ACTA 0 PHTH ALM 0 LOG I CA (1988) Supplement 185

Myopia in arctic regions A survey

Gordon J. Johnson

London, England

Key words: Arctic zone, refraction in - Inuit myopia - myopia, epidemic of - myopia, dietary changes - environmental factors - heredity.

There is strong evidence that in most of the native populations of the Arctic and sub-Arctic regions the prevalence of myopia is substantially higher in young adults and teenagers than in the previous generation. This has been referred to as an ‘epi- demic’ of myopia, and it has co-incided with the cultural and dietary changes resulting from the closer contact of the native groups with the ‘western’ way of life characteristic of the Cau- casians of North America and Europe.

Although components of refraction such as axial length of the eye and radius of corneal curvature are inherited, there is good agreement that there is no correlation of overall refraction between parents and children, while a correlation does exist between siblings. Attention has there- fore concentrated on environmental factors, of which an increase in close work due to compulsory schooling, and a change in diet are the leading contenders.

The problem has been that it has not been possible to separate the effect of these two factors in epidemiological studies because the change in schooling and change in diet almost ivariably occurred in a given settlement at the same time. They may of course be combining to produce the effect. At the present time the balance of opinion and what evidence is available appears to favour the near-work hypothesis, possibly aggravated by the near work being performed in poor illumina- tion during the darkness of the long arctic winter.

The following is a survey of the papers available so far, dealing with the topic.

Prevalence of myopia in arctic populatiqns. early reports

Data on the prevalence of myopia in Inuit (Eskimo) and North American Indian Popula- tions of the Arctic are relatively recent. Traditio- nally myopia has been considered rare, on account of explorers emphasizing Inuit’s excellent distance vision for hunting.

Bind in 1947 (1) found no cases of myopia in the Eastern Canadian Arctic amongst the 250 Inuit he examined before his ship sank.

In a detailed study of the eastern Greenland community of Angmagssalik Eskimos, published in 1954, Skeller (2) recorded myopia of more than -0.75 in only 13 eyes out of 1123 ‘spherical’ eyes examined, with cycloplegia with either homa- tropine or atropine, according to age, and reti- noscopy. No myopia equal to or greater than -1.25 was found amongst those with ‘spherical’ refraction (difference between the two planes equal to or less than 0.5 D). Nevertheless, if all degrees of myopia are taken, from -0.25 to - 1.25, the proportion of the total eyes was much higher amongst both males and females aged under 30 than equal to or greater than 30 years.

Elizabeth Cass (3) wrote that her figures in 1962 showed 4.7% of myopia in adults, and 16.6% in children of the Eskimos she examined in the Canadian western Arctic. Earlier in the same article she made the bold statement: ‘Myopia is unknown among the pure blooded adult Eskimo’. This apparent discrepancy is qualified in her later

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article (1973): ‘However, when I first went North, myopia was never present amongst the older Indians and Eskimos unless white blood was present. But the children who went to residential schools, or whose parents came and lived in the settlements, all began to develop myopia (4).

An ‘epidemic’ of myopia amongst Inuit

Following observations by their colleagues Box and Johnson, it was Dr Francis Young and his associates who first drew the attention of the ophthalmic world to the very high prevalence of myopia in Barrow, Alaska, amongst Eskimos below the age of 40 (5). If the population between 11 and 40 was considered, 146 out of 284 subjects or 5 1.4% showed at least 0.25 dioptre of myopia in the right eye. This far exceeded the proportion of myopia usually demonstrated in any American or European population.

Young and colleagues looked at the parent/ children correlations in this population. Most of the parents who were in the age group 30 and above were not myopic. Only 16 out of 19 1 (8.4%) in this age group showed any myopia, while 133 out of their 227 offspring (58.6%) were myopic. Amongst the 54 people of the first generation aged 56 and above there was not a single example of myopia.

