Cataracts as an epidemiologic problem

INCIDENCE OF CATARACT EXTRACTION AFTER DIABETIC VITRECTOMY

PURPOSE

To determine the frequency of visually significant cataracts after vitrectomy for complications of diabetic retinopathy.

METHODS

We studied 40 patients and 56 concurrent control patients in a retrospective, consecutive, comparative case series in an institutional setting. Entry criteria included phakic patients with a clear lens or mild lens opacity undergoing anatomically successful diabetic vitrectomy, without lens removal at the time of vitrectomy, without intraocular gas or silicone oil use, and with at least 1 year of postoperative follow-up examination information. Two comparative phakic control groups with the diagnosis of macular hole or epiretinal membrane were selected, also with follow-up examination information of at least 1 year postoperatively. The occurrence of cataract extraction was the principal outcome measure. Its validity as a measure of cataract formation was evaluated by ascertainment of improved visual acuity after cataract extraction. A secondary endpoint analysis included eyes that needed cataract extraction at the final follow-up examination.

RESULTS

For the primary analyses (clear lens preoperatively), there were 26 patients in the study group, 38 in the macular hole control group, and 18 in the epiretinal membrane control group. The cumulative cataract extraction rates at 2 years were 15%, 66%, and 53% respectively. By using multivariate survival analysis, the patient age was an important factor, with a younger age associated with a lower rate of progression to nuclear sclerosis. After controlling for age, the difference in these three groups was still statistically significant. In the four patients with diabetes undergoing cataract surgery, the visual acuity improved at least two lines in only one of the eyes and did not change in three eyes. After expanding the outcome measures to include study patients with mild lens opacities at baseline or those judged to be in need of cataract surgery at the final follow-up examination, there was still a strongly statistically significant difference between the three groups.

CONCLUSION

The rate of cataract extraction after vitrectomy in patients with diabetes is lower than in patients without diabetes undergoing vitrectomy and suggests a lower rate of cataract formation. This inference should be considered when attributing subnormal vision in a patient who has had a diabetic vitrectomy to a cataract. This is especially significant because the risk ratio in patients with diabetes in general and in patients with a previous vitrectomy is likely less favorable compared with the general population.

Effect of cigarette smoking on copper, lead, and cadmium accumulation in human lens

AIM

To identify cigarette smoking as a risk factor for development of cataract, to determine the importance of copper, lead, and cadmium in cataractogenesis, and to learn about any relation between those elements.

METHODS

Copper, lead, and cadmium concentrations were measured by atomic absorption spectrophotometry in 37 cataractous and nine normal human lenses.

RESULTS

All three element accumulations in lenses with cataract were statistically meaningful. Lenticular copper, lead, and cadmium were increased significantly with cigarette smoking. Cadmium had a positive correlation both with lead and copper in cataractous lenses.

CONCLUSION

The accumulation of copper, lead, and cadmium occurs in cataract. The probable source of cadmium in humans is cigarettes. Lenticular cadmium accumulation also increases copper and lead precipitation in the lens. Cigarette smoking might be cataractogenic.

Epidemiology and the health care revolution

PURPOSE

Revolutions in the health care marketplace, with their implied dependence upon the population perspective, have renewed interest in epidemiologic methods and their application.

METHODS

As a way of organizing questions, data, and answers, epidemiology is once again the core scientific discipline for a multidimensional paradigm shift that emphasizes five facets of health care. First, the health of enrolled populations, rather than merely treatment of sick individuals presenting for care. Second, assessment of the "time, place, and person" of disease burden--who is healthy, who is not, and what it will take to maximize their health. Third, the causative factors for disease and the factors or characteristics that promote health. Fourth, the development of evidence-based clinical guidelines for clinicians and consumers alike. Fifth, evaluation of the impact providers are having on the health of populations (outcomes), individually and collectively.

RESULTS

Thoughtful consideration of all of the above factors depends upon epidemiologic data and insights brought to a firm and conclusive end point capable of supporting policy.

CONCLUSIONS

Credibility will require that epidemiologists (and the symbiotic media) exercise far greater restraint in drawing definitive conclusions and speculations from often starting but meager data.

