Ординатура / Офтальмология / Английские материалы / Progress in Lens and Cataract Research_Hockwin_2002

Diffuse skylight

50 : Upper limit indoors or in twilight

Direct sunlight

30 : Upper limit for sunlight on grass

15 : Upper limit for sunlight on snow or sand

0 : Horizon

15 : Normal line of sight

70 to 80 : Lower limit

Fig. 4. A summary of some of the geometrical factors that influence corneal exposure to UVR and the complexity of measurement of the UVR exposure dose.

is highest in barren areas and seaside conditions, where the horizon sky is not blocked and where ground reflectance is relatively high [58]. From these findings, one would not expect to see a high incidence of pterygium in an environment where people were only working over green grass pastureland throughout their lifetime if the UVR hypothesis is valid. Figure 4 summarizes some of the geometrical factors that influence corneal exposure. Reflections off clouds in the sky can be significant in the UV-B. White clouds are highly reflective, rather like sea foam. Overcast or hazy skies tend to scatter the UV in skylight and redistribute the energy leading to an increase in the UV coming from the horizon sky. Hence we come to the apparently surprising conclusion that the factors listed at the beginning of this chapter indeed mislead one with regard to environmental UV exposure. Mountain people are typically living in valleys, not the very top of a mountain, and frequently are engaged in animal husbandry of grazing animals, hence they are in mountain green pasture lands and their horizon sky is occluded by mountains. Hence their ocular exposure can actually be less than someone living at sea level near the sea or in large barren areas, as in arid countries.

Environmental Differences

The foregoing suggests that one should in theory be able to differentiate the relative importance of UVR, direct infrared radiation, and ambient temperature

as etiological factors in cataract by selecting populations where these factors are clearly different. For example, the lens of a glass blower working in an airconditioned room is exposed to an unusual thermal load immediately behind the iris (which selectively absorbs visible and near-infrared radiation) [32]. A sauna bather or worker in most hot environments is not exposed to a significant level of UVR concomitantly with the thermal stress. A person in a very high temperature environment should have a lens of almost uniform temperature, and a mountain skier or desert nomad has a very high UVR dose near the central axis of the lens, with a decreasing dose toward the equator, other than the nasal equatorial quadrant where temporal focusing creates a ‘hot spot’. Heat flow, thermal sequelae, movement of metabolites, and UVR scatter in the lens do not preclude other areas of the lens from being affected. These differences suggest several possible epidemiological studies that could serve to distinguish the impact of these different factors.

Judging from the current clinical evidence from the important studies of the variation of nuclear and cortical cataract with latitude presented by Professor Sasaki [3], the etiological role of heat may actually be more important than UVR – at least for some types of cataract. If nuclear cataract does not show greater density along the more heavily exposed optical axis as should be postulated in case of UVR photooxidation of nuclear lens proteins along the optic axis, it might be more logical to assume that heat could be more important than UVR for the development of nuclear opacities. One could even argue that the beginning of cortical cataracts in the inferior nasal quadrant could result from a slightly higher temperature in the nasal region than in the temporal region due to internal temperatures and blood flow. However, the Coroneo hypothesis would suggest the same relationship for UVR exposure.

Taylor et al. [17] argued that ecological studies were severely flawed because they have an underlying assumption that all persons in a given locale are exposed to the same dose. He termed this, ‘the ecological fallacy’; however, it is equally important to accurately portray the environmental dose in each locale when estimating individual exposure. I would modify the OAER of Rosenthal et al. [56] by the following to come up with an ocular exposure factor, OEF, where:

Table 3 provides my best effort to summarize the collective experience of our ocular exposure studies and gives estimates for each of the factors from F1 to F6. I have attempted to parallel some formulations used in UV skin cancer studies, but I have modified these for the eye’s exposure.

Once factors have been assigned for each exposure condition, they should be multiplied together to determine the relative ocular exposure factor (ROEF) using equation 3.

