CaseWise 9

Overhanging Bleb

Following trabeculectomy the filtering bleb can vary in size, height, vascularity and function with time. An overhanging bleb is known to occur following glaucoma surgery. It is thought to be associated with increasing use of antimetabolites intra-operatively¹. The term overhanging filtering blebs refers to oversized filtering blebs that hangs over the cornea². Intervention is required if there is induced foreign body sensation, epiphora, astigmatism, associated decrease in visual acuity and possible cosmetic blemish. Various treatment modalities, including cryotherapy², laser³, and surgical excision⁴, have been described.
Case Details
A man, 60 years of age presented with discomfort and foreign body sensation in his right eye since 1 month. He had undergone right eye trabeculectomy  with MMC surgery 2 years back. His BCVA was 6/9 in both eyes. His IOP was 14 mmHg in both eyes with a vertical C:D of 0.7 in both eyes. There was an overhanging bleb measuring 5 x 6 mm from 11 O’ clock to 2 O’ clock (Fig. 1). Seidel test showed no leak. We advised him to undergo surgery for excision of the bleb. A month post surgery remaining part of the bleb was  functional and better in appearance, reaching upto the limbus. IOP was stable at 14mmHg. Seidel test was negative and he was symptomatically much better. 

Surgical steps of bleb excision: 

1. After anaesthetising the eye, 6-0 silk traction sutures were taken at the inferior limbus to roll the globe downwards for better exposure of the bleb.
2. The overhanging portion of the bleb was gently dissected from the cornea using a crescent blade
3. The overhanging portion of the bleb was lifted with toothed forceps
4. Once separated from the cornea the bleb was excised with Wescott scissors at the limbus
5. Seidel test done to assess bleb leakage was found to be negative.
   

Discussion:
Sheie et al. hypothesised that an overhanging bleb is a filtering cicatrix that has been massaged downward over the cornea by the action of the eyelid, and that the bleb is in contact only with the corneal surface⁵. Tang Y et al. have proposed that gravity also takes part in the formation of overhanging filtering blebs⁶. Histopathology of the excised tissue in a case report showed a neoplasm like  hyperplasia⁴ (Fig. 6). We believe that erratic or dysfunctional proliferation within the bleb may enable the aqueous to seep forwards creating an over hanging bleb. One must be cautious that the dissection is done beyond the extent of the functional bleb so as to avoid damaging the bleb itself. A safe technique would be to dissect the overhanging bleb in front of the limbus avoiding any obvious blood vessels. Post operatively the patient may be followed up for signs of hypotony and bleb leakage or the elevation of intra ocular pressure. We describe here the surgical technique for removing the overhanging part of a functional bleb. This helped to reduce the cosmetic blemish and discomfort.

References
1.Lanzl IM, Katz LJ, Shindler RL, Spaeth GL. Surgical management of the symptomatic overhanging filtering bleb. J Glaucoma. 1999;8(4):247–249. doi: 10.1097/00061198-199908000-00006.(https://journals.lww.com/glaucomajournal/Abstract/1999/08000/Surgical_Management_of_the_Symptomatic_Overhanging.6.aspx)

2.El-Harazi SM, Fellman RL, Feldman RM, et al. Bleb window cryopexy for the management of oversized, misplaced blebs. J Glaucoma 2001;10:47-50.(https://www.ncbi.nlm.nih.gov/pubmed/11219639)

3. Fink AJ, Boys-Smith JW, Brear R. Management of large filtering blebs with the argon laser. Am J Ophthalmol 1986;101:695-9.(https://pubmed.ncbi.nlm.nih.gov/3717254/)

4. Ou-Yang PB, Qi X, Duan XC. Histopathology and treatment of a huge overhanging filtering bleb. BMC Ophthalmol. 2016;16(1):175. Published 2016 Oct 6(https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5053132/)

5. Scheie HG, Guehl 3rd JJ. Surgical management of overhanging blebs after filtering procedures. Arch Ophthalmol. 1979;97(2):325–6.(https://pubmed.ncbi.nlm.nih.gov/550808/)

6. Tang Y, Wang T, Qu Y. Complications of filtration bleb prolapse with cystic change after glaucoma surgery. Int J Ophthalmol (Chinese Version). 2009;9(11):2254.