Hyperguides

Ophthalmology / Cornea & anterior segment

Managing Post-keratoplasty Glaucoma

Peter J.G. Maris, Jr., MD · Stanley J. Berke, MD · Henry D. Perry, MD
Article

Peter J.G. Maris, Jr., MD · Stanley J. Berke, MD · Henry D. Perry, MD

Clinical Presentation

Introduction

The incidence of glaucoma after penetrating keratoplasty is concerning to the clinician. Increased intraocular pressure (IOP) can not only damage the optic nerve, but also compromise the function of the corneal graft. Both of these processes can severely decrease visual function. Pressure elevation often occurs in the early postoperative period and may resolve within a few days or weeks. Chronic glaucoma, occurring one to several months Post-keratoplasty, can be treated aggressively. According to reports, up to one third of corneal graft failures are caused by increased IOP.1 Glaucoma is particularly problematic following keratoplasty in aphakic and pseudophakic individuals. Endoscopic cyclophotocoagulation of the ciliary processes done at the time of initial penetrating keratoplasty in patients at risk for or with established glaucoma is often effective in controlling postoperative IOP elevation.


Mechanisms of Post-keratoplasty Glaucoma

Multiple risk factors and mechanisms implicated in the development of glaucoma after penetrating keratoplasty exist.

Preexisting Glaucoma
The most significant risk factor for Post-keratoplasty glaucoma is the presence of glaucoma preoperatively. In one study of 502 patients with keratoplasty, 80% of patients with preexisting glaucoma went on to develop progression of their glaucoma postoperatively, whereas only 8% of patients without preoperative glaucoma went on to develop glaucoma postoperatively.2

Aphakia
Aphakic status represents another risk factor for postoperative glaucoma. However, this risk factor may be confounded by the relatively high incidence of glaucoma in aphakic eyes. Zimmerman and colleagues theorized that the loss of zonular tension and scleral spur tension that occurs in aphakic eyes after intracapsular cataract extraction alters support of the posterior trabecular meshwork. During penetrating keratoplasty, the incision into Descemet’s membrane by trephination can cause collapse of the anterior trabecular meshwork support. The combined reduced support of the trabecular meshwork from both directions results in decreased conventional outflow of aqueous through the trabecular meshwork and subsequent IOP elevation.3

The use of through-and-through sutures in aphakic penetrating keratoplasties resulted in significantly lower IOP than the use of conventional suturing technique. It is believed that through-and-through suturing maintains the continuity of tension along Descement’s membrane, thereby reducing trabecular meshwork collapse. Similarly, the use of corneal grafts that are slightly larger than the diameter of the recipient bed is associated with less trabecular meshwork distortion and subsequent resistance to outflow.4 Studies have shown a lower incidence of peripheral anterior synechiae (PAS) formation5 and better IOP control Post-keratoplasty6 when using larger corneal buttons as compared to same-sized grafts.

Peripheral Anterior Synechiae Formation
Shallowing of the anterior chamber in the immediate or early postoperative period can result in PAS formation and the subsequent development of angle-closure glaucoma. This situation can be exacerbated by any coexistent inflammation or uveitis. Likewise, if the eye remains hypotonous for an extended period, either intraoperatively or, more commonly, postoperatively, choroidal effusions with anterior rotation of the ciliary body and iris may result, which can lead to further PAS formation and the potential for subsequent acute or chronic angle closure.7

Corticosteroid Response
Topical corticosteroid preparations are standard in the care of patients with post-penetrating keratoplasty to inhibit the immune response, decrease intraocular inflammation, and prevent and treat corneal graft rejection. The long use of topical corticosteroids is likely responsible for IOP elevations in many patients. Studies have shown 30% of the general population will have a mild response of 5 mm Hg to 7 mm Hg while 5% will have an increase of 15 mm of Hg or more. In susceptible patients, the increase in IOP occurs about 4 to 6 weeks after beginning topical therapy.8 Ninety-two percent of patients with glaucoma can be expected to have an increase in IOP associated with topical corticosteroid therapy.8 In corticosteroid responders, the IOP increase is attributable to decreased outflow facility and can usually be reversed with cessation of topical steroid treatment.