Table 3. Relative global exposure dose estimate factors for ocular exposure

1 These factors are not really independent, and because of the interplay, it is only possible to provide some typical values. However, for a given location, it is possible to provide much more accurate estimates. For example, the influence of elevation above sea level is important, but must be examined along with these other factors.

Conclusions

Some skeptics may question whether the hypothesis that UV sunlight is an etiological factor in pterygium, cataract and droplet keratopathies; however, from the public health and preventive medicine point of view, we really must consider UV as a likely factor. Indeed, it would be very surprising if the UV component in sunlight were not a significant (or even primary) factor in pterygium and cortical cataract. The causal factors in UV photocarcinogenesis of the skin and in accelerated skin ageing are clearly operative in the lens and cornea, so the chronic stimulation of repair processes in both the nasal quadrant of the lens epithelial cell nuclei and in the germinal cells of the limbus by UV (and possibly irritation by wind and dust) accelerates the ageing process, increasing the risk of corneal and conjunctival neoplasia. In older patients, the repair processes at the molecular and cellular level are impaired, and these factors become even more important. Heat clearly should be able to potentiate all of these effects – particularly in the lens.

Our studies of the geometrical aspects of ocular UVR exposure suggest the great importance of techniques such as Scheimflug photography of the lens to map the geometrical development of different types of cataracts and then compare them to the relative variations in lens temperature and UVR exposure in different environments. Before we discard ecologically based studies, we should examine the levels of uncertainty in individual exposure with the levels of uncertainty posed by grouping a population. In the case of temperature, there is far less individual variation in one geographical locale than UVR exposure. Both the average lens temperature and UVR exposure are greater in the tropics, and both should increase for outdoor workers in the tropics. The recently reported epidemiological study of age-related cataract incidence in Tibet [59] would support the UV hypothesis because of the horizon-sky exposure on the Tibetan plain and the lower temperature. If the following key factors were to be applied in future epidemiological studies (some even retrospectively to previously collected data), there could be considerable improvement:

(1)Ambient temperature measurements: Include consideration of average outdoor temperatures and indoor temperatures in the evaluation.

(2)Ambient UV measurements: Measurement of the horizon-sky UV-B compared to global UVB measurements for typical meteorological conditions would remove the ambiguity of the influence of clouds, haze, air pollution, and even some terrain, vegetation and structures.

(3)Sky shielding: Since near-horizon sky is the only source of direct UV exposure for the eye outdoors, ignoring this factor has produced wrong assignments of exposure level; hence the impact of buildings and terrain must be considered.

(4)Duration of exposure: Rate time of exposure differently based upon horizon-sky measurements.

(5)Ground reflectance: More than any other component, this must be better evaluated.

(6)Correctly assess the impact of hats, sunglasses and clear spectacles: This has generally not been properly assessed in the past, and if properly considered, could produce very different risk factors.

Hopefully, with more refined study techniques, the scientific questions posed by Weale [60] related to UV and cataract in 1982 may yet be answered.

References

1United Nations Environment Program, World Health Organization, International Commission on Radiation Protection: Environmental Health Criteria 160, Ultraviolet Radiation. Geneva, World Health Organization, 1994.

2World Health Organization: The Effects of Solar UV Radiation on the Eye. Report of an Informal Consultation, Geneva 30 August–September 1993, Publication WHO/PBL/EHG/94.1. Program for the Prevention of Blindness. Geneva, World Health Organization, 1995.

3Sasaki K, Sasaki H, Kojima M, Shui YB, Hockwin O, Jonasson F, Cheng HM, Ono M, Katoh N: Epidemiological studies on UV-related cataract in climatically different countries. J Epidemiol 1999;9:S33–S38.

4Sliney DH: Physical factors in cataractogenesis: Ambient ultraviolet radiation and temperature. Invest Ophthalmol Vis Sci 1986;27:781–790.

5Dolin PJ: Ultraviolet radiation and cataract: A review of the epidemiological evidence. Br J Ophthalmol 1994;78:478–482.

