UBM - A Tracker for Trabeculectomy

Abstract

Trabeculectomy is the most popular form of glaucoma filtration surgery and remains the "gold standard" for surgical reduction of Intraocular Pressure (IOP) in uncontrolled glaucoma [1]. It has a success rate of 67% to 94% [2].This partial-thickness filtration operation reduces intra ocular pressure via the creation of a limbal fistula through which aqueous humor drains into the subconjunctival space, establishing a filtering bleb. Long-term success depends on preoperative and intraoperative conditions. Yet, it also depends highly on the persistence of filtration efficiency at the bleb site. Therefore, postoperative observation and care of developing filtering bleb in clinical practice is an important tool in reaching the target pressure after filtration surgery in higher percentage of the patients [1].Bleb function is believed to depend on the degree of bleb fibrosis and obstruction of intrascleral aqueous humor flow [3]. Bleb appearance has been assessed using slit-lamp bio microscopy, gonioscopy, Ultrasound Bio Microscopy (UBM) and Optical Coherence Tomography (OCT). Examining bleb morphology for indications of fibrosis or blockage of fluid flow should be useful in evaluating bleb function.Slit-lamp bio microscopy only illustrates bleb morphology and not the bleb's internal structures. Gonioscopy helps in assessing the internal window and the peripheral iridectomy anatomical position and shape. Cross-sectional imaging modalities such as UBM and Anterior Segment Optical Coherence Tomography (AS-OCT) can depict internal structure of blebs. This therefore, provides information about the structure and possible functionality of filtering blebs [4], complimentary to that obtained by slit-lamp bio microscopy and gonioscopy.Imaging technique AS-OCT, is useful in the evaluation of the iridocorneal angle and post trabeculectomy blebs. It is faster than UBM and eliminates the need for a water bath and eyecup in contact with the globe, therefore is a more comfortable procedure for the patient. However, it has limitations of inability to evaluate any aetiology behind the iris. Impression cytology and In vivo confocal microscopy, alone and together, are also new methods to evaluate the bleb but there are many limitations to its extent of evaluation. Incidentally, there has been limited work undertaken in it. The vascular assessment of the bleb using indocyanine green is a new method to assess the bleb, yet it is also not used because of its invasive nature and limited amount of research work in it [4,5]. Therefore, in this case series only UBM was taken into consideration to observe efficacy in monitoring bleb functions as also to record its capability in non-functioning of bleb to establish probable cause of its failure.Charles Pavlin and Stuart Foster [5][6][7] developed UBM at the Princess Margaret Hospital at Toronto, Canada in 1989. UBM is a high frequency (50MHz) ultrasound technology using water bath that permits non-invasive in vivo imaging of the structural details of the anterior ocular segment at near microscopic...

Ultrasound biomicroscopy in glaucoma assessment

“…Trabeculectomy is one of the most important surgery methods in glaucoma and UBM is an important tool in bleb follow up [ 58 , 59 ]. It allows the functional evaluation of the bleb and its filtration rate and, in case of postoperative complications, it allows the exact localization of the lesion and the development of an appropriate treatment plan.…”

“…It allows the functional evaluation of the bleb and its filtration rate and, in case of postoperative complications, it allows the exact localization of the lesion and the development of an appropriate treatment plan. The reflectivity of the sclera and the aspect of the scleral flap represent predicting factors in the bleb outcome [ 58 ].…”