The Nambour study of ocular disease. I. Design, study population and methodology

In association with a study of actinic skin disease, we undertook a comprehensive survey of ocular disease in a population sample of the town of Nambour, Queensland, Australia. Particular emphasis was placed on those diseases with a putative relationship to exposure to solar radiation. In addition to collecting prevalence data, a randomized controlled trial was commenced to determine, among other things, if daily ingestion of 30 mg of beta-carotene supplements reduces the incidence or progression of ocular diseases possibly related to solar radiation exposure. The study design, population and methodology of the study are described in detail as a background to the future reporting of the results. The study should provide unique epidemiological information about eye disease in an Australian community setting due to the representative nature of the subjects and the comprehensive examination performed.

Age-related changes in the human lens: a comparison of Scheimpflug photography and lens density index

Two quantitative techniques, Scheimpflug photography and the lens density index (LDI), were used to measure lens density in 52 patients. In the Scheimpflug technique, a digitized slitlamp camera provides peak and average nuclear density based on a densitometric analysis of the lens nucleus. The LDI is a psychophysical measurement of the difference between retinal scotopic thresholds for two wave-lengths of light. Both the Scheimpflug technique and LDI revealed an age-related increase in lens density. Peak and average nuclear density were highly correlated with the LDI.

The scope of the cataract problem in the Middle East and the Mediterranean

The region is characterized by diversity in cultural, political, economic and health conditions. Blindness in the region varies from 6.4% to 0.2% with cataract ranking highly as an underlying cause. There is a need to develop national policies to deliver affordable, technically suitable, and cost effective management plans to reduce cataract. Economic, demographic, health, and manpower statistics are essential information to be considered in formulating such policies.

Racial differences in the cause-specific prevalence of blindness in east Baltimore

BACKGROUND

Bilateral blindness unrelated to simple refractive error is twice as prevalent among blacks as among whites, although the difference narrows among the elderly. The reasons for this race- and age-related pattern are uncertain.

METHODS AND RESULTS

A randomly selected, stratified, multistage cluster sample of 2395 blacks and 2913 whites 40 years of age and older in East Baltimore underwent detailed ophthalmic examinations by a single team. We identified 64 subjects who were blind in both eyes. The leading causes of blindness were unoperated senile cataract (accounting for blindness in 27 of the total of 128 eyes), primary open-angle glaucoma (17 eyes), and age-related macular degeneration (16 eyes). Together, these three disorders accounted for 47 percent of all blindness in this sample. Unoperated cataract accounted for 27 percent of all blindness among blacks, among whom it was four times more common than among whites; whites were almost 50 percent more likely than blacks to have undergone cataract extraction before the age of 80 (P less than 0.002). Primary open-angle glaucoma accounted for 19 percent of all blindness among blacks; it was six times as frequent among blacks as among whites and began 10 years earlier, on average. By contrast, age-related macular degeneration resulting in blindness was limited to whites, among whom it was the leading cause of blindness (prevalence, 2.7 per 1000; 95 percent confidence interval, 1.2 to 5.4); it affected 3 percent of all white subjects 80 years of age or older.

CONCLUSIONS

The pattern of blindness in urban Baltimore appears to be different among blacks and whites. Whites are far more likely to have age-related macular degeneration, and blacks to have primary open-angle glaucoma. The high rate of unoperated cataracts among younger blacks and among elderly subjects of both races suggests that health services are underused. Half of all blindness in this urban population is probably preventable or reversible.

A new method for documenting lens opacities

We tested an anterior segment camera and digital analyzer on 32 eyes of 22 patients to determine whether its measurement of lens opacities correlated with measurements obtained by a standardized clinical grading system. The lenses were graded clinically for nuclear opacity, nuclear color, cortical opacity, and posterior subcapsular opacity. The lenses were then photographed and analyzed with this new device, and the results were compared. The camera system showed good reproducibility. Its results correlated well with the clinical gradings for nuclear capacity (P = .001) and cortical opacity (P = .001) but less well with posterior subcapsular opacity (P = .3), although there were only seven eyes with posterior subcapsular opacities. This camera system could help document and follow up lens opacity with more accuracy and reproducibility than has been previously possible.

