Distribution of lens opacities in the Italian-American Case-Control Study of Age-Related Cataract. The Italian-American Study Group

Insights into the biochemical and biophysical mechanisms mediating the longevity of the transparent optics of the eye lens

In the human eye, a transparent cornea and lens combine to form the "refracton" to focus images on the retina. This requires the refracton to have a high refractive index "n," mediated largely by extracellular collagen fibrils in the corneal stroma and the highly concentrated crystallin proteins in the cytoplasm of the lens fiber cells. Transparency is a result of short-range order in the spatial arrangement of corneal collagen fibrils and lens crystallins, generated in part by post-translational modifications (PTMs). However, while corneal collagen is remodeled continuously and replaced, lens crystallins are very long-lived and are not replaced and so accumulate PTMs over a lifetime. Eventually, a tipping point is reached when protein aggregation results in increased light scatter, inevitably leading to the iconic protein condensation-based disease, age-related cataract (ARC). Cataracts account for 50% of vision impairment worldwide, affecting far more people than other well-known protein aggregation-based diseases. However, because accumulation of crystallin PTMs begins before birth and long before ARC presents, we postulate that the lens protein PTMs contribute to a "cataractogenic load" that not only increases with age but also has protective effects on optical function by stabilizing lens crystallins until a tipping point is reached. In this review, we highlight decades of experimental findings that support the potential for PTMs to be protective during normal development. We hypothesize that ARC is preventable by protecting the biochemical and biophysical properties of lens proteins needed to maintain transparency, refraction, and optical function.

Association of G>A transition in exon-1 of alpha crystallin gene in age-related cataracts

Aim

To identify the presence of a known or novel mutation/SNP in Exon-1 (ex-1) of alpha crystallin (CRYAA) gene in different types of age-related cataract (ARC) patients.

Materials and Methods

Single strand Conformation Polymorphism (SSCP) analysis was carried for the detection of single nucleotide polymorphism (SNP) in ex-1 of alpha crystallin (CRYAA) gene which was confirmed by sequencing.

Results

The SSCP analysis of ex-1 of CRYAA gene revealed mobility shift in patients and controls, which was due to G>A transition at 6^th position in exon-1 of CRYAA gene. All the three genotypes, GG, AA and GA, were detected in patients and controls indicating that G>A substitution is polymorphic. The analysis showed significant risk for heterozygotes (GA) as compared to pooled frequencies of homozygotes (GG + AA), which was 1.81 times for all the types of cataracts in general and 2.5 times for Nuclear Cataract and twice for Cortical Cataract.

Conclusion

The GA heterozygotes were at higher risk for developing NC and CC types of cataracts, where as the GG homozygotes for MT and AA homozygotes for PSC types were at risk. To our knowledge, an association of G>A transition found in ex-1 of CRYAA gene with ARC, with differential risk of genotypes for individual type of cataracts has not been reported previously.

Ten-year incidence of age-related cataract and cataract surgery in an older Australian population. The Blue Mountains Eye Study

PURPOSE

To estimate the 10-year incidence of cataract and cataract surgery in an older Australian population.

DESIGN

Prospective population-based study.

PARTICIPANTS

Persons at least 49 years old living in 2 postcode areas west of Sydney, Australia.

METHODS

Eye examinations were performed at baseline and at 5- and 10-year follow-up visits. Lens photographs were taken and graded by masked graders using the Wisconsin Cataract Grading System.

MAIN OUTCOME MEASURES

Incidences of nuclear cataract, cortical cataract, posterior subcapsular cataract (PSC), and cataract surgery.

RESULTS

Ten-year person-specific incidences were 36.0% for nuclear cataract, 28.0% for cortical cataract, 9.1% for PSC, and 17.8% for cataract surgery. Corresponding rates were 31.7%, 24.4%, 8.2%, and 14.4%, respectively, in men and 39.3%, 30.8%, 9.8%, and 20.1%, respectively, in women. The incidence for each type of cataract and cataract surgery was positively associated with age (P<0.0001). Women had a significantly higher incidence than men for nuclear cataract (P = 0.04), cortical cataract (P = 0.007), any cataract (P = 0.0006), and cataract surgery (P = 0.03) after adjusting for age. There was no significant gender difference for PSC. The mean age at cataract surgery was 75.8 years, and there was no significant gender difference (P = 0.9). Among persons who developed any cataract, 22% had more than one type and 1.3% had all 3 types present. Nuclear cataract and PSC were significantly associated with visual impairment (visual acuity worse than 20/40).

