Objective
To examine the long-term changes of the axial length in adults with high myopia.
Design
Open-label, consecutive, retrospective case series.
Methods
The medical records of 101 patients (184 eyes) with high myopia (myopia ≥−6 diopters or axial length ≥26.5 mm) were studied. The axial length of the eye was measured by A-scan ultrasonography. The significance of the changes in the axial length during follow-up was determined. The effects of the age, axial length, and the presence of a posterior staphyloma at the initial examination on the axial length elongation were determined.
Results
The mean follow-up period was 8.2 years. The median axial length increased significantly from 28.6 mm at the initial examination to 29.4 mm at the final examination in the 184 eyes. The axial length remained stable (≤1-mm difference) in 69%, whereas the axial length increased by more than 1 mm in 31% of the eyes. For these 31%, the median axial length increased by 1.55 mm. An increase of the axial length per year was significantly greater in older patients than their younger cohorts, and the increase in eyes with a posterior staphyloma was significantly greater than in eyes without a staphyloma. Multiple regression analyses showed that the axial length elongation was positively and significantly correlated with patient age at the initial examination.
Conclusions
In highly myopic adult patients, the axial length continued to increase. Older individuals with posterior staphyloma were more susceptible to having a larger increase in the axial length. A progression of posterior staphyloma with increasing age is considered a key factor for the continuous increase of axial length in adults with high myopia.
Pathologic myopia is a major cause of irreversible vision decrease, and is especially prevalent among Asians. Thus, the Tajimi Study in Japan found that myopic macular degeneration was the leading cause of unilateral and bilateral blindness and that pathologic myopia was the second most frequent cause of low vision and blindness in Chinese individuals who were more than 40 years of age. Pathologic myopia is characterized by an excessive elongation of the axial length of the eye. Although the growth of the axial length of the eye was found to reach adult length by the age of 13 years in 1852 eyes with refractive errors of ±5.00 diopters (D), it has not been determined if the axial length continues to increase in adults with high myopia. A PubMed search extracted only 1 article describing an increase in the axial length after adolescence in highly myopic patients. Fledelius and Goldschmidt examined 9243 individuals born in Copenhagen in 1948 and identified 39 with myopia of 6 D or more. These 39 participants underwent comprehensive ophthalmologic examinations, and measurements showed that the mean axial length increased significantly from 26.7 ± 1.3 mm at age 26 years to 27.5 ± 2.1 mm at age 54 years, an average increase of 0.8 mm. However, they studied only 39 patients, and the mean axial length of their eyes was 26.7 mm. In addition, the age of the subjects examined was limited to 26 through 54 years, and the findings in older individuals were not presented.
The High Myopia Clinic of the Tokyo Medical and Dental University has been in existence for 38 years, and during this time, more than 1000 patients with high myopia have been examined and followed up. This High Myopia Clinic has allowed us to follow up a large population of highly myopic patients for long periods, and because myopia and its complications usually are not treated, we have been able to follow the natural course of these highly myopic eyes.
During our conventional examinations, we noted that the axial lengths of some of the eyes of elderly patients with high myopia were increasing. This was unexpected because it is generally expected that the axial length attains adult values by 13 years. Thus, the purpose of this study was to verify that the axial length continues to increase in elderly patients with high myopia and to determine the factors associated with the increase in the axial length. We were able to show that the axial length increased significantly in adults with high myopia during the follow-up period and that older individuals (≥45 years) with a posterior staphyloma were more likely to have a greater increase of the axial length than their younger cohorts. A progression of a posterior staphyloma with increasing age was found to be a key factor for the continuous increase of the axial length.
Methods
We reviewed the medical records of 2710 eyes of 1355 consecutive patients with high myopia who had visited our High Myopia Clinic from 1996 through 2005 and had been followed up for at least 5 years. The inclusion criteria were: (1) myopic refractive error (spherical equivalent) of 6.0 D or more or axial length of 26.5 mm or more, (2) age at the initial examination of 18 years or more, (3) minimum follow-up period of 5 years, and (4) A-scan ultrasonographic measurement of the axial length at each examination. The exclusion criteria were: (1) history of vitreoretinal surgery, cataract surgery, or refractive surgery; (2) moderate to severe cataract that would prevent an accurate measurement of the axial length (grade 3 or more, Emery and Little classification ); (3) retinal pathologic features that would prevent accurate fixation during the measurement of the axial length; and (4) eyes with active choroidal neovascularization at the initial examination or during the follow-up, because exudative changes such as serous retinal detachment can affect the axial length.
Of the 2710 eyes, 2526 eyes were excluded: 1568 eyes because their follow-up period was less than 5.0 years, 190 eyes because they had less than −6.0 D of myopia or axial length of less than 26.5 mm, 86 eyes because they had less than −6.0 D of unilateral myopia, 18 eyes because they had a severe cataract that prevented precise measurements of the axial lengths, 149 eyes because they had choroidal neovascularization at the initial examination, and 52 eyes for other retinal pathologic features that prevented steady fixation during the measurements or prevented an exact measurement of the axial length. The retinal pathologic features included macular chorioretinal atrophy, retinal detachments, amblyopia, and phthisis bulbi. Four hundred fifty-two eyes also were excluded because of a history of cataract surgery, and 11 eyes were excluded because of prior vitreoretinal surgery. In the end, we investigated 184 eyes of 101 patients, and the high myopia was unilateral in 18 patients, that is, only 1 eye met the inclusion criteria.