The Oxford modular cataract image analysis system

A modular system of acquisition and analysis of Scheimpflug, retro-illumination and fluorescence images of the in vivo human crystalline lens is described. Image analysis is directed towards the following goals: Scheimpflug slit-images are analysed for: (1) The optical density of nuclear cataract present; (2) The dimensions of the lens and the lenticular zones; (3) The curvatures of the lens and lenticular zones. Retro-illumination images are analysed for: (1) The percentage area which is occupied by cataract; (2) A combined measure (weighted integral) describing both the amount of cataract present and its optical density. Lenticular auto-fluorescence images are analysed for the mean density (fluorescence) of the lens as a whole. A pilot study of the repeatability of the methods is presented.

Visual outcome and complications after cataract extraction in Saudi Arabia

Cataract is the leading cause of blindness in Saudi Arabia. The author studied 1383 patients who had undergone cataract extraction (total of 1520 procedures) from October 1985 to March 1986 at the King Khaled Eye Specialist Hospital, Riyadh, Saudi Arabia. All patients were observed for at least two months. Of 1520 eyes 555 (37%) achieved a visual acuity of 20/40 or better, 309 (20%) a visual acuity of 20/50-20/60 after surgery, and 656 (43%) eyes a visual acuity of 20/70 or less. The number of eyes that had intraoperative complications was 176 (12%). The number of eyes that had postoperative complications was 539 (35%). Some eyes had more than one complication. The main factors responsible for failure to achieve visual acuity of 20/40 or better were: (1) error of refraction in 492 (32%) eyes; (2) pre-existing corneal scarring and opacity in 211 (14%) eyes; (3) climatic droplet keratopathy in 134 (9%); and (4) presumed visual loss due to glaucoma in 134 (9%) eyes.

Does milk have a cataractogenic effect? Weighing of clinical evidence

We undertook a prospective study to test Simoons' hypothesis that in certain susceptible races milk exerts a cataractogenic effect. Overall milk intake in low lactase deficiency areas did not correlate with cataract occurrence. Subgrouping of cataract patients revealed that greater milk intake did show positive correlation with cortical cataracts. Cortical cataracts were also markedly more common in females. Analysis of data from three different regions showed greater milk intake in cortical cataract patients only. Our data indicate the importance of specifying cataract type in cataract studies and highlight the problem this approach brings forth. We noted no different trends in subjects from northwest and southeast India, although the number of subjects from the southeast was considerably less. Patients with early cortical cataracts may be advised to restrict milk intake.

Association of systemic hypertension and diabetes mellitus with cataract extraction. A case-control study

The authors conducted a case-control hospital-based study to assess the prevalence of systemic diseases and drugs in 161 cataract extraction patients and 196 surgical patients matched by age, sex, and race. The data were analyzed using matched multiple logistic regressions. A statistically significant increased risk of cataract extraction was found in patients with systemic hypertension (odds ratio [OR] = 1.49, 95% confidence interval [CI] = 1.06-2.09) and diabetes mellitus (OR = 1.79, 95% CI = 1.23-2.60). Estimation of the combined effect of systemic hypertension and diabetes mellitus resulted in an even higher risk for cataract extraction (OR = 2.66, 95% CI = 1.67-4.23). A positive association of cataract extraction and treatment of systemic hypertension with the diuretic furosemide was also found (OR = 1.95, 95% CI = 1.02-3.74).

Cataracts and cigarette smoking. The City Eye Study

The City Eye Study is a nine year longitudinal prospective epidemiological study. During the first three year phase the study recruited 1029 volunteers, aged between 54 and 65 years, primarily from companies and organisations working in or around the City of London. The analysis of the first cohort data shows a significant association between nuclear lens opacities and moderate to heavy cigarette smoking. The Relative Risk for nuclear lens opacity and cigarette smoking ranges from 1.0 for past light-smokers through 2.6 for past heavy-smokers, to 2.9 for present heavy smokers.

The dimensions of the problem of eye disease among the elderly

America is aging rapidly. Within the next 30 years, those over 65 years of age will grow to form 17% of the population of the United States; the number of people over 85 will more than double. Currently, the rates of eye disease such as cataract, macular degeneration, diabetic retinopathy, and glaucoma are highest in the older group. The risk of blindness is ten times greater for those over age 65 than for younger individuals. This combination of high rates of disease in the fastest growing segment of the population means that the demand for eye care services will increase dramatically. Undoubtedly, new approaches will appear to deal with the epidemiologic reality.

