Prevalence of lenticular abnormalities in a population-based study: Oxford Clinical Cataract Grading in the Melton Eye Study

Analyzing Effect of Waterclefts on Visual Functions Via Optical Simulations

Purpose

To investigate the impact of the size and location of waterclefts (WC), which are one of several cataract subtypes, on visual function by optical simulation analysis.

Methods

An optical simulation software (CODE V) was used to develop a schematic eye model and several sizes of WC central and peripheral types that were located below the anterior and posterior subcapsules of the crystalline lens, and analyses of refraction, higher-order aberrations (HOA), and the modulation transfer function (MTF) were performed.

Results

An increase in the WC size increased the refraction and HOA and decreased the MTF. The impact of the WC below the posterior subcapsule on the visual function was more enhanced than that below the anterior subcapsule. Large WC demonstrated a remarkable hyperopic shift in refractive power as well as an increase in HOA. The MTF decreased slightly with increasing WC size at a spatial frequency of 20 cycles/mm, and it decreased remarkably at 60 cycles/mm.

Conclusions

The impact on the visual function increased with increasing WC size. It was revealed that eyes with WC below the posterior subcapsule are more hyperopic than those with WC below the anterior subcapsule, and the former have a higher HOA and lower MTF than the latter.

Degradation of connexin 50 protein causes waterclefts in human lens

Cataracts are mainly classified into three types: cortical cataracts, nuclear cataracts, and posterior subcapsular cataracts. In addition, retrodots and waterclefts are cataract subtypes that cause decreased visual function. To maintain an orderly and tightly packed arrangement to minimize light scattering, adhesion molecules such as connexins and aquaporin 0 (AQP0) are highly expressed in the lens. We hypothesized that some main and/or subcataract type(s) are correlated with adhesion molecule degradation. Lens samples were collected from cataract patients during cataract surgery, and mRNA and protein expression levels were measured by real-time RT-PCR and western blotting, respectively. The mRNA levels of adhesion molecules were not significantly different among any cataract types. Moreover, AQP0 and connexin 46 protein expressions were unchanged among patients. However, connexin 50 protein level was significantly decreased in the lens of patients with WC cataract subtype. P62 and LC3B proteins were detected in the WC patients' lenses, but not in other patients' lenses. These results suggest that more research is needed on the subtypes of cataracts besides the three major types of cataract for tailor-made cataract therapy.

Association between ultraviolet radiation exposure dose and cataract in Han people living in China and Taiwan: A cross-sectional study

Purpose

We investigated associations between ocular ultraviolet (UV) radiation exposure dose and cataract opacities among Han people living in China and Taiwan, to assess the effects of UV exposure intensity.

Methods

This cross-sectional study included Han people aged ≥40 years (1,801 individuals, 450 in Sanya, 636 in Taiyuan, and 715 in Taichung) as subjects who completed a questionnaire including items about diabetes, smoking, steroid use, work history, and time spent outdoors, and underwent an ophthalmic examination. Right eye axial length was measured using A-mode ultrasonography or IOLMaster. Slit-lamp imaging under maximum mydriasis was used to classify cataracts into three major types [cortical (COR), nuclear (NUC), and posterior subcapsular cataracts (PSC)] and two subtypes [retrodots (RD) and waterclefts (WC)] by one ophthalmologist. COR was divided into opacity presence (CEN+) or absence (CEN-) in the central 3-mm diameter area of the pupil. COR was also subdivided into three groups according to opacity shape: axle-shaped opacity concomitant with WC, wedge-shaped opacity around the pupil to the eye center, and ring-shaped opacity in the lens equator along the pupillary margin. The cumulative ocular UV exposure (COUV) was calculated. A logistic regression analysis was used for multivariate analysis.

Results

Cataract odds ratios in high COUV eyes were 5.35 for NUC, 1.87 for PSC, and 1.35 for RD. In eyes with WC, risk of COR ring-shaped opacity significantly increased but that of wedge-shaped opacity (CEN+) significantly decreased. In eyes without WC, risk of COR axle-shaped opacity (CEN–) and ring-shaped opacity significantly increased but that of wedge-shaped opacity (CEN+) significantly decreased.

