Ciliary body length revisited by anterior segment optical coherence tomography: implications for safe access to the pars plana for intravitreal injections

Abstract

Purpose To investigate the dependence of the ciliary body length (CBL) on the axial length (AL) and to draw conclusions on implications regarding safe pars plana access for intravitreal injections and vitreoretinal surgery. Methods A total of 200 individuals (mean age 42 years, SD ± 15.4) were enrolled in the study. Objective refraction and AL were obtained. Spherical equivalent (SE) was calculated. Anterior segment optical coherence tomography (ASOCT) was used to image and measure the CBL. Results The mean SE was − 1.64 diopters (SD ± 3.15, range − 14.5 to + 9 diopters) and the mean AL was 24.19 mm (SD ± 1.65, range 19.8–32.2 mm). There was a significant correlation between SE and AL (r2 = 0.62, p < 0.0001). Mean CBL correlated significantly with age (r2 = 0.11, p < 0.0001), AL (r2 = 0.23, p < 0.0001) and SE (r2 = 0.25, p < 0.0001). The mean CBL was 3351 μm (SD ± 459, range 2184–4451 μm). Three separate groups were defined by their AL with a normal AL group (AL 22.5 to 25 mm), a short AL group (AL < 22.5 mm) and a long AL group (AL > 25 mm). The mean CBL in the normal AL group was 3311 μm (SD ± 427), in the short AL group 2936 μm (SD ± 335) and in the long AL group 3715 μm (SD ± 365), and differed significantly (p < 0.0001) when compared. Conclusion For interventions requiring pars plana access (as an intravitreal injection or vitreoretinal surgery), an incision distance of 3.5–4.0 mm posterior to the limbus is recommended. In our research, however, a difference of 0.77 mm in mean CBL between the group with short AL and the group with long AL is demonstrated, implying that the mean CBL in very short and very long eyes differs significantly. These findings suggest that the AL should be taken into account for pars plana access and that it would be advisable to prefer the shorter or longer recommended distance (3.5 and 4.0 mm, respectively) from the limbus, which correlates with the AL. If AL is > 25 mm, a distance of 4.0 mm from the limbus should be chosen; and if AL is < 22.5 mm, a distance of 3.5 mm seems adequate. Trial registration number and date NCT00564291, 27 Nov 2007

Anterior Segment Optical Coherence Tomography in Determination of Entry Site for Vitrectomy in Highly Myopic Eyes

“… 3 The length of the pars plana when measured in vivo with anterior segment optical coherence tomography (OCT), varies significantly among eyes with different axial lengths. 4 …”

“…3 The length of the pars plana when measured in vivo with anterior segment optical coherence tomography (OCT), varies significantly among eyes with different axial lengths. 4 Recently, there are an increasing number of patients with highly myopic eyes 5,6 presenting with conditions such as myopic traction maculopathy or retinal detachment. [7][8][9] However, it is very difficult to perform membrane peeling in those eyes due to the increased axial length.…”