed and treated in previous years . This latter group has eyes that have cataracts but are not yet treated; are aphakic and have IOLs implanted; are aphakic and have no IOLs implanted. Forecasts are obtained by starting with baseline estimates of the number of people and eyes in each category and computing the changes that occur from year to year through the use of a population dynamics model. Unlike other approaches that use a few mathematical formulas to project into the future, this model considers explicitly the events that occur from year to year and is thus classified as a discrete-event forecasting model. The benefit of using such a model is that we have complete flexibility in evaluating specific hypothetical activity for any given future period. J CATARACT REFRACT
FORMERLY DIAGNOSED CATARACT PATIENTS
EYES NO lOL'S
Fig. 1.
NONCATARACT EYES APHAKIC IOL EYES
(Coopersmith) Population dynamics of cataract diagnosis and treatment, including IOL implantations .
The dynamics of the model from one year to the next are depicted in Figure 2 . Based on prevalence of cataract surgery and population changes because of aging or death, new incidence of cataract patients can be computed. The number of eyes diagnosed per patient and the percentage of these eyes treated surgically in the first year contributes to cataract surgeries, with cataract eyes untreated adding to the pool for the following year. Contributions to cataract surgery are also made from patients diagnosed in previous years who have surgery for previously untreated cataracts and for newly diagnosed cataracts. Intraocular lens implantation rates are produced from new cataract surgery through conversion, aphakic patients who had cataract surgery in previous years, and revisions of previously implanted IOLs. Cataracts not converted from this year's surgery or from previous years' surgery contribute to the next year as aphakic eyes.
MODEL RESULTS Best Fit Forecast Available data and best estimates were used initially SURG- VOL 13, MAY 1987
305
THIS YEAR
NEXT YEAR PATIENTS WHO NEVER HAD
PATIENTS WHO NEVER HAD
CATARACTS
CATARACTS
1
NEW INCIDENCE NEWLY DIAGNOSED CATARACT PATIENTS
NEWLY DIAGNOSED CATARACT PATIENTS CATARACT) EYES (NONCATARACT) \ EYES
PREVALENCE
FRACTION TREATED
OF CATARACTS
FORMERLY DIAGNOSED CATARACT PATIENTS
C:CA~~~~CT~
NONCATARACT
Fig. 2.
(Coopersmith) Population dynamics of cataract diagnosis and treatment including IOL implantations from one year to the next.
for 1983 as a baseline to forecast 1984 and 1985. Using 1984 and 1985 actual surgeries and IOL implantations, adjustments were made to less reliable model data to "fine tune" forecasts to within 2% of actual. This set of calibrated data was used to produce the results in Table 10. Cataract surgeries are forecast to increase from 1,155,000 in 1986 to 1,266,000 in 1990; IOL implants will increase from 1,125,000 to 1,251,000
over this period. Note that percentage change shows decelerating growth. Actual 1986 surgeries became available just prior to publication. While actual 1986 figures are substantially higher than baseline, most of the increase came in the latter half of 1986, during which time there was concern over anticipated changes in reimbursement policies in 1987. If the increase is due to a short-term
Table 10. Forecast of cataract surgeries and IOL implantation to 1990. Best fit model data derived by fitting 1984 and 1985 from 1983 data.