The phenomenon of a rapid increase in the younger generation was soon confirmed in Cana- dian Inuit. In 1972 a major survey of 16 Arctic settlements which were accessible was conducted by the Government of Canada and four Canadian universities. A total of 2833 Inuit and 844 Indians were examined (6,7). Myopia was 4-8 times more frequent in younger Eskimos (aged 15-30 years) than in older persons. This was termed an ‘epide- mic of myopia’ amongst the young people because its prevalence far exceeds that expected from the experience of the elders. The peak of myopia was atage 15.

Alsbirk & Forsius (8) reported the results of cycloplegic refraction as part of their study of anterior chamber depths in Augpilagtoq (Green- land), Igloolik (Eastern Canadian Arctic) and Wainwright (Alaska). Differences were insignifi- .cant in the case of middle aged and older people who were, on average, slightly hypermetropic. But the three young groups differed greatly, myopia of - 1.7 D being characteristic of Igloolik, while the young in Augpilagtoq were the same as their parents. The Inuit of Wainwright up to age 30 were intermediate with respect to myopia.

Thus at this time (reported in 1973) the ‘epidemic of myopia’ amongst the Canadian Inuit was supported, while it was not apparent i Greenland.

T w o years later (1975) Morgan et al. (9) pub- lished similar findings from two Canadian settle- ments - Gjoa Haven and Spence Bay - not included in the earlier Arctic survey. The pre- valence of myopia was determined for each sex and for two age groups, 15-29 and 30 and over. For males it was 18.5% compared with 3.2%, and for females 43% compared with 5.5% in those 30 years and older.

However, Woodruff & Samek (10) found that the Eskimos of the Belcher Islands failed to ex- hibit the trend to myopia which Morgan and Boniuk showed in Eskimos of the high Arctic.

An increase in myopia in a Labrador communi- ty in those aged 10-40 compared with the gene- ration 40 and over has been reported by Johnson et al. ( 11). This applied equally to the population believed to be of pure Eskimo extraction as well to those where there was known to be an admixture of white genes.

On the other hand, no adolescent ‘epidemic of myopia’ was found by Alsbirk (12) in the Umanaq district of West Greenland. Myopia was fairly frequent in all adult age groups. The develop- ment of this area throughout this century has been fairly steady, the adults all having attended school and using a written language.

Recently a very high prevalence of myopia has been recorded in Yupik Eskimos of South We- stern Alaska by Alward et al. (13). All the sur- vivors of a birth cohort from 10 remote villages were followed. Refractive data was obtained on 92% of the 278 survivors. In 68% there was myopia of -0.50 D or more. The mean refractive error was higher for women. The authors say that no higher rate of myopia has been reported in any population group sampled in an unbiased manner.

American Indian populations

The figures for Indians of the Yukon and North- west Territories seen in the Arctic survey were analysed by Morgan 8c Munro (6). As with the Eskimos, they found a peak prevalence of myopia between ages 15 and 25, reaching 30% at age 20.

A total of 95 1 records of Sioux Lookout Indians of north western Ontario, seen as part of the eye care service, were analysed by Boniuk (7), and compared with data on 504 Indians from Big Trout Lake and Fort Hope in the Northwest

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Territories. Both groups of Indians displayed a sharp rise in prevalence of myopia in the 10-25 year age group, similar to the pattern in Eskimos of the western Arctic. The pattern was compar- able in the two Indian groups, but differed in degree, the Sioux Lookout group being affected in higher proportion.

Woodruff & Samek (14) also obtained data on samples of the Indian population of Sioux Look- out, and in addition from Moose factory and Moosenee and from the Thunder Bay zone. Their figures supported the statement that myopia was present in epidemic proportions in younger Ame- rican Indians, but there was a lesser percentage of myopic persons in the age group 10-30 years than suggested by the results of Morgan or Boniuk. They felt that their samples were less biased by visual selection. Also, the percentage of myopia was greatest in the 10- 14 year age group, whereas Morgan’s sample showed the highest per- centage in the 20th year.

White populations in far north

A total of 4863 school children aged from 6- 16 years were screened in the Murmansk area, in the Yamato-Neuetsk and Chukotka regions (areas with a severe climate), and in the Krasnodar area (in the south) (15). Myopia was found in 11-39% of the children in the north but only 5-8% of those in the south.