Factors influencing visual outcome after cataract extraction among Arabs in Kuwait

Of 409 consecutive Arab patients in Kuwait who had extractions for idiopathic (senile and presenile) cataract 385 were followed up for a minimum period of one year. Among these the final visual outcome was 6/12 or better in 208 eyes (54%) but visual acuity was 6/18 or less in 177 eyes (46%). Of these 177 eyes 127 eyes (71.8%) had poor vision due to preoperative ocular disorders and 31 (17.5%) due to surgical complications. The main ocular conditions which limited visual recovery were the presence of corneal opacities, hypermaturity of cataract, advanced glaucoma, senile macular degeneration, diabetic retinopathy, and postoperative retinal detachment in this order of frequency. The prevalence of these disorders in cataract patients among the Arab population was identified and is discussed.

The Oxford Clinical Cataract Classification and Grading System

A composite slit-lamp based system for the clinical classification and grading of cataract is described. Cataract features are classified morphologically, and individual features are graded by comparison with standard diagrams mounted adjacent to the slit-lamp. Attention has been paid to relevant aspects of measurement theory, with equal interval steps between the grades. The image degrading effect of the cataract is assessed using a 'resolution target projection ophthalmoscope'. The method may be used in conjunction with photographic and image analysing techniques.

Impact of referral bias on evaluation of cataract surgery

Patients from a defined population (Olmsted County, Minnesota) who underwent cataract extraction during 1980 were compared with referral patients operated on at the Mayo Clinic to determine whether selective referral of patients introduces bias into studies conducted at academic centers. Rates of cataract extraction in Olmsted County increased continuously with increasing age and, in the older groups, were greater among females than males. The overall age- and sex-adjusted annual rate, 120 per 100,000 population, was considerably lower than that for 1980 in the United States, 209 per 100,000 population. A significantly greater proportion of referral patients had coexistent diabetes mellitus (P less than .05) and underwent other ophthalmic surgical procedures in combination with cataract extraction (P less than .001). Previous ophthalmic disorders were also more frequent among referral patients. Because selection for referral can distort data, this possible source of bias must be considered when interpreting data.

Cataracts and cataract operations (1)

Cataract operations are commonly performed in either a primary-care or a tertiary-care center. A plethora of information (some of which is unfounded) has been disseminated in the lay news media about the advances in the surgical techniques of cataract removal. This article reviews some of the recent concepts about the formation of cataracts and the modern approaches for their extraction. It is directed at the nonophthalmologic primary-care physician who refers patients for evaluation or performs the ancillary tests in preparation for a cataract operation. Space limitations prevent a complete review of the subject. Some of the controversial aspects of cataract surgical procedures are addressed objectively, but bias is unavoidable.

Dehydrational crises from severe diarrhoea or heatstroke and risk of cataract

The first of a series of epidemiological studies in progress in India has shown a strong association between risk of cataract and remembered episodes of dehydrational crises from severe cholera-like diarrhoeal disease. The findings suggest that severe diarrhoea is a major risk factor in early development of cataract and might account for about 36% of cases in the study area.

Epidemiologic aspects of cataract surgery. III: Frequencies of diabetes and glaucoma in a cataract population

A Danish data source was examined to determine age and sex specific rates of diabetes and glaucoma in a large cataract extracted population. Comparisons with population rates were done. An excess prevalence of diabetes in the cataract population below 70 years was found. For cataract extracted males and females below the age of 40 years, the diabetes prevalence was 15 to 25 times the prevalence in a general population. This prevalence excess decreases with age to normal levels at 75 years of age. Furthermore, we found higher relative frequencies of diabetes among cataract extracted females than among males. Mean age at time of surgery was significantly lower for the diabetic cataract patients. Also for primary glaucoma, an excess prevalence was found in the cataract population. For cataract extracted males and females aged 40 to 49 years the glaucoma frequency was 4-5 times the frequency in a general population. This excess relative frequency decreases with age. The glaucomatous cataract patients have a higher mean age at the time of cataract surgery. A large number of factors seems to contribute to the excess frequencies of diabetes and glaucoma found in the cataract extracted population.