Year
Total Cataract Surgeries (000)
Percentage ChangelYear
Primary IOL Implants
Percentage ChangelYear
TotalIOL Implants
Percen tage ChangelYear
1986
1,155
+4.4
1,097
+5.0
1,135
+5.8
*(1986
1,261
+14.0
1,210
+ 15.8
1,2.50
+ 10.1)
1987
1,193
+3.3**
1,146
+ 4.5**
1,183
+4.2**
1988
1,223
+2.5
1,174
+2.4
1,210
+2.3
1989
1,244
+ 1.7
1,194
+ 1.7
1,230
+ 1.7
1990
1,266
+ 1.8
1,215
+ 1.8
1,251
+ 1.7
Baseline 1985 (000): Cataract surgeries 1,106; primary IOL implants 1,045; total IOL implants 1,073. * Actual1986 surgeries became available just prior to publication. Most ofthe unanticipated increase in 1986 was observed in the second half of the year, suggesting that differences between actual and forecast may be related to anticipated changes in reimbursement policies in 1987. Explanation of these differences and their impact on forecasts is currently being studied as a subject for publication later in 1987. **Percentage changes are based on forecasted 1986 figures, not actual. 306
J CATARACT
REFRACT SURG-VOL 13, MAY 1987
change in time to surgery, long-term baseline forecasts may still be realized. Otherwise, one or a combination of the scenarios described below might be more representative. We are currently studying the impact of events occurring over 1986, with results to be published later in 1987. The best-fit forecast data provide a base from which we can analyze "what if' alternatives through changing rates of activity. These analyses are discussed in order of increasing optimism, i.e., highest long-term forecasts. 1. What if average time to surgery is decreased? Increasing the fraction treated in the first year of diagnosis by five points produces the results in Table 11. The major impact is immediate, with
surgeries increasing by 9% in 1986 but leveling off to under 2% growth for subsequent years. 2. What if bilateral treatment within the first year of diagnosis increases? A 5% increase in the number of eyes diagnosed per new cataract patient produces the results in Table 12. The immediate rate of increase in cataract surgeries is 6.4%. Growth then decelerates gradually, resulting in a 1990 forecast of 1,309,000. 3. What if more patients can be persuaded to have their eyes examined? Two cases are evaluated: The first (Case 3.A) assumes that cataracts will be detected earlier but there will be no net increase in prevalence for the oldest age group. An increase in prevalence for ages 45 to 74 reaching 10% above
Table II. Forecast of cataract surgeries and IOL implantations to 1990. Assumption: Fraction treated in first year of diagnosis increased by 5 points; represents accelerated treatment of new patients.
Year
Total Cataract Surgeries (000)
Percentage Change/Year
Primary IOL Implants (000)
Percentage Change/Year
TotalIOL Implants (000)
Percentage Change/Year
1986
1,206
+9.0
1,146
+9.7
1,184
+10.3
1987
1,227
+ 1.7
1,178
+2.8
1,216
+2.7
1988
1,247
+ 1.6
1,197
+ 1.6
1,234
+ 1.5
1989
1,262
+ 1.2
1,212
+ 1.3
1,248
+ 1.1
1990
1,281
+ 1.5
1,230
+ 1.5
1,265
+ 1.4
Baseline 1985 (000): Cataract surgeries 1,106; primary IOL implants 1,045; total IOL implants 1,073. Table 12. Forecast of cataract surgeries and IOL implantations to 1990. Assumption: 5% increase over baseline rate of number of eyes diagnosed per new cataract patient; represents an increase in bilateral treatment within one year of diagnosis.
Year
Total Cataract Surgeries (000)
Percentage Change/Year
Primarv IOL Implants (000)
Percentage Change/Year
TotalIOL Implants (000)
Percentage Change/Year
1986
1,177
+6.4
1,119
+7.1
1,157
+7.8
1987
1,227
+4.2
1,177
+5.2
1,215
+5.0
1988
1,261
+2.8
1,211
+2.9
1,248
+2.7
1989
1,286
+2.0
1,234
+ 1.9
1,271
+ 1.8
1990
1,309
+ 1.8
1,257
+ 1.9
1,293
+ 1.7
Baseline 1985 (000): Cataract surgeries 1,106; primary IOL implants 1,045; total IOL implants 1,073. Table 13. Forecast of cataract surgeries and IOL implantations to 1990. Assumption: 10% increase in prevalence for ages 45 -74, but not for 75 and older-trended to 1990; represents trend in earlier detection, but no increase in eventual prevalence.
Year
Total Cataract Surgeries (000)
Percentage Change/Year
Primarv IOL Implants (000)
Percentage Change/Year
Total IOL Implants (000)
Percentage Change/Year
1986
1,235
+11.7
1,174
+12.3
1,212
+ 12.7
1987
1,313
+6.3
1,260
+7.3
1,298
+7.1
1988
1,366
+4.0
1,311
+4.0
1,348
+3.9
1989
1,403
+2.7
1,347
+2.7
1,383
+2.6
1990
1,436
+2.4
1,379
+2.4
1,414
+2.2
Baseline 1985 (000): Cataract surgeries 1,106; primary IOL implants 1,045; total IOL implants 1,073.
