2.2
Ocular Morbidity of Pathological Myopia
V. Swetha E. Jeganathan*,†,‡,§, Seang-Mei Saw‡,¶
and Tien-Yin Wong†,‡
Introduction
The epidemic of myopia is a public health concern, particularly in East Asia (Singapore, Taiwan, Hong Kong, Japan).1–4 In Singapore, the prevalence of myopia is one of the highest worldwide, affecting 9% to 15% preschool children,5–7 29% primary school children,8 70% of high school students,9 80% in military conscripts,10,11 and almost 90% of medical students.12 The Tanjong Pagar Survey first suggested that the prevalence of myopia (< −0.5 D) in Chinese adults 40 years and older wasnearly twice the rates in similarly aged Caucasian populations, including the Melbourne Visual Impairment Project.13,14 Furthermore, compared to ethnic Malays, the Chinese in Singapore have a higher prevalence of myopia (37.8% versus 33.3%).13,15 A large proportion of Singaporeans have pathological myopia (< −6 D), which has been observed across the whole age range spectrum,16 including 15% of Singapore’s military conscript population.11 The prevalence of high myopia is especially significant in parts of East Asia, with rates of 9–21%, compared with 2–4% in Caucasians.10 In the Tanjong Pagar Eye Study, Chinese women had significantly higher rates of high myopia than men, with bimodal age pattern of myopia, higher prevalence in the 40 to 49 and 70 to 81 age groups, and lower prevalence
*Corresponding author. E-mail: jvswetha@yahoo.com
†Centre for Eye Research Australia, University of Melbourne, Victoria, Australia.
‡Singapore Eye Research Institute, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
§Tun Hussein Onn National Eye Hospital, Malaysia.
¶Department of Community, Occupational & Family Medicine, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
97
98 Jeganathan et al.
between those age ranges.13 In comparison, the prevalence of pathological myopia (< −7.9 D) is less than 0.4% in most Western countries.17
Of particular concern is that the prevalence and severity of myopia has increased significantly in Singapore over the last two decades across a whole spectrum of ages.3 Serial cross-sectional data from the Singapore Armed Forces, reveal that the prevalence of low vision myopia in military conscripts aged 18 to 25 years has increased from 26% in the late-1970s, to 43% in the 1980s, 66% in the mid-1990s, and 83% by the late 1990s, accompanied by a two-fold rise in the proportion with pathological myopia (< −8 D) from 2% (1993) to 4% (1997).10,18,19 A similar trend of increasing myopia prevalence has been observed in schoolchildren.20 The risk factors for myopia include higher education, urban residential status, higher income, professional occupation, and increased near work.4 However, the underlying explanation for the worsening trend of myopia prevalence and severity is poorly understood and is likely complex and multifactorial, given that East Asian countries with high myopia have similar socioeconomic demographic risk factors as in the West.21
Pathological myopia is the fourth leading cause of blindness in Singapore,22 and may be associated with a myriad of potentially blinding, irreversible conditions such as retinal detachment and myopic macular degeneration.23 Patients with pathological myopia (≤ −10 D) have also been shown to experience impaired quality of life.24 Lower utility values in myopic Singapore high school children are a good example.25 Despite previous studies supporting the numerous associations between pathological myopia and ocular complications,16 limitations in study design prevent inference of causality.
Definition of Pathological Myopia
The terms “pathological myopia,” “degenerative myopia,” “malignant myopia,” or “high myopia” are commonly used interchangeably; however, there is no standardized definition of pathological myopia to date. Duke and Elder first defined pathological myopia as myopia accompanied by degenerative changes in the sclera, choroid, and retinal pigment epithelium, associated with compromised visual function.26 Tokoro later defined pathological myopia as myopia caused by excessive and progressive axial elongation.27 Some studies have defined pathological myopia as high myopia (≤ −6 D) and/or axial length of >25.5 mm.10,18,28 Furthermore,
99 Ocular Morbidity of Pathological Myopia
there is no standardized cut-off for pathological myopia to date. Common definitions of pathological myopia include spherical equivalent of at least −6 D, −8 D, or −10 D.
