Myopia is one of the most common ocular abnormalities.1 In the United States, 25% of the adult population were found to be myopic, whereas the prevalence rates were reported to be as high as 80% in Asian populations.1, 2 It can be classified as physiological or pathologic.3 Physiological myopia is a normal variation in the refractive error resulting from excessive convergent power caused by the cornea or the lens. Pathologic myopia is usually associated with an elongated globe and a refractive error of at least -6.00 D and/or an axial length of >25.5 mm.2, 3 The tissue alterations in high myopia affect the sclera, choroid, and retina, which can result in a number of ocular findings and potential complications.4–6
The prevalence of pathologic myopia or high myopia varies from 0.2–13.1% of the general population having the lowest prevalence in the black population and the highest in Asian populations.1, 2 High myopia with an increased axial length has been reported to be associated with a higher incidence of peripheral retinal degenerations such as lattice degeneration, retinal tears and holes, and an overall increased incidence of retinal detachment.5, 6 The prevalence varies widely, however, depending on the ethnic group examined, the method of examination, and the study criteria. Celorio4 found lattice degeneration in 33% of high myopes, whereas Kirker6 found only a 3% incidence in high myopes.
Similarly, earlier data about the correlation between axial length and peripheral retinal changes were inconsistent and sometimes conflicting. Pierro observed a positive correlation between longer axial length and the presence of lattice degeneration, paving stone degeneration, and white without pressure.5 This correlation, however, could not be shown between high myopia and peripheral retinal pigment, retinal tears and retinal detachment.5 Celorio noted the greatest prevalence of lattice degeneration in eyes with axial lengths of 26.0 to 26.9 mm (-6.00 to -8.70 D), but the prevalence of lattice degeneration exhibited an inverse relationship with even longer axial length.4 There were intrinsic limitations about these previous studies because the data were collected retrospectively, and recruited subjects were institution-based with a sample bias toward symptomatic individuals.
A community-based study screening asymptomatic patients with high myopia avoids many of the predispositions introduced by these previous studies. Like many Asian populations, Hong Kong Chinese people have a high prevalence of high myopia. The purpose of this community-based study was to determine the true prevalence and characteristics of peripheral retinal findings in high myopes of the Hong Kong Chinese population and to investigate the relationship among axial length, refractive error, and peripheral retinal degeneration. The results will help determine the necessity and type of ocular screening and disease prevention programs to be used in similar populations.
MATERIALS AND METHODS
This was a cross-sectional prevalence survey of high myopia (≤-6.00 D) conducted in October 1996. The protocol was approved by the Institutional Review Board at the Chinese University of Hong Kong and informed consent was obtained from each of the invited participants.
All subjects were recruited from the community after advertising through the media. The inclusion criteria were as follows: ethnic Chinese with myopia of ≤-6.00 D in at least one eye, an age of 18 years or older, and willingness to sign the study consent. Patients with a history of prematurity, retinal detachment, or those who had a full retinal examination in the past were excluded to minimize selection bias toward symptomatic patients. Eyes with media opacity such as corneal scar or cataract were also excluded from the study.
Each participant received a comprehensive ocular examination. This included best-corrected visual acuity (BCVA) with Snellen chart by certified optometrists, intraocular pressure (IOP) by noncontact tonometer (Rechert XPERT NCT Plus [Buffalo, NY]), slit-lamp anterior segment examination, noncycloplegic and cycloplegic autorefraction (Topcon KR 7100 [Japan]), and ultrasound biometry (A-scan; Storz Compuscan LT [St. Louis, MO]). A dilated retinal examination was performed in a dark room with indirect ophthalmoscope and scleral indentation together with biomicroscopy examination using a Goldmann three-mirror contact lens.
Ocular measurements, including refraction, spherical equivalent, IOP, findings of retinal status, and peripheral retinal lesions and axial length, were recorded.
A total of 213 patients with a refractive error of ≤-6.00 D by cycloplegic autorefraction were examined. One hundred seventy patients had bilateral high myopia, whereas 43 had unilateral high myopia. For those with bilateral high myopia, the correlation in spherical equivalent between the right and left eye was 0.87. The data of the right eye of these patients were used for further analysis. For unilateral cases, only the data of the highly myopic eyes were used. The mean age ± standard deviation (SD) was 33.5 ± 10.6 years (range = 18–73 years). The female to male percentage was 68.5% to 31.5%. The mean spherical equivalent ± SD was -10.10 ± 4.23 D (range = -6.00 to -27.00 D). The distribution of the spherical equivalent refraction in the screened population is shown in Figure 1. The mean astigmatism was -1.29 ± 1.13 D (range = 0.00 to -5.50 D). The measured axial length was 26.69 ± 1.68 mm (range = 25.18–33.62 mm) (Fig. 2). The refractive status was strongly correlated with increasing axial length (r = -0.753, p < 0.001). One hundred fifty-two of 213 eyes (71.4%) had peripheral retinal degeneration. Twenty-four eyes (11.3%) had a single discrete peripheral retinal degeneration, whereas most of the eyes (60.1%) had more than one lesion either of different pathology or at different sites (Table 1). Pigmentary degeneration was the most common peripheral retinal change and was present in 51.2% of eyes with high myopia. It was followed by white without pressure (31.0%) and lattice degeneration (12.2%). Retinal holes or breaks were found in 7.5% of patients and retinal detachment was seen in one eye (0.5%). Most of the lesions were found in the peripheral retina of temporal quadrants, and the prevalence of lesions in both superior and inferior quadrants was similar (Table 2).