J CATARACT REFRACT
SURG-VOL 13, MAY 1987
307
Table 14. Forecast of cataract surgeries and IOL implantations to 1990. Assumption: 10% increase in prevalence for ages 45 - 65 and 75 and older. Prevalence for 65 - 74 raised to NIH figure of 28.5%; represents earlier detection and net gain in eventual prevalence. Percentage ChangelYear
Primary IOL Implants (000)
Percentage ChangelYear
TotalIOL Implants (000)
Percentage ChangelYear
1,413
+27.8
1,342
+28.4
1,381
+28.7
1,555
+10.0
1,493
+11.3
1,530
+10.8
1988
1,658
+6.6
1,592
+6.6
1,629
+6.5
1989
1,737
+4.8
1,668
+4.8
1,705
+4.7
1990
1,809
+4.1
1,737
+4.1
1,774
+4.0
Year
Total Cataract Surgeries (000)
1986 1987
Baseline 1985 (000): Cataract surgeries 1,106; primary IOL implants 1,045; total IOL implants 1,073.
baseline data in 1990 produces results displayed in Table 13. Overall higher growth rates show cataract surgeries reaching 1,436,000 by 1990 with a corresponding increase in IOL implants to 1,414,000. A second (Case 3.B) allows for a slightly higher increase in prevalence and further allows for a net increase in prevalence for the oldest age group. An increase in prevalence for the age groups 45 to 64 and 75 and over, reaching 10% above baseline in 1990, and an increase in the 65 to 74 year age group, reaching the NIH estimate of28.5% (from 23.0%), produce the most optimistic results as shown in Table 14. High annual percentage growth decelerating from + 27.8% to + 4.1 % increases cataract surgeries to 1,809,000 in 1990, with IOL implantation numbering 1,774,000.
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e
Figure 3, which shows actual cataract surgeries for 1982 to 1985, indicates that the most optimistic case might be unrealistic. What is apparent is that surgeries will continue to increase but at decelerating rates. We feel that the model has demonstrated its usefulness in evaluating possibilities for the future. We hope to have the opportunity to analyze the impact of specific potential changes in technology and delivery of patient care as proposed by the medical community and industry. REFERENCES 1. U.S. Bureau of the Census, Current Population Reports, Series
P-25, No. 952, Projections of the Population of the United States, by Age, Sex and Race: 1983 to 2080, U.S. Government Printing Office, Washington, DC, 1984
308
J CATARACT
5
o.
0 . 7.L.----.::;: _ _ +-_ +I - -t--~-i_--~- _4_ .-- +__ B4 B5 B6 B7 B8 B9 90 B2
Year
Fig. 3.
(Coopersmith) Projected trends in cataract surgery-1982 to 1990.
2. U.S. Department of Health and Human Services, NIH Publication No. 84-2473, Report of the Cataract Panel , Vision Research. A National Plan. 1983-1987, Volume Two/Part Three, U.S. Government Printing Office, Washington, DC, 1983 3. Vital and Health Statistics, U.S. Department of Health and Human Services. Public Health Service. National Center for Health Statistics, Series 13, Nos. 34, 61, 70; Advanced Data: September 28, 1984 - No. 101, September 27, 1985 - No. 112
REFRACT SURG-VOL 13, MAY 1987
ABSTRACT Extending the recently observed dramatic growth rates of cataract surgel'y and intraocular lens implantation into the future is not necessarily valid because of changes in population size, new incidence of cataracts, and rates of treatment for patients diagnosed in cUlTent as well as in previous years, Accelel'ated treatment of the pool of previously diagnosed patients caused a sharp growth in cataract surgery since 1980, but at the same time reduced patients and thus the potential for continued high growth rates, This paper de 'cribes a model that produces forecasts through explicit consideration of the many aspects of population dynamics. It provides an opportunity to examine how forecasts might vary under different assumptions about advances in medical technology. Key Words: cataract pre alenc , cataract surg ry, forecasting, intraocular lens implantation
Since 1982, Health Products Research, Inc. , has been monitoring the number of cataract surgeries and intraocular lens (IOL) implan tations for the IOL industry through the IOL Market Surljey. From 1983 to 1984, cataract surgery grew at an accelerating rate, as shown in Table 1, but now shows signs ofleveling off. Intraocular lens implantation also grew rapidly during this time because of changes in technology and more surgeons implanting lenses (Tables 2 and 3). The convers ion rate, defined as the percentage of cataract surgeries in which IOLs are implanted, grew from 68% in 1982 to 96% in 1986 as shown in Table 4. In 1986, between 1.2 and 1.3 million cataract surgeries and IOL implantations were perform ed. Extending recently observed trends, while intuitively appealing, may not be realistic, especially in light of the apparent leveling of rapid growth in 1985.