Discussion Explanation for the increase in myopia

The following explanations have been suggested by Morgan & Munro (6) for the observed pattern:

1) Earlier mortality for myopes, with sub- sequent lower rates in older populations.

2 ) A recent increase in fecundity of myopes, in the past 30 years, giving rise to more young myopes.

3) Hybridization with ‘new’ genes (white) not previously affecting the native people.

4) A change in selection with culture (i.e. male myopes may have been rejected as husbands in earlier times because of hunting problems, but may now be selected because of alternative liveli- hoods).

5) Dietary change, pre-natal, peri-natal, or post- natal, especially an increase in carbohydrate in- take. This could affect eye structure.

6) Change in eye use giving rise to myopia.

7) A reversal or ‘spontaneous cure’ of myopia

8) Combinations of the above.

Schooling has been frequently blamed.

after age 25.

There is no evidence so far either from the literature or in experience for an increased mor- tality of young adult myopes, for a cultural change that makes myopes more desirable as husbands or fathers, or that there has been a recent increase in the fecundity of native myopes.

Although longitudinal studies would be re- quired to demonstrate a reversal or ‘spontaneous cure’ of myopia after the age of 25, there is no suggestion or suspicion in any of these arctic studies that the adults had a higher degree of myopia when they were younger.

Although Cass (3) attributed the epidemic of myopia at least partly to an admixture of ‘white’ genes, it is likely that several changes were taking place simultaneously in these communities as they became exposed to the influence of white Cana- dians and Americans. Labrador has been visited by white seamen and whalers for centuries, and there have been white settlers for several genera- tions. In our study, Eskimos of pure lineage were considered separately from those of mixed an- cestry ( 11). The increased prevalence of myopia in those under 35 followed the same pattern in both groups, but was more pronounced in the pure Eskimos.

Woodruff 8c Samek (14) pointed out that myopia occured with approximately the same prevalence in all sets of their sample of Indians from three different zones. It was unlikely that ‘new genes’ could be distributed over so vast an area and among so many isolated settlements in so consistent a manner.

Is the increase in myopia taking place in the offspring of parents who are already myopic? Most studies do not find any significant correla- tion between the refractions of parents and children, while the correlations between siblings were high and significant. Young et al. (5), for example, studied 4 1 families comprising 197 sub- jects in this way. Except for severe hyperopia, refractive characteristics of Inuit parents and children correlated poorly. They interpreted their results as suggesting that there was no major hereditary component involved in development of myopic refractions among the offspring and

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that a strong environmental component was likely to be operating.

Young’s findings and conclusions were severely criticised in a letter by Sorsby (16) on the basis that the distribution of the refractions presented un- usual features, suggesting that there was a strong element of self-selection of the volunteers, and that there was questionable validity in any corre- lation study on refraction carried out, while the offspring were still undergoing changes in re- fraction. The objections were, for the most part, adequately answered by Young in a subsequent letter. The data of Morgan et al. (9) did not support the hypothesis that proband’s relatives have a prevalence of myopia greater than the expected values calculated from age- and sex- specific population frequencies, as would be ex- pected if the condition had a strong genetic or familial tendency.

In Gjoa Haven and Spence Bay the cohort of young myopes did not consist of the offspring of a few older myopes. However, in Labrador it emerged that 76 (of the total of 116) myopes came from 20 families in which myopia was present in 2 or more generations (11). While there was no correlation between parents and children for Te-

fraction, a significant correlation existed for axial length - one of the ocular components believed by Sorsby and Benjamin to be inherited. Inheritance of axial length, corneal diameter and lens position had also been confirmed by Alsbirk in a study of Greenland Eskimos.

Environmental factors

There is agreement among all the authors who have studied the phenomenon of incresed myopia in the Arctic and sub-Arctic that a strong environ- mental factor is at work, but this does not necessarily imply that there is no genetic compo- nent: the environmental factor preventing com- plete harmonization of the refractive components is more likely to have its effect on an eye with a genetically determined axial length.