The relative axial length was significantly greater in eyes with one or more lesions (27.01 ± 1.75 mm) compared with eyes that did not have any lesions (25.88 ± 1.19 mm) (t-test, p < 0.001). Pigmentary or pavingstone degeneration were more common in eyes with longer axial lengths (p < 0.001, p = 0.042, respectively) (Table 3). The same difference could not be demonstrated for peripheral lattice degeneration. The prevalence of retinal tears or holes was 6.4% and 30.0% in eyes with axial length of <30 mm and ≥30 mm, respectively (chi-squared test, p = 0.006).7
There have been numerous previous studies documenting peripheral retinal findings in myopes. In a general eye clinic, 600 consecutive patients with a mean refractive error of -1.77 D (range = +2.25 to -8.00 D) were studied prospectively and 5.2% were found to have lattice degeneration.8 In other studies, high myopes have been reported to have a greater prevalence of lattice degeneration.4–6, 9–11 Gozum et al. studied 212 eyes and reported that lattice degeneration was associated with high myopia and tended to increase with axial length, although the association did not reach statistical significance.10 Karlin et al. studied the retinal periphery of 1437 predominantly myopic eyes; their results revealed a statistically significant association of increasing axial length with four types of retinal degeneration, namely white without pressure, pigmentary degeneration, pavingstone degeneration, and lattice degeneration.11
Many of these reviews, however, showed a large variation in findings depending on the method of enrollment of patients (especially symptomatic and retinal-based practices) and the ethnic background of the subjects. High myopia is a significant ocular problem in Hong Kong partly because of its high prevalence in the Chinese population. Our study seeks to minimize the bias noted in some of the previous studies by using a community-based sample of subjects and by eliminating patients with a history of retinal problems. Although our study included a homogeneous population of Hong Kong Chinese adults, our study sample would have some bias as a result of self-selection of the patient population. However, the results of this study provide additional information on peripheral retinal findings in the ethnic Chinese population and allow for the planning and recommendation for future screening programs in Hong Kong.
The most common peripheral retinal lesion noted was pigmentary degeneration followed by white without pressure. Lattice degeneration was present in 12.2% of eyes, whereas retinal detachment was present in only 0.5% of this asymptomatic population. Retinal detachment is more common in eyes associated with the presence of peripheral retinal degeneration, especially lattice degeneration. There was an association between axial length and peripheral retinal findings (t-test, p < 0.001). Importantly, a very long axial length may be a risk factor for peripheral retinal tears or holes as demonstrated by a statistically significant correlation (p = 0.006). Only 6.4% of those with an axial length of <30.0 mm compared with 30.0% of those with an axial length of ≥30.0 mm have peripheral retinal tears or holes. Pierro also had similar findings in his study in which he found that eyes with white without pressure, paving stone degeneration, or lattice had a significantly greater axial length.5
The prevalence of lattice degeneration in highly myopic Chinese people is 12.2%, which is higher or at least similar to that reported in ethnic groups.4, 6 Although lattice degeneration is the most significant predisposing factor for retinal breaks or detachments, especially in eyes presenting with acute posterior vitreous detachment,12, 13 it was still not clear if these lesions should be routinely treated. Byer demonstrated a low incidence of retinal detachment in a prospective study of 276 consecutive untreated patients (423 eyes) with lattice degeneration. Clinical and subclinical retinal detachments occurred only in 0.7% and 6.7% of the eyes, respectively, and he suggested prophylactic treatment for lattice might not be justified and should be discontinued.14 However, the majority of the patients in Byer’s group were emmetropic or mildly myopic and relatively young in age. The low incidence of retinal detachments during the follow-up period may be associated with lesser occurrence of posterior vitreous separation during the study period in the study group.14–16
In a case–control study of idiopathic retinal detachment, myopia was demonstrated to be an important risk factor.15 In highly myopic patients reporting a high risk of detachment during their lifetime, the natural course or history of lattice degeneration may be different, and this is supported by studies in individuals with lattice degeneration and high myopia exceeding -5.0 D.16, 17 Burton recommended close follow-up of lattice degeneration in highly myopic patients and suggested prophylactic laser therapy.17 Tillery et al. also reported high myopia as an additional risk factor for phakic retinal detachment apart from the round atrophic holes in lattice degeneration.18
Knowing the accurate statistics of peripheral retinal lesions in highly myopic populations in Hong Kong will allow health policymakers to devise appropriate ocular screening or examination programs. Our study has demonstrated that lattice degeneration is a common peripheral retinal lesion in patients with refractive error of -6.00 D or less, and these were associated with longer axial length. In addition, other studies in highly myopic eyes have shown an increased incidence of retinal detachment in such eyes. In populations with high myopia, routine ocular screening examinations for peripheral lesions are recommended. Patients with findings of lattice degeneration should be informed about the symptoms of acute posterior vitreous detachment and retinal detachment, and be advised to report for ophthalmic evaluation should such symptoms occurs.
Supported in part by the Action For Vision (AFV) Eye Foundation, Hong Kong.
Dennis S. C. Lam
Department of Ophthalmology and Visual Sciences
The Chinese University of Hong Kong
3/F, Hong Kong Eye Hospital
147K Argyle Street
Kowloon, Hong Kong
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Keywords:© 2005 American Academy of Optometry
prevalence; peripheral retinal degeneration; lattice; Chinese; high myopia; survey