The 1986 figures were released just prior to p ublication and represent a deviation from this leveling. However, most of the 1986 increase was observed in the second half of 1986, suggesting that this increase might be related to anticipated changes in reimburs ement policies in 1987. We have included the 1986 figures in this paper for completeness. Analysis of what-they might imply for the future is a subject of current research to be released later in 1987 . It is clear from historical data that a wide range of forecasts of cataract surgeries can be obtained , depending on what one assum es regarding future new incidence and advances in technology that could affect the interval behveen diagnosis and surgery. NEED FOR A FORECASTING MODEL Because of the uncertainty of the future res ulting
From Rider College , Lawrenceville, New Jersey (Coopersmith ), and Health Products Research , Inc., North Branch, Nell; Jersey. Presented in part at the Symposium on Cataract , IOL and Refra ctive Surgery, Los Angeles , April 1986. Reprint requests to Lewis W Coopersmith, Ph.D., Vice President and Director, Health Products Research , Inc .. 3520 U.S. Ruute 22, P.O Box 5178, North Branch , New J ersey 08876-5178. 302
J CATARACT
REFRACT SURG- VOL 13, MAY 1987
Table 1. U.S. cataract surgeries, 1982-1986.
Year
(000)
IntracaEsular % Change Per Year
1982 1983
402 305
-24
1984 1985 1986
245 133 95
-20 -46 -29
Extracapsular %
(000)
Total
55 39
325 488
24 12
762 974 1,166
8
Total
% Change
%
Per Year
Total
(000)
+28 +20
%
Per Year
Total
+9 +27 +10 +14
100 100 100 100 100
727
45 61 76 88 92
+50 +,56
% Change
793 1,007 1,107 1,261
From IOL Market Survey, Health Products Research, Inc. Table 2. U.S. intraocular lens implants, 1982-1986. Anterior Chamber IOL
Posterior Chamber IOL
Iris-Fixated IOL
% Change
%
% Change
%
%
Per Year
Total
Per Year
Total
(000)
% Change
Per Year
Total
(000)
48
23 ,5
-78 -80
5 1 <1
513 6,52
Year
(000)
1982 1983 1984 198,5
242 223 239 186
1986
140
17
248 424 703 888
+71 +66 +26
11
1,110
+25
47 34 2,5
-8 +7 -22 -25
(000)
65 75 83 89
1
Total % Change
%
Per Year
Total
100 100 100 100
+27 +44 +14 +16
942 1,073 1,250
100
From IOL Market Sun;ey, Health Products Research, Inc. Table 3. U.S. intraocular lens implants, 1982-1986. Primary % Change Per Year
Year
(000)
1982 1983
493 625
+27
1984 1985 1986
912 1,045 1,210
+46 +15 +16
Secondary %
Total
% Change
%
Per Year
Total
(000)
4 4 3 3 3
513 652 942 1,073 1,250
Total
(000)
96 96 97 97 97
20 27
+35
30 28 40
+11 -7 +43
% Change
%
Per Year
Total
100 +27 +44 +14 +16
100 100 100 100
From IOL Market Survey, Health Products Research, Inc.
from mixed signals from past observed growth, a structured modeling approach is needed to obtain desired accuracy in forecasts and evaluate how forecasts might change under varying assumptions related to diagnosis and treatment. Accurate forecasts are needed by (1) physicians-to help plan the direction of their practices; (2) industryto properly meet the need for devices, pharmaceuticals, and related services; and (3) government and other third parties-to assure the availability of financial support for insured patients. A model is needed to evaluate the cause of past observed rapid growth and to determine whether or not similar trends can be expected in the future. The model should contain enough detail to answer quesJ CATARACT REFRACT
Table 4. Use of IOLs during cataract surgeries (OOOs).
Year
IOLs in Primary Surgery
1982 1983 1984
493 625 912
1985 1986
1,045 1,210
Cataract Surgeries
Percent Conversion
727 793 1,007 1,107 1,261
68 79 91 94 96
From IOL Market Survey, Health Products Research, Inc.
tions such as the following: Was accelerated growth due to more new patients or earlier treatment of the pool of previously diagnosed eyes? With the incidence of biSURG-VOL 13, MAY 1987
303
lateral cataracts, what if the time to surgery for the second eye is decreased? What if more patients can be encouraged to have their eyes examined, therefore increasing the recorded prevalence of cataracts?
Table 6. Percent prevalence of senile lens changes by age group.
