Relative lens vault in subjects with angle closure

BMC Ophthalmology Relative lens vault in subjects with angle closure Young Kook Kim 4 5 Beong Wook Yoo 3 5 Hee Chan Kim 2 5 Tin Aung 5 6 Ki Ho Park 0 1 5 0 Department of Ophthalmology, Seoul National University Hospital , Seoul , Korea 1 Department of Ophthalmology, Seoul National University College of Medicine , Seoul , Korea 2 Department of Biomedical Engineering, College of Medicine and Institute of Medical and Biological Engineering, Medical Research Center 3 Bioengineering Major, Graduate School, Seoul National University , Seoul , Korea 4 Department of Ophthalmology, Jeju National University Hospital , Jeju , Korea 5 Seoul National University , Seoul , Korea 6 Department of Ophthalmology, Singapore National Eye Center, Singapore , Singapore Background: The purpose of this study was to investigate the association of a novel biometric parameter, relative lens vault (LV), with primary angle-closure (PAC) and primary angle-closure glaucoma (PACG). Methods: We evaluated 101 subjects with PAC (G) and 101 normal subjects that were age- and gender-matched. Based on anterior-segment optical coherence tomography scans, and using customized software, the anterior vault (AV) and LV were measured. They were defined as the maximum distances between the horizontal line connecting the two scleral spurs and the posterior corneal surface and anterior lens surface, respectively. The relative LV was calculated by dividing the LV by the AV. Results: Significant differences between PAC (G) eyes and normal eyes were found in the LV (1.06 0.41 vs. 0.36 0.37 mm, P < 0.001), relative LV (0.34 0.23 vs. 0.11 0.25, P < 0.001), and axial length (22.96 0.94 vs. 24.02 1.33 mm, P < 0.001). However, the two groups' values of the AV relative to those of axial length were quite similar (both 0.14 0.03, P = 0.91). The relative LV values distinguished between PAC (G) eyes and normal eyes better than the LV values (area under the receiver operator characteristic curve: 0.97 vs. 0.92, P = 0.032). Conclusions: Our results suggest that relative dimensions of the eyeball's anterior portion in PAC (G) eyes might be within the normal range. And the value of LV relative to that of the AV (i.e., the relative LV) is more closely related to PAC (G) than is the absolute value of LV. - Background The scleral spur, marked by a prominent inner extension of the sclera on anterior-segment optical coherence tomography (AS-OCT) is an important anatomical landmark in quantitative anterior chamber angle measurements [1]. It serves as a reference point determining the relative position of the trabecular meshwork and of parameters such as the angle-opening distance, the angle-recess area, and the trabecular-iris area [2,3]. Recently, the lens vault (LV), also determined relative to the scleral spur, was introduced as a novel biometric-parameter [4]. The LV, defined as the perpendicular distance between the horizontal line joining the two scleral spurs and the anterior pole of the crystalline lens [4], represents the anterior portion of the lens, and, as such, is strongly and independently associated with angle closure [5]. An increased LV indicates an increased lens thickness and/or bulk anterior to the scleral spur plane, which subsequently increases the risk of angle closure. Many studies on different populations have shown the LV to be associated with angle-closure risk [4-8]. However, the possibility of the LV affecting angle closure differently according to the anterior chamber depth (ACD) is overlooked. If the ACD is deep enough, the LV, even when large, would be less likely to increase the risk of angle-closure. Conversely, if the patients anterior chamber is shallow, the angle-closure risk would relatively increase even when the LV is small. These hypotheses suggest that LV relative values (to the anterior chamber) may be more closely related to angle-closure risk than are absolute values. In the present study, we investigated, based on ASOCT scans, two novel biometric parameters: the anterior vault (AV), which represents the sum of the LV and the ACD, and the relative LV (rLV), which represents the ratio of the LV to the AV. Additionally, we aimed to evaluate the importance of the rLV in distinguishing between eyes with and without angle closure. Methods All of the study participants were examined between January 2010 and August 2013 at the glaucoma and cataract service of Seoul National University Hospital, Seoul, Korea. All eligible participants were consecutively enrolled by retrospective medical-record review. At the initial clinic visit, all underwent a complete ophthalmic examination, including medical history review, best-corrected visual acuity measurement, slit-lamp biomicroscopy, Goldmann applanation tonometry (Haag-Streit, Koniz, Switzerland), funduscopic examination (90 diopter lens), stereoscopic optic disc photography, retinal nerve fiber layer photography, and gonioscopy, performed in the dark using a Sussman 4-mirror lens at high magnification (x16). Indentation gonioscopy with the same lens was used to establish the presence or absence of peripheral anterior synechiae. The cataract type and grade was evaluated, based on the Lens Opacity Classification System II [9]. Additionally, AS-OCT imaging (Visante, Carl Zeiss Meditec, Dublin, CA) and axial length (AL) measurement (IOL Master; Carl Zeiss Meditec) were performed at the initial or follow-up clinic visit. This study, approved by the Seoul National University Hospital institutional review board adhered to the tenets of the Declaration of Helsinki. Informed consent was obtained from all subjects. Angle-closure group and normal-control group classification Angle closure was defined as primary angle-closure (PAC) or primary angle-closure glaucoma (PACG). The PAC, PACG, and open-angle criteria used were as follows: PAC: the pigmented posterior trabecular meshwork was not visible on nonindentation gonioscopy for 180 degrees or more in the primary position, with peripheral anterior synechiae and/or raised intraocular pressure (IOP), and no glaucomatous optic neuropathy [10]. PACG: PAC associated with glaucomatous optic neuropathy (defined as loss of neuroretinal rim with vertical cup-to-disc ratio of >0.7 or inter-eye asymmetry of >0.2, and/or presence of glaucomaassociated notching) [10]. Open angle: the pigmented posterior trabecular meshwork was visible on nonindentation gonioscopy for 180 degrees or more in the primary position, with the IOP 21 mmHg, and no peripheral anterior synechiae/glaucomatous optic neuropathy [10]. Patients were excluded if they had undergone prior intraocular surgery or if their AS-OCT images were of a quality sufficiently poor to make scleral spur or anterior lens surface identification difficult. All of the subjects with PAC(G) previously had undergone laser peripheral iridotomy. Subjects who had PAC(G) and met the relevant eligibility criteria made up the PAC(G) group; subjects who had open angles a (...truncated)