Preliminary evaluation of a simple photographic cataract classification for epidemiological surveys

A preliminary evaluation of the agreement between clinical and photographic cataract classification and its reproducibility by utilizing a very simple classification system is presented. Photographic classification was based on color Zeiss 75-SL transparencies. Results indicate that photo-derived cataract classification based on slitlamp photographs has good validity for nuclear opacities but tends to underestimate posterior subcapsular cataracts.

Associations Between Plasma Levels of Vitamins and Cataract in the Italian-American Clinical Trial of Nutritional Supplements and Age-Related Cataract (CTNS): CTNS Report #2

PURPOSE

To investigate the association at baseline between plasma levels of selected vitamins and the presence and type of cataract in the participants in The Italian-American Trial of Nutritional Supplements and Age-related Cataract.

METHODS

At baseline, the participants (1020, 710 with "early cataract" and 310 with "no cataract," 55-75 years of age) received an ocular examination, photographic lens grading, and measurement of plasma levels of vitamins A, C, E, beta-carotene, and of red blood cell glutathione reductase activity.

RESULTS

In multiple logistic models adjusted for potential confounders, high vitamin C levels were associated with a protective effect on nuclear (N) [OR: 0.54; 95% CI: 0.30, 0.97] and posterior subcapsular (PSC) cataract (OR: 0.37; 95% CI: 0.15, 0.93). High vitamin E levels were associated with increased prevalence of cortical cataract (C) (OR: 1.99; 95% CI: 1.02-3.90), PSC (OR: 3.27; 95% CI: 1.34, 7.96) and of any cataract (OR: 1.86; 95% CI: 1.08, 3.18).

CONCLUSIONS

In agreement with some earlier studies, we found higher plasma levels of vitamin C to be associated with reduced prevalence of N and PSC cataracts. The finding of an increased prevalence of some types of cataract with higher levels of vitamin E was unexpected, has not been previously reported, and could be due to unadjusted confounding.

Transcriptional up-regulation of the protooncogenes c-fos and c-jun following vitreous removal and short-term in vitro culture of bovine lenses

Chemical (mainly oxidative) and mechanical (anterior capsule injury) stresses have been reported to up-regulate the expression of the protooncogenes c-fos and c-jun in the lens. Another potentially stressful, yet largely unexplored condition, inherent to all experiments requiring the in vitro culturing of isolated lenses, is vitreous removal. Based on the results of an extensive RNA gel blot analysis conducted on epithelial/capsule preparations isolated from calf lenses dissected and cultured under different conditions, we show, here, that lens isolation and short-term culture (1-2.5 hr, without any significant GSH depletion) result in a strong and time-dependent up-regulation of the c-jun and c-fos mRNAs. This response, which relies on transcriptional protooncogene activation and is more intense for c-fos than for c-jun, is in part prevented by the preservation of the lens-vitreous contact, but not by the culture of vitreous-stripped lenses on a vitreous bed. Supplementation of the culture medium with the antioxidant N -acetyl-cysteine slightly reduced the c-jun, but not the c-fos response. Protooncogene up-regulation thus appears to be mainly determined by the disruption of critical lens-vitreous interactions. Since this response takes place in the epithelial cells, these data also point to the existence of a communication mechanism whereby a posteriorly applied mechanical stress is transmitted to, and perceived by, the anterior lens surface.

Retroillumination versus reflected-light images in the photographic assessment of posterior capsule opacification

PURPOSE

To investigate the relative merit of retroillumination and of reflected light slit-lamp-derived photographs in the assessment of the opacification of the posterior lens capsule.

METHODS

Retroillumination and slit-lamp-derived reflected-light photographs were taken on 23 consecutive eyes with posterior capsule opacification (PCO) in uncomplicated pseudophakia. Subjective grading was performed on both types of photographs to evaluate the extent and density of posterior capsular opacification. Best-corrected visual acuity (BCVA) before and after YAG laser capsulotomy was used to assess the impact of capsular opacification on visual function.

RESULTS

After capsulotomy all patients attained a BCVA > or = 46 letters (> or =20/32) with a mean increase of 25 letters, indicating that PCO was the cause of visual impairment in these patients. The relative capacity of retroillumination and of reflected-light photographs to adequately capture the extent and the severity of posterior capsule opacification varied considerably. Reflected-light images, in addition to frequently producing higher severity scores for the opacity than retroillumination photographs, in 4 of 23 eyes (17.4%) proved to be the only technique able to document the presence of PCO.