6Roger FC, Cuthill JA, Fyvelor PJ, Lenham AP: Ultraviolet radiation as a possible cause of corneal degenerative changes under certain physiographic conditions. Acta Ophthalmol 1974;52:777.

7Van Heynigen R: The human lens. I. A comparison of cataracts extracted in Oxford (England) and Shikarpur (W. Pakistan). Exp Eye Res 1972;13:136.

8Hiller R, Giacometti L, Yuen K: Sunlight and cataract: An epidemiological investigation. Am J Epidemiol 1977;105:450.

9Wright RE: The possible influence of solar radiation on the production of cataract in certain districts of southern India: A preliminary investigation. Indian J Med Res 1936;24:917.

10Young JDH, Finley RD: Primary spheroidal degeneration of the cornea in Labrador and Northern Newfoundland. Am J Ophthalmol 1973;71/1:129.

11Hollows F, Moran D: Cataract – the ultraviolet risk factor. Lancet 1981;ii:1249.

12Vines AP: An Epidemiological Sample Survey of the Highlands, Mainland and Island Regions of the Territory of Papua and New Guinea. Port Moresby, Government Printer, 1967.

13Seung WS: A survey of senile cataracts among high altitude living Tibetans in Chang-du district, Tibet. Chin J Ophthalmol 1979;15:100.

14Brilliant LB, Grasset NC, Phkhrel RS, Kolstad A, Lepkowski JM, Brilliant GE, Hawks WN, Pararajasegaram R: Associations among cataract prevalence, sunlight hours, and altitude in the Himalayas. Am J Epidemiol 1983;118/2:250.

15Miranda MN: Environmental temperature and senile cataract. Trans Am Ophthalmol Soc 1980; 78:255.

16Chatterjee A: Cataract in Punjab; in Symposium on the Human Lens in Relation to Cataract. Ciba Foundation Symposium 19. Amsterdam, Associated Scientific Publishers, 1973.

17Taylor HR, West SK, Rosenthal FS, Munoz B, Newland HS, Abbey H, Emmett EA: Effect of ultraviolet radiation on cataract formation. N Engl J Med 1988;319:1429–1433.

18Wulf HC: Effects of ultraviolet radiation from the sun on the Inuit population; in Petursdottir G, Sigudsson SH, Karlsson MM, Axelsson J (eds): Circumpolar Health, '93: Proceedings of the 9th International Congress on Circumpolar Health. Nordic Council for Arctic Medical Research, Oulu, Finland, 1994, pp 416–422.

19Hedblom EE: Snowscape eye protection. Arch Environ Health 1961;2:685–704.

20Pitts DG, Cameron LL, Jose JG, Lerman S, Moss E, Varma SD, Zigler S, et al: Optical radiation and cataracts; in Waxler M, Hitchins V (eds): Optical Radiation and Visual Health. Boca Raton, FL, CRC Press, 1986, pp 5–41.

21Young R: Age-Related Cataract. New York, Oxford University Press, 1991.

22Zuclich JA: Ultraviolet-induced photochemical damage in ocular tissues. Health Phys 1989;56: 671–682.

23Jose JG, Pitts DG: Wavelength dependency of cataracts in albino mice following chronic exposure. Exp Eye Res 1985;41:545–563.

24Bachem A: Ophthalmic ultraviolet action spectra. Am J Ophthalmol 1956;41:969–975.

25Pitts DG, Cullen AP, Hacker PD: Ocular effects of ultraviolet radiation from 295 to 365 nm. Invest Ophthalmol Vis Sci 1977;16:932.

26Pirie A: Photo-oxidation of proteins and comparison of photo-oxidized proteins with those of the cataractous human lens. Isr J Med Sci 1972;8:1567.

27Lerman S: Human ultraviolet radiation cataracts. Ophthalmic Res 1980;12:303.

28Zigman S, Schultz J, Yulo T, Griess G: The binding of photo-oxidized tryptophan to a lens gammacrystallin. Exp Eye Res 1973;17:209.