Treatment of Post-keratoplasty Glaucoma

Medical Therapy
Treatment of secondary glaucoma in the Post-keratoplasty setting should always begin promptly upon diagnosis. Medical therapy remains the first line of treatment, unless the clinical situation mandates a surgical response (ie, laser iridotomy in the case of postoperative pupillary block). Beta-blocker, carbonic anhydrase inhibitors, and alpha-agonists, all of which decrease the production of aqueous, are effective in reducing IOP and can be instituted as therapy Post-keratoplasty.10 Miotics and prostaglandin analogues are not recommended as medical therapy as these drugs may increase inflammation and compromise the corneal graft due to their influence in further breaking down the blood-ocular barrier. In general, the clinician should attempt to decrease or eliminate the necessity for topical glaucoma medications as these agents themselves, or the preservatives they are manufactured with, can cause corneal toxicity, thus putting the graft at risk for dysfunction or failure.

Surgical Treatment
If the IOP remains uncontrolled on medical therapy, surgical treatments need to be contemplated. Eyes undergoing penetrating keratoplasty typically have complicated ocular histories and have endured previous surgery. In these eyes, the conjunctiva is often scarred, and further surgery can incite additional inflammation. For this reason, filtering procedures (ie, trabeculectomy) have a high rate of failure and often inadequately control IOP.

One way to overcome the obstacle of anterior conjunctival scarring is to implant a glaucoma filtration device (ie, Molteno, Ahmed, or Baerveldt valves), which will shunt the aqueous via a tube to the posterior drainage reservoir. A major drawback to this treatment is the possibility of corneal graft rejection due to chronic inflammation from a foreign body reaction to the tube or due to corneal endothelial contact with the tube. One study of the long-term results of eyes undergoing penetrating keratoplasty and glaucoma drainage tube implantation showed a 43.6% rate of corneal graft failure at 3 years.11 Additional studies have contended that by positioning the end of the tube in the posterior chamber or vitreous after performing a vitrectomy, the likelihood of success with glaucoma filtration devices can be increased.12

Cycloablative Techniques
Cyclodestructive techniques can decrease the production of aqueous by the ciliary body, thereby reducing IOP. Ciliary destruction has been reserved for the more refractory cases of glaucoma where the visual prognosis is generally poor. Those cases can include neovascular glaucoma, post-traumatic glaucoma, glaucoma associated with aphakia, severe congenital glaucoma, post-retinal surgery glaucoma, and glaucoma associated with penetrating keratoplasties. In the past, contact cyclophotocoagulation gained favor as a method of treating these types of refractory glaucoma. In contact techniques, the tips of hand-held probes are placed 1 mm to 2 mm posterior to the limbus on the conjunctiva and sclera and can deliver either Nd:YAG or diode laser energy to the ciliary body.13

More recently, an intraocular technique of cyclodestruction, called endoscopic cyclophotocoagulation, has been used with success to treat patients with refractory glaucomas, such as those following penetrating keratoplasty.


Endoscopic Cyclophotocoagulation


Slide 1

Operative Technique
Uram developed the technology for endoscopic cyclophotocoagulation (ECP). ECP calls for the selective ablation of the aqueous-secreting ciliary processes while sparing adjacent ocular tissues and structures.14 In eyes undergoing ECP at the time of penetrating keratoplasty, two surgical approaches can be adopted. For both, the pupil should be dilated preoperatively with cyclopentolate 1% and phenylephrine 2.5%, and either peribulbar or retrobulbar anesthesia should be achieved with an equal mixture of Lidocaine and Bupivacaine. In one surgical approach, a clear-corneal temporal wound can be created close to the limbus with a 2.2-mm or 2.5-mm keratome blade. An alternative would be to attempt a partial open sky approach by trephinating incompletely through the patient’s corneal tissue and opening the wound only a few clock hours to accommodate the endoscope probe’s width. Next, viscoelastic material is injected through the incision and beneath the iris to fill and enlarge the ciliary sulcus.


