|Year : 2021 | Volume
| Issue : 2 | Page : 230-235
Post trabeculectomy situations: Hypotony
Priyanka Sudhakar, Meena G Menon
Department of Ophthalmology, Glaucoma Clinic, Sankara Eye Hospital, Bengaluru, Karnataka, India
|Date of Submission||09-Apr-2021|
|Date of Decision||14-Apr-2021|
|Date of Acceptance||15-Apr-2021|
|Date of Web Publication||21-Aug-2021|
Dr. Meena G Menon
Sankara Eye Hospital, Bengaluru, Karnataka
Source of Support: None, Conflict of Interest: None
Hypotony, characterized by a low intraocular pressure <6.5 mm Hg or <5 mm Hg with possible clinical complications, can lead to dreaded complications, posttrabeculectomy. It leads to a breakdown of blood-aqueous barrier, leading to an inflammatory cascade, scarring, and bleb failure, in the long term. It also predisposes to blebitis and other hypotony-related complications. Identifying the cause of hypotony, such as bleb leak or overfiltration, is vital to addressing the underlying cause. It can be managed conservatively with pressure patching, and medically with steroids or cycloplegics, or would require surgical bleb revision, depending on the cause and extend of underlying damage. In this article, we review the definition, pathophysiology, risk factors for hypotony, and posttrabeculectomy and identify the various possibilities, and their respective management strategies.
Keywords: Bleb leak, blebitis, hypotony, hypotony maculopathy, overfiltration
|How to cite this article:|
Sudhakar P, Menon MG. Post trabeculectomy situations: Hypotony. Kerala J Ophthalmol 2021;33:230-5
| Introduction|| |
Although low intraocular pressure (IOP) is a desirable outcome, the ocular effects of an IOP that is “too low” pose an even greater risk structurally and functionally. “Statistical” hypotony is defined as IOP >3 standard deviation (SD) below the mean (<6.5 mm Hg). According to the Guidelines on Design and Reporting of Glaucoma Surgical Trials by the World Glaucoma Association, the accepted norm is a numerical cut-off of 5 mm Hg for non-physiological IOP, along with possible clinical complications that could compromise vision. “Clinically significant” hypotony, on the other hand, is when a patient's IOP is so low that there is resultant visual loss. The reported incidence ranges from 1.6% to 12.4% in clinical trials and 7.2% to 42.2% in observational studies.
Formation of a healthy, well-functioning bleb is essential for a successful outcome following trabeculectomy. The significance of this is demonstrated in an article by Benson et al. where a 5-year survival showed evidence of a statistically significant difference (P = 0.0492) with patients in the hypotony group failing more rapidly than the control group. In addition, the number of trabeculectomies that failed in each study year, (most of which failed within the 1st year), were more in the hypotonous group.
The pathophysiology of failure is illustrated in [Figure 1].
Hypotony has been postulated to an increased breakdown of the blood-aqueous barrier as compared to nonhypotonous posttrabeculectomy eyes, thus causing a release of inflammatory mediators into the aqueous and through the filtering bleb into the surrounding tissues. These mediators are responsible for scarring of the underlying tissues, thereby resulting in failure of trabeculectomy.
Hypotony maculopathy is a sight-threatening complication characterized by chorioretinal folds, increased vascular tortuosity, and disc edema. Statistically, it implies that the IOP is 3 SD below the mean or IOP is <6 mm Hg. It has a reported incidence of <1% to up to 30%. A lower incidence of 1.3% has been documented posttrabeculectomy with mitomycin C (MMC) 0.5 mg/ml for 5 min. Causes of vision loss in hypotony maculopathy include (a) mechanical distortion of photoreceptors, (b) permanent changes in retinal pigment epithelium and neurosensory retina, and (c) hypotony-induced astigmatism. The identified risk factors include:,,
- Young myopic males
- Use of antimetabolites (MMC >5FU)
- Primary trabeculectomy
- Higher preoperative IOP
- Preoperative use of oral CAI
- Caucasians >African-Americans.