The influence of near work

The two main environmental factors which have been brought forward as the explanation for the‘epidemic’ of myopia amongst young Inuit and Indians have been an increase in close work asso- ciated with the introduction of schooling, and a change in the traditional native diet. The problem with all these studies has been that the change in

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schooling has usually coincided with other cul- tural changes, including access to high carbo- hydrate foods shipped in from the South

For Young et al. (5) the major change in Barrow, Alaska, was the advent of compulsory schooling. They also emphasized that at this lati- tude there are 4.5 months during which less than 6 h of daylight is possible. Also, in the Eskimos homes there were usually very low levels of artifi- cial light. Thus long periods of darkness require use of eyes for 8 h or more at low levels.

Woodruff (14) argued against poor lighting being a factor because the prevalence of myopia amongst young Indians was greatest at Moosenee where the lighting in the school was better than in other settlements.

Only two papers were able to provide evidence that myopia was associated with increased school- ing. In Spence Bay and Gjoa haven both male and female myopes had had more years of school than their non-myopic comtemporaries (9). Myopes also attended school more regularly than did non-myopics. Scholastic achievement was meas- ured by Johnson et al. (1 1) in two ways: mean school grade achieved by the Inuit was higher for myopes than hyperopes but this was not so for the mixed population; second, more myopes in both groups achieved Grade 8 than did those with other refractions.

Change in diet

Boniuk (7) and also Alward et al. (13) bring forward both diet and near work as the environ- mental factors responsible, but do not separate them. Morgan 8c Munro (6) favour diet but with- out any firm reasons.

Cass emphasized the extent of the change in the Eskimo diet from high protein, low salt and car- bohydrate to one of low protein, high carbo- hydrate and salt (3,4). Woodruff & Samek (10) felt that the relative freedom from myopia in the Belcher Islands was due to the fact that most of their diet came from wild meat.

Young (5) however, reasoned against a change in diet being the most important factor on the north slope of ,Alaska because it was the adult males who were employed who were having at least one American type meal a day prepared by American chefs, while the wives and children of these employees were still eating essentially the basic Eskimo diet of caribou, whale and other mammals.

There is really insufficient firm data on the details of dietary change to be able to go any further. However, a change of diet may be acting synergistically with other factors such as close work, perhaps in poor lighting.

Association of refraction with body stature

I f a change of diet is associated with the refractive changes it might be expected that this would be reflected in an alteration of body stature. Three papers have some information. Morgan et al. (9) found no difference in height or weight between myopes and non-myopes of either sex or for two age groups. Alsbirk (18) could show no association between height and refraction.

On the other hand, Johnson et al. (11) found that the mean height of both Inuit and mixed populations aged 20-40 was greater than that of those over 40 (males by 7.24 cm, females by 3.55 cm). There was a significant positive correlation between height and axial length of the eye in this population over the age of 20. There were also significant differences in the mean axial length for different refractive states, the myopic eyes having the largest axial length. Unfortunately the refractive errors were not correlated directly with height.

Does the increase in myopia matter?

First there is no evidence in any of the literature from the Arctic regions that there was reduction in corrected visual acuity as a result of myopia. Second, the large increases in young myopic indi- viduals were in general in the low range of re- fractive error.

Although Bind found no myopia himself, pre- vious records showed correction ordered for one patient with - 15.00 D of myopia.

In the study of American Indians by Woodruff ( 14), a total of 40 18 individuals were examined, giving readings of refractive errors for 7577 eyes. The number of refractive errors more myopic than -7.00 dioptres was 47 eyes, in which the spherical equivalent ranged from -7.12 to - 15.00 dioptres. Boniuk found myopia greater than -50 in 4.2% of 957 Indians.

In the Canadian Arctic Survey myopia greater than 5.00 D was ‘not a major problem in either race’ (6). In the Eskimos of the Belcher Islands there was no myopia over -3.00 D (lo), nor in Labrador over -5.00 D (11).

In Eastern Greenland Skeller (2) found no myopia over -1.25 D, while in the West Alsbirk

(12) had refractive errors more negative than -5.00 in only one eye of two men (- 10.00 D and -5.50 D), and in one eye of two women (-6.25 D and -6.00 D), i.e.: in one eye of 0.8% of the people bilaterally refracted.