CONCLUSION

Age- and gender-specific cataract incidences in this study were similar to those reported from the U.S. Beaver Dam Eye Study. In this study, 72% of the participants were affected by cataract or had had cataract surgery over the 10-year follow-up period.

The risk of posterior subcapsular cataracts in granulocyte donors

BACKGROUND

Therapeutic use of adrenal corticosteroids is a risk factor for the development of posterior subcapsular cataract (PSC). Because corticosteroids are given to donors of apheresis granulocytes (PMNs) to improve yield, this study was performed to determine the prevalence of PSCs in PMN donors relative to a matched control group of apheresis platelet (PLT) donors.

STUDY DESIGN AND METHODS

This study was a cross-sectional study stratified by age, sex, and lifetime apheresis experience at three sites. Individuals who had made at least five PMN donations preceded by corticosteroids were eligible. The presence of PSC was ascertained by grading digital retroillumination images of both lenses. A random subset of participants underwent clinical eye examinations by ophthalmologists masked as to study group. A logistic regression model was used to compute odds ratios (ORs).

RESULTS

Granulocyte donors had given a mean of 13 donations (range, 5-39 donations) over a mean period of 8.5 years (range, 0.3-25.2 years). The mean corticosteroid exposure, in cortisol equivalents, was 2840 mg (range, 1067-9040 mg). Six of 89 PMN donors had photographic evidence of PSCs versus 4 of 89 controls. This difference was not significant (OR, 1.54; 95% confidence interval [CI], 0.46-5.08). Five of 33 PMN donors and 3 of 30 PLT donors had evidence of PSC by clinical examination. This difference was also not significant (OR, 1.61; 95% CI, 0.35-7.39).

CONCLUSION

This study does not support the hypothesis that corticosteroid stimulation of PMN donors is associated with an increased risk of developing a PSC.

Identification of a major locus for age-related cortical cataract on chromosome 6p12-q12 in the Beaver Dam Eye Study

Age-related cataracts are one of the leading causes of visual impairment and blindness among the elderly worldwide. Among age-related cataracts, cortical opacities rank as the second most common type; however, little is known about their molecular pathogenesis or genetics. To identify susceptibility loci for cortical cataracts, we genotyped a subset of families (102 families; n = 224 sib pairs) from the Beaver Dam Eye Study and performed a model-free genome-wide linkage analysis for markers linked to a quantitative measure of cortical opacity. We obtained evidence for linkage at marker D1S1622 on chromosome 1p35 (P < 0.0002) and at marker D6S1053 on 6q12 (P < 0.00008) in the initial scan. Five additional regions on 1q31, 2p24, 2q11, 4q28, and 15q13 that are suggestive of linkage (P < or = 0.01 or logarithm of the likelihood ratio > or = 1.18) were observed. The region on chromosomes 6p12-q12 was selected for fine mapping, and the intermarker distance was reduced to 3 cM by adding 11 markers in the interval between D6S1017 and D6S1021. After fine mapping, significant evidence of linkage remained on chromosome 6p12-q12 at D6S1053 (P < 0.00005). The current genome scan for age-related cortical cataracts may lead to identification of novel genes, because few regions identified in the current scan have previously been implicated in congenital or age-related cataracts.

Operated and unoperated cataract in Australia

PURPOSE

To quantify the prevalence of cataract, the outcomes of cataract surgery and the factors related to unoperated cataract in Australia.

METHODS

Participants were recruited from the Visual Impairment Project: a cluster, stratified sample of more than 5,000 Victorians aged 40 years and over. At examination sites interviews, clinical examinations and lens photography were performed. Cataract was defined in participants who had: had previous cataract surgery, cortical cataract greater than 4/16, nuclear greater than Wilmer standard 2, or posterior subcapsular greater than 1 mm2.

RESULTS

The participant group comprised 3,271 Melbourne residents, 403 Melbourne nursing home residents and 1,473 rural residents. The weighted rate of any cataract in Victoria was 21.5%. The overall weighted rate of prior cataract surgery was 3.79%. Two hundred and forty-nine eyes had had prior cataract surgery. Of these 249 procedures, 49 (20%) were aphakic, 6 (2.4%) had anterior chamber intraocular lenses and 194 (78%) had posterior chamber intraocular lenses. Two hundred and eleven of these operated eyes (85%) had best-corrected visual acuity of 6/12 or better, the legal requirement for a driver's license. Twenty-seven (11%) had visual acuity of less than 6/18 (moderate vision impairment). Complications of cataract surgery caused reduced vision in four of the 27 eyes (15%), or 1.9% of operated eyes. Three of these four eyes had undergone intracapsular cataract extraction and the fourth eye had an opaque posterior capsule. No one had bilateral vision impairment as a result of cataract surgery. Surprisingly, no particular demographic factors (such as age, gender, rural residence, occupation, employment status, health insurance status, ethnicity) were related to the presence of unoperated cataract.

