Commentary: Reliability, repeatability, and accuracy of Sirius topographer in assessing anterior segment morphology following laser peripheral iridotomy in primary angle-closure disease.

Abstract

Primary angle-closure disease (PACD) is the major form of glaucoma globally and is one of the leading causes of blindness worldwide. It has been estimated that by 2030, 21 million patients will be suffering from PACD, of whom 88% will be Asians.[1] Slit lamp Van Herick grading and gonioscopy are commonly available clinical tools for diagnosing PACD. The angle-closure disease is defined as raised intra-ocular pressure because of obstruction of the trabecular meshwork leading to blockage of aqueous outflow. If it is associated with glaucomatous optic nerve cupping along with field changes, the disease is labeled as angle-closure glaucoma.[2] PACD is classified as primary angle-closure suspects (PACS), primary angle closure (PAC), and primary angle-closure glaucoma (PACG) as per the International Society Geographical and Epidemiological Ophthalmology (ISGEO).[3] The angle closure can be primary or secondary. Primary angle closure is bilateral and not associated with any known systemic or ocular disorder. Secondary angle closure is usually unilateral and is associated with a known systemic or ocular disorder. Anti-glaucoma medications have a limited role in PACG, and laser peripheral iridotomy (LPI) is the primary treatment modality for acute and chronic angle-closure glaucoma in its early stages. LPI relieves the pupillary block and reduces the intra-ocular pressure by reversing the oppositional angle closure. By this, the conversion of PACS and PAC into PACG is prevented. Through a peripheral iris opening, LPI allows migration of aqueous substances from the posterior to anterior chamber (AC), opens the AC angle, and deepens the AC.[4] However, LPI may not always be sufficient to prevent progressive angle closure and the development of optic neuropathy. As per previous studies, persistent iridotrabecular contact after LPI has been reported in nearly 20% of eyes. It is imperative to understand these anatomical changes after LPI to label the favorable physiological modifications and the risk factors predisposing to progressive glaucoma after LPI.[5] These dynamic morphological changes observed are of research interest to ophthalmologists, and a large number of studies have been published on a similar concept. These morphological changes have been studied using anterior segment optical coherence tomography (ASOCT), ultrasound biomicroscopy (UBM), A-scan ultrasound, Scheimpflug imaging, and IOL master.[6] Scheimpflug imaging modalities such as Pentacam (Model HR, Oculus, Inc., Wetzlar, Germany), Sirius (Costruzione Strumenti Oftalmici, Florence, Italy), and Galilei (G4, Ziemer Ophthalmic Systems AG, Port, Switzerland) are considered more reliable, repeatable, and accurate to study anterior segment morphology after LPI. In the current study, the authors have used Sirius topographer to study the same, which is an add-on to the currently available literature.[7] Lei et al.[8] studied the anterior segment morphological changes after LPI in 15 PAC patients using ASOCT. The parameters studied were central AC depth (CACD), pupillary diameter, lenticular thickness, and AC volume. The iris configuration and peripheral AC depth were evaluated qualitatively. The mean AC depth improved to 1.970 ± 0.235 from 1.939 ± 0.228, which increased by 1.6%. The AC volume changed to 84.14 ± 17.45 microl from 73.86 ± 14.58 microl, the peripheral AC depth and mean IOP improved, and the iris configuration flattened. They concluded that LPI increases all subjects’ central and peripheral AC depth and volume. Antoniazzi et al.[9] studied the AC morphology using Pentacam in patients after LPI. A total of 20 eyes were evaluated for AC volume, depth, and angle before and after LPI. They noted statistically significant differences before and after LPI in all AC measurements and concluded that Pentacam is an excellent objective tool to ascertain the efficacy of LPI. Mansouri et al.[10] studied the AC morphological changes in 35 PAC and PACG European eyes using UBM. The authors evaluated the baseline trabecular-iris angle (TIA) in superior, nasal, inferior, and temporal quadrants under both dark and light conditions along angle opening distance (AOD). The mean TIA values before LPI in superior, nasal, inferior, and temporal quadrants were 3.59 ± 4.5 degrees, 6.37 ± 4.9 degrees, 9.33 ± 7.6 degrees, and 8.65 ± 7.3 degrees, respectively. After LPI, the mean values increased to 12.58 ± 6.9 degrees, 15.40 ± 6.8 degrees, 16.37 ± 7.4 degrees, and 15.95 ± 11.3 degrees, respectively. They concluded that there was a significant angle widening in all four quadrants, and UBM is a viable tool to assess AC morphological changes before and after LPI. In another analysis by Acet et al.,[11] AC parameters were studied before and after LPI using Sirius Scheimpflug-Placido Disc Topographer during a follow-up of 6 months. A total of 109 eyes with PACD were evaluated for AC volume, depth, and angle measured by Sirius topographer pre-operatively and compared post-operatively at 1, 3, and 6 months after LPI. The AC volume, central AC depth, and AC angle increased significantly (P < 0.05) in all patients at 1 month; the parameters which showed significant change at 3 and 6 months were AC angle and AC volume with central AC depth, respectively. The authors concluded that Sirius topographer detects substantial changes in AC parameters after LPI in all groups. However, PACG showed significant alterations in AC parameters at 6 months. The current study[7] by the authors was a prospective analysis from the South Indian cohort utilizing Sirius topographer to study AC parameters after LPI in PACD. The authors have correctly detailed the inclusion and exclusion criteria, and the methodology is crisp. The authors have considered all the parameters, including iridocorneal angle (ICA), AC depth (ACD), AC volume (ACV), central corneal thickness (CCT), horizontal visible iris diameter (HVID), horizontal anterior chamber diameter (HACD), and corneal volume (CV) in both the eyes using Glaucoma analysis program of Sirius Scheimpflug-Placido disc corneal topography, which is probably the first one using Sirius topographer in Indian eyes with PACD. The analysis showed a statistically significant difference in ICA that increased from 34.13 ± 2.64 degrees to 34.75 ± 2.84 degrees (p-value < 0.041); the ACD increased from 2.21 + 0.25 mm to 2.35 ± 0.27 mm (p-value < 0.01); the AC volume increased from 98.19 ± 12.13 mm3 to 104.15 ± 11.26 mm3 (p-value < 0.001). A good sample size and use of a non-contact accurate Sirius topographer are notable strengths of the study, and additionally, the findings are in accordance with previous studies. More studies utilizing Scheimpflug topography with longer follow-ups are needed to ascertain its utility and accuracy. In the future, a study employing Gallilei (Ziemer Ophthalmic Systems AG, Port, Switzerland) imaging system can be attempted in eyes with PACD, which will provide further insights into comparative analysis and accuracy of Scheimpflug-Placido disc corneal topography systems.