Comparison Between Anterior Segment Optical Coherence Tomography and Ultrasound Bio Microscopy Parameters in Glaucoma Assessment

Glaucoma is comprised of a group of optic neuropathies that share certain biological and clinical characteristics including progressive loss of the RGCs that causes specific, irreversible changes to the optic disc and visual field Visualization of the anterior chamber (AC) angle is a critical step in the diagnosis of glaucoma, especially angle-closure variants. .

UBM has been used in imaging and quantitative evaluation of anterior ocular segments since the 1990s. It allows in vivo observation of the anatomy and pathology of the anterior segments, from the conjunctiva and cornea to the iris and basal vitreous body, which provides significant information on glaucoma, cysts, neoplasms, trauma and foreign bodies. UBM also provides biometric information of anterior segment structures, such as anterior chamber (AC) depth, anterior chamber angle (ACA), and iris thickness. UBM provides more detailed information compared to slit-lamp, gonioscopy or B-scan examinations for diagnosis and follow-up of PAC eyes.In some cases UBM elucidates the mechanism of elevated intraocular pressure by showing the relationship between the peripheral iris and the trabecular meshwork. It can be used to study the causes of secondary glaucoma, for example, the pigment dispersion syndrome, lens-induced glaucoma, ciliary block, cysts, and solid tumors of the anterior segment. It can also assess the effects of various interventions such as laser iridotomy, trabeculectomy, and non-penetrating drainage surgery. Precise quantitative evaluation of the anterior chamber angle structures can help in diagnosis and management of various pathologies related to glaucoma . Optical coherence tomography (OCT) is a widely used non-invasive fundus imaging technique. Since the first application of OCT in the cornea in 2002], anterior segment-optical coherence tomography (AS-OCT) has developed rapidly. There are two major OCT platforms on the market: time domain-optical coherence tomography (TD-OCT) and spectral (or Fourier) domain-optical coherence tomography (SD/FD-OCT) . With a higher imaging resolution than UBM, AS-OCT makes it easier for the operator and software to identify ACA structures. such as: the scleral spur (SS), iris surface, Schwalbe's line, even trabecular meshwork (TM), and Schlemm's canal. This provides more precise analysis of the angle opening distance (AOD) from the SS, ACA, trabecular iris angle (TIA), and trabecular iris space area (TISA)