DATA Building a usable and reliable model requires consideration of both available and obtainable data, as well as appropriate methodology (which is considered in the next section). The most reliable population data is from the u.s. Bureau of the Census. l Table 5 shows population growth for the five age groups that we feel will allow the proper level of analytical detail. From now until 1990, this shows less than 2% growth in the 45to 64-year-old group, with decelerating growth in the upper age groups. Death rates are also provided. Prevalence of cataracts is reported for a number of sources in an NIH publication. 2 Combining reported figures provides the data in Table 6. Measurable prevalence begins at 5% for ages 45 to 64, increases to 23% for ages 65 to 74, and reaches a maximum of 50% for persons 75 and older. One reported source had prevalence for the 65 to 74 age group as high as 28.5%. Government reports on vital health statistics 3 provide information on the distribution of cataract surgeries over the age groups under study. This, plus Health Products Research, Inc.'s, IOL Market Survey data on cataract surgeries and IOL implantation, provides a basis for determining current numbers of aphakic eyes. Key information that was missing when this research project was begun were rates of treatment for diagnosed patients. To obtain this information, questions were sent to 300 ophthalmologists to determine the following: (1) For all patients who are newly diagnosed as having cataracts, what percentage come to surgery within various time frames? (2) At the time only one eye was treated surgically, what percentage came to surgery for the second eye within various time frames? The survey was administered by having 150 randomly
Age (Years)
Percent Prevalence
Under 25
0.1
25 - 44
0.4
45 - 64
5.0
65 - 74
23.0
75 and Over
50.0
From U.S. Department of Health and Human Services 2
selected ophthalmologists answer the first question, and a separate random sample of 150 answer the second. Results of the two surveys are displayed in Tables 7 and 8, respectively. As one would expect, time to surgery decreases with increasing age. It should be noted that "Never" could reflect the responding physician's never treating the patients, not necessarily the patient's never receiving treatment. Also of interest in Table 8 is the percentage of second eyes that are treated within six months of surgery on the first eye. Results in Tables 7 and 8 allow derivation of useful data for the forecasting model, which are displayed in Table 7. Results of time frame survey. Question: For all patients who are newly diagnosed as having cataract(s), what percentage come to surgery within the time frame indicated? Age (years)
Up to 1 Mo.
1-6 7-12 Mos. Mos.
1-2 Yrs.
>2 Yrs.
Never
Sample Size
Under 25
<1
9
5
3
21
61
54
25 - 44
<1
9
5
10
36
39
53
45 - 64
<1
13
14
25
24
23
59
65 - 74
<1
25
28
23
14
9
51
75 and Over
<1
28
27
16
10
18
59
From IOL Market Sun;ey, Health Products Research, Inc.
Table 5. U.S. population by age group showing year-to-year percentage change. Under 25 % Change
45 - 64 (000)
75,806
+2.7
44,764
-0.3
77,511
+2.2
-0.3
78,795
+ 1.7
90,200
-0.3
80,182
90,130
-0.1
81,376
(000)
1985
91,578
1986
91,022
-0.6
1987
90,707
1988
90,428
1989 1990 Death Rate (%)
25 - 44
% Change
Year
(000)
(000)
+0.3
44,942 45,552
+ 1.8
46,001
+ 1.5
46,453
73,792
0.11
65 - 74
% Change
(000)
17,128
+ 1.6
12,136
+3.2
+0.4
17,408
+ 1.6
12,517
+3.1
+1.4
17,627
+ 1.3
12,900
+3.1
+ 1.0
17,835
+ 1.2
13,280
+2.9
+2.0
18,035
+ 1.1
13,663
+2.9
44,652
0.16
16,855
0.9
From U.S. Bureau of the Census 1 304
J CATARACT REFRACT
75 and Older
% Change
SURG-VOL 13, MAY 1987
2.5
% Change
11,754
8.1
Table 8. Results of time frame survey.
PATIENTS WHO NEVER HAD
Question: Consider all cataract patients at the time only one eye was treated surgically. What percentage came to surgery for the second eye within the time frame indicated? Age (years)
Up to 1 Mo.
1-6 7-12 Mos. Mos.
1-2 Yrs.
CATARACTS
>2 Sample Yrs. Never Size
Under 25
9
11
5
2
31
41
65
25 - 44
4
9
11
16
40
20
68
45 - 64
8
14
18
20
29
11
73
65 - 74
10
24
20
22
17
7
73
75 and Over
16
24
16
18
13
13
73
NEW INCIDENCE NEWLY DIAGNOSED CATARACT PATIENTS CATARACT EYES
From IOL Market Survey, Health Products Research, Inc .