In these 101 patients (184 eyes), there were 41 men and 60 women with a median age of 46.0 years (range, 18 to 73 years). The median refractive error was −12.0 D (range, −6.5 to −24.0 D) and the median axial length was 28.5 mm (range, 25.1 to 33.3 mm). One hundred six eyes (57.6%) had an obvious staphyloma in the posterior fundus. There were 16 eyes whose myopic refractive error met the criterion of −6.0 D or more but whose axial lengths were less than 26.5 mm, that is, they had refractive myopia. The mean follow-up period was 7.0 years, with a range of 5 to 14 years.
We divided the patients into 2 groups by their age at the initial examination, their axial length at the initial examination, and by the presence of a posterior staphyloma and statistically analyzed whether the increase of the axial length was affected by these factors. The clinical characteristics of the patients younger than 45 years and of those 45 years or older at the initial examination are shown in Table 1 . Although the differences in the refractive error and the axial length between these 2 groups was not significant, the follow-up period was significantly longer in younger patients, and a posterior staphyloma was significantly more common in the older patients. The clinical characteristics of the eyes with and without a posterior staphyloma at the initial examination are shown in Table 2 . The patients who had a posterior staphyloma were significantly older and were significantly more myopic than the patients without a posterior staphyloma. In addition, the axial length at the initial examination was significantly longer in eyes with a posterior staphyloma than those without a posterior staphyloma. The clinical characteristics of the eyes with an axial length 28.5 mm or more or of less than 28.5 mm at the initial examination are shown in Table 3 .
| <45 Years of Age (66 Eyes of 34 Patients) | ≥45 Years of Age (103 Eyes of 59 Patients) | P Value | |
|---|---|---|---|
| Median age at initial examination (range), yrs | 28 (18 to 40) | 57 (45 to 75) | |
| Median refractive error, D | −11.0 | −12.8 | n.s. |
| Median axial length (range), mm | 28.2 (25.5 to 31.6) | 28.6 (26.1 to 32.6) | n.s. |
| Posterior staphyloma | 28 eyes (42.4%) | 74 eyes (71.8%) | <.001 |
| Median follow-up (range), yrs | 10 (5 to 13) | 6 (5 to 14) | <.01 |
| Without Posterior Staphyloma (78 Eyes of 41 Patients) | With Posterior Staphyloma (106 Eyes of 53 Patients) | P Value | |
|---|---|---|---|
| Median age at initial examination (range), yrs | 38 (18 to 68) | 51 (23 to 75) | <.0001 |
| Median refractive error, D | −10.5 | −13.0 | <.01 |
| Median axial length (range), mm | 27.8 (25.1 to 31.6) | 29.1 (25.8 to 32.6) | .002 |
| Follow-up (range), yrs | 8 (5 to 14) | 7 (5 to 14) | n.s. |
| <28.5 mm (95 Eyes of 58 Patients) | ≥28.5 mm (89 Eyes of 55 Patients) | P Value | |
|---|---|---|---|
| Median age at initial examination (range), yrs | 46 (18 to 73) | 46 (18 to 75) | n.s. |
| Median refractive error (range), D | −10.3 | −15.0 | <.001 |
| Median axial length (range), mm | 27.4 (25.1 to 28.56) | 29.9 (28.6 to 33.3) | |
| Posterior staphyloma | 43 eyes (45.3%) | 63 eyes (70.8%) | <.001 |
| Median follow-up (range), yrs | 8 (5 to 14) | 6 (5 to 14) | n.s. |
All of the patients underwent a complete ophthalmologic examination, including the measurement of the refractive error (spherical equivalent), measurement of the axial length, and dilated fundus examination at least once per year. The axial length was measured by A-scan ultrasonography (Ultrascan; Alcon, Fort Worth, Texas, USA) at least 10 times for each eye at each examination, and the average value was used for the statistical analyses. Before each recording, the A-scan Ultrascan was calibrated for accuracy against a standard length. Tissue velocities were set at 1550 m/s and at 1548 m/s for cataractous eyes.
For each ultrasonographic measurement, we confirmed the presence of 4 sharp spikes corresponding to the surface of the cornea, the front and back surfaces of the lens, and the surface of the retina. These spikes were used to measure the axial length, thickness of the lens, and the depth of the vitreous chamber. The presence of a posterior staphyloma was determined by binocular stereoscopic ophthalmoscopy. The corneal curvature was measured with an autorefractor/keratometer (KR-7100P; Topcon, Inc, Tokyo, Japan).
Statistical Analyses
The significance of the difference in the axial length, lens thickness, vitreous chamber depth, and corneal curvature at the initial examination and the final examination was determined by paired t tests. The patients were separated into different groups according to their age at the initial examination, axial length at the initial examination, and the presence of posterior staphyloma. The changes in the axial length per year between the groups were analyzed by the Mann–Whitney U test. The differences in the prevalence of posterior staphyloma were compared between groups using chi-square tests. In addition, we analyzed the factors that might be associated with the axial length increase using multiple regression analyses. A P value <.05 was accepted as statistically significant.
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