Prevalencia y causas de ceguera en Perú: encuesta nacional / National survey on the prevalence and causes of blindness in Peru

OBJETIVO: Estimar la prevalencia de ceguera y deficiencia visual en adultos de Perú y precisar sus causas, evaluar la cobertura y la calidad de los servicios de cirugía de catarata y determinar las barreras que impiden acceder a esos servicios. MÉTODOS: Estudio poblacional transversal con muestreo aleatorio por conglomerado en dos pasos de personas de 50 años o más, representativo de todo el país, mediante la metodología estándar de la Evaluación Rápida de Ceguera Evitable. Se midió la agudeza visual y se examinó el cristalino y el polo posterior por oftalmoscopía directa. Se calculó la cobertura de cirugía de catarata y se evaluó su calidad, además de las causas de tener una agudeza visual < 20/60 y las barreras para acceder a ese tratamiento. RESULTADOS:Se examinaron 4 849 personas. La prevalencia de ceguera fue 2,0% (intervalo de confianza de 95%: 1,5-2,5%). La catarata fue la causa principal de ceguera (58,0%), seguida por el glaucoma (13,7%) y la degeneración macular relacionada con la edad (11,5%). Los errores de refracción no corregidos fueron la principal causa de deficiencia visual moderada (67,2%). La cobertura de cirugía de catarata fue de 66,9%, y 60,5% de los ojos operados de catarata logró una AV ≥ 20/60 con la corrección disponible. Las principales barreras para someterse a la cirugía de catarata fueron el alto costo (25,9%) y no saber que el tratamiento es posible (23,8%). CONCLUSIONES: La prevalencia de ceguera y deficiencia visual en Perú es similar a la de otros países latinoamericanos. La baja cobertura de cirugía de catarata y el envejecimiento poblacional indican que para aumentar el acceso a estos servicios se debe mejorar la educación de la población en salud ocular y la capacidad resolutiva de los servicios oftalmológicos y de cirugía de catarata, y reducir su costo.

OBJECTIVE: To estimate the prevalence of blindness and visual impairment among adults in Peru and to determine their causes, to evaluate the coverage and quality of the cataract surgical services and to investigate the barriers that inhibit access to these services. METHODS: A cross-sectional population study with two-stage random cluster sampling of individuals of ≥ 50 years old, representative of the entire country, using the standard methodology of the Rapid Assessment of Avoidable Blindness. Visual acuity was assessed and the condition of the lens and posterior pole examined by direct ophthalmoscopy. Cataract surgical coverage was calculated. Its quality, as well as the causes of visual acuity < 20/60 and the barriers to accessing surgical treatment were assessed. RESULTS: A total of 4 849 people were examined. Blindness prevalence was 2.0% (confidence interval of 95%: 1.5-2.5%). The main causes of blindness were cataract (58.0%), glaucoma (13.7%) and age-related macular degeneration (11.5%). Uncorrected refraction errors were the principal cause of moderate visual impairment (67.2%). Cataract surgical coverage was 66.9%. 60.5% of the eyes operated for cataracts achieved a visual acuity ≥ 20/60 with available correction. The main barriers to cataract surgery were the high cost (25.9%) and people being unaware that treatment was possible (23.8%). CONCLUSIONS: The prevalence of blindness and visual impairment in Peru is similar to that of other Latin American countries. Given the low cataract surgical coverage and the aging of the population, access to the services could be improved by increasing the population education on eye health and the response capacity of the ophthalmological and cataract surgical services, and by reducing the costs of the latter.

Ethylmercuric chloride: the responsible agent in thimerosal hypersensitivity.

The causative agent of thimerosal allergy (sodium ethylmercury thiosalicylate) has not previously been thoroughly investigated. To evaluate whether the organic mercury component or the thiosalicylic acid molecule induces thimerosal sensitization, 23 patients positive to thimerosal were patch tested with ethylmercuric chloride, thiosalicylic acid and 8 different derivatives of mercury. To date, ethylmercuric chloride has not been tested in thimerosal allergy. 19/23 patients (82%) showed positive patch test reactions to ethylmercuric chloride. 4/23 patients negative to ethylmercuric chloride reacted positively to thimerosal 0.1% but not to thimerosal 0.05%. 8/23 patients (35%) also reacted to other mercurials. 20 controls negative to thimerosal showed negative patch test reactions to ethylmercuric chloride. Neither patients nor controls reacted to thiosalicylic acid. These results indicate that testing with thimerosal 0.1% leads to false-positive reactions and that the ethyl mercury component is the responsible agent in thimerosal allergy.

Patch test reactions in children, adults and the elderly. A comparative study in patients with suspected allergic contact dermatitis.

