2.3
Myopia and Glaucoma
Shamira A. Perera* and Tin Aung*,†
Introduction
Myopia is associated with glaucoma. The evidence in this area stems from large-scale epidemiological studies and clinical studies. The finding that a person is myopic has certain implications for their subsequent investigation and assessment from a glaucoma perspective, and influences the interpretation of tests, clinical assessment, and management. This chapter will summarize the association between myopia and glaucoma, the possible reasons for the associations that have been determined, and the clinicopathological correlation of the sequelae of myopia on glaucoma assessment.
The Association Between Myopia and POAG
Information from epidemiological studies
The association between refractive error and glaucoma has been the subject of many clinical trials and population-based studies.1–4 Most have suggested that moderate to high myopia is associated with the increased risk of primary open angle glaucoma (POAG),5,6 low-tension glaucoma,7,8 and ocular hypertension.9–12
For a Caucasian population in the Blue Mountains Eye Study (BMES) in Australia, eyes with moderate myopia were two times more likely to have POAG, after adjusting for age, sex, and other risk factors.13
*Singapore Eye Research Institute & Singapore National Eye Center, Singapore. E-mail: shamiraperera@hotmail.com
†Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore.
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122 S.A. Perera and T. Aung
Importantly, a dose-response pattern between the increasing severity of myopia and prevalence of glaucoma was observed. However, this was not appreciated in the other two large epidemiological studies (Barbados and Beaver Dam Eye Studies).14,15 In the Barbados Eye Study, a myopic refraction was one of several risk factors for POAG in adult black people.16 The Beaver Dam Eye study showed that after taking into account the effects of age, sex, and other risk factors, persons with myopia were 60% more likely to have glaucoma than those with emmetropia.15 (Table 1)
The Malmö eye survey4 found that the prevalence of glaucoma was dose-related to the level of myopia. This association was particularly strong at lower intraocular pressure levels.17
However, not all studies have found significant relationships; notably no association between myopia and POAG was found in the Ocular Hypertension Treatment Study (OHTS) in an ethnically mixed population of Americans.3 An interesting study looking at inter eye differences in refractive error and the inter eye degree of glaucomatous optic nerve damage showed that the refractive error did not play a major part, at least for eyes not exceeding –8 D.17
Asian populations: Myopia and POAG
In Asian populations, myopia is generally more common18 and the incidence is increasing. The Beijing Eye Study from China found a significant relationship between POAG and high myopia <−6 D19 compared to the remaining eyes. In contrast, in hyperopic eyes, emmetropic eyes and eyes with low to moderate myopia (myopic refraction up to −6 diopters or less), the frequency of glaucoma did not vary significantly.
The Meiktila Eye Study, conducted in Myanmar, also found an association with myopia, albeit weaker than the other studies.20 Similarly, the population-based study in Singapore Malays (SiMES) showed an association between moderate or higher myopia (worse than –4 D) and POAG. Persons with moderate or higher myopia had an almost three times higher risk of POAG compared to emmetropes. In Singapore Malays, there was an association between increasing axial length (AL) (measured using the IOLMaster, Carl Zeiss Jena, Germany) and POAG. This association of moderate or higher myopia and POAG was no longer significant after controlling for AL, suggesting that axial myopia rather than other
Table 1. Prevalence and Odds Ratio of POAG, by Refractive Status, SiMES, BDES and BMES, Right Eye only
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|
SiMES |
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|
|
BDES |
|
|
|
|
BMES |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Baseline Refractive |
No. of |
% with |
Age-Sex OR |
No. of |
% with |
Age-Sex OR |
No. of |
% with |
Age-Sex OR |
||||
Status |
|
Eyes |
POAG |
(95% CI) |
Eyes |
POAG |
(95% CI) |
|
Eyes |
POAG |
(95% CI) |
||
|
|
|
|
|
|
|
|
|
|
||||
Myopia |
583 |
3.3 |
1.7 (0.9, 3.2) |
1073 |
3.0 |
1.6 (0.9, 2.6) |
475 |
4.4 |
2.0 (1.1, 3.7) |
||||
Emmetropia |
1511 |
1.7 |
1.0 |
|
1583 |
2.2 |
1.0 |
|
1533 |
1.8 |
1.0 |
||
Hyperopia |
788 |
1.9 |
0.9 (0.5, 1.7) |
734 |
4.0 |
1.1 (0.7, 1.7) |
1646 |
1.5 |
0.6 (0.3, 1.0) |
||||
Refraction |
|
|
|
|
|
|
|
|
|
|
|
|
|
Less than −3.00 |
217 |
3.7 |
2.1 (0.9, 4.8) |
339 |
3.0 |
1.7 (0.8, 3.5) |
165 |
4.2 |
2.4 (1.0, 5.7) |
||||
−1.00 to −3.00 |
366 |
3.0 |
1.5 (0.7, 3.2) |
734 |
3.0 |
1.5 (0.9, 2.6) |
310 |
4.5 |
1.9 (1.0, 3.7) |
||||
−0.75 to +0.75 |
1511 |
1.7 |
1.0 |
|
1583 |
2.2 |
1.0 |
|
1533 |
1.8 |
1.0 |
||
+1.00 to +2.25 |
651 |
1.8 |
0.9 (0.4, 1.8) |
1256 |
3.7 |
1.1 (0.7, 1.7) |
1029 |
1.2 |
0.5 (0.2, 1.0) |
||||
More than +2.25 |
137 |
2.2 |
0.9 (0.3, 3.2) |
600 |
4.7 |
1.1 (0.7, 1.8) |
617 |
1.9 |
0.6 (0.3, 1.3) |
||||
Myopia: −1.00 diopters or less; Emmetropia: between −0.75 and +0.75 diopters; Hyperopia: +1.00 diopters or greater. Abbreviations: SiMES — Singapore Malay Eye Study; BDES — Beaver Dam Eye Study; BMES — Blue Mountains Eye Study.
Glaucoma and Myopia 123