By Lucy Piper, Senior medwireNews Reporter
A dome-shaped macula appears to result from the relative thickening of the central macular sclera, researchers have found.
They used a new swept-source optical coherence tomography technique to penetrate the retinal pigment epithelium and observe the choroid and sclera using a light source at 1 µm wavelength.
Of 528 eyes in 276 Japanese patients studied, a dome-shaped macula was identified in 49 (9.3%). In these patients, the sclera thickness was significantly greater at the centre than in the parafoveal surrounding areas. And central sclera thickness was significantly and negatively associated with age and axial length.
Macular complications were observed in the eyes of 14 patients with dome-shaped maculae and these patients had a significantly lower mean logarithm of the minimum angle of resolution best corrected visual acuity (0.30 vs 0.37), thinner central choroidal thickness (66.1 vs 111.9 µm) and greater bulge height (187.6 vs 97.5 µm) than those with no complications.
The macular complications identified were choroidal neovascularisation (CNV) in six patients and pigment epithelial detachment (PED) in eight patients.
The CNV group was significantly older and had a significantly longer axial length than the PED and no complications groups, at an average of 31.4 mm versus 27.1 mm and 28.4 mm, respectively. Also, central choroidal thickness in the CNV group was significantly thinner to that in the no complications group, at 46.7 µm versus 111.9 µm.
By comparison, the PED group had a significantly thicker central sclera, at an average of 693.9 µm, compared with 434.5 µm for the CNV group and 470.0 µm for the no complications group. The average bulge height in this group (233.1 µm) was higher than that of the CNV group (126.8 µm) and significantly so compared with the no complications group (97.5 µm).
The researchers, led by Hideharu Ohsugi (Tsukazaki Hospital, Himeji, Japan), say their findings indicate that a dome-shaped macula is the result of a relatively thicker sclera.
“[T]he thickness of the macular peripheral region in dome-shaped macula eyes displays similar thinning as in highly myopic eyes; and although the scleral thinning occurs in the macular region, because the extent of the thinning is less than that in the ordinary highly myopic eyes, it is likely that the relative thickness is present in the central region”, they explain in the American Journal of Ophthalmology.
This thickening of the macular sclera may lead to PED, they add, and as the thinning of central sclera progresses due to long-term changes and the elongation of the axial length, CNV and visual impairment may occur.
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