To the best of our knowledge, this is the first study to classify the locations of tessellations in normal eyes in an epidemiological survey. The localization of the tessellations was determined from the fundus photographs, and the reproducibility was very good.
We first compared the results with our earlier study of young university students living in Kagoshima, Japan.
13 In the present study, 45.4% of the eyes were without tessellation, 22.9% of showed peripapillary type tessellation, 8.3% of the lower type, 7.1% of the macular type, 6.8% of the posterior pole type, and 0.4% of the nasal type. In our previous study, 34.9% of the eyes had no tessellation, 40.2% in the macular type, followed by 18.3% in peripapillary type, 13.4% in posterior pole type, 10.9% in inferior type, and 9.6% in nasal type.
13 That group had an average age of 26.0 ± 4.1 years, an average refractive errors was −4.71 ± 3.41 diopters, and an average ocular AL of 25.43 ± 1.45 mm, which differed from the present study of ≥40 years. More specifically, in young adults, there are many eyes with longer AL and macular type tessellation than the individuals in the Kumejima study. The subjects with macular type tend to have a longer AL and be more prevalent in younger subjects, so the results are consistent with each other. Second, our earlier study involved mainly young individuals in comparison to the Kumejima study. The younger individuals had good nutrition during their growing days and a different lifestyle, that is, more television viewing and computer use and fewer outdoor activities.
19,20 Previous studies have shown that younger individuals tend to be taller and their axial length longer, with significant and positive correlation between height and axial length.
21–28 Nutritional improvement may be one of the causes for longer axial length in the younger generation, and improvements in physique are due mainly to improvements in nutrition. This difference in the generations might affect the prevalence of tessellation type. Further, since Kumejima is isolated from its surroundings by the sea and interisland transport has been highly limited historically, it is considered a genetically different population from the people in the Kagoshima area.
14,15
Tessellations are considered to be related to staphylomas because both are caused by excessive extension or deformation of eye. Hsiang et al.
6 reported on the distribution in the locations of staphylomas in a hospital-based Japanese population. They studied 209 eyes with high myopia, and they used locations similar to those used by Curtin in his classification of staphylomas. Ohno-Matsui found that 23.4% of the staphylomas were the posterior pole type, 52.7% the macular type, 4.3% the peripapillary type, 2.7% the inferior type, and 17% the complicated type.
6 In comparison, our results showed that the incidences of the posterior pole tessellation and macular tessellation were high, while those of the peripapillary tessellation type, nasal tessellation type, and inferior tessellation type were low. In a hospital-based study, eyes with visual disturbances—such as macular retinochoroidal atrophy and choroidal neovascularization—dominate the subjects that would inevitably lead to a bias that posterior staphylomas are the dominant type. Nonetheless, those with tessellations or staphylomas in the inferior, nasal, and parapapillary regions may not have visited the hospital because they did not have any visual impairments.
Our results showed that posterior pole tessellations and macular tessellations had significantly longer AL than those of other groups. In posterior pole and macular tessellation groups, the tessellation contains the macular area, so the AL measured on the visual axis is longer than those in other groups. Conversely, the AL is shorter in the inferior, peripapillary, and nasal tessellation groups where tessellations do not cover the macular area.
In the Kumejima population, the subjects with the posterior pole tessellation type were older than in the other tessellation types. Additionally, the BCVA (logMAR) in the posterior pole type (mean −0.025) was significantly worse than in “no tessellation” group (mean −0.067;
P < 0.001). This may be because atrophic changes of the retinochoroidal tissue in older individuals might enhance the tessellation-like appearance of whole posterior pole of the eye.
10
Subjects with the inferior tessellation type were taller than the subjects with the other tessellation types, but the AL of their eyes was not longer than those of other types. In this study, the BH of the subjects was positively correlated with the AL (
r = 0.35,
P < 0.001), which is consistent with many earlier studies.
21–28 These results indicate that tessellation of the inferior type may not be affected only by the AL. The upper half of the eye is not necessarily the mirror image of the lower half of eye.
29,30 It has been reported that in embryonic development of the eye, the inducer is different for each retinal quadrant, and these molecules also affect development of the body.
31 However, which molecules affect development of both the eye and body have not been determined. Further basic research is needed to determine which molecules affect the vertical asymmetry in the eyes with the inferior type of tessellation and BH.
There are limitations in this study. First, a number of eyes were excluded from analysis, which may have caused a selection bias. The fundus was photographed with a nonmydriatic camera to increase the number of participants and avoid the possibility of mydriatic-induced complications. As a result, there were cases in which the surrounding area was too dark for assessment, and they were excluded. Cases with media opacities (such as cataracts) were also excluded. Additionally, eyes with diseases (such as glaucoma and retinal diseases) were also excluded because tessellation can be exaggerated or obscured in such eyes. These may be selective biases and are the limitations of this research. Second, we classified the location of the tessellations subjectively. Although the inter-rater agreement of the two independent masked examiners was high, further study is needed using an objective method to classify the tessellations.
In conclusion, the results showed that the location of the tessellation based on the population-based data and revealed that peripapillary location of the tessellations was most frequent in the individuals of Kumejima. The eyes with the posterior pole and macular tessellations had longer AL, the subjects with the posterior pole type were older, and the subjects with the inferior type were taller than other groups. This information can be used to compare future pathologic myopia studies. Determination of similar data in different races is needed.