Conclusions

Increased COUV level among Han people may be a risk factor for the development of nuclear cataracts, PSC, retrodots and ring-shaped cortical cataract. Risk of ocular UV exposure for cortical cataract may differ by opacity shape.

Lens retrodots and vacuoles and their associations with the prevalence and incidence of age-related cataract

AIM

To assess the prevalence of retrodots and vacuoles and their associations with the prevalence and long-term incidence of age-related cataract in an older Australian cohort.

METHODS

Of 3654 baseline participants of the Blue Mountains Eye Study aged 49+ years (1992-1994), 2335 and 1952 were re-examined after 5 and 10 years, respectively. Lens photographs were graded for cataract, retrodots, and vacuoles. Eye-specific data were used to assess the associations between retrodots or vacuoles at baseline and the prevalence and 10-year incidence of nuclear, cortical, and posterior subcapsular (PSC) cataract and cataract surgery.

RESULTS

At baseline, retrodots were present in 142 persons (4%) and vacuoles in 1333 persons (40%). Prevalence of both lens features increased with increasing age (P for trend <0.0001). After adjusting for age and gender, vacuoles were associated with prevalent PSC cataract at baseline (odds ratio (OR), 1.60, 95% confidence interval (CI), 1.25-2.05). After adjusting for age, gender, smoking, hypertension, diabetes, education, and use of inhaled/oral steroids, baseline retrodots were associated with an increased incidence of cataract surgery (OR 2.90, 95% CI 1.71-4.91), while 3+ vacuoles at baseline were associated with an increased risk of PSC cataract (OR 3.56, 95% CI 2.13-5.95) and cataract surgery (OR 1.84, 95% CI 1.22-2.77).

DISCUSSION

Lens retrodots and vacuoles were found to be positively associated with 10-year incidence of cataract surgery, and vacuoles associated with PSC cataract, a finding suggestive of shared risk factors or pathogenesis between these two lens features and the development of PSC cataract.

The lens as a model for fibrotic disease

Fibrosis affects multiple organs and is associated with hyperproliferation, cell transdifferentiation, matrix modification and contraction. It is therefore essential to discover the key drivers of fibrotic events, which in turn will facilitate the development of appropriate therapeutic strategies. The lens is an elegant experimental model to study the processes that give rise to fibrosis. The molecular and cellular organization of the lens is well defined and consequently modifications associated with fibrosis can be clearly assessed. Moreover, the avascular and non-innervated properties of the lens allow effective in vitro studies to be employed that complement in vivo systems and relate to clinical data. Using the lens as a model for fibrosis has direct relevance to millions affected by lens disorders, but also serves as a valuable experimental tool to understand fibrosis per se.

Higher-order ocular aberrations caused by crystalline lens waterclefts

PURPOSE

To compare visual acuity and ocular higher-order aberrations (HOAs) in eyes with waterclefts, a type of crystalline lens opacity, and in normal eyes.

SETTING

Department of Ophthalmology, Kanazawa Medical University, Ishikawa, Japan, and Faculty of Medicine, University of Iceland, Reykjavik, Iceland.

METHODS

In this nested case-control study of subjects attending the third examination of the Reykjavik Eye Study in 2008, eyes with pure waterclefts and control eyes with no lenticular opacity were evaluated. All candidates had complete ophthalmic examinations and wavefront analysis. Higher-order aberrations in the watercleft group and the control group were compared.

RESULTS

The watercleft group comprised 30 eyes and the control group, 194 eyes. The mean corrected distance visual acuity (CDVA) in the watercleft group was statistically significantly lower than in the control group (P<.01). There was a significant relationship between CDVA and HOA in both groups. Total HOA and trefoil and coma aberrations were statistically significantly higher in the watercleft group than in the control group (P<.05).