CONCLUSIONS

Our results indicate that, with respect to retroillumination images, reflected-light photography has an increased ability to adequately capture the presence and the severity of PCO and that the use of only retroillumination images may lead to its underestimation. This may be relevant to clinical studies aiming to evaluate incidence and progression of this condition.

The ageing lens

The human lens grows by a process of epithelial cell division at its equator and the formation of generations of differentiated fibre cells. Despite the process of continuous remodelling necessary to achieve growth within a closed system, the lens can retain a high level of light transmission throughout the lifetime of the individual, with the ability to form sharp images on the retina. Continuous growth of the lens solves the problem imposed by terminal differentiation within a closed, avascular system, from which cells cannot be shed. The lens fibre tips arch over the equator to meet anteriorly and posteriorly and form branching sutures of increasing complexity. The stages of branching may create the optical zones of discontinuity seen on biomicroscopy. The lens is exposed to the cumulative effects of radiation, oxidation and postranslational modification. These later proteins and other lens molecules in such a way as to impair membrane functions and perturb protein (particularly crystallin) organisation, so that light transmission and image formation may be compromised. Damage is minimised by the presence of powerful scavenger and chaperone molecules. Progressive insolublisation of the crystallins of the lens nucleus in the first five decades of life, and the formation of higher molecular weight aggregates, may account for the decreased deformability of the lens nucleus which characterises presbyopia. Additional factors include: the progressive increase in lens mass with age, changes in the point of insertion of the lens zonules, and a shortening of the radius of curvature of the anterior surface of the lens. Also with age, there is a fall in light transmission by the lens, associated with increased light scatter, increased spectral absorption, particularly at the blue end of the spectrum, and increased lens fluorescence. A major factor responsible for the increased yellowing of the lens is the accumulation of a novel fluorogen, glutathione-3-hydroxy kynurenine glycoside, which makes a major contribution to the increasing fluorescence of the lens nucleus which occurs with age. Since this compound may also cross-link with the lens crystallins, it may contribute to the formation of high-molecular-weight aggregates and the increases in light scattering which occur with age. Focal changes of microscopic size are observed in apparently transparent, aged lenses and may be regarded as precursors of cortical cataract formation.

Oxidative stress and age-related cataract

The authors review the available evidence supporting the possible role of oxidative stress in cataract formation from an epidemiological and a clinical point of view. They discuss in more detail what is presently known about the molecular mechanisms of response of the mammalian lens to an oxidative insult and report unpublished data on gene modulation upon oxidative stress in a bovine lens model. Main research endeavors that seem to be a most promising source of new insights into the problem of age-related cataract formation are briefly discussed.

Molecular basis of open-angle glaucoma in Italy

Glaucoma is a group of ocular diseases characterized by an optic neuropathy in which degeneration of retinal ganglion cells leads to a characteristic excavation of the optic nerve head. Primary open-angle glaucoma (POAG) can be subdivided into two groups according to age of onset:- 1. the more common middle- to late-age onset, chronic open-angle glaucoma (COAG) diagnosed after the age of 40 years; 2. the rarer juvenile open-angle glaucoma (JOAG), which is diagnosed between the age of 3 years and early adulthood. Recently, the gene coding for the trabecular meshwork-induced glucocorticoid response protein (TIGR), located in chromosome 1 (1q23-25), was found mutated in patients affected by POAG. In this work we describe the clinical and molecular genetic features of several Italian families affected by autosomal dominant POAG, collected in various regions of Italy.

Influence of cataract surgery on progression of lens opacities in the fellow eye

OBJECTIVE

To evaluate whether, in the Italian-American natural history study, cataract surgery in one eye influences the incidence/progression rate of lens opacities in the fellow eye.

DESIGN

Follow-up study of age-related cataract.

PARTICIPANTS

A total of 1399 participants with age-related cataracts were regularly followed for 5 years and cataract status evaluated by the Lens Opacities Classification System II on slit-lamp and retroillumination lens photographs. A total of 228 participants had cataract surgery in 1 eye during the study period, and 192 had sufficient follow-up visits to be included in the analysis.

MAIN OUTCOME MEASURE

The incidence/progression of cataract was defined as two or more consecutive visits with a severity grade greater than the baseline grade.

RESULTS

When entered into a Cox model, incidence/progression of specific cataract types was not associated with cataract surgery on the fellow eye and was not significantly different from that observed in participants who had no cataract surgery.

CONCLUSIONS

Cataract extraction does not influence incidence/progression rate of specific lens opacities in the fellow eye.

Self-assessment of the quality of vision: association of questionnaire score with objective clinical tests

PURPOSE

To investigate the association of a quality of life-visual function questionnaire with an objective clinical test of visual function.