Prevalence of ocular disease in a population study of subjects 65 years old and older

During a two-year period a randomly selected age-stratified sample of subjects 65 years old and older living in Gisborne, New Zealand, was examined by an ophthalmologist to investigate visual acuity and the prevalence of the major disorders of vision in old age. A total of 481 subjects (a response rate of 86.2%) completed the study. When the results were weighted to remove the effect of stratified sampling, the following prevalence rates for the population 65 years and over were obtained: cataract, 30.1% with no sex difference and an increasing prevalence with increasing age; senile macular degeneration, 6.4% with no sex difference and an increasing prevalence with increasing age; glaucoma, 3.6% with no sex difference except for women 90 years old or older who had a higher rate. The prevalence of glaucoma increased with increasing age in women, but in men there was no clear pattern; diabetic retinopathy, 0.5%. In the population 65 years old and older, we estimated that 81% of the men and 68.8% of the women had best corrected visual acuities of 6/9 (20/30) or better in the better eye.

A geographic approach to senile cataracts: possible links with milk consumption, lactase activity, and galactose metabolism

Examined in this article is presently available evidence for the hypothesis that some types of senile cataracts may be brought on by decades-long consumption of milk and milk products. The author approaches the question from a background of research in the geography and history of dairying as these relate to present-day differences among the world's peoples in prevalence of primary adult lactose malabsorption, which is based on a deficiency of the enzyme lactase in adulthood. Among peoples who have consumed milk in lactose-rich forms over a long historical period, there seems to have been a mutation for persistence of high lactase activity throughout life (PHLA), which distinguishes them from human populations of nonmilking tradition and from most land mammals. PHLA permits greater intestinal hydrolysis of lactose and absorption of galactose by adults. The mutation for PHLA, however, was not accompanied by a second one raising galactokinase activity to high levels through life. The result may be that adults who consume large quantities of milk, who have high lactase activity, lactose hydrolysis, and galactose absorption, suffer repeated small galactose challenges, accumulation of galactitol in the lens, and a greater likelihood of developing senile cataracts.

The environment and the lens

The association of various personal, occupational, and environmental factors with cataracts and pseudoexfoliation of the lens (PXF) was examined in a group of Australian Aborigines. Cataracts occurred more commonly in the elderly but were also associated with high levels of ultraviolet radiation and sunlight and were more commonly seen in lower latitudes. PXF was also seen more commonly in the elderly, especially among males. PXF occurred particularly commonly in stockmen and was related to latitude and global radiation. It was positively associated with the occurrence of cataract and with climatic droplet keratopathy. It is suggested that senile cataracts are related to the amount of ultraviolet radiation and PXF to global radiation.

Defects of vision through aphakic spectacle lenses

The following defects of aphakic vision will be reviewed: (1) magnification, which causes false orientation (due to excessive overall magnification of aphakic spectacles, resulting in false depth, and false projection) and distortion (due to excessive peripheral magnification of aphakic spectacles, resulting in pincushioning and concave contracture of the peripheral visual field); (2) swim; (3) image aberrations due to defects of focus through the periphery of aphakic spectacle lenses, resulting from radial astigmatism, curvature of image plane, spherical aberration, coma, and chromatic aberration; (4) restricted peripheral visual field due to small lens size, the roving ring scotoma, and the unrefracted area outside the field of view of aphakic spectacle lenses; (5) near vision problems; (6) weight, thickness, and cosmetic appearance of aphakic eyeglasses; and (7) inaccurate spectacle prescription due to faulty measurement of vertex distance, inaccurate lens duplication, pantoscopic tilt, turning of head during refraction, and rotation of eye during refraction.

Association of presenile cataracts with heterozygosity for galactosaemic states and with riboflavin deficiency

Red cells and the lens of the eye are non-nucleated cells; moreover, they have metabolic similarities. Cataracts develop in childhood in homozygotes for galactosaemic abnormalities, which can be detected by biochemical measurements in red blood-cells. It has not been determined whether heterozygotes for these defects are at greater risk for cataract development later in life. Similarly, riboflavin deficiecy for which the erythrocyte is a sensitive indicator, has been associated with cataracts in animals. Red-cell studies were carried out in 22 patients, aged under 50, with cataracts. Heterozygosity for galactokinase deficiency was detected in 5 patients, for galactose-uridyl transferase in 2, and evidence of an erythrocytic deficiency of riboflavin in 8. Even when Black subjects were excluded from analysis because of their high incidence of polymorphism for galactokinase, these findings are significantly different from those expected from population surveys and suggest that many patients with presenile cataracts have a biochemical abnormality which can be detected by examination of red blood-cells and which may be corrected by dietary restrictions or supplements.