Bleb migration onto cornea

Occasionally after a successful operation for external drainage, the conjunctival bleb dissects down into the cornea.179 Here it forms a translucent white blister, which slowly extends toward the central cornea (Fig. 36-35). If the patient complains of foreign body sensation, the chronic intermittent use of topical lubricating drops or ointment or non-steroidal anti-inflammatory eyedrops (e.g., ketorolac 0.5% or diclofenac 0.1%) may bring relief.180 If symptoms persist, the encroaching bleb can be removed by dissecting it off the cornea like a pterygium.181 Pathologically, this blister is largely acellular and filled with amorphous material.When the limbus is reached, the tissue can be excised without collapsing the filtering bleb.After several days of aqueous weeping, such ‘amputated’ blebs usually heal, especially if steroid drops are sparingly used.

Diffuse blebs

Thick-walled diffuse blebs are more cosmetically acceptable, comfortable, and less prone to infection or leakage than are thin-walled blebs. Diffuse blebs appear as pale and subtle conjunctival elevations, often with tiny, interepithelial microcysts on their surface. These microcysts are most abundant near the limbus and are best

seen with the slit lamp by directing the light to a spot adjacent to the viewing area (scleral scatter or retroillumination technique). Although rigid contact lenses appear to be safe with thick blebs, endophthalmitis has been reported.79 There is little information about the long-term safety with thick blebs of soft contact lenses; but as with all patients who have undergone filtration surgery, awareness of the warning signs of infection is obligatory.

Overfunctioning blebs

A very large diffuse bleb can be an irritant to the patient and a source of hypotony.These blebs may appear more commonly with the use of antimetabolites, excessive suture lysis or manipulation, or aggressive digital massage. They sometimes appear to encircle the entire limbus (‘gutter blebs’), causing bogginess to all the bulbar conjunctiva (Fig. 36-36). More often they are limited to two quadrants. If the pressure is properly controlled, the patient often will accept the symptoms. As with blebs that have migrated onto the cornea, large blebs presumably interrupt the normal distribution of the tear film and hence cause discomfort. Relief may be obtained by using ocular lubricants, such as artificial tear drops or ointments, or by using topical non-steroidal anti-inflammatory eyedrops, such as ketorolac 0.5% or diclofenac 0.1%.180

If hypotony exists in conjunction with an overfunctioning bleb, an attempt can be made to delimit the bleb without loss of its

Fig. 36-34  Surgical bleb reduction. A Vicryl suture closure of the relaxing incision can be performed to ensure that the entire wound remains water tight. A bleb can be seen at the site of the revised bleb.

(From Lieberman MF: Complications of glaucoma surgery. In: Charlton J, Weinstein G, editors: Ophthalmic surgery complications, Philadelphia, Lippincott-Raven, 1995.)

Fig. 36-36  A large diffuse bleb that nearly encircles the cornea but is most prominent nasally. Pressure was 12 mmHg. After 8 years the pressure had risen to 17 mmHg.

Fig. 36-37  Cryotherapy for bleb reduction. With the patient under topical anesthesia, a glaucoma probe can be applied on top of and surrounding the exuberant bleb, with a freeze allowed to enlarge approximately 2 mm on each side of the probe for approximately 5 seconds. Care should be taken for the iceball to thaw fully before the probe is removed so as not to disrupt the underlying bleb tissue.

(From Lieberman MF: Complications of glaucoma surgery. In: Charlton J, Weinstein G, editors: Ophthalmic surgery complications, Philadelphia, Lippincott-Raven, 1995.)

Fig. 36-38  Cautery bleb reduction. With the patient under topical anesthesia, a standard hyfrecator electrocautery applies mild burns in rows surrounding the exuberant bleb. Applications should be made to barely blanch the conjunctiva, applying light pressure on the device to compress the conjunctiva and its underlying fluid down to the episcleral surface. The cautery is usually not applied to the bleb surface itself.

(From Lieberman MF: Complications of glaucoma surgery. In: Charlton J, Weinstein G, editors: Ophthalmic surgery complications, Philadelphia, Lippincott-Raven, 1995.)

function.All of the techniques that have been described7,182 have in common the ability to induce inflammation: cryotherapy,183 electric needle hyfrecation,184 argon laser,185 trichloroacetic acid applications,186,187 or transconjunctival obstruction sutures at the limbus with absorbable suture to delimit lateral guttering. As is common when there are many techniques available, each is unpredictable in its efficacy.

Cryotherapy can be controlled nicely, penetrates well into the episcleral region, and is widely available (Fig. 36-37). Three or four applications across the distal end of the bleb are used; if the bleb is not too elevated, applications across its surface can also be attempted. With the patient under topical anesthesia, the probe is pressed against the conjunctiva until a ring of ice approximately 4 mm wide encircles the probe. To avoid tearing the conjunctival surface, the probe should not be removed from the globe until the tip has thoroughly thawed. These applications are repeated as needed. It is better to do too little and add more after 1 or 2 weeks than to overdo it and close down the filtering bleb.This procedure can cause operative and postoperative pain.

The techniques of electrocautery (electric needle hyfrecation) and trichloroacetic acid application restrict treatment to the zone surrounding the bleb’s extent. In the former technique, in which only topical anesthesia is used, a standard hyfrecator electrocautery at moderate settings applies mild burns in rows surrounding the exuberant bleb (Fig. 36-38). Applications should be made to barely blanch the conjunctiva, applying light pressure on the device to compress the conjunctiva and its underlying fluid down to the episcleral surface. The cautery is usually not applied to the bleb surface itself.

Using the chemical technique, a wooden applicator is dipped into a supersaturated solution of trichloroacetic acid. This is prepared fresh from a small spoonful of anhydrous crystals placed in

Fig. 36-39  Chemical bleb reduction. A wooden applicator is dipped into a supersaturated solution of trichloroacetic acid and carefully applied in several rows surrounding the exuberant bleb, with care taken to avoid leakage of the chemical onto the corneal surface. The bleb surface itself is

usually avoided. Light chemical blanching and whitening is seen after a few seconds of application. This technique may be uncomfortable for the patient, and topical atropine and patching are often useful.

(From Lieberman MF: Complications of glaucoma surgery. In: Charlton J, Weinstein G, editors: Ophthalmic surgery complications, Philadelphia, Lippincott-Raven, 1995.)

10 ml of sterile water and stirred until all the crystals go into solution. A minimal drop on an applicator is carefully and repetitively applied in several rows surrounding the exuberant bleb, with care taken to avoid dripping the chemical onto the corneal surface (Fig. 36-39). The surface of the bleb is usually avoided. Light chemical blanching and whitening is seen after a few seconds of application. This technique may be uncomfortable for the patient, and topical atropine and patching may be useful. An untimely blink or tearing can wash the trichloroacetic acid onto the cornea causing epitheleal burns and denudation. For this reason, this technique has been largely abandoned.