METHODS

We have developed a questionnaire to assess self-reported visual satisfaction in ophthalmic patients suffering from chronic eye conditions causing visual impairment. The questionnaire was administered to 120 patients suffering from age-related cataract, chronic open angle glaucoma, age-related macular degeneration, branch retinal vein occlusion, and presbyopia or minor refractive defects. All the participants also underwent determination of visual acuity, contrast sensitivity, glare, and visual field.

RESULTS

The questionnaire has a good reproducibility, a high internal consistency, and is able to discriminate between the different groups of patients. The total questionnaire score is significantly associated with the results of all visual function tests with the exception of glare. When entered into a multiple linear regression model, near visual acuity and contrast sensitivity are still considerably associated with the total questionnaire score. The psychological attitude of the patient towards his/her health problem is also associated with the total average score.

CONCLUSIONS

Overall, the model explains 49% of the variance in the average questionnaire score.

An independent evaluation of the Age-Related Eye Disease Study (AREDS) cataract grading system

PURPOSE

To assess intra- and interobserver reproducibility of the Age-Related Eye Disease Study (AREDS) system for grading lens opacities and to provide data on its capacity to reliably detect changes in lens status.

METHODS

Independent and replicate grading of 40 sets of lens photographs (one slit-lamp and two retroillumination photographs) were performed by three experienced observers. Patients were participants in the Collaborative Italian-American Clinical Trial of Nutritional Supplements which is testing the effect of a mineral-multivitamin supplement on age-related cataract (CTNS). Scatterplots and intraclass correlation were used to assess measurement error.

RESULTS

Analysis revealed good intra- and interobserver reproducibility of the system. Greatest intraobserver measurement error showed 100% of pairs within 10% areal difference for cortical cataract, 97.5% within 15% areal difference for posterior subcapsular cataract, and 100% within 1 density unit difference for nuclear opacity. Greatest interobserver measurement error showed 95% of pairs within 10% areal difference for cortical cataract, 97.5% within 15% areal difference for posterior subcapsular cataract, and 97.5% within 1.5 density unit difference for nuclear opacity.

CONCLUSIONS

The AREDS lens opacities grading system appears to be sufficiently reliable to detect changes of at least 10% areal involvement for cortical, 15% areal involvement for posterior subcapsular, and 1.0 units for nuclear opacities. It therefore seems sufficiently sensitive to adequately monitor progression of lens opacities in a longitudinal study of patients with early cataract. Its applicability in a population with advanced or complex mixed opacities must await further testing.

Vitreous fluorophotometry and changes in blood-retinal barrier permeability induced by bendazac lysine

Vitreous fluorophotometry was used to investigate the effect of Bendazac lysine on the blood retinal barrier in 12 insulin-dependent diabetics with mild background retinopathy. The study was a randomized, double blind, cross-over trial, drug versus Placebo. Each treatment period was of 4 months. The vitreous penetration coefficient was reduced by 21% (95% c.i. 12, 30; p = 0.001) by treatment with respect to Placebo.

Location and severity of cortical opacities in different regions of the lens in age-related cataract

PURPOSE

To examine the distribution of cortical opacities across the lens in the Italian-American Natural History Study of Age-Related Cataract and to study the association between an index of sunlight exposure and the location of cortical cataract within the lens.

METHODS

Lens photographs of one eye of 731 persons with cortical opacities (503 with pure and 228 with mixed types of opacity) were included in the analysis. A radial grid superimposed on the photographs was used to assess presence, location, and severity of wedge-shaped cortical opacities.

RESULTS

Both the prevalence and the extent of cortical opacities were highest in the inferior-nasal quadrant and lowest in the superior-nasal quadrant of the lens. In polychotomous logistic regression, persons with the greatest excess areal involvement in the inferior half of the lens were more likely to have high exposure to sunlight, as measured by a sunlight index, than persons with excess involvement in the superior half of the lens (odds ratio, 1.73; 95% confidence interval 1.03, 2.93). Excess areal involvement of the inferior lens also was associated with the pure type of cortical cataract and with the total extent of the opacity.

CONCLUSIONS

Age-related cortical opacities occur more frequently inferiorly than superiorly and, to a lesser extent, nasally than temporally. Possibly higher exposure of these lens segments to sunlight may explain this preferential location of cortical opacities.

Glutathione S-transferase M1 genotype and age-related cataracts. Lack of association in an Italian population

PURPOSE

To investigate possible associations between the gene number and allelic forms of glutathione S-transferase M1 (GSTM1) and the occurrence of nucleic and cortical age-related cataracts.

