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From The Dana Center for Preventive Ophthalmology, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland.
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Abstract |
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METHODS. All participants in the Salisbury Eye Evaluation (SEE) project and their locally resident siblings were questioned about a personal and family history of cataract or cataract surgery. Lens grading at the slit lamp, using standardized photographs and a grading system, was performed for both SEE participants (probands) and their siblings. Cognitive testing and a history of systemic comorbidities were also obtained for all probands.
RESULTS. Sensitivity of a history of cataract provided on behalf of a sibling was 32%, specificity 98%. The performance was better for a history of cataract surgery: sensitivity 90%, specificity 89%. For self-report of cataract, sensitivity was also low at 55%, with specificity at 77%. Self-report of cataract surgery gave a much better performance: sensitivity 94%, specificity 100%. Different cutoffs in the definition of cataract had little impact. Factors predicting a correct history of cataract included high school or greater education in the proband (odds ratio [OR] = 1.13, 95% confidence interval [CI]1.02–1.25) and younger sibling (but not proband) age (OR = 0.94 for each year of age, 95% CI 0.90–0.99). Gender, race and Mini-Mental Status Examination (MMSE) result were not predictive.
CONCLUSIONS. Whereas accurate self and family histories for cataract surgery may be obtainable, it is difficult to ascertain cataract status accurately from history alone.
Age-related cataract is a sufficiently prevalent condition7 that studies involving large groups of older persons not specifically selected for the cataract phenotype might still be expected to have significant power. The cataract phenotype can be characterized as a continuous variable, allowing even unaffected individuals to contribute useful information. Recent large epidemiologic studies of cataract have generally relied on specialized photographic equipment and highly trained observers to ascertain phenotype.8 9 Large genetic studies of age-related cataract have generally taken a similar approach.4 5 10 Clinical assessment of the lens without photographic documentation11 may be a less expensive option, but still requires specialized equipment and highly trained personnel. These approaches to defining the cataract phenotype, while insuring a high degree of reliability, are resource-intensive and may not be practical for studies of other age-related diseases that might seek to incorporate information on cataract. The question arises as to whether such rigorous direct ascertainment of phenotype is necessary for accurate genetic studies of cataract and whether an oral history of cataract might be of use.
The present study focuses on a group of persons aged 72 years and more recruited for genetic studies of age-related cataract from an ongoing population-based study of aging and visual disabilities.12 Subjects were asked about a history of cataract and cataract surgery in themselves and in their locally resident siblings. These self-reports and family histories were then validated against lens grades. A number of demographic, cognitive, and medical factors were also studied as potential predictors of an accurate history. To the best of our knowledge, this is the first study to attempt to validate an oral history of cataract and cataract surgery in this fashion.
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Materials and Methods |
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Those siblings for whom permission was obtained to make contact were sent a letter describing the study, and a stamped, self-addressed postcard which they were to return to the study center if they did not wish to be contacted further. Those siblings from whom no postcard was received within 2 weeks were contacted by telephone, and a brief questionnaire administered to confirm their relationship to the SEE participant who had identified them as a sibling. The siblings were then invited to a central site in either Baltimore or Salisbury, where lens grades, a personal history of cataract and cataract surgery, and blood for genetic analysis as detailed earlier were obtained. Siblings were not asked about the cataract or cataract surgery history of the SEE participant (i.e., proband) to whom they were related.
The specific text of the questions regarding cataract and cataract surgery follows:
Probands.
"Has your sibling ever been diagnosed with cataract? Has your sibling ever had surgery for cataract?" (This question was asked separately for each sibling.)
Probands and Siblings.
"Have you ever been told you have cataract? Have you ever had eye surgery? If yes, what type of surgery?"
In addition to this information, the following data were obtained for both SEE participants and their siblings: age, race, gender, and number of current medications. Additional information obtained for SEE participants only included: medical history (including specific comorbidities and an overall comorbidity score), Mini-Mental State Examination13 (MMSE) and educational history. A MMSE score of 18 or more had been a requirement for entry into the SEE study at baseline, 7 years earlier. Additional information for siblings included only a determination of their relationship to the SEE participant who had identified them (full sibling related by blood, half sibling, or not biologically related).
The primary definition of cataract used in this study required the presence of one or more of the following in either eye: nuclear cataract grade 2 or higher (of a possible 4); cortical cataract 2/16 or higher; presence of any posterior subcapsular cataract (PSC), pseudophakia, or aphakia. A subject was determined to have had previous cataract surgery if either pseudophakia or aphakia was detected on slit lamp examination in either eye. The impact of different definitions of cataract was also examined (detailed later).
Informed consent was obtained from all subjects before participation in any phase of this investigation. The protocol for this study adhered to the tenets of the Declaration of Helsinki and was approved by the Joint Committee for Clinical Investigation of the Johns Hopkins University School of Medicine before enrollment of any subjects.
Statistical Methods
The t-test and 
2 test were performed to determine significance of observed differences involving continuous and categorical variables, respectively. The logistic regression and generalized estimating equation (GEE)14 model was used to evaluate the associations between demographic characteristics/clinical factors and the accuracy of recollection for cataract status. The level established for statistical significance was a two-tailed P < 0.05. Data process and analyses were performed on computer (SAS ver.8.2; SAS Institute, Inc., Cary, NC).