CONCLUSIONS

Although the overall prevalence of cataract is quite high, no particular subgroup is systematically underserviced in terms of cataract surgery. Overall, the results of cataract surgery are very good, with the majority of eyes achieving driving vision following cataract extraction.

The epidemiology of cataract in Australia

PURPOSE

To describe the prevalence and risk factors for cataract in an Australian population aged 40 years and older.

METHODS

Participants were recruited by a household census and stratified, random cluster sampling to represent residents of Victoria, Australia, aged 40 years and older. The following information was collected: initial visual acuity and best-corrected visual acuity, demographic details, health history, dietary intake of antioxidants, lifetime ocular ultraviolet B exposure, and clinical eye examination, including lens photography. Cortical opacities were measured in sixteenths. Cortical cataract was defined as opacity greater than or equal to 4/16 of pupil circumference. Nuclear opacities were graded according to the Wilmer cataract grading scheme, and cataract was defined as greater than or equal to nuclear standard 2.0 of four standards. The height and width of any posterior subcapsular opacity was measured and recorded. Posterior subcapsular cataract was defined as posterior subcapsular opacity greater than or equal to 1 mm2. The worse eye was selected for analysis. Backward stepwise logistic regression was used to quantify independent risk factors for cataract.

RESULTS

A total of 3,271 (83% of eligible) of the urban residents, 403 (90% of eligible) nursing home residents, and 1,473 (92% of eligible) rural residents participated. The urban residents ranged in age from 40 to 98 years (mean, 59 years), and 1,511 (46%) were men. The nursing home residents ranged in age from 46 to 101 years (mean, 82 years), and 85 (21%) were men. The rural residents ranged in age from 40 to 103 years (mean, 60 years), and 701 (47.5%) were men. The overall weighted rate of cortical cataract was 11.3% (95% confidence limits, 9.68%, 13.0%) excluding cataract surgery and 12.1% (95% confidence limits, 10.5%, 13.8%) including cataract surgery. The risk factors for cortical cataract that remained in the multivariate logistic regression model were age, female gender, diabetes duration greater than 5 years, gout duration greater than 10 years, arthritis diagnosis, myopia, use of oral beta-blockers, and increased average annual ocular ultraviolet B exposure. Overall, 12.6% (95% confidence limits, 9.61%, 15.7%) of Victorians aged 40 years and older had nuclear cataract including previous cataract surgery, and 11.6% (95% confidence limits, 8.61%, 14.7%) had nuclear cataract excluding previous cataract surgery. In the urban and rural cohorts, age, female gender, rural residence, brown irides, diabetes diagnosed 5 or more years earlier, myopia, age-related maculopathy, having smoked for greater than 30 years, and an interaction between ocular ultraviolet B exposure and vitamin E were all risk factors for nuclear cataract. The rate of posterior subcapsular cataract excluding previous cataract surgery was 4.08% (95% confidence limits, 3.01%, 5.14%), whereas the overall rate of posterior subcapsular cataract including previous cataract surgery was 4.93% (95% confidence limits, 3.68%, 6.17%) . The independent risk factors for posterior subcapsular cataract in the urban and rural cohorts that remained were age in years, rural location, use of thiazide diuretics, vitamin E intake, and myopia.

CONCLUSIONS

The expected increase in the prevalence of cataract with the aging of the population highlights the need to plan appropriate medical services and public health interventions for primary and secondary prevention. Many of the identified risk factors for cataract in the population have the potential for being modified through public health interventions.

Reproducibility of the Wisconsin cataract grading system in the Blue Mountains Eye Study

PROBLEM

To measure the inter- and intra-grader reliability of the Wisconsin cataract grading system for grading of nuclear, cortical, and posterior subcapsular cataract (PSC) in the Blue Mountains Eye Study.

METHODS

Random samples of lens photographs from study subjects were regraded by each grader according to the Wisconsin cataract grading system. The results were compared using quadratic weighted kappa statistics to derive measures of inter- and intra-grader reliability for the grading of nuclear (5 grades), PSC (3 grades), and cortical cataract (3 grades).

RESULTS

Inter-grader reliability (quadratic weighted kappa) for grading of nuclear cataract varied between 0.82 and 0.79; kappa was 0.78 for cortical cataract and 0.57 for PSC. Intra-grader reliability was slightly higher than inter-grader reliability for all three cataract types.