29Borkman R, Lerman S: Evidence for a free-radical mechanism in aging and UV irradiated ocular lenses. Exp Eye Res 1977;25:303.

30Dillon J, Garner MH, Roy D, Spector A: The photolysis of lens proteins: Molecular changes. Exp Eye Res 1982;34:651.

31Cullen AP: Additive effects of ultraviolet radiation. Am J Optom Physiol Opt 1980;57:808.

32Sliney DH, Wolbarsht ML: Safety with Lasers and Other Optical Sources. Plenum, NewYork, 1980.

33Sliney DH: Epidemiological studies of sunlight and cataract: The critical factor of ultraviolet exposure geometry. Ophthalmic Epidemiol 1994;1/2:107–119.

34Sliney DH: Ocular exposure to environmental light and ultraviolet – The impact of lid opening and sky conditions. Dev Ophthalmol 1996;27:53–75.

35Sliney DH: UV radiation ocular exposure dosimetry. J Photochem Photobiol B 1995;31:69–77.

36Klein BEK, Klein R, Linton KLP: Prevalence of age-related lens opacities in a population. The Beaver Dam Eye Study. Ophthalmology 1992;99:546–552.

37Weale R: Human ocular aging and ambient temperature. Br J Ophthalmol 1981;65:869.

38Miranda MN: The geographic factor in the onset of presbyopia. Trans Am Ophthalmol Soc 1979; 77:603.

39Harding JJ: The untenability of the sunlight hypothesis of cataractogenesis. Doc Ophthalmol 1995; 88:345–349.

40Schwartz B: Environmental temperature and the ocular temperature gradiant. Arch Ophthalmol 1965;74:237.

41Schwartz B, Feller MR: Temperature gradients in the rabbit eye. Invest Ophthalmol 1962;1:513.

42Freeman RD, Fatt I: Environmental influences on ocular temperature. Invest Ophthalmol 1973;12:596.

43Rosenbluth RF, Fatt I: Temperature measurements in the eye. Exp Eye Res 1977;25:235.

44Ernst JT, Potts AM: Pathophysiology of the distal portion of the optical nerve. IV. Local temperature as a measure of blood flow. Am J Ophthalmol 1971;72:435.

45Lagendijk JJW: A mathematical model to calculate temperature distributions in human and rabbit eye during hyperthermic treatment. Phys Med Biol 1982;27:1301.

46Taylor HR: The environment and the lens. Br J Ophthalmol 1980;64:303–310.

47Mapstone R: Determinants of corneal temperature. Br J Ophthalmol 1968;52:729.

48Rysa P, Sarvaranta J: Corneal temperature in man and rabbit, observations made using an infra-red camera and a cold chamber. Acta Ophthalmol 1974;52:810.

49Lydahl E: Infrared cataract. Acta Ophthalmol 1984(suppl 166):1–63.

50Sliney DH: Eye protective techniques for bright light. Ophthalmology 1983;90:937–944.

51Deaver DM, Davis J, Sliney DH: Vertical visual fields-of-view in outdoor daylight. Lasers Light Ophthalmol 1996;7/2/3:121–125.

52Kraiss KF, Moraal J: Introduction to Human Engineering. Cologne, Verlag TUC Rheinland, 1976, p 119.

53Coroneo MT, Müller-Stolzenburg NW, Ho A: Peripheral light focusing by the anterior eye and the ophthalmohelioses. Ophthalmic Surg 1991;22:705–711.

54Coroneo MT: Pterygium as an early indicator of ultraviolet insolation: An hypothesis. Br J Ophthalmol 1993;77:734–739.

55Maloof AJ, Ho A, Coroneo MT: Influence of corneal shape on limbal light focussing. Invest Ophthalmol Vis Sci 1994;35:2592–2598.

56Rosenthal F, Phoon C, Bakalian A, Taylor H: The ocular dose of ultraviolet radiation to outdoor workers. Invest Ophthalmol Vis Sci 1988;29:649–656.