CONCLUSIONS

Waterclefts significantly affected CDVA. Eyes with waterclefts had higher coma and trefoil aberrations, suggesting that the increased HOAs caused reduced visual acuity in eyes with waterclefts.

Risk factors for cataract subtypes waterclefts and retrodots: two case–control studies

Waterclefts and retrodots are independently associated with visual impairment, yet a review identified no data on risk factors.

PURPOSE

To investigate risk factors for these two human lens cataract subtypes.

METHOD

Two nested case-control studies: The host study comprised 1078 subjects (55 years) attending the Somerset and Avon Eye Study (SAES). In total, 197 watercleft cases (Oxford grade 0.2 in either eye) and 199 retrodot cases (Oxford grade 1.0 in either eye) were individually age/gender matched to controls. Detailed ophthalmic and potential risk factor data were collected, including body mass index (BMI), smoking, alcohol, diabetes, hypertension, analgesics, vitamin supplementation, nutrition, sunlight exposure, dehydration, hormonal (women), blood lipids, glucose, urea, creatinine, uric acid, and vitamin levels.

RESULTS

For waterclefts, univariable analysis identified BMI, alcohol intake, vitamin status, sunlight, urea, creatinine, and uric acid as possible risk factors. Multivariable analysis identified two independent associations. Total number of 'any' analgesics in the previous year: adjusted P<0.01 (U-shaped risk profile, unadjusted high vs medium use (=reference) OR 2.39, 95% CI 1.35-4.26 with medium use vs none (=reference) OR 0.43, 95% CI 0.26-0.72); total sunlight: adjusted P=0.03 (unadjusted highest exposure vs lowest (=reference) OR 3.25, 95% CI 1.11-9.50). For retrodots, univariable analysis identified alcohol, HRT, and lipids. Multivariable analysis identified two independent associations. Mean number of alcohol units consumed per month, adjusted P=0.02 and HDL cholesterol levels, adjusted P=0.02 (unadjusted ORs NS both).

CONCLUSION

This is the first available published information on risk factors for the human cataractous lens features waterclefts and retrodots.

Transforming growth factor-beta-induced epithelial-mesenchymal transition in the lens: a model for cataract formation

The vertebrate lens has a distinct polarity and structure that are regulated by growth factors resident in the ocular media. Fibroblast growth factors, in concert with other growth factors, are key regulators of lens fiber cell differentiation. While members of the transforming growth factor (TGFbeta) superfamily have also been implicated to play a role in lens fiber differentiation, inappropriate TGFbeta signaling in the anterior lens epithelial cells results in an epithelial-mesenchymal transition (EMT) that bears morphological and molecular resemblance to forms of human cataract, including anterior subcapsular (ASC) and posterior capsule opacification (PCO; also known as secondary cataract or after-cataract), which occurs after cataract surgery. Numerous in vitro and in vivo studies indicate that this TGFbeta-induced EMT is part of a wound healing response in lens epithelial cells and is characterized by induced expression of numerous extracellular matrix proteins (laminin, collagens I, III, tenascin, fibronectin, proteoglycans), intermediate filaments (desmin, alpha-smooth muscle actin) and various integrins (alpha2, alpha5, alpha7B), as well as the loss of epithelial genes [Pax6, Cx43, CP49, alpha-crystallin, E-cadherin, zonula occludens-1 protein (ZO-1)]. The signaling pathways involved in initiating the EMT seem to primarily involve the Smad-dependent pathway, whereby TGFbeta binding to specific high affinity cell surface receptors activates the receptor-Smad/Smad4 complex. Recent studies implicate other factors [such as fibroblast growth factor (FGFs), hepatocyte growth factor, integrins], present in the lens and ocular environment, in the pathogenesis of ASC and PCO. For example, FGF signaling can augment many of the effects of TGFbeta, and integrin signaling, possibly via ILK, appears to mediate some of the morphological features of EMT initiated by TGFbeta. Increasing attention is now being directed at the network of signaling pathways that effect the EMT in lens epithelial cells, with the aim of identifying potential therapeutic targets to inhibit cataract, particularly PCO, which remains a significant clinical problem in ophthalmology.