In the Blue Mountains Eye Study (BMES), myopic retinopathy included the presence of staphyloma, lacquer cracks, Fuch’s spot, and/or myopic chorioretinal thinning or atrophy.29 Other signs include β-peripapillary atrophy, cytotorsion (tilting of the optic disc), and the T-sign found in central retinal vessels.30 Shih and co-authors used a grading system by Avila for myopic macular chorioretinopathy.31 MO indicated a normal posterior pole with no tessellation pattern in the macular area; M1 indicated tessellation and choroidal pallor pattern in the macular area; M2 indicated choroidal pallor and tessellation, and the border of an ectasia posteriorly was visualized; M3 indicated pallor and tessellation with several yellowish lacquer cracks in Bruch’s membrane and posterior staphyloma; M4 showed choroidal pallor and tessellation, with lacquer cracks with posterior staphyloma and focal areas of deep choroidal atrophy; M5 indicated choroidal pallor and tessellation with lacquer cracks, posterior staphyloma, geographic areas of atrophy of retinal pigment epithelium and choroids, and choroidal neovasculariation were visualized. M3 or greater was defined as “with maculopathy.”32 Jonas graded peripapillary tessellation from 0 for “no tessellated fundus” to 3 for “very marked tessellated fundus.”33 Thus, the systematic grading of fundus photographs in population-based epidemiologic studies is important in assessing the prevalence and extent of myopia-associated pathology. However, there are few grading systems developed for pathologic myopia that have been consistently used across multiple study populations.
Cataract
The association between pathological myopia and cataract is well known.16,34,35 Evidence from epidemiological studies on the relationship of high myopia and cataract are summarized in Table 1.15,35–43 Several population and clinic-based studied have confirmed a strong and consistent association between high myopia and age-related nuclear sclerosis (NS) in adults aged more than 40 years.15,39,40–42,44–47 In the Singapore Malay Eye Study of 3000 Malay adults aged 40 to 80 years, there was a U-shaped relationship between increasing age and the prevalence of myopia, which was partially explained by the age-related increase in the
Table 1. Summary of Published Data on Myopia and Cataract
|
|
|
Study |
Sample |
Age |
|
Definition of |
Summary of Main |
Source |
Year |
Place |
Design |
Size (n) |
(Years) |
Methodology |
Myopia |
Findings |
|
|
|
|
|
|
|
|
|
Brown |
1987 |
Oxford, |
CCS |
220 |
≥ 40 |
SR Lens |
Excluded high |
Crude OR of myopia = 1.06 |
and Hill35 |
|
United |
|
|
|
photography |
myopia |
95% CI (0.6, 1.9). |
|
|
Kingdom |
|
|
|
(cataract) |
(−12 D) |
|
Lim et al.; |
1999 |
Sydney, |
PBCS |
7308 |
49–97 |
AR and SR |
High myopia |
OR of cataract prevalence, |
Blue |
|
Australia |
|
|
|
Lens |
(≤ −6 D) |
adjusted for age, sex, smoking, |
Mountains |
|
|
|
|
|
Photography |
|
hypertension, diabetes, steroids, |
Eye Study36 |
|
|
|
|
|
|
|
sun related skin damage: |
|
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|
PSC = 4.9 (2.1, 11.4) |
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CC = 2.9 (1.4, 6.0) |
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|
NS = 1.4 (0.8, 2.4). |
McCarthy |
1999 |
Melbourne, |
PSC |
5147 |
≥ 40 |
AR Lens |
≤ −1 D |
OR of cataract prevalence: |
et al.; |
|
Australia |
|
|
|
photography |
|
PSC = 3.59 (2.5, 5.15), |
Visual |
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(cataract) |
|
adjusted for age, rural, |
Impairment |
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diuretics, vitamins A and E, |
Project37 |
|
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|
ultraviolet light; CC = 1.76 |
(1.3, 2.4), adjusted for age, gender, iris, arthritis, diabetes, gout, beta-blockers, ultraviolet light, glaucoma NS = 2.73 (1.9, 3.92), adjusted for age, gender, diabetes, smoking and education.