Higher degrees occurred amongst the Yupik, who were also the population with the highest rates of myopia in the younger age group: 17 individuals (6.8% of 252 subjects) had myopia between -5.50 D and- 10.63 D (13).

N o case of retinal detachment or serious ocular complications has been attributed to myopia in any of these populations. Nevertheless, we must keep in mind Perkin’s (19) demonstration in Britain that even lower degrees of myopia, less than -5.00 D, are associated with an increased risk of retinal detachment, glaucoma and possibly cataract.

References

1. Bind E (1950): Carrying optometrical service to the Eskimos of the Eastern Arctic. Am J Optom and Arch Am Acad Opt 2: 24-3 1.

2. Skeller I (1954): Anthropological and ophthalmolo- gical studies on the Angmagssalik Eskimos. Medde- lelser om GrGnland 107: 1-211.

3. Cass E (1966): Ocular conditions amongst the Ca- nadian Western Arctic Eskimo. Exerpta Med Int Gong Ser 146. Proc 20th Int Congr Ophthalmol.

4. Cass E (1973): A decade of northern ophthalmo- logy. Can J Ophthalmol8: 2 10-2 17.

5. Young F A, Leary G A, Baldwin W R et al. (1969): The transmission of refractive errors within Eskimo families. Am J Optom Arch Am Acad Opt 46: 676-685.

6. Morgan R W & Munro M (1973): Refractive pro- blems in northern natives. Can J Ophthalmol 8:

7. Boniuk V (1973): Refractive problems in native

8. Alsbirk P H & Forsius H (1973): Anterior chamber

266-228.

peoples. Can J Ophthalmol 8: 229-233.

9.

depth in Eskimos from Greenland, Canada (Igloo- lik) and Alaska (Wainwright). Can J Ophthalmol 8:

Morgan R W, Speakman J S & Grimshaw S E (1975): 265-269.

Inuit Myopia: an environmentally induced ‘epide- mic’? Can Med Ass J 112: 575-577.

10. Woodruff M E & Samek M J (1976): The refractive status of Belcher Island Eskimos. Can J Pub1 Health

11. Johnson G J, Matthews A & Perkins E J (1979): Survey of ophthalmic conditions in a Labrador Community. I. Refractive errors. Br J Ophthalmol 63: 440448.

67: 3 14-3 19.

2 Myopia 17

12. Alsbirk P H (1979): Refraction in adult West Green- land Eskimos. A population study of spherical re- fractive errors, including oculometric and familial correlations. Acta Ophthalmol (Copenh) 57: 84-95.

13. Alward W L M, Bender T R, Demske J A & Hall D B (1985): High prevalence of myopia among young adults Yupik Eskimos. Can J Ophthalmol 20: 241- 245.

14. Woodruff M E & Samek M J (1977): A study of the prevalence of spherical equivalent refractive states and anisometropia in Amerind populations in On- tario. Can J Pub1 Health 68: 4 14424.

15. Rozenblum Y Z (1984): Refraction in schoolchild- ren in the Far North and ways of preventing myopia. Vestn Oftalmol 10 1: 34-39 (in Russian).

16. Sorsby A & Young F A (1964): Transmission of refractive errors within Eskimo families (corre- spondence). Am J Optom Arch Am Acad Opt 46: 246; 246-249.

7. Young F A, Baldwin W R, Leary G A et a1 (197 1): Comparison of cycloplegic and non-cycloplegic re- fractions of Eskimos. Am J Optom Arch Am Acad Opt 48: 8 14-825.

8. Alsbirk P H (1977): Variation and heritability of ocular dimensions. A population study among adult Greenland Eskimos. Acta Ophthalmol (Copenh) 55: 443-456.

19. Perkins E S (1979): Morbidity from myopia. Sight Sav Rev 49: 11-19.

Author's address:

Professor Gordon J. Johnson, Institute of Ophthalmology, Moorfields Eye Hospital, Dept. of Preventive Ophthal. 27-29, Cayton Street London EClgEJ, England