Date Published: June 10, 2019
Publisher: Public Library of Science
Author(s): Noriko Tanaka, Kosei Shinohara, Tae Yokoi, Kengo Uramoto, Hiroyuki Takahashi, Yuka Onishi, Shintaro Horie, Takeshi Yoshida, Kyoko Ohno-Matsui, Gemmy Cheung.
To determine the early signs of posterior staphylomas in highly myopic eyes of younger subjects by swept-source ultra-widefield optical coherence tomography (WF-OCT).
This was an observational case series study. Highly myopic subjects younger than 20 years old who were examined consecutively by prototype WF-OCT were studied. High myopia was defined according to the Ministry of Health and Welfare, Japan classification. A posterior displacement of the sclera and two OCT features indicating the staphyloma edges were used as markers of a staphyloma.
Fifty-five eyes of 30 patients with the mean age of 12.3 years, and the mean axial length of 27.9 mm were studied. Seven of the 55 eyes (12.7%) had a posterior displacement of the sclera and were diagnosed as having a staphyloma. Among the two OCT features of the staphyloma edges, a gradual thinning of the choroid toward the staphyloma edge and gradual re-thickening of choroid from the staphyloma edge toward the posterior pole were found in these 7 eyes. However, the other feature of an inward protrusion of the sclera at the staphyloma edge, was obvious in only 2 eyes. The subfoveal choroid and choroid nasal to the optic disc were significantly thinner in eyes with a staphyloma than those without it.
The changes of the choroidal thickness toward the staphyloma edge with the posterior displacement of the sclera were considered an early sign which precedes an inward protrusion of sclera at the staphyloma edge.
A posterior staphyloma is a hallmark abnormality of the globe of eyes with pathologic myopia.[1–4] Spaide defined a posterior staphyloma as, “an outpouching of the wall of the eye with a radius of curvature less than the radius of curvature of the surrounding eye wall”. The results of earlier studies showed that highly myopic eyes with a posterior staphyloma had significantly poorer vision and higher frequencies of anatomical anomalies than highly myopic eyes without a staphyloma.[5–7]
The procedures used in this study conformed to the tenets of the Declaration of Helsinki and were approved by the Ethics Committee of Tokyo Medical and Dental University (The approval number: M2000-2278). A signed informed consent was obtained from all the participants and their parents or guardians. This study was performed on highly myopic subjects younger than 20-years-of-age who were consecutively examined by WF-OCT between February and October 2017. High myopia was defined as a myopic refractive error (spherical equivalent) greater than -8.0 diopters (D) for those >8 years and -6.0 diopters (D) for those between 6 and 8 years, or an axial length longer than 26.5 mm, according to the definition of the Ministry of Health and Welfare, Japan. The refractive errors were measured under the pupil dilatation with 0.5% tropicamide/phenylephrine. The exclusion criteria were; patients with poor quality OCT images, a history of vitreoretinal surgery, and systemic or ocular diseases which could cause or are associated with high myopia, e.g., congenital stationary night blindness.
The study included 56 eyes of 30 patients. One eye was excluded due to the suspect of congenital stationary night blindness. No eyes were excluded due to the poor quality. Eventually 55 eyes of 30 consecutive patients were studied. The mean age was 12.3 ± 4.0 years with a range of 6 to 19 years. The mean refractive error (spherical equivalent) was -10.8 ± 2.9 diopters (D) with a range of -17.5 to -6.8 D. The mean axial length was 27.9 ± 1.6 mm with a range of 25.0 to 32.6 mm.
With the use of WF-OCT, the clear and objective detection of posterior staphylomas was possible in the current study. The results showed that among the 55 highly myopic eyes of 30 subjects, 7 eyes (12.7%) had a posterior staphyloma. Although staphylomas are generally considered to be pathological changes that develop in later life, the results showed that posterior staphylomas can be present at a much younger age than they had been believed.