(Continued )
.al et Jeganathan 100
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Table 1. |
(Continued ) |
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Study |
Sample |
Age |
|
Definition of |
Summary of Main |
Source |
Year |
Place |
Design |
Size (n) |
(Years) |
Methodology |
Myopia |
Findings |
|
|
|
|
|
|
|
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|
Wu et al.; |
1999 |
Barbados |
PBCS |
4036 |
40–84 |
AR |
≤ −0.5 D |
A higher prevalence of |
Barbados |
|
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myopia was positively |
Eye Study38 |
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associated (P < 0.05) with |
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NS, PSC, glaucoma, and |
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ocular hypertension. |
Dandona et al.; |
1999 |
Hyderabad, |
PBCS |
2321 |
≥16 |
AR |
≤ −0.75 D |
With multivariate analysis, |
the Andhra |
|
India |
|
|
|
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|
myopia was higher in |
Pradesh Eye |
|
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subjects with NS ≥ 3.5 |
Disease Study39 |
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(OR 9.10; 95% CI, |
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5.15–16.09), and those |
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with education of class |
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11 or higher (OR 1.80; 95% |
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CI, 1.18–2.74). |
Wong et al.; |
2001 |
USA |
PBCS |
4470 |
43–84 |
AR (baseline); |
≤ −1 D |
Myopia not associated with |
Beaver Dam |
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|
Lens |
|
incident cataract. OR of |
Eye Study |
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photography |
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prevalent cataract for |
(FU = 5 years)40 |
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(prevalent |
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myopia, adjusted for age, |
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cataract at |
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gender, diabetes, smoking, |
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baseline and |
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education: PSC = 1.23 |
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incident |
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(0.75, 2.03) CC = 0.86 |
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cataract at |
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(0.64, 1.16) NS = 1.74 |
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5 years) |
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(1.28, 2.37). |
(Continued )
Myopia Pathological of Morbidity Ocular 101
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Table 1. |
(Continued ) |
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Study |
Sample |
Age |
|
Definition of |
Summary of Main |
Source |
Year |
Place |
Design |
Size (n) |
(Years) |
Methodology |
Myopia |
Findings |
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|
Younan et al.; |
2002 |
Sydney, |
PBCS |
2334 |
≥ 49 |
AR and SR |
≤ −3.5 D |
OR of incident cataract: |
Blue Mountains |
|
Australia |
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(baseline); |
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PSC = 4.4 (1.7, 11.5) |
Eye Study |
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Lens |
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adjusted for age, sex, |
(FU = 5 years)41 |
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photography |
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education, obesity, |
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(cataract at |
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hypertension, NS. |
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5 years) |
≤ −6.0 D |
CC = 0.5 (0.2, 2.0), adjusted for |
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age, sex, education, alcohol, |
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uv light, diabetes, obesity, |
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stroke, NS. |
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≤ −6.0 D |
NS = 3.3 (1.5, 7.4) adjusted for |
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age, sex, smoking, education, |
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iris, inhaled steroids. |
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Incident cataract surgery was |
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significantly associated with |
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any myopia (OR 2.1, 95% |
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CI 1.1–4.2), as well as |
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moderate (−3.5 to more than |
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−6 D; OR 2.9, 1.2–7.3) and |
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high myopia (OR 3.4, 95% |
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CI 1.0–11.3). |
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(Continued ) |
.al et Jeganathan 102
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Table 1. |
(Continued ) |
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Study |
Sample |
Age |
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Definition of |
Summary of Main |
Source |
Year |
Place |
Design |
Size (n) |
(Years) |
Methodology |
Myopia |
Findings |
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|
Wong et al.; |
2003 |
Singapore |
PBCS |
1232 |
40–81 |
SR, if |
−1.35 D vs |
Adjusted for age, gender, |
Tanjong |
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unavailable |
−0.11 D |
education, diabetes, and |
Pagar Survey42 |
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AR |
−1.80 D vs |
smoking. NS was associated |
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−0.39 D |
with myopia (p < 0.001); |
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PSC was associated with |