CONCLUSION

In the Blue Mountains Eye Study, the Wisconsin cataract grading system provided good reproducibility, comparable to that reported from the Beaver Dam Eye Study, endorsing its usefulness in cataract epidemiology.

Effects of estrogen use on lens transmittance in postmenopausal women

OBJECTIVE

Lens autofluorescence originates from an accumulation of fluorescent substances that are associated with the process of cataractogenesis and lens aging. The aim of this study was to determine whether postmenopausal estrogen use reduces age-related nuclear sclerosis in women.

DESIGN

The authors designed a case-controlled study.

PARTICIPANTS

Nineteen postmenopausal women reporting estrogen use for more than 4 years (group 1), 20 postmenopausal women reporting no estrogen use (group 2), and 23 age-matched men (group 3) were studied.

INTERVENTION

The authors performed fluorophotometry.

MAIN OUTCOME MEASURES

Corneal and lens autofluorescence and lens transmittance were measured.

RESULTS

Lens transmittance values were 0.905 +/- 0.03, 0.839 +/- 0.08, and 0.841 +/- 0.08 in the three groups, respectively. There was a statistically significant difference between group 1 and the other two groups (P < 0.01).

CONCLUSIONS

These data are suggestive of a protective effect of estrogen use on the lenses of postmenopausal women.

Prevalence of cataract in Australia: the Blue Mountains eye study

PURPOSE

The authors determined the age and gender-specific prevalence of nuclear, cortical, and posterior subcapsular cataract (PSC) in a representative sample of older Australians.

METHODS

As part of a population-based study of eye disease in the Blue Mountains, west of Sydney, 3654 people aged 49 to 96 years underwent a detailed eye examination, including lens photography (slit-lamp and retroillumination). The photographs were assessed by masked graders using the Wisconsin Cataract Grading System, with acceptable reproducibility.

RESULTS

Past cataract surgery had been performed in either eye of 6.0% and in both eyes of 2.9% of participants in this study, equally in men and women. Moderate or advanced nuclear opacities were present in 53.3% of women and 49.7% of men. Moderate cortical cataract was present in 25.9% of women and 21.1% of men. Posterior subcapsular cataract was less frequent, found in 6.2% of women and 6.5% of men. After adjusting for age, these gender differences were statistically significant only for cortical cataract. The age-specific prevalence rates found for early and late cataract or for past cataract surgery are very similar to rates reported in the Beaver Dam Eye Study (BDES), Wisconsin, using the same definitions. Comparison of age-specific rates for each cataract type indicated lower rates for nuclear cataract, slightly lower rates for PSC and slightly higher rates for cortical cataract compared with the BDES. However, the rates for nuclear cataract were the only statistically significant differences between the two studies. Previously described susceptibility of the lower nasal lens to cortical cataract was confirmed, supporting a potential role of sunlight exposure in its development.

CONCLUSIONS

The Wisconsin cataract grading system was used in an older Australian population with acceptable reproducibility. The Blue Mountains Eye Study found similar age-specific prevalence rates for most of the types and stages of cataract compared with the BDES.

The epidemiology of cataract: a review of the literature

Cataract is a major cause of blindness, accounting for nearly half of all blindness worldwide. Epidemiological research provides the principles and methods to assess the extent of cataract, and supplies the necessary information for policy planning. Obtaining accurate epidemiological data on cataract is essential to ascertain and estimate the cost of primary and secondary eye health care needs. Determining risk factors is also necessary to reduce the economic and social repercussions associated with the disease. The following paper presents a review of the epidemiology of cataract in the middle to elderly age group.

Distribution of cataract types in the Italian-American case-control study and at surgery in the Parma area

PURPOSE

To compare the distribution of cataract types at surgery with the distribution detected in an ophthalmology clinic-based case-control study in the same geographic area (Parma, Italy).

METHODS

The distribution of cataract type assessed according to the Lens Opacities Classification System I in 284 consecutive patients 45 years of age or older, who were admitted for cataract surgery to the Institute of Ophthalmology in Parma during 1994, was compared with the distribution assessed in 1008 participants in the Italian-American case-control study of age-related cataract in the Parma metropolitan area from 1987 to 1989.

RESULTS

Analysis of cataract distribution indicates in the surgical group, compared with the case-control population, a significant increase of nuclear (N) and posterior subcapsular (PSC) opacities (any), a reduction of pure forms of cortical and N cataracts, and a marked increase of mixed types of opacities with a simultaneous N and PSC component.

CONCLUSION

Although cortical opacities are probably the most prevalent type of age-related lens change in the general population of Parma metropolitan area, the type of cataract most frequently responsible for the decision of patients to undergo cataract surgery is a mixed type of opacity with an N-PSC component.