Cataract formation and prevention

Cataract, a leading cause of blindness worldwide, is a multifactorial eye disease. In developing countries the incidence of cataract among young generations is not uncommon due to malnutrition, excess exposure to ultraviolet radiation and so on. In developed countries, age-related cataract affecting the population over 65 years of age is a major concern. Oxidative stress was suggested to inflict damage to the lens and induce opacification, and a variety of antioxidant nutrients were tested for the prevention or delay of cataract development. Although promising results were obtained in animal studies of various antioxidants, epidemiological studies on human populations do not seem to support their protective effects unequivocally. It is unlikely that age-related cataract in man, similar to the ageing process itself, will be prevented or delayed by therapeutic drugs in the foreseeable future. At present, keeping a health-conscious life style (i.e., no smoking) may be the most effective and least expensive strategy to prevent the onset of age-related cataract.

Epithelial transdifferentiation and cataract in the human lens

Anterior subcapsular cataracts cause a serious loss of vision and are normally associated with ocular trauma, inflammation or clinical skin conditions. They appear to be accompanied by epithelial cell growth and transdifferentiation where unscheduled production of a number of proteins, including alpha smooth muscle actin (alpha-sma), occurs. Clinical studies have also revealed an up-regulation of the TGFbeta signalling pathway in such cataracts. The present study, using phase contrast and immunofluorescent techniques, was undertaken to investigate the extent of alpha-sma expression in traumatic cataracts, in capsulorhexis specimens obtained during cataract surgery and in aged human lenses from donor eyes. The donor lenses were also exposed to trauma or TGFbeta in culture to observe their relative contribution to alpha-sma production. Dense anterior subcapsular cataracts were relatively rare (<1%), but all showed a pronounced up-regulation of alpha-sma, which was located both in anterior cells of normal appearance and in nucleated fibroblastic cells lying beneath the anterior epithelium. Surprisingly, more than 50% of capsulorhexis specimens from mature cataracts showed expression of alpha-sma, although to a limited extent. Alpha-sma was not expressed in any of the clear donor lenses and culture for 8 days in EMEM did not induce expression. Interestingly, unlike their young animal counterparts, human lenses failed to show the presence of alpha-sma when exposed to 10 ng ml(-1) TGFbeta. However, after culture, lenses with pre-existing cortical opacities did express alpha-sma, as did clear lenses subjected to injury or trauma. It appears that the greater the stress, the greater is the expression of alpha-sma. Cataract, and especially cortical cataract, should therefore be seen as associated with stress-induced signalling pathways in the lens that lead to the transdifferentiation of the anterior epithelial cells.

Prevalence of cataract in the Speedwell Cardiovascular Study: a cross-sectional survey of men aged 65-83

AIMS

To ascertain the prevalence of cataract in a representative group of men who have been followed since 1979 for cardiovascular disease.

METHODS

Of 2348 men aged 45-63 recruited in 1979 to the Speedwell Cardiovascular Study, 1420 were alive and willing to take part in further studies in 1997. They were sent a questionnaire about their eye health and invited to an ophthalmological examination at Bristol Eye Hospital. Cataract was graded using the Lens Opacities Classification System III (LOCS III) method.

RESULTS

Of the 1420 men, 26 died before they could be examined. Out of the remaining 1394 men, 949 presented for examination and full information was available for 936. Some information about eye health was obtainable for 394 men and 51 were not contactable. The prevalence of cataract increased with age and 36 men (3.8%) had had previous cataract surgery in either or both eyes. Of the remaining 903 men with no previous history of cataract surgery, cortical cataract was present in the right eye of 75 men (8.3%), nuclear (opalescence) in 128 (14.2%) and posterior subcapsular in 15 (1.7%). Five men (0.6%) had visual acuity of 6/60 or worse attributable to cataract in the right eye and 232 (25%) had visual acuity in one or both eyes of 6/24 or less at least partially attributable to cataract. There was no association between social class and the presence of cataract.