(
NONCATARACT EYES
Table 9. Model data derived from physician time frame survey. % Newly Diagnosed
Eyes Treated in First Year
% Patients with Two Eyes Diagnosed in First Year
Under 25
14
20
Age (Years) 25 - 44
14
13
45 - 64
28
20
65 - 74
53
33
75 and Over
55
40
Table 9. The percentage of newly diagnosed eyes treated in the first year is applied to new incidence to determine one source of cataract surgery. The percentage of patients with two eyes diagnosed is a measure of bilateral treatment within a year of diagnosis.
MODEL STRUCTURE AND METHODOLOGY The forecasting model considers the population that contributes to the need for treatment and the various rates of treatment resulting in surgery. For a given year, Figure 1 shows the population divided into groups in which cataracts are and are not prevalent. Some prevalent patients have been diagnosed in the current year (new incidence) and some have been diagnosed and treated in previous years . This latter group has eyes that have cataracts but are not yet treated; are aphakic and have IOLs implanted; are aphakic and have no IOLs implanted. Forecasts are obtained by starting with baseline estimates of the number of people and eyes in each category and computing the changes that occur from year to year through the use of a population dynamics model. Unlike other approaches that use a few mathematical formulas to project into the future, this model considers explicitly the events that occur from year to year and is thus classified as a discrete-event forecasting model. The benefit of using such a model is that we have complete flexibility in evaluating specific hypothetical activity for any given future period. J CATARACT REFRACT
FORMERLY DIAGNOSED CATARACT PATIENTS
EYES NO lOL'S
Fig. 1.
NONCATARACT EYES APHAKIC IOL EYES
(Coopersmith) Population dynamics of cataract diagnosis and treatment, including IOL implantations .
The dynamics of the model from one year to the next are depicted in Figure 2 . Based on prevalence of cataract surgery and population changes because of aging or death, new incidence of cataract patients can be computed. The number of eyes diagnosed per patient and the percentage of these eyes treated surgically in the first year contributes to cataract surgeries, with cataract eyes untreated adding to the pool for the following year. Contributions to cataract surgery are also made from patients diagnosed in previous years who have surgery for previously untreated cataracts and for newly diagnosed cataracts. Intraocular lens implantation rates are produced from new cataract surgery through conversion, aphakic patients who had cataract surgery in previous years, and revisions of previously implanted IOLs. Cataracts not converted from this year's surgery or from previous years' surgery contribute to the next year as aphakic eyes.
MODEL RESULTS Best Fit Forecast Available data and best estimates were used initially SURG- VOL 13, MAY 1987
305
THIS YEAR
NEXT YEAR PATIENTS WHO NEVER HAD
PATIENTS WHO NEVER HAD
CATARACTS
CATARACTS
1
NEW INCIDENCE NEWLY DIAGNOSED CATARACT PATIENTS
NEWLY DIAGNOSED CATARACT PATIENTS CATARACT) EYES (NONCATARACT) \ EYES
PREVALENCE
FRACTION TREATED
OF CATARACTS
FORMERLY DIAGNOSED CATARACT PATIENTS
C:CA~~~~CT~
NONCATARACT
Fig. 2.
(Coopersmith) Population dynamics of cataract diagnosis and treatment including IOL implantations from one year to the next.
for 1983 as a baseline to forecast 1984 and 1985. Using 1984 and 1985 actual surgeries and IOL implantations, adjustments were made to less reliable model data to "fine tune" forecasts to within 2% of actual. This set of calibrated data was used to produce the results in Table 10. Cataract surgeries are forecast to increase from 1,155,000 in 1986 to 1,266,000 in 1990; IOL implants will increase from 1,125,000 to 1,251,000
over this period. Note that percentage change shows decelerating growth. Actual 1986 surgeries became available just prior to publication. While actual 1986 figures are substantially higher than baseline, most of the increase came in the latter half of 1986, during which time there was concern over anticipated changes in reimbursement policies in 1987. If the increase is due to a short-term
Table 10. Forecast of cataract surgeries and IOL implantation to 1990. Best fit model data derived by fitting 1984 and 1985 from 1983 data.
