Participants

The inclusion criteria for the case eyes (HM) was a myopic refractive error of 6.00 D or more, and less than 6.00 D for low-moderate myopia control eyes. The exclusion criteria were the presence of media opacities (i.e., corneal haze or cataract), refractive astigmatism over 1.00 D, corneal ectasia, active anterior (i.e., keratitis) and/or posterior segment anomalies except for staphyloma, and a history of previous ocular surgery or ocular trauma. All participants had to belong to the same ethnic group to avoid bias. The Caucasian type was chosen because in Spain the vast majority of the population is Caucasian. All participants had a comprehensive ocular examination including manifest refraction, ocular biometry, a detailed ophthalmoscopic evaluation and optical coherence tomography imaging. In the present study, posterior staphyloma was defined like Spaide did as “an outpouching of the wall of the eye that has a radius of curvature that is less than the surrounding curvature of the wall of the eye“ [16]. Dome-shaped macula was defined as unexpected inward bulge of the macular area that can be accurately identified in optical coherence tomography images [17]. If participants showed a bending involving the macular area (observed in optical coherence tomography images) due to the presence of an inferior staphyloma [14], they were classified into the inferior staphyloma group.

Participants were recruited from the IOBA-Eye Institute outpatient clinic. A total of five groups were created for this study: four HM case groups and one low-moderate myopia control group were created initially based on the refractive error and ocular characteristics evaluated by indirect ophthalmoscopy and spectral-domain optical coherence tomography (Topcon Corp., Tokyo, Japan) examinations. The low-moderate myopia control group was comprised of healthy eyes with a refractive error below 6.00 D of myopia, HM group 1 included HM eyes (myopia ≥6.00 D) without staphyloma, HM group 2 included HM eyes (myopia ≥6.00 D) with inferior staphyloma, HM group 3 included HM eyes (myopia ≥6.00 D) with posterior staphyloma without a dome-shaped macula, and HM group 4 included HM eyes with posterior staphyloma and a dome-shaped macula.

The total sample size calculated was 64, at least 13 per group, based on 80% power with a 5% significance level and a large effect size for an analysis of covariance study (1 covariable) that included five groups. The participants were recruited consecutively for all groups and it was completed only when a sample size of 14 was reached in all groups.

In order to assess if there were differences in HOAs between myopic eyes with or without staphyloma, all participants were also classified into two new groups: eyes with and without staphyloma. The no-staphyloma group was comprised of low-moderate myopia and HM eyes without staphyloma; and the staphyloma group was comprised of HM eyes with inferior or posterior staphyloma.