Measurement error in assessing the size of cortical cataracts from retroillumination photographs

This study describes a new method of quantifying anteriorly located cortical cataracts using retroillumination photographs and computer planimetry. Cortical cataracts were graded clinically and then photographed using the Neitz retroillumination camera twice by each of 2 photographers. The cataract outlines were traced onto a transparent overlay, and computer planimetry was performed using a Scan Maker 600ZS, a MAC II Computer and specially developed software. We estimated the measurement error of the method and its associated effect on sample size estimates for clinical studies. We calculated that the variability in this technique would contribute about 21 additional subjects to overall sample size estimates in studies comparing the mean areas of cortical opacities. In many studies this would be a small addition to total sample size requirements. This technique provides clinically useful measurements of the size of a cortical opacity as seen on a retroillumination photograph. This may be useful for future clinical studies on natural progression of cortical cataracts as well as for clinical trials of anticataract drugs.

Prevalence and risk factors of lens opacities in the elderly in Finland. A population-based study

PURPOSE

The distribution and prevalence of lens opacities and visual impairment caused by cataract were studied in an epidemiologic cross-sectional population study of inhabitants 70 years of age or older in three communities in Oulu County, Finland.

METHODS

Of the 560 eligible subjects, 500 (89.3%) were examined. The best-corrected visual acuity for distance in both eyes was determined. The diagnosis of lens opacities was based on clinical biomicroscopy. The findings were compared with standardized photographs of the Lens Opacities Classification System II.

RESULTS

One hundred sixty-five (33.0%) persons in the study population had a clear lens in both eyes. Cataract, aphakia, or pseudophakia was recorded in one or both of the eyes in 64.4% (322 persons) of the participants. The prevalence increased with age from 44.6% of persons (n = 88) in the 70- to 74-year-old age group to 97.6% of persons (n = 41) in the 85- to 89-year-old age group. A total of 56.4% of persons had cataract, aphakia, or pseudophakia in both eyes. Nuclear, cortical, and posterior subcapsular opacities were detected in 38.5%, 37.6%, and 27.7% of the participants, respectively. Exfoliation was present in one or both eyes in 22.1% of the participants. There was no difference in the prevalence of cataract between the sexes when age was considered. Visual impairment to 20/50 or worse was at least partly due to cataract in 23.8% of the right eyes and 22.4% of the left eyes. Significant risk factors for cataract were age and the presence of exfoliation in men and age, occupational exposure to sunlight, and current cigarette smoking in women.

CONCLUSIONS

Almost two thirds of the population 70 years of age or older had lens opacities, and in 23.1% of the eyes visual impairment to 20/50 or worse was at least partly due to cataract. Including the patients who had undergone surgery, 30.3% of all the eyes of persons 70 years of age or older can be considered for cataract surgery.

Incidence and progression of cortical, nuclear, and posterior subcapsular cataracts. The Italian-American Cataract Study Group

A total of 1,399 persons, between 45 and 79 years of age, who had been identified in a clinic-based case-control study were invited to participate in a follow-up study. The follow-up study was designed to estimate the incidence and progression of cortical, nuclear, and posterior subcapsular cataracts and to evaluate the usefulness of the Lens Opacities Classification System II in a longitudinal study. Survival analyses were performed on 1,193 persons with at least three visits, by using data obtained from Zeiss slit-lamp and Neitz retroillumination lens photographs. The three-year cumulative incidence for persons age 65 to 74 years (the largest age group) was 18%, 6%, and 6% for cortical, nuclear, and posterior subcapsular cataracts, respectively. Progression was much higher than incidence for each type of opacity. Regression, which probably comes mostly from misclassification in the gradings, was modest for cortical and nuclear cataracts but was sizeable for posterior subcapsular cataracts. Patient age, baseline lens status, cataract grading system, definition of change, and analytic methodology can have important effects on estimates of cataract incidence and progression.

Genetic etiology of nuclear cataract: evidence for a major gene

Sibling correlations and segregation analysis were used to examine the familial distribution of age-sex-adjusted measures of nuclear sclerosis in 1,247 individuals from 564 sibships in the Beaver Dam Eye Study. There are highly significant sibling correlations for all sibs, and separately for sister-sister, sister-brother, and brother-brother pairs. Two transformed normal distributions give the best fit to the data. The hypothesis of mendelian transmission of a major effect cannot be rejected, but the hypothesis of a random environmental major effect is rejected. The parameters of the tau AB free model showed close similarity to the values expected under a mendelian hypothesis. Our results suggest that a single major gene can account for 35% of the total variability of age-sex-adjusted measures of nuclear sclerosis.