Year
Total Cataract Surgeries (000)
Percentage ChangelYear
Primary IOL Implants
Percentage ChangelYear
TotalIOL Implants
Percen tage ChangelYear
1986
1,155
+4.4
1,097
+5.0
1,135
+5.8
*(1986
1,261
+14.0
1,210
+ 15.8
1,2.50
+ 10.1)
1987
1,193
+3.3**
1,146
+ 4.5**
1,183
+4.2**
1988
1,223
+2.5
1,174
+2.4
1,210
+2.3
1989
1,244
+ 1.7
1,194
+ 1.7
1,230
+ 1.7
1990
1,266
+ 1.8
1,215
+ 1.8
1,251
+ 1.7
Baseline 1985 (000): Cataract surgeries 1,106; primary IOL implants 1,045; total IOL implants 1,073. * Actual1986 surgeries became available just prior to publication. Most ofthe unanticipated increase in 1986 was observed in the second half of the year, suggesting that differences between actual and forecast may be related to anticipated changes in reimbursement policies in 1987. Explanation of these differences and their impact on forecasts is currently being studied as a subject for publication later in 1987. **Percentage changes are based on forecasted 1986 figures, not actual. 306
J CATARACT
REFRACT SURG-VOL 13, MAY 1987
change in time to surgery, long-term baseline forecasts may still be realized. Otherwise, one or a combination of the scenarios described below might be more representative. We are currently studying the impact of events occurring over 1986, with results to be published later in 1987. The best-fit forecast data provide a base from which we can analyze "what if' alternatives through changing rates of activity. These analyses are discussed in order of increasing optimism, i.e., highest long-term forecasts. 1. What if average time to surgery is decreased? Increasing the fraction treated in the first year of diagnosis by five points produces the results in Table 11. The major impact is immediate, with
surgeries increasing by 9% in 1986 but leveling off to under 2% growth for subsequent years. 2. What if bilateral treatment within the first year of diagnosis increases? A 5% increase in the number of eyes diagnosed per new cataract patient produces the results in Table 12. The immediate rate of increase in cataract surgeries is 6.4%. Growth then decelerates gradually, resulting in a 1990 forecast of 1,309,000. 3. What if more patients can be persuaded to have their eyes examined? Two cases are evaluated: The first (Case 3.A) assumes that cataracts will be detected earlier but there will be no net increase in prevalence for the oldest age group. An increase in prevalence for ages 45 to 74 reaching 10% above
Table II. Forecast of cataract surgeries and IOL implantations to 1990. Assumption: Fraction treated in first year of diagnosis increased by 5 points; represents accelerated treatment of new patients.
Year
Total Cataract Surgeries (000)
Percentage Change/Year
Primary IOL Implants (000)
Percentage Change/Year
TotalIOL Implants (000)
Percentage Change/Year
1986
1,206
+9.0
1,146
+9.7
1,184
+10.3
1987
1,227
+ 1.7
1,178
+2.8
1,216
+2.7
1988
1,247
+ 1.6
1,197
+ 1.6
1,234
+ 1.5
1989
1,262
+ 1.2
1,212
+ 1.3
1,248
+ 1.1
1990
1,281
+ 1.5
1,230
+ 1.5
1,265
+ 1.4
Baseline 1985 (000): Cataract surgeries 1,106; primary IOL implants 1,045; total IOL implants 1,073. Table 12. Forecast of cataract surgeries and IOL implantations to 1990. Assumption: 5% increase over baseline rate of number of eyes diagnosed per new cataract patient; represents an increase in bilateral treatment within one year of diagnosis.
Year
Total Cataract Surgeries (000)
Percentage Change/Year
Primarv IOL Implants (000)
Percentage Change/Year
TotalIOL Implants (000)
Percentage Change/Year
1986
1,177
+6.4
1,119
+7.1
1,157
+7.8
1987
1,227
+4.2
1,177
+5.2
1,215
+5.0
1988
1,261
+2.8
1,211
+2.9
1,248
+2.7
1989
1,286
+2.0
1,234
+ 1.9
1,271
+ 1.8
1990
1,309
+ 1.8
1,257
+ 1.9
1,293
+ 1.7
Baseline 1985 (000): Cataract surgeries 1,106; primary IOL implants 1,045; total IOL implants 1,073. Table 13. Forecast of cataract surgeries and IOL implantations to 1990. Assumption: 10% increase in prevalence for ages 45 -74, but not for 75 and older-trended to 1990; represents trend in earlier detection, but no increase in eventual prevalence.