Hypotony maculopathy is diagnosed clinically and with the aid of fundus fluorescein angiography where it is seen as alternating bands of hyper- and hypofluorescence due to the choroidal folding, and leakage from the optic nerve but not from retinal capillaries. Optical coherence tomography could show retinal macular thickening with or without intraretinal cyst and serous.
The possible causes of low IOP posttrabeculectomy can be categorized based on anterior chamber (AC) depth and bleb height, as shown in [Table 1].
| Bleb leak|| |
Reported incidence of an early bleb leak is 0 to 30%, while that of a late bleb leak in thin cystic and avascular blebs is 5.2% to 6%, as compared to thick walled blebs where it is reported to be 1.1% to 1.3%.,,,, The notable risk factors include (a) use of antimetabolites and (b) fornix-based incisions. The characteristic features which are suggestive of bleb leak include:
- Flat bleb
- Shallow/well-formed AC
- Seidel's positive
The usual cause for conjunctival buttonholes is the penetration of the tissue by the tip of a sharp instrument, which, in turn, usually occurs in cases with extensive conjunctival scarring such as chronic inflammatory conditions, prior external ocular surgeries. To diagnose a buttonhole intraoperatively, the conjunctiva should be carefully examined at the end of the procedure either by filling the AC and raising the filtering bleb and looking for an escape of multiple small air bubbles from the site of the defect, or with the use of a dye. The importance of identifying bleb leaks and treating them is due to its predisposition to (a) hypotony and related complications, (b) blebitis and endophthalmitis, and (c) bleb failure.
Hypotony without a visible bleb should raise a suspicion of a possible leak, which can be confirmed by performing the Seidel's test, which helps in localizing the site of the leak. In this procedure, a fluorescein strip is used to paint the bleb, and the bleb is then visualized under high magnification on the slit-lamp biomicroscope to look for a stream of aqueous from the bleb surface. The outcome of this test can be categorized as follows, based on the amount of aqueous flow:
- Point leak (pinpoint staining of the conjunctiva)
- Bleb sweating (transconjunctival ooze as pearls: also called physiological Seidel/pseudo-Seidel)
- Frank bleb leak (stream of aqueous).
In a study by Gollakota et al., the importance of recognizing these patterns has been highlighted, as the sweating blebs are cystic, elevated, and still functional. At the same time, they carry a higher risk of complications prior to bleb repair (such as blebitis, hypotony, maculopathy), but a better bleb survival, post bleb repair, and thus benefit from an early intervention.
The site of leak marks the thinnest and most avascular area of the bleb. Histopathological examination in studies has suggested a breakdown of conjunctival epithelium with thinning and stromal necrosis in the concerned area.
Bleb leaks can be classified based on (a) onset or (b) associated clinical features [Table 2] and [Table 3].
Initial treatment involves the use of pressure patch, in a method known as torpedo bandage, as illustrated in the pictures below. The idea is to apply pressure over the bleb and not the eye [Figure 2] and [Figure 3].
|Figure 2: Ask the patient to look down and then apply the rolled torpedo bandage over the upper lid|
Click here to view
The use of aqueous suppressants is debatable. The principle behind it is that it reduces the amount of aqueous that can flow through the leak, thus continuously disrupting epithelial healing.
Soft contact lenses (CLs) have a visual and cosmetic advantage overpressure patching for these patients. The principles behind its use include: (a) It tamponades the area of aqueous leak, thus slowing or stopping aqueous flow and reduces mechanical aggregation from the lid, thus promoting epithelial restoration (b) It helps maintain good bleb morphology and function. These lenses can be left in situ for as long as 3 weeks. There are three properties which are important before dispensing contact lenses for the same:
- For defects close to or <2 mm from the limbus: 14 or 15.5 mm CL (12)
- For defects 2-4 mm away from the limbus: 17 or 20 mm CL (12).
Modulus: LowDk value: High.