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myopia (p < 0.001). |
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Adjustment for vitreous |
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chamber depth attenuated |
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the association between PSC |
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(not NS) and myopia by |
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65.5%. |
Chang et al.; |
2005 |
Salisbury, |
PBCS |
2520 |
65–84 |
AR |
|
OR for incident cataract: |
Salisbury Eye |
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United |
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−0.50 D and |
NS = 2.25 (P < 0.001) |
Evaluation |
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Kingdom |
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−1.99 D |
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Project43 |
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−2.00 D and |
NS = 3.65 (P < 0.001) |
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−3.99 D |
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−4.00 D and |
NS = 4.54 (P < 0.001) |
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−5.99 D |
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−6.00 D or |
NS = 3.61 (P = 0.002) |
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more |
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−0.50 D and |
PSC = 1.59 (P = 0.11), |
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−1.99 D |
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−2.00 D and |
PSC = 3.22 (P = 0.002) |
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−3.99 D |
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(Continued )
Myopia Pathological of Morbidity Ocular 103
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Table 1. |
(Continued ) |
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Study |
Sample |
Age |
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Definition of |
Summary of Main |
Source |
Year |
Place |
Design |
Size (n) |
(Years) |
Methodology |
Myopia |
Findings |
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−4.00 D and |
PSC = 5.36 (P < 0.001), |
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−5.99 D |
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−6.00 D or |
PSC = 12.34 (P < 0.001). |
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more |
No association was found |
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≤ −0.5 D |
between myopia and CC. |
Saw et al.; |
2008 |
Singapore |
PBCS |
2974 |
40–80 |
SR, if |
In a multiple logistic regression |
|
Singapore |
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unavailable- |
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model, female sex, age, higher |
Malay Eye |
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AR |
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educational level, and cataract |
Study15 |
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were associated with myopia. |
AR: autorefraction, CI: confidence interval, CC: cortical cataract, CCS: case control study, D: dioptres, NS: nuclear sclerosis, OR: odds ratio, PBSC: popula- tion-based cross-sectional study, PSC: posterior subcapsular cataract, SR: subjective refraction.
.al et Jeganathan 104
105 Ocular Morbidity of Pathological Myopia
prevalence of cataract, increasing density of lens nucleus with age, causing a myopic shift in refraction (i.e. index myopia).15 The Tanjong Pagar Survey of 1200 Chinese adults aged 40 to 80 years further supports this hypothesis; NS was associated with myopia (p < 0.001) without any change to axial length or the biometric components.43 In the BMES of Caucasian adults, there was a statistically significant association between high myopia (≤ −6 D) and incident NS.41 A myopic refractive shift occurred in persons with NS levels 4 or higher, attesting the contribution of NS to the mild myopic shift that neutralizes the age-related hyperopic shift occurring in older persons.48 Furthermore, according to the Beaver Dam Eye Study (BDES) five-year follow up, much of the myopic change after the age of 70 may be attributed to increasing NS.40 The NS is often missed because any increase in refraction is generally attributed to an increase in the pathological myopia. Oxidative lens damage is known to occur early in myopic eyes.49 Furthermore, it is unknown whether myopia is a risk factor for NS because NS is known to affect refraction and cause myopia.
The relationship between myopia and posterior subcapsular cataract (PSC) is controversial. In BMES, incident PSC was associated with the presence of myopia (OR 2.1, 95% CI 1.0–4.8), moderate to high myopia (−3.5 D or less, OR 4.4, 95% CI 1.7–11.5).41 Moreover, eyes with the onset of myopia before age 20 years had the greatest risk of PSC (OR 3.9; CI 2.0–7.9), suggesting the possibility of a dose response between the levels of myopia and PSC.36 The Tanjong Pagar Survey showed that PSC was related to deeper anterior chamber, thinner lens, and longer vitreous chamber; and adjusting for these components, especially vitreous chamber depth, attenuated the association of myopia significantly, suggesting that the refractive association of this form of cataract was axial.50 As PSC does not appreciably affect refraction, it was suggested that the relationship between PSC and myopia is causal i.e. myopia may be a risk factor for the development of PSC. In contrast, cortical cataract was not related to myopia, either cross-sectionally or longitudinally in
these studies.15,39,40–42,44–47
Incident cataract surgery was significantly associated with myopia, (OR 2.1, 95% CI 1.1–4.2) as well as moderate (−3.5 to more than −6 D; OR 2.9, 1.2–7.3) and high myopia (OR 3.4, 95% CI 1.0–11.3).41 The BDES found an association between myopia and five-year risk of cataract surgery; most likely due to the presence of PSC, which is known to be the most important lens opacity predicting the need for cataract surgery.41