METHODS

Patients with cortical cataract, nuclear cataract, mixed and cortical cataract, and no cataract were sytematically selected from subjects evaluated in the Italian-American Study of the Natural History of Age-Related Cataract. The patients were typed for the A, B, and null alleles of GSTM1 using a variation of the amplification refractory mutation system.

RESULTS

Forty-nine percent of patients (50/102) with cortical cataracts, 45% (13/29) with nuclear cataracts, 51% (36/71) with mixed nuclear and cortical cataracts, and 50% of controls (49/98) were homozygous for the null GSTM1 allele. Twenty-five percent of patients (26/102) with cortical cataracts, 24% (7/29) with nuclear cataracts, 31% with mixed nuclear and cortical cataracts, and 27% of controls (26/98) displayed only the A allele for GSTM1. Twenty-four percent of patients (24/102) with cortical cataract, 24% (7/29) with nuclear cataracts, 14% (10/71) with mixed nuclear and cortical cataract, and 18% of controls showed only the B allele for GSTM1. Two percent of patients (2/102) with cortical cataracts, 7% (2/29) with nuclear cataracts, 4% (3/71) with mixed nuclear and cortical cataracts, and 5% of controls (5/98) showed both A and B alleles for GSTM1.

CONCLUSIONS

No associations between the GSTM1 alleles, including the null allele, and cataracts were detected in this study.

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.

A dose-response effect between a sunlight index and age-related cataracts. Italian-American Cataract Study Group

To explore the existence of a dose-response relationship between sunlight exposure and risk of age-related cataracts, we analyzed data collected from 1008 patients with cataracts and 469 control subjects enrolled in the Italian-American Case-Control Study of Age-Related Cataracts. Fourteen variables related to sunlight exposure history were included in the questionnaire administered to the study participants. A sunlight index was constructed and its relationship to the presence of cataracts was modeled by logistic regression. After adjustments for potential confounding variables and for age and sex, a significant dose-response effect (P = 0.01) was detected between the sunlight exposure index and the presence of pure cortical cataracts. With the exception of corticonuclear cataracts, all the other mixed types of opacity also showed a dose-response association with the sunlight index. These data support the hypothesis that sunlight exposure is a risk factor in the development of cortical cataracts, and demonstrate the existence of a dose-response relationship in this association.

Influence of type and severity of pure forms of age-related cataract on visual acuity and contrast sensitivity. Italian American Cataract Study Group

PURPOSE

To compare the relationship between logMAR visual acuity (VA) and cataract severity and between contrast sensitivity (CS) and cataract severity in pure types of age-related lens opacities.

METHODS

Analysis included patients followed in the ongoing Italian-American Study of the Natural History of Age-Related Cataract. Lens opacities were classified and graded according to the Lens Opacities Classification System II (LOCS II). Visual acuity was measured with the Early Treatment Diabetic Retinopathy Study Chart. Contrast sensitivity was measured with the Pelli-Robson chart.

RESULTS

Data from 1,076 eyes were used for the analysis (366 clear lenses; 550, 124, and 36 eyes with cortical, nuclear and posterior subcapsular cataract, respectively). In age-adjusted analyses, increasing severity of all three cataract types was associated with progressively higher logMAR VA, which translates into poorer acuity, and lower CS scores. For both VA and CS, the effect of increasing severity was greatest for nuclear and least for cortical opacities. After adjusting for age and VA, CS scores were no longer associated with cataract type and severity, with the exception of advanced cortical opacities.

CONCLUSIONS

Increased cataract severity, as determined by LOCS II grading, is strongly associated with both VA and CS scores. Contrast sensitivity scores obtained from testing at low spatial frequency do not seem to offer additional information over standard VA testing in early cortical and posterior subcapsular opacities nor in nuclear cataracts.

Lens sodium channels are inactivated by anti-MIP26 antibodies

Sodium-specific channels can be functionally identified in phosphatidylcholine liposomes incorporating detergent-solubilized membrane proteins from pig lens epithelium and outer cortex. The transport of sodium is saturable, specific and protease-sensitive. MIP26 was identified in the solubilized membrane fraction and in the liposomes by means of Western blot analysis. Pre-treatment of liposomes with anti-MIP26 antiserum abolished the transport of sodium. These data indicate that MIP26 is associated to a sodium selective transport activity.

Enzyme activities in human lens epithelium of age-related cataract

PURPOSE

To investigate associations between enzyme activity of glutathione reductase (GR) with and without added flavin adenine dinucleotide (FAD), glutathione peroxidase (GPX), and 6-phosphogluconic dehydrogenase (6PGDH) in the lens epithelium collected at surgery, and some nutritional and biochemical variables determined in the same individuals during the Italian-American Case-Control Study of age-related cataract.