The age- and sex-related distribution of positive patch test reactions was investigated in 234 children (0-7 years, n = 72 and 8-14 years, n = 162), 1200 adults (20 to 50 years) and 295 elderly patients (> or = 70 years) with suspected allergic contact dermatitis using a European standard series. In girls from 0 to 7 years, the most frequent contact allergens were thimerosal (37.5%) and nickel (27.5%), in girls from 8 to 14 years, nickel (28.7%) and thimerosal (26.6%), in women, thimerosal (25.3%) and nickel (25.2%), and in elderly women, nickel (12.6%) and balsam of Peru (9.7%). The most frequent contact allergens in boys from 0 to 7 years were ethylmercuric chloride (28.1%) and thimerosal (25.0%), in boys from 8 to 14 years, thimerosal (30.9%) and ethylmercuric chloride (14.7%), in men, thimerosal (21.1%) and ethylmercuric chloride (13.7%) and in elderly men, nickel (11.2%) and balsam of Peru (6.7%). Females showed more positive reactions than males. Whilst 0 to 7 year-old girls and boys showed relatively more frequent reactions, the elderly of both sexes were clearly less affected. Nickel is the most frequent contact allergen in females of 8 years and more. In men, thimerosal is most frequent and reactions to balsam of Peru show a peak incidence in the elderly. Results indicate that patch testing should be considered in children and elderly patients with appropriate indications.

Thimerosal positivities: patch testing to methylmercury chloride in subjects sensitive to ethylmercury chloride.

The aim of this paper was to evaluate whether methylmercury chloride (MeHgCl) aq., when patch tested in a group of thimerosal-positive subjects reacting to ethylmercury chloride (EtHgCl), might be a reliable model for the better understanding of interactions between alkylmercury compounds and the skin. 19 out of 21 consecutive patients who previously had given positive patch-test reactions to both ethylmercury chloride 0.0165% eth.(EtHgCl, 0.615 mM) and MeHgCl 0.031% aq.(1.23 mM), and negative reactions to thiosalicylic acid 0.05% (3.24 mM) aq./eth. 50/50, were repatch tested to 8 microl of MeHgCl 0.031% aq. and to 8 microl of aq. solutions containing MeHgCl mixed with cysteine, glutathione, ZnSO4, MgSO4, MnSO4, ZnCl2, MgCl2 and MnCl2, respectively. The results showed that cysteine, glutathione and Zn(II) salts were able to abolish the positive reactions, demonstrating the rôle played by both thiol groups and Zn(II) itself. Patch tests concomitantly carried out in 16 out of 19 patients to 8 microl of aqueous MeHgCl and to 8 microl of aqueous solutions containing MeHgCl and MeHgCl mixed to fragment 56-61 of metallothionein I (MT I), MT I and MT II-Zn, respectively, revealed that all the MTs tested were able to reduce or to inhibit the reactions, demonstrating the effect of the thiol groups. Due to the close chemical similarities to EtHgCl and to its water solubility, MeHgCl seems to be a suitable model for evaluating the reactivity of alkylmercury compounds in the skin. We speculate that both EtHg- and MeHg-derivatives are xenobiotics with similar reactivity. However, the lack of clinical relevance of the reactions to both alkyl compounds lead us to conclude that, since environmental exposure does not seem to play a pivotal rôle, they probably have mostly to do with compounds included in in the standard series, and are elicited by reduced function of physiological SH chelators.

Hypersensitivity to thimerosal: the sensitizing moiety.

There has been increasing interest in characterizing the sensitizing moiety of thimerosal [TIM], following the finding that patients with photosensitivity to piroxicam are allergic to the thiosalicylic acid [TIO] moiety of TIM. For this purpose, the authors have conducted 2 studies in TIM-sensitive patients. In the 1st, of 175 patients tested with TIO and ammoniated mercuric chloride [HGAM], 45.7% reacted only to TIM, whereas 45.7% reacted also to TIO and 17.7% also to HGAM; 9.1% reacted to both TIO and HGAM. In the 2nd, of 47 patients tested with TIO and ethylmercuric chloride [ETHG], 87.2% reacted to ETHG, 44.7% to TIO and 31.9% reacted to both. None of the patients reacted only to TIM. The authors conclude that thimerosal allergy is due either to the mercuric moiety or to thiosalicylic acid, with no cases of sensitivity only to the whole molecule of TIM. TIM-sensitive patients are mainly allergic to the mercuric moiety, but among them there are a large number of TIO-sensitive patients, and these should be advised to avoid piroxicam.

Thimerosal positivities: the role of organomercury alkyl compounds.

Contact allergy to thimerosal (TH) has not been considered a marker for mercury allergy, since there is a low degree of cross-sensitivity to inorganic as well as to organic mercury salts. 40 subjects, who previously gave a positive patch test reaction only to thimerosal 0.1% pet. (Hermal), when simultaneously repatch-tested to solutions containing TH, mersalyl acid, p-amino-phenylmercuric acid, mercuric acetate and thiosalicylic acid, respectively, gave positive reactions only to TH. 36 out of 40 subjects were divided into 2 groups of 18 subjects and simultaneously repatch-tested to solutions containing TH, methylmercury chloride (MeHgCl), thiosalicylic acid, and, ethylmercury chloride (EtHgCl), respectively. EtHgCl was tested in the 1st group at 0.031% and in the 2nd group at 0.015%. The results showed that all subjects gave concomitant positive reactions to TH, EtHgCl and MeHgCl. EtHgCl 0.031% gave a higher number of reactions than EtHgCl 0.015%, underlining the rôle of the solvent in these reactions. Patch test results in 300 consecutive patients to a standard series, to which MeHgCl was added, showed that MeHgCl and TH were never able to give isolated positive reactions, and that the concomitant positive reactions occurred in only 3.6% of subjects. In conclusion, our data seem to suggest that the positive reactions to TH found in our patients were due to EtHgCl, and that the structural similarities with MeHgCl were so close that the skin reacted against each as if they were identical.