Year
Total Cataract Surgeries (000)
Percentage Change/Year
Primarv IOL Implants (000)
Percentage Change/Year
Total IOL Implants (000)
Percentage Change/Year
1986
1,235
+11.7
1,174
+12.3
1,212
+ 12.7
1987
1,313
+6.3
1,260
+7.3
1,298
+7.1
1988
1,366
+4.0
1,311
+4.0
1,348
+3.9
1989
1,403
+2.7
1,347
+2.7
1,383
+2.6
1990
1,436
+2.4
1,379
+2.4
1,414
+2.2
Baseline 1985 (000): Cataract surgeries 1,106; primary IOL implants 1,045; total IOL implants 1,073.
J CATARACT REFRACT
SURG-VOL 13, MAY 1987
307
Table 14. Forecast of cataract surgeries and IOL implantations to 1990. Assumption: 10% increase in prevalence for ages 45 - 65 and 75 and older. Prevalence for 65 - 74 raised to NIH figure of 28.5%; represents earlier detection and net gain in eventual prevalence. Percentage ChangelYear
Primary IOL Implants (000)
Percentage ChangelYear
TotalIOL Implants (000)
Percentage ChangelYear
1,413
+27.8
1,342
+28.4
1,381
+28.7
1,555
+10.0
1,493
+11.3
1,530
+10.8
1988
1,658
+6.6
1,592
+6.6
1,629
+6.5
1989
1,737
+4.8
1,668
+4.8
1,705
+4.7
1990
1,809
+4.1
1,737
+4.1
1,774
+4.0
Year
Total Cataract Surgeries (000)
1986 1987
Baseline 1985 (000): Cataract surgeries 1,106; primary IOL implants 1,045; total IOL implants 1,073.
baseline data in 1990 produces results displayed in Table 13. Overall higher growth rates show cataract surgeries reaching 1,436,000 by 1990 with a corresponding increase in IOL implants to 1,414,000. A second (Case 3.B) allows for a slightly higher increase in prevalence and further allows for a net increase in prevalence for the oldest age group. An increase in prevalence for the age groups 45 to 64 and 75 and over, reaching 10% above baseline in 1990, and an increase in the 65 to 74 year age group, reaching the NIH estimate of28.5% (from 23.0%), produce the most optimistic results as shown in Table 14. High annual percentage growth decelerating from + 27.8% to + 4.1 % increases cataract surgeries to 1,809,000 in 1990, with IOL implantation numbering 1,774,000.
t C3
[!] . . . case
1.
---~
Ke y Best F i t
.-
Case 1
eJ [!l - .. - ..
-- --- - --- -{!]
.<: ... .[!] [!l - - ~~~- ~ :~ - - eJ Case 3 . B
[!]- '-' - ' - ' - :.-'-'-'-' ~----'
M
i
1 1
1 .7
i
.}!1'
0
n
1.
5
-~ --
0
f
_. eJ
1 .
S
u
r 9
e
1.1
r i
SUMMARY
e
Figure 3, which shows actual cataract surgeries for 1982 to 1985, indicates that the most optimistic case might be unrealistic. What is apparent is that surgeries will continue to increase but at decelerating rates. We feel that the model has demonstrated its usefulness in evaluating possibilities for the future. We hope to have the opportunity to analyze the impact of specific potential changes in technology and delivery of patient care as proposed by the medical community and industry. REFERENCES 1. U.S. Bureau of the Census, Current Population Reports, Series
P-25, No. 952, Projections of the Population of the United States, by Age, Sex and Race: 1983 to 2080, U.S. Government Printing Office, Washington, DC, 1984
308
J CATARACT
5
o.
0 . 7.L.----.::;: _ _ +-_ +I - -t--~-i_--~- _4_ .-- +__ B4 B5 B6 B7 B8 B9 90 B2
Year
Fig. 3.
(Coopersmith) Projected trends in cataract surgery-1982 to 1990.
2. U.S. Department of Health and Human Services, NIH Publication No. 84-2473, Report of the Cataract Panel , Vision Research. A National Plan. 1983-1987, Volume Two/Part Three, U.S. Government Printing Office, Washington, DC, 1983 3. Vital and Health Statistics, U.S. Department of Health and Human Services. Public Health Service. National Center for Health Statistics, Series 13, Nos. 34, 61, 70; Advanced Data: September 28, 1984 - No. 101, September 27, 1985 - No. 112
REFRACT SURG-VOL 13, MAY 1987