METHODS

One hundred eighty-three epithelium capsule samples were collected from 174 patients undergoing surgery. Data on enzyme activity were obtained from 52 samples for 6-PGDH and from 53 samples for GR and for GPX. The Lens Opacity Classification System II was used to classify and grade cataracts.

RESULTS

No correlation was found between enzyme activity in lens epithelium and the same enzymatic activity in erythrocytes (with the exception of a negative correlation between lens and erythrocyte 6PGDH activity), or the type and severity of cataract. No correlation was found between lens GPX activity and plasma selenium and between lens GR activation coefficient (GRAC) and riboflavin intake. Lens GR with added FAD and lens GRAC were significantly correlated to plasma vitamin E level. Lens GRAC was positively correlated to a nutritional vitamin index.

CONCLUSIONS

Present data stress the difficulty in verifying the assumption that biochemical indices collected on plasma and on erythrocyte actually reflect the status of these factors in the lens itself.

Sugar alcohols in the lens epithelium of age-related cataract

We have measured the levels of glucose and sugar alcohols in the lens epithelium of 24 non-diabetic and 21 diabetic patients undergoing extracapsular cataract extraction for age-related cataract. Lens status was assessed preoperatively according to the Lens Opacities Classification System II. In comparison to non-diabetics, the lens epithelia of diabetic patients have increased levels of glucose and sorbitol, and lower content of myo-inositol. Both myo-inositol decrease and sorbitol accumulation are strictly related to the fasting blood sugar level. No correlation or trend was detected in diabetic subjects between myo-inositol or sorbitol level and cataract type. In non-diabetic patients nuclear opacification was associated with a significant increase of myo-inositol level in lens epithelium.

The effect of cataract severity and morphology on the reliability of the Lens Opacities Classification System II (LOCS II)

Data collected from 3646 eyes in the Italian-American Natural History Study of Age-Related Cataract were used to investigate whether the reliability of the Lens Opacities Classification System II (LOCS II) by the severity of the opacity that is being graded or is influenced by the presence and severity of coexisting opacities. Reliability was assessed by comparing the slit-lamp gradings of two clinical examiners (346 eyes) and the gradings performed at the slit lamp with gradings of photographs (3646 eyes). The severity of cortical and nuclear opacities did not affect the reproducibility of slit-lamp gradings, but clinical grading of posterior subcapsular opacities became more reliable as the severity of the posterior subcapsular opacities increased. More advanced coexisting opacities decreased the agreement in the slit-lamp diagnosis of nuclear, but not cortical or posterior subcapsular, opacities. Comparisons of clinical and photographic gradings showed very good to excellent agreement for nuclear and cortical opacities, regardless of the severity of the specific opacity or the severity of the coexisting opacities. Agreement in diagnosing posterior subcapsular opacities was decreased in eyes with milder posterior subcapsular opacities and in eyes with more severe coexisting nuclear and/or cortical opacities. The effect of the severity of the opacity being graded and the severity of coexisting opacities on the reliability of the LOCS II must be considered in studies that use the system to classify and grade cataracts.

Increased ion traffic through non-specific cation pathways in the ageing human lens. Evidence from radiotracer fluxes studies

86Rb efflux studies were carried out on normal human lenses in vitro. The data confirmed previous studies showing that 86Rb efflux increases with age. Removal of Ca2+ from the lens perifusate increased 86Rb efflux at all ages. The fractional increase above baseline was highest in the younger lenses, while the net increase of the 86Rb efflux induced by a Ca(2+)-free medium increased with age. This study supports the idea that Ca(2+)-sensitive, non-specific cation channels are present in the human lens and that their contribution to membrane permeability increases as the lens ages.

Mammalian lens inter-fiber resistance is modulated by calcium and calmodulin

The relationship between Ca2+ and lens fiber cell communication was investigated in the isolated intact rat lens by using radiotracer and electrophysiological techniques. The lens internal calcium was increased by adding the SH oxidant diamide (1 mM), by incubating in a sodium-free (n-methylglucamine) solution or by increasing external calcium from 1 to 10 mM. A 12 hours incubation in diamide produced a ten-fold increase in 45Ca uptake into the lens which was accompanied by a ten-fold increase in internal resistance. Incubation in Na-free solution or in 10 mM Ca2+ both produced a 5-fold increase in 45Ca content, while the increase in internal resistance was five and six fold respectively. This uncoupling was prevented in the diamide and Na-free treated lenses by omitting Ca2+ from the incubation medium. Fiber cell uncoupling was noticed in each of these experimental conditions after approximately 5 hours incubation, and good recovery was obtained in the high calcium solution if the stress was removed. The calmodulin antagonists calmidazolium (3 microM) and W7 (100 microM) both prevented uncoupling in the high calcium solution, provided there was a 2 hours preincubation period in calcium-free solution containing antagonist before the stress was applied. These data indicate that lens fiber cell communication is required by Ca2+ and calmodulin.