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Results |
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By contrast, a history of cataract surgery, whether provided on behalf of oneself or a sibling, was generally accurate. A self-reported cataract surgical history had a sensitivity of 94%, specificity of 100%, and positive predictive value of 100%. Cataract surgical history on behalf of a sibling performed nearly as well: sensitivity 90%, specificity 89%, and positive predictive value of 95%.
To ascertain whether a change in the definition of cataract might improve the performance of self or sibling cataract history, we examined two alternative definitions. A more relaxed definition of cataract (nuclear grade, ≥1.5; cortical, ≥1/16, any PSC) lowered the sensitivity of a sibling history of cataract to 20%, while dropping specificity to 94%. The effect on validity of a self-reported history of cataract was similar. A more stringent cataract definition (nuclear grade ≥3.0, cortical ≥4/16, any PSC) raised the sensitivity of a sibling history to 49%, while lowering specificity to 96%. Again, the effect on self-reported history of cataract was similar. It appears that no change in the definition of cataract would significantly improve the validity of an oral cataract history with respect to direct examination of the lens.
To determine which factors might be predictive of an accurate cataract or cataract surgical history, separate logistic regression and GEE models were created with a correct self or sibling history as an outcome variable respectively, and several demographic, cognitive, and medical factors as outlined in the Methods section as potential predictors. SEE participants with a high school or greater education were significantly more likely to provide an accurate cataract history on behalf of a sibling (odds ratio [OR]1.13, 95% confidence interval [CI] 1.02–1.25). The number of medications taken by a SEE participant was also predictive of a more accurate history on behalf of a sibling, although with borderline significance (OR of 1.11 for each additional medicine, 95% CI 1.00–1.23).
Although a younger sibling age was predictive of a more accurate cataract history as obtained from the SEE participant (OR 0.94 for each year of age, 95% CI 0.90–0.99), the age of the SEE participant him- or herself was not significantly predictive. Other factors that were determined not to be predictive of an accurate history of cataract in behalf of self or sibling included: gender, race, presenting or best corrected visual acuity, systemic comorbidity score of the SEE participant, having visited an eye care professional within the past year; specific comorbidities including diabetes, hypertension, stroke, and Parkinson’s disease; and SEE participant’s score on the MMSE.
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Discussion |
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The main practical difficulty with such an approach would be the resultant impact on the study’s power. The prevalence of previous cataract surgery within a given population course depends on access to cataract surgical services and the age of the population. A recent meta-analysis7 has estimated the prevalence of previous cataract surgery among U.S. residents older than 40 years as 5.1% in 2000, compared with an estimated prevalence of significant cataract in the same group of 17.2%. The proportion with previous cataract surgery is estimated to increase to 14.6% among persons aged 75 to 79 years and 29.2% for those aged 80 years and more.
It appears that knowledge about the presence of cataract is not precise, even among this group of persons who are participating in an eye study and have regular contact, for the most part, with eye care providers. There may be several reasons for this: in contradistinction to night blindness, for example, cataract may or may not be symptomatic, depending on the degree of opacity and the particular visual needs of the subject. Moreover, even among eye care providers, the definition of cataract depends on imposing arbitrary cutoffs on an essentially continuous process, lens opacity. Finally, cataract is a slowly progressive condition, so that even persons with significant decrement in visual acuity may be less likely to notice the gradual change.
The finding that higher educational attainment is predictive of a more accurate cataract history on behalf of a sibling is not unexpected. Younger age of a sibling was also correlated with a greater likelihood of an accurate cataract family history as provided by the SEE participant, perhaps because a diagnosis of cataract in a younger person would be more striking or memorable. It is more difficult to understand why the number of medications used by SEE participants would be predictive of an accurate cataract family history. The number of medications may perhaps best be understood as an index of the SEE participants’ accuracy of recollection, in the sense that subjects who were able to manage and recall more medications perhaps had a better grasp of medical details.
It is also somewhat surprising that neither the SEE participants’ mental status nor their overall comorbidity score was predictive of the accuracy of their cataract history. This is probably in part because persons with significant dementia were excluded from the study at baseline, thus decreasing the chances that an association between mental status and accuracy of history would be observed. Similarly, this group of participants, all of whom have maintained sufficient mobility to participate in a longitudinal study over 7 years, may in fact be somewhat less likely to reveal associations between the burden of medical comorbidity and ability to provide an accurate history. Finally, the same may be true of visual acuity: only 6.8% of probands had best corrected visual acuity of less than 20/40. It may be that studies including more participants with significant cognitive, physical, and visual disabilities would be more likely to reveal such associations.
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Footnotes |
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Submitted for publication October 14, 2002; revised March 3, 2003; accepted March 5, 2003.
Disclosure: H. Bowie, None; N.G. Congdon, None; H. Lai, None; S.K. West, None
The publication costs of this article were defrayed in part by page charge payment. This article must therefore be marked "advertisement" in accordance with 18 U.S.C. 
1734 solely to indicate this fact.
Corresponding author: Nathan G. Congdon, Wilmer 120; 600 N. Wolfe St., Baltimore, MD 21287; ncongdon{at}jhmi.edu.
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References |
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