57Mohan M, Sperduto R, Angra S, Milon R, Mathur R: India-US case-control study of age-related cataracts. Arch Ophthalmol 1989;107:670–676.

58Hirst L: Distribution, Risk Factors, and Epidemiology of Pterygium; in Taylor HR (ed): Pterygium. The Hague, Kugler, 2000, pp 15–27.

59Hu T-S, Zhen Q, Sperduto RD, Zhao J-L, Milton RC, Nakajima A: Age-related cataract in the Tibet Eye Study. Arch Ophthalmol 1989;107:666.

60Weale R: Senile cataract. The case against light. Ophthalmology 1983;90:420–423.

David H. Sliney, US Army Center for Health Promotion and Preventive Medicine, Aberdeen Proving Ground, MD 21010-5403 (USA)

Tel. 1 410 436 3002, Fax 1 410 436 5054, E-Mail David.Sliney@att.net

Hockwin O, Kojima M, Takahashi N, Sliney DH (eds): Progress in Lens and Cataract Research. Dev Ophthalmol. Basel, Karger, 2002, vol 35, pp 60–69

High Prevalence of Nuclear Cataract

in the Population of Tropical and

Subtropical Areas

Hiroshi Sasaki a, Fridbert Jonassond, Ying Bo Shui a,e, Masami Kojima a, Masaji Onob, Nobuyo Katohc, Hong-Ming Cheng f, Nobuo Takahashi a, Kazuyuki Sasaki a

aDepartment of Ophthalmology, Kanazawa Medical University, Uchinada,

bEnvironmental Health Science Division, National Institute for Environmental Studies, Tsukuba, and c Department of Public Health, Juntendo University, Tokyo, Japan; d Department of Ophthalmology, University of Iceland, Reykjavik, Iceland;

eOphthalmology and Vision Science, Washington University Medical School,

St. Louis, Mo., and f Schepens Retina Associates, Boston, Mass., USA

Abstract

The authors have conducted cataract epidemiological studies in four climatically and racially different places and compared the data. The survey places were Noto and Amami in Japan, Reykjavik in Iceland, and Singapore. The evaluation and grading of lens opacities were done using graphic analysis of Scheimpflug and retro-illumination images. The prevalence of nuclear opacity was extremely high in the Singapore group, followed by Amami. The main type of lens opacity was nuclear in the Singapore group and cortical in the Noto and Icelandic groups. The characteristic lens opacity in Amami was in between the above two groups. No significant difference was seen in the prevalence of nuclear opacity between males and females in any of the groups. Although the common factors of the living conditions in the subjects with a high prevalence of nuclear opacity appear to be high UV exposure and high ambient temperature, future investigations should be made to disclose the possible cause.

Copyright © 2002 S. Karger AG, Basel

Introduction

Many epidemiological studies have shown that nuclear and cortical opacities are the two main types of lens opacity seen in elderly persons [1–5]. Aging is an important factor of nuclear opacity, with other factors such as smoking [6–8],

Table 1. Number of volunteers examined for lens analysis

low intake of vitamins [6, 9, 10] or myopia [8] also being reported. We found that the prevalence of nuclear opacity was higher in the subjects living in the southern part of Japan than in those in the central and the northern parts [11].

In this study, we investigated the prevalence of three main types of opacities in the recently performed epidemiological studies in two climatically different places in Japan [12], in Singapore [13] and Iceland [14].

Methods

Residents, aged 50 years and older living in Noto and Amami, Japan, and Singapore and Iceland were surveyed. The subjects in Noto were from the ongoing Noto Japan study. The local government of Monzen contacted 2,000 citizens aged 50–79 years. Of the 2,000, 58 were excluded because of death, being out of the town, or the inability to contact them. 1,942 were contacted and 977 of them (50.3% of the eligible) were subsequently examined. The details of the other studies have been described elsewhere [12–15]: 314 joined the surveys in Amami, 1,045 in Iceland and 517 in Singapore. The number of subjects with lens changes in Noto, Amami, Singapore and Iceland was 918, 276, 993 and 468, respectively (table 1). All of the subjects in Noto and Amami were Japanese, those in Iceland were Caucasian and 98% of those in Singapore were Chinese. The annual average temperature and UV-B radiation was 15.1 °C and 190 units/m2 in Noto, 21.3 °C and 240 units/m2 in Amami, 5.0 °C and 50 units/m2 in Iceland and 26.7 °C and 380 units/m2 in Singapore.

