analysing bleb morphology after trabeculectomy using anterior segment Optical Coherence Tomography

MethodologyThis prospective observational and descriptive study will be approved by the Institutional Ethics Committee of Nethradhama Eye Hospital and will adhere to the tenets of the Declaration of Helsinki. Verbal and written informed consent will be obtained from all patients participating in the study.

Surgical ProcedureFollowing creation of a fornix based conjunctival flap a sponge soaked in Mitomycin C at a concentration of two hundred micrograms was applied under the conjunctiva for a duration of two minutes taking care that the Mitomycin C soaked sponge did not come in contact with the edge of the conjunctival flap. A partial thickness rectangular scleral flap was created followed by creation of a sclerostomy measuring two by two millimeters using scissors or Kelly punch. Closure of the scleral flap was performed using two side permanent sutures and one apical releasable ten zero nylon suture. The conjunctiva was closed using ten zero nylon sutures. Postoperatively antibiotic and steroid eye drops were administered in a tapering dose over a period of two months.

Imaging and Evaluation of Filtering BlebAll blebs will be imaged using slit lamp photography under standardized illumination and magnification settings. All blebs will also be imaged using anterior segment optical coherence tomography using the Cirrus HD OCT five hundred system manufactured by Carl Zeiss Dublin California United States using a standardized imaging protocol.

Optical coherence tomography is a high resolution tomographic and biomicroscopic imaging device designed for anterior segment imaging and measurement with an axial resolution of eighteen micrometers. The principle of imaging is based on low coherence interferometry using a thirteen hundred ten nanometer superluminescent light emitting diode. Similar to an ultrasound B scan the Cirrus OCT acquires multiple A scans and aligns them to construct two dimensional images.

Patients will be instructed to look downward and the upper eyelid will be gently elevated to expose the bleb adequately while ensuring that no pressure is exerted on the globe or the bleb. Two scans namely radial and tangential will be obtained through the point of maximum bleb elevation.

Assessment ParametersAnterior segment optical coherence tomography images will be evaluated by a single trained observer who will be masked to the clinical data. Blebs will be assessed qualitatively for bleb height bleb wall thickness in millimeters bleb wall reflectivity categorized as low medium or high and bleb pattern classified as uniform or multiform. Scleral flap configuration measured in millimeters will also be evaluated. Additional features assessed include the scleral flap morphology and the route of aqueous flow beneath the scleral flap.