CONCLUSIONS

The prevalence of cataract in a representative cohort of men followed since 1979 for cardiovascular disease was comparable to that previously reported in the UK and is consistent with studies from around the world. It appears that substantial amounts of visual loss, attributable to cataract, are present in men. Further studies establishing the reasons for this should be undertaken.

The population requirement for cataract extraction: a cross-sectional study

PURPOSE

To examine the distribution in the population of indications for cataract extraction in order to relate demand for this procedure to the capacity for satisfying it.

METHODS

An age-stratified random population sample of 2783 individuals aged 55 years and over was taken from inner-city, urban and rural areas of Avon and Somerset. The requirement for cataract extraction was estimated on the basis of measures of vision-related quality of life, refracted visual acuity, and application of the Oxford Clinical Cataract Classification and Grading System. Data were also collected concerning suitability for surgery, including relative contraindications to surgery and whether participants considered their eyesight bad enough to merit surgery. Three sets of composite indications were defined.

RESULTS

Estimated prevalent requirements for cataract extraction for the three sets of composite criteria were: 29 per 1000 aged over 55 years (95% CI 20-41) for the most inclusive criterion; 17 per thousand (95% CI 10-27) for the intermediate criterion; and 7 per thousand (95% CI 3-14) for the most stringent criterion. These rates are equivalent to a national prevalent requirement for England of 384,000 for the most inclusive criterion. If the approximately 15% of individuals whose desire or fitness for surgery was questionable are removed from this estimate, the prevalent requirement, including the backlog from previous unsatisfied demand, becomes 325,000 individuals.

CONCLUSIONS

The findings suggest only a modest imbalance between supply and demand for cataract surgery. In particular there was a very small prevalence of untreated severe cataract, less than the annual health service surgical capacity, suggesting that the current National Health Service surgical capacity is adequate for cases of severe cataract.

The assessment of lens opacities in clinical practice: results of a national survey

AIM

To investigate the examination of lens opacities in routine ophthalmic clinical practice.

METHOD

A questionnaire survey was mailed to 703 consultant ophthalmologists in the UK. The surgeons were asked which lens feature(s) they assessed in their clinics when deciding whether to offer cataract surgery.

RESULTS

489 replies were received. A broad range of lens opacities was assessed, with differences between surgeons for some opacities with high prevalences in the population, particularly cortical opacities. Many (74% of 467) surgeons assessed one or more lens opacities (anterior subcapsular cataract, vacuoles, water clefts, coronary flakes, focal dots, retrodots, fibre folds) which may be visually important but which have received relatively little attention by researchers.

CONCLUSIONS

Some classes of lens opacity which are traditionally measured by researchers may be ignored in clinical practice and opacities which are traditionally ignored by some researchers are regarded as clinically important by a substantial number of surgeons.

Associations between lens features assessed in the Oxford Clinical Cataract Classification and Grading System

PURPOSE

To study the associations between eleven lens features graded according to the Oxford Clinical Cataract Classification and Grading System (OCCCGS).

METHOD

560 subjects taking part in the Melton Eye Study had their lenses graded according to the OCCCGS by one of two examiners. Associations between features were examined using log-linear models for categorised grades. Adjustment was made for age, sex and grader.

RESULTS

Within subjects, the two nuclear features, white nuclear scatter and brunescence, are closely related with one another, as are coronary flakes and focal-dots, but these two groupings are negatively associated. Cortical spoke, fibrefolds and waterclefts are all associated with one another and this group is positively associated with coronary flakes and focal-dots. Posterior subcapsular and anterior subcapsular opacity are associated with one another and with cortical spokes. A within-eye analysis gives similar results.

CONCLUSION

These associations may be important in defining cataract subtypes and in identifying minor features that indicate early cataract development.