Bleb Grading

(Version 1.0 J.Clarke)

Introduction for Graders

The treatment of glaucoma can be medical or surgical. The commonest surgical procedure is the trabeculectomy. This is the creation of a channel from the front fluid chamber (the anterior chamber) through the tough wall of the eye (sclera) to allow the fluid (aqueous) to drain slowly under the superficial layers of the eye. These layers are known as the conjunctiva and tenons, with the conjunctiva being the most superficial. The draining aqueous lifts these tissues and appears as a blister known as a bleb. The appearance of this bleb is variable and post-operative modification of the trabeculectomy will depend on this appearance. The aim of the surgery is to reduce the intra-ocular pressure. There are various components to the bleb and this grading system aims to define these.

Figure 1 The main anatomical features of a trabeculectomy
  The protocol for bleb grading assumes that blebs have uniform components. This in reality is often not the case and the grader is encouraged to match the patient photograph depending on the "best fit" or best match from the standard photographs.
  The category the most difficult to assess is the area (category 1). Along with the standard photographs is a printed copy with arrows depicting the extent of the bleb area. This is best seen by comparing the printed sheet with magnified views of the standard photographs. Particularly for this category magnified images are essential.

Figure 2. The passage of aqueous through the scleral trap door and the extent of the diffusion

The diffusion of the aqueous under the conjunctiva can be recognised by various subtle findings. These include elevation of the conjunctiva at the limbus (margin of cornea and conjunctiva) forming a shallow limbal gutter. A "boggy" appearance caused by the elevation of the conjunctiva allows the superficial conjunctival vessels to be distinct and the deeper episcleral vessels are less well defined. At the margin of the diffusion the superficial and deep vessels reunite and look very similar.

It is hoped that this system will allow for accurate bleb grading and a useful tool in the management of glaucoma.