Posterior staphyloma is a protrusion of the posterior shell of the eyeball, and is considered to be a hallmark lesion of pathologic myopia. The development of a staphyloma is accompanies by a streaching of the posterior fundus, resulting in various kinds of secondary disorders, including chorioretinal atrophy, choroidal neovascularization (CNV), and macular retinoschisis. Eyes with posterior staphyloma have a higher incidence of vision loss.
Despite the importance of posterior staphyloma, little is known about them. This study aimed to study the characteristics of posterior staphyloma and how they may change with age.
The investigators analyzed 209 eyes of 108 consecutive patients with myopia of at least -8.0 diopters at their Tokyo clinic. The grade of staphylomas was determined from B-scan ultrasonographic images. The type of staphyloma was determined by ophthalmoscopy. The participants were divided into two groups: younger than 50 years and 50 years and older. The long-term progression of staphylomas was analyzed in nine patients who were followed up for more than 20 years.
The researchers found 90 percent of 209 eyes had a staphyloma. The prevalence of staphylomas and more advanced grades of staphylomas (> grade 2) were significantly higher in the older than in the younger patients.
The grade of the posterior staphyloma was determined from the B-scan and A-scan ultrasonographic images (Click to view figure). An elongated eye with a smooth scleral contour was graded as zero. A grade 1 staphyloma had a depth of 2 mm or less, a grade 2 staphyloma had a depth of 2-4 mm, a grade 3 staphyloma had a depth of 4-6 mm, and a grade 4 staphyloma had a depth of more than 6 mm. The higher grades of staphylomas were associated with more severe myopic retinal degeneration.
The type of posterior staphyloma was determined by the location, size, and severity (Click to view figure) and was classified according to the criteria of Dr Brian Curtin. The staphylomas were classified into 10 types: types I through V were primary staphylomas, and types IV through X were compound staphylomas. Type II staphyloma was the most prominent overall; however, in older subjects, the incidence of type II was decreased significantly, and that of type IX was increased significantly. The eyes with type IX staphyloma tended to have more severe myopic retinal degeneration than eyes with type II staphylomas. The long-term follow-up study demonstrated a progression from type II to type IX with increasing age.
The severity myopic macular degeneration was significantly higher in eyes with higher grade staphylomas. However, the prevalence of CNV (total CNV and active CNV) was not different among different grades of staphylomas in this study.
The researchers conclude that a staphyloma was present in 90% of the patients with high myopia, and the prevalence of staphylomas was significantly higher in older patients (96.7% in those 50 years of age and older) than in younger patients (80.7% in patients younger than 50 years).
The prevalence of grade 2 staphyloma (2-4mm) was significantly higher in patients older than 50 years than in those younger than 50 years. This indicates that not only the incidence of posterior staphyloma but also the depth of the staphyloma increased as the patient ages. The reason why the morphologic features of posterior staphyloma worsen with increasing age has not been clarified fully, but some authors have reported alterations in the composition of the sclera occur with age.
These results suggest that the morphologic features of staphylomas worsens as the patient ages. The progression from type II to type IX probably increases the mechanical tension on the macular area of highly myopic eyes, which then leads to myopic fundus lesions.