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

The Lens Opacities Classification System I (LOCS I) was used to classify lens opacities in the clinic-based Italian-American Case-Control Study of Age-Related Cataract. Data on the distribution of cataract types among the 1008 patients (age range, 45-79 years) are presented. A single type of cataract was found in 65% of all cases in whom both lenses could be graded. Among all patients and among patients with only one type of cataract, cortical opacities occurred most frequently and posterior subcapsular opacities least frequently. In patients with bilateral cataracts there was a high degree of concordance of cataract type and severity. The high degree of concordance of cataract type between eyes and the decreasing prevalence of unilateral cataract with increasing age suggest that patients with unilateral cataract are at high risk of developing the same opacity in the fellow eye. Cortical cataracts were found more frequently in women, and in patients with unilateral cataract, the left eye was more frequently affected. Clinic-based data on the distribution of cataract may be of assistance in planning future clinical studies of cataract.

Human lens membrane cation permeability increases with age

Parallel studies of the ionic balance and membrane permeability characteristics of normal human lenses were carried out in three countries (USA, England and Italy). Similar age-related changes were found in each laboratory. The lens membrane potential and resistance declined markedly with age while internal Na+ and free Ca2+ increased. There was a concomitant stimulation of Na+ and K+ transmembrane fluxes. These data indicate that in the ageing process there is an increasing contribution to membrane ion traffic from a channel, or channels, that permit Na+, K+ and Ca2+ to pass. The increase in permeability coincides exactly with the increase in optical density that occurs in the ageing human lens.

An independent evaluation of the Lens Opacities Classification System II (LOCS II). The Italian-American Cataract Study Group

The Lens Opacities Classification System II (LOCS II) has been offered for use in clinical studies of cataract. The system uses slit lamp and retroillumination photographic standards to grade lens opacities into classes of increasing severity. The authors evaluated the reproducibility and validity of LOCS II before its possible use in a natural history study of age-related cataract. The authors found excellent inter- and intraobserver reproducibility when the LOCS II standard photographs were used for clinical or photographic gradings of cataract. There was a tendency to underestimate posterior subcapsular cataracts on photographic gradings compared with slit-lamp gradings. The accuracy of the photographic gradings of posterior subcapsular opacities tended to decrease as the severity of coexisting opacities increased.

Diamide alters membrane Na+ and K+ conductances and increases internal resistance in the isolated rat lens

The voltage and conductance of the isolated rat lens were measured using a two-internal-microelectrode technique and the potassium permeability was calculated by applying Goldman theory to 86Rb efflux data. The SH oxidizing agent diamide induces a multiphasic response in lens voltage, conductance and potassium permeability. The initial response (less than or equal to 30 min) to 1 mM diamide consists of a small depolarization (approximately 10 mV) of membrane potential accompanied by a significant decrease in conductance. The 86Rb efflux and permeability data also show an initial decrease. As this initial response is abolished by TEA (20 mM) it is probably due to an inactivation of voltage-sensitive potassium channels. After 30 min exposure to 1 mM diamide both the electrical conductance and the rate of depolarization increase. The 86Rb permeability also increases. Since the conductance increase is abolished by replacing Na+ by methyl glucamine and as it is reduced by amiloride (10(-4) M) the second phase is probably due to the activation of nonspecific cation channels. The third phase is only apparent after prolonged (approximately 12 hr) incubation in 1 mM diamide and consists of a marked increase in the bulk resistance component of the lens impedance. It is suggested that this component arises from an increase in the resistance of the fibre cell gap junctions. This cellular uncoupling may be due to calcium entering the lens through the nonspecific cation channels.

Oxidative cross-linking of fodrin parallels a membrane conductance increase in the mammalian lens

An oxidative cross-linking of the lens spectrin-like protein fodrin was induced by incubating WKY-rat lenses in the presence of the SH-reagent diamide. The oxidation of fodrin was paralleled by an increase in lens membrane conductance. The time relationship between these two events as well as the reversibility of both, achieved by incubating the lens in the presence of dithiothreitol, indicate that normal permeability characteristics of the lens membranes require the integrity of the membrane attached cytoskeleton.