Slide 2

The endoscope (Slide 1), which consists of a 20-gauge probe, allows for a 70° field of view and contains a xenon fiberoptic light source, a helium-neon laser-aiming beam, and an 810-nm wavelength diode laser. Once inserted into the eye (Slide 2), the probe permits simultaneous visualization of the ocular structures on a television monitor and photocoagulation of the ciliary processes. Approximately 180° to 360° of ciliary processes are photocoagulated using power settings of 0.3 W to 0.35 W and continuous surgeon-controlled duration by means of a foot-petal. Only the raised portions of the ciliary processes are treated until whitening and shrinkage occur (Slide 3). Care should be taken to avoid excessive energy, which may cause the ciliary process to explode (or pop) with bubble formation. This can lead to undue inflammation and further breakdown of the blood-aqueous barrier. After performing adequate photocoagution, the endoscope is withdrawn. In the case of the partial open sky technique, the penetrating keratoplasty is continued according to standard technique. If the limbal incision approach was employed, the wound is closed with one or two interrupted 10-0 nylon sutures, and then the penetrating keratoplasty portion is undertaken.

Postoperative Care
At the completion of surgery, subconjunctival injections of Solu-Medrol, gentamycin, and cefazolin are administered. Oral Acetazolamide is administered after the procedure and during the evening of the surgery. On postoperative day 1, patients are started on a regimen of topical antibiotics (typically discontinued after 1 week) and topical steroids. Preoperative topical glaucoma medications are withheld until the need for further IOP control arises. Topical steroids are tapered as the inflammation subsides.


Slide 3

Results
Although literature is scarce on the subject of combined PKP and ECP, one study of 10 glaucoma patients receiving the combined procedures revealed promising results. Eighty percent of patients met success criteria (IOP,22 mm Hg) at last follow-up, which was 30 months after PKP. The average reduction in the number of medications for IOP control at last follow-up was 1.4 from the preoperative average. Additionally, there were no cases of corneal graft failures in the group.15,16 The ability of these grafts to retain clarity postoperatively at 30 months represents a significant improvement over other studies in which penetrating keratoplasty was performed in eyes with glaucoma drainage devices. After 2 years of follow-up in these studies, graft failure was reported to range from 30% to 74.2%.11,17

Complications
Although the technique of ECP spares the conjunctiva and induces less damage to adjacent ocular tissues, ECP carries the potential for any of the complications that accompany intraocular surgery. In the largest study of 68 eyes from 68 patients with various types of refractory glaucomas, the postoperative complication profile was as follows: fibrin exudate in 24% of patients; hyphema in 12% of patients; cystoid macular edema in 10% of patients; and choroidal effusions in 4% of patients. In that study, however, there were no instances of phthisis, endophthalmitis, retinal detachment, or sympathetic ophthalmia.13 Endoscopic cyclophotocoagulation done concurrently with cataract extraction has similarly resulted in few postoperative complications. In one analysis of 25 cases of combined ECP and phacoemulsification of cataract in patients with medically controlled glaucoma who were followed for 1 year, no patient experienced visual loss or a significant complication postoperatively.17 In another study of 10 patients who received combined ECP and phacoemulsification, only one patient experienced a postoperative complication, which consisted of a transient vitreous hemorrhage.18


Conclusion

Post-penetrating keratoplasty glaucoma will continue to challenge the corneal surgeon. The need to control IOP after penetrating keratoplasty is important for not only the integrity of the optic nerve, but also the clarity and longevity of the transplanted cornea. When traditional means of controlling IOP are inadequate or not recommended, endoscopic cyclophotocoagulation is an effective therapeutic strategy. The treatment can be highly titrated to suit the clinical circumstances, and the recovery is much less complicated than that for other surgical modalities.


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