The methodology used for all the surveys was the same. Prior to examination, a 26-item questionnaire [16] was distributed to and completed by the participants. Unfinished questionnaires were finished onsite with the assistance of the survey staff. The participants were then subjected to the following: autorefraction to determine refractive error, subjective distant visual acuity measurement, a noncontact intraocular pressure test (Nidek NT-2000), undilated slit-lamp biomicroscopy of the anterior segment, Scheimpflug photography and graphic analysis system to ascertain the depth of the anterior chamber and the angle width, and specular microscopy (Konan) of the corneal endothelium. Cases suitable for papillary dilatation were instilled with topical tropicamide 0.5% and phenylephrine-HCl 0.5%. The lens and the fundus were examined under maximal dilation by slit-lamp biomicroscopy and the lens appearance was again recorded as Scheimpflug and retroillumination images with an anterior eye segment analysis system (Nidek EAS-1000). The fundus and optic disc were recorded by stereophotography (Nidek 3Dx/NM).

Classification and grading of lens opacities were based in principle on objective graphic analysis. The classification and grading of cortical and subcapsular opacities were done with the Japanese Cataract Epidemiology Study Group (JCCESG) System [16]; nuclear opacities were classified from grade 1 to 4 according to the Kanazawa Medical University Grading System [17]. Previous reports used the same system except that grades 3 and 4 were grouped together under grade 3. The same investigator who was well versed in the classification system made the final diagnoses of all cases.

The present study concentrated on the prevalence and classification of lens opacities. Other aspects included the examination of risk factors, localization of cortical opacities, morphologic analysis of the exterior of the eye, observation of the corneal endothelium, and glaucoma detection. These results will be reported elsewhere. Data were collected in the following manner. (1) Eyes with more advanced opacities were used for data analysis that involved the number of subjects with lens opacities as well as the opacity types and grading. (2) If both eyes of the same subject had the same grade but different types of lens opacities, classification was done for the right eye only. (3) When comparing the prevalence of the three main types of lens opacities, i.e., cortical, nuclear and subcapsular, if both eyes had the same type of opacities but different grades, classification was done only for the eye with the higher opacity grade.

Statistical analyses for the present study included the t test, 2 test and MantelHaenszel test.

Results

Prevalence of Lens Opacities of All Types by Gender and Age

Table 2 shows the prevalence of lens opacities of all types by age in both males and females. The prevalence increased with age in all of the groups with grades 1–3 opacities and in those with above grade 1 opacities. The prevalence of grades 1–3 opacities in the populations of Singapore and Amami was higher than those in Iceland and Noto. In the subjects in their 60s, 70s and 80s in Noto and in their 70s in Iceland, the prevalence of lens opacity was significantly higher in females than in males. The prevalence of above grade 1 opacities was highest in Singapore, followed by Amami and Noto, and was lowest in the subjects in Iceland.

Prevalence of Four Different Types of Lens Opacities by Age and Extent

The results are shown in table 3. The prevalence of pure cortical opacity in participants in their 50s was the highest among the four opacity types in all the groups. The prevalence of pure nuclear and mixed type opacities increased with aging. In Icelanders, the main type was pure cortical opacity with 50.4% in their 60s, 54.8% in their 70s and 32.1% in their 80s. Nuclear opacity was seen in the Singaporean participants even in their 50s. The prevalence of pure nuclear and the mixed types of opacities was higher than that of the cortical type in Singaporeans in their 60s, with almost 80% of the participants showing the mixed type of opacity in their 70s. The main type of lens opacity of the Noto