Vitamin A uptake from retinol-binding protein in a cell-free system from pigment epithelial cells of bovine retina. Retinol transfer from plasma retinol-binding protein to cytoplasmic retinol-binding protein with retinyl-ester formation as the intermediate step

We have investigated the steps by which retinol, released from plasma retinol-binding protein (RBP), enters the cells and is accumulated for the most part as a retinyl-ester, only a small fraction of it being present as a complex with cytoplasmic retinol-binding protein (CRBP). For this purpose, we have developed a cell-free system composed of plasma membrane-enriched fractions from bovine retinal pigment epithelium which selectively incorporates exogenous vitamin A when presented as a retinol-RBP complex. Upon incubation in the presence of [3H]retinol-RBP, isolated plasma membrane fractions take up and esterify retinol. A 4-fold reduction of total vitamin A incorporation is observed in conditions which specifically inhibit retinyl-ester formation, thus indicating that the two processes of retinol uptake and esterification are functionally coupled. Evidence is presented that retinol bound to a plasma membrane receptor sharing functional and structural similarities with CRBP is the actual substrate for esterification. Vitamin A accumulation seems to require retinol esterification to allow the recycling of a limited number of free, plasma membrane-associated, retinol receptors. Mobilization of retinol stored as a membrane-bound retinyl-ester is mediated by a membrane-associated hydrolase activity selectively controlled by the level of apo-CRBP which acts as a carrier for the released retinol. Up to 90% of membrane-bound vitamin A is released upon incubation in the presence of apo-CRBP (11 microM) with concomitant formation of retinol-CRBP. The overall process, in which retinol never needs to leave its binding proteins, allows the accumulation of vitamin A in the form of a membrane-bound retinyl-ester and its regulated mobilization as a retinol-CRBP complex.

Cytoskeleton abnormalities in human senile cataract

The cytoskeletal pattern of the most superficial layers (cortex and epithelium) of senile cataractous lenses has been analyzed by PAGE-SDS. While the nuclear type of cataract and age-matched transparent human lenses have superimposable protein patterns, lenses with cortical cataract demonstrate appreciable modifications of their cytoskeletal composition. The most evident change is the decrease of fodrin and the marked reduction or even the absence of the 98 Kd band. Fodrin may be completely removed from the water insoluble fraction (WIF) of cortical cataract by extraction in low ionic strength buffer, a treatment which only partially solubilizes this protein in transparent control lenses.

86-Rb efflux in normal and cataractous human lenses

86Rb efflux has been studied in normal lenses and in human senile cataracts. The rate constant (Ki) of the efflux gradually increases in cataractous lenses with progression of lens damage. Efflux experiments run in the presence of BaC12 suggest that a progressive activation of BaC12 inhibitable efflux routes occurs in cataractous lenses. In the final stages of opacification the ineffectiveness of BaC12 enriched or Ca++ free media on the efflux suggests that a direct disruption of the lens membranes has occurred.

The isolation by self forming gradients of Percoll of plasma membrane enriched fractions from bovine retinal pigment epithelium

A method is described for the preparation of plasma membrane enriched fractions from bovine retinal pigment epithelium (RPE) by means of differential centrifugation followed by the use of self forming gradients of Percoll. A detailed analysis of the distribution of organelle specific markers (nuclei, mitochondria, lysosomes, endoplasmic reticulum, cytosol) in the different fractions is presented. Comparison of 125I-wheat germ agglutinin (WGA) binding with more conventional plasma membrane enzyme markers demonstrates that also in RPE radiolabeled lectin is a specific and extremely sensitive marker to follow quantitatively the distribution of outer cell membranes. Results of 125I-WGA displacement experiments indicate that plasma membranes are mostly (90%) composed of right side out vesicles or sheets. On the basis of 125I-WGA radioactivity the overall recovery of plasma membranes was about 10% and purification over 15 fold. NADH cytochrome c reductase activity, which is shown to be a specific marker for endoplasmic reticulum in retinal pigment epithelium, has been utilized to evaluate microsomal contamination of the plasma membrane preparation.

Amino-acid transport and protein synthesis in the rabbit lens: absence of cryoprobe effect

Recently developed organ-culture techniques have been used to investigate the effects of cryoprobe treatment on rabbit lenses. Uptake of 14C-tyrosine into cryoprobe treated and control lenses was followed for 96 h. Lens proteins were separated by gel filtration and incorporation of label measured in the individual crystallins. The cryoprobe treatment had no measurable effect on lens water, Na+, K+ or Ca++ content, tyrosine transport or the incorporation of tyrosine into the crystallins, during the period of the experiment.