Fibrin tissue adhesive
Specifically, in glaucoma literature, Asrani and Wilensky have been credited with describing the use of autologous fibrin tissue glue to treat bleb leaks. Fibrin glue is a two-part admixture containing a protein base and thrombin–calcium chloride activating solution, containing fibrinogen, plasminogen, fibronectin, and factor XIII in bovine aprotinin solution. It has been postulated to create collagen crosslinking lending strength to tissue adherence through fibrin–fibronectin bonds, and thus help sealing leaking wounds. Its rapid activation time of 20–30 s makes it appealing for intraoperative use. It can be used either as a sequential method or simultaneously using Duploject. However, since fibrin glue requires a dry surface to be effective, its application over a continuously leaking bleb as was originally suggested was thought to prevent a stable fibrin clot formation. Thus, certain modifications have been suggested to avert the situation, by filling the chamber and bleb with air, thus increasing the surface tension of the air–aqueous interface as well as keeping the surface dry. Fibrin glue however carries a theoretical possibility of transmission of HIV, hepatitis C virus, and prion-related diseases.
The following are the current indications for surgical repair:
- Bleb dysesthesia
- Large sweating bleb with hypotony maculopathy
- Frank bleb leak
The aim of bleb repair is not only closure of bleb leak or resolution of hypotony but also to preserve the bleb function. The reported overall success rates of bleb repair with various techniques were 80% to 86% at 1 year, which decreased to 50% at 5 years.,, [Table 4] enlists, in brief, the various techniques involved in surgical repair of a leaking bleb.
| Overfiltration|| |
This occurs as a result of decreased outflow resistance when aqueous outflow exceeds the production. The identified risk factors for overfiltering blebs include (a) use of antimetabolites and (b) early laser suture lysis. It is characterized by an elevated bleb, shallow/well-formed AC, and a negative Seidel's test. The probable causes include (a) loose scleral flap sutures, (b) large scleral fistula, or (c) an exceptionally large area of filtering bleb. [Table 5] highlights the management strategies involved.
Surgical revision of overfiltration is warranted, especially when associated with hypotony maculopathy. It involves the use of compression sutures, which were traditionally described by Palmberg, and were called Palmberg compression sutures. Here, two longitudinal transconjunctival sutures are placed on either side of the scleral flap edge to provide adequate resistance to aqueous outflow, and thus limit the amount of aqueous egress. There have been modifications in this technique, one of which, as described by Yu et al., involves the use of two figure-of-eight transconjunctival sutures place horizontally over the scleral flap proximal to the limbus and the second one on the distal flap edge. The sutures could then be lysed sequentially, in cases of elevated IOP postoperatively, until an adequate IOP is achieved.
| Cilichoroidal Detachment|| |
Imbalance between the fluid pressure in the eye and in the choroidal vasculature causes fluid to accumulate in the space between the choroid and the sclera, causing a detachment. Ciliochoroidal detachment, however, is more common after full-thickness surgery than trabeculectomy. The detachment is usually transient resolving with the administration of topical and systemic corticosteroids. However, presence of serum along with large protein molecules makes spontaneous resolution unlikely. Preoperative identification of high-risk eyes such as nanophthalmos and those with an elevated episcleral venous pressure, and subsequently taking adequate measures, helps in avoiding such complications. Indications for surgical drainage include (a) flat AC with lens cornea touch and (b) kissing choroidals.
| Cyclodialysis Cleft|| |
Cyclodialysis clefts are formed when the ciliary body becomes detached from the scleral spur. An abnormal free communication between the AC and the suprachoroidal space is formed thus increasing the uveoscleral flow, resulting in profound hypotony. The cleft size, however, does not affect the degree of hypotony. They can be identified by gonioscopy; however, this can often be limited in soft eyes, in which case ultrasound biomicroscopy or anterior segment optical coherence tomography can be done. Management strategies are described in [Table 6].
| Iridocyclitis: Aqueous Shutdown|| |
Decreased aqueous production occurs as a result of increased inflammatory response leading to the breakdown of blood-aqueous barrier, releasing pro-inflammatory mediators causing a ciliary body shock and shutdown. Hence, eyes predisposed to or presenting with substantial amount of postoperative inflammation, warrants an aggressive course of topical steroids.
| Retinal Detachment|| |
Although a very rare complication, serous RD and uveal effusion syndrome have been described posttrabeculectomy in nanophthalmic eyes with short axial length (14–17 mm).
Other less common causes of postoperative hypotony are listed in [Table 7].
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]