Active and passive rubidium influx in normal human lenses and in senile cataracts

The aim of this study was to investigate the mechanisms responsible for the osmotic imbalance which occurs in a majority of human senile cataracts. Active and passive influx of rubidium has been determined in vitro in human lenses both normal and cataractous. It is concluded that the active transport of cations is on the average normal in senile cataractous lenses. It is possible that the activity of the cation pump is defective in a few cataractous lenses but no direct evidence of this can be given. The results indicate that cryo-extracted lenses may be utilized in this type of study provided that cryo-treatment during surgery is kept at the lowest possible level.

Crystallization and preliminary X-ray data of human plasma retinol-binding protein

Crystals of human plasma retinol-binding protein have been obtained from 4.5 M-NaCl buffered at pH 6.8 with 20 mM-cacodylate. The crystals are trigonal with space group R3 and unit cell dimensions, referred to the hexagonal system, a = b = 104.2 A and c = 74.5 A. The crystals diffract to a resolution of 2.0 A.

Galactosemic enzyme levels in presenile cataracts

Galactose-1-phosphate uridyl transferase and galactokinase activities have been measured in the red blood cells of a group of patients with "idiopathic" presenile cataract and of a group of nondiabetic patients with senile cataract. The activity of both galactosemic enzymes was found to be within the normal range in all the patients with presenile cataract. In the group of patients with senile cataract, galactokinase activity was normal in all 24 subjects examined, and galactose-1-phosphate uridyl transferase activity was moderately reduced in 3 of 14.

Bilateral papilloedema in long term therapy with lithium carbonate

A 31-year-old white woman developed bilateral papilloedema whilst on lithium carbonate therapy for five years because of manic depressive illness. Oedema of the optic disc disappeared after lithium administration had been discontinued. To our knowledge this is the second case of this kind which has been reported in literature.

Interocular transfer of a visual aftereffect in early-onset esotropia

The interocular transfer of the tilt aftereffect was studied in strabismic patients with early-onset esotropia and in controls. Squinting subjects were divided into a microtropia subgroup with anomalous binocular vision and a large-angle esotropia subgroup with total suppression of the deviated eye. Patients with alternating microtropia and large-angle esotropia showed normal or moderately reduced interocular transfer of the aftereffect. Patients with monocular microtropia with medium- or low-degree amblyopia showed a reduced monocular visual aftereffect in the dominant eye and practically no transfer to the nondominant eye. Adaptation of the nondominant eye and transfer of the aftereffect to the dominant eye was normal. The interocular transfer of the tilt aftereffect is a poor indicator of the state of binocularity of a squinting subject, and the clinical usefulness of this test is limited.

Vertical retraction syndrome

A 14-year-old white boy, the second of 5 brothers, showed a congenital deficit of ocular motility in his left eye, characterized by limited elevation, marked retraction of the globe and narrowing of the palpebral fissure during upward gaze. The ocular movements in the other directions of gaze were normal with normal binocular vision and stereopsis. The characteristics of the motility defect and the results of the forced duction test suggest the possibility of an anomaly of superior rectus scleral insertion rather than of an innervational defect or of a muscular fibrosis.

Normal interaction of plasma retinol-binding protein from retinitis pigmentosa with bovine pigment epithelium

The interaction between retinol-binding protein and normal bovine pigment epithelium has been studied with the use of iodinated retinol-binding protein isolated from the plasma of patients with the recessive form of retinitis pigmentosa and of normal subjects. It is concluded that the capacity of the plasma carrier protein to interact with the retinol-binding protein receptor of bovine pigment epithelium is unimpaired in retinitis pigmentosa with autosomal recessive inheritance.

Binding of retinol to isolated retinal pigment epithelium in the presence and absence of retinol-binding protein

Isolated human and bovine pigment epithelium actively binds H3-retinol when vitamin A alcohol is present in the incubation medium bound to human retinol-binding protein. Pigment epithelium is unable to bind retinol present in the incubation solution as the free form, i.e., not bound to its physiologic carrier protein. It is suggested that an interaction between retinol-binding protein and the membranes of pigment epithelial cells is essential for the active transport of retinol into pigment epithelium.

Serum levels of retinol-binding protein in different genetic types of retinitis pigmentosa

The level of retinol-binding protein (RBP) was determined by a single radial immunodiffusion technique in the serum of patients with retinitis pigmentosa (RP) carefully classified according to their specific genetic type, i.e., autosomally recessive, dominant, sex-linked, and other such as those forms associated with Laurence-Moon-Bardet-Biedl or Winkelman's disease. Highly purified human normal RBP was used as a standard. In none of the patients with RP studied was the serum level of RBP found to be significantly different from that of the control subjects.