LENSES AFTER SURGERY
Contact Lenses After Trabeculectomy
With proper patient selection and education, these patients can be successful lens wearers.
By Gregory W. DeNaeyer, OD, FAAO
Dr. DeNaeyer is the clinical director for Arena Eye Surgeons in Columbus, Ohio. His primary interests include specialty contact lenses. He is also a consultant or advisor to MedLens Innovations, Inc. Contact him at email@example.com.
Glaucoma is an optic neuropathy that potentially leads to blindness when not detected and treated. It is estimated that glaucoma is responsible for 15 percent of blindness worldwide, making it the third leading cause of blindness (AAOph, Basic & Clinical Science, Glaucoma Course, 2007). Twenty-first century technology is allowing for earlier detection and improved treatment options.
Trabeculectomy is a surgical option for some glaucoma patients when medical management has failed. However, the introduction of a conjunctival bleb can cause difficulties for those patients who want or need contact lenses postoperatively. This article will discuss the use of contact lenses for post-trabeculectomy patients who want or need lenses to correct for ametropia or to mask surface irregularity. We will also discuss how to use contact lenses as a medical management tool to treat a leaking bleb.
Options After Surgery
Incisional surgery for open-angle glaucoma is usually indicated for treatment when medical and laser surgery management has become inadequate or the patient is intolerant or noncompliant with medications (AAOph, Basic & Clinical Science, Glaucoma Course, 2007). This protocol has been supported by the Collaborative Initial Glaucoma Treatment Study (CIGTS) (Singh, 2004).
Trabeculectomy is a type of filtering procedure that creates a pathway for aqueous to drain from the anterior chamber through a flap in the sclera and into the subconjunctival space, where it is later absorbed. As fluid builds up it creates a dome of con-junctival tissue referred to as a bleb (Figure 1). Antifibrotic agents, such as 5-Fluorouracil (5-FU) and Mitomycin C (MMC), are frequently used before and after surgery to prevent scarring and secondary failure of the filter.
Figure 1. Bleb with underlying scleral flap.
Patients who have undergone trabeculectomy may want contact lenses postoperatively because they had them before the surgery or they may need them because of aphakia or corneal irregularity. The resultant bleb is the primary concern when evaluating these patients for contact lenses.
The prevailing thought used to be that it was unsafe to fit patients who have blebs, as mechanical injury from the contact lens could lead to blebitis or endophthalmitis. In 1981, Bellows and McCully reported four patients who had unplanned filtering blebs following cataract surgery developing endophthalmitis after being fit with contact lenses. Three patients were wearing “hard” contact lenses and one was wearing soft lenses. However, more recently, evidence has surfaced that contact lens wear after trabeculectomy can have a high success rate. Samples et al (1990) successfully fit all eight eyes attempted with GP lenses post-trabeculectomy without reported complications. Lois et al (1997) successfully fit all six eyes in a study using soft and GP contact lenses on patients who had filtering blebs.
In 2005, Pederson reported an 85 percent success rate fitting GP lenses on patients who have filtering blebs with no complications of blebitis or endophthalmitis. However, two eyes in this study were treated for bleb laceration and staining of the bleb. This highlights why fitting contact lenses on patients who have filtering blebs can potentially lead to a more severe complication such as blebitis and endophthalmitis. A contact lens, whether soft or GP, can mechanically cause erosive damage to the bleb. The use of MMC and 5-FU can result in a bleb that is thin, which can make it more susceptible to damage and subsequent infection.
Soft Contact Lenses Soft contact lenses are an option for vision correction for patients who have blebs. Because the diameter of most standard soft lenses are usually around 14.00mm, there is a likelihood of interaction between the lens and the bleb. In most cases the soft lens will have to vault over at least the bottom one-third of the bleb. Obviously this will be accomplished more easily if the bleb is relatively low-lying versus one that has significant elevation.
Using a lens with a low modulus is recommended, as the lens can drape more easily over the bleb without negatively affecting fit or comfort. Frequent replacement lenses and appropriate care systems will minimize bacterial binding that could increase the risk of an adverse event.
GP Contact Lenses GP lenses are rigid in nature and have more potential to cause mechanical trauma to the bleb compared to a soft lens. You can use GP lenses to correct ametropia and aphakia, but they are the best option for masking corneal irregularity. An intrapalpebral approach is best for corneal GPs (Figure 2). A high-riding lens or one that moves excessively has the potential to injure a vulnerable bleb. When using a GP lens to mask corneal irregularity resulting from corneal disease, trauma, or surgery, maintaining centration sometimes can be difficult or impossible. Without a bleb, scleral type lenses are normally a good option in these cases as they center well on corneas with extreme irregularity. The bleb presents a problem for scleral lens fitting because the rigid scleral lens will not drape over the bleb as a soft lens would. However, notches can be beveled into a scleral lens (Figure 3) that will enable it to bypass the bleb (Figure 4). In this case the patient has to align the notch with the location of the bleb upon application so that it fits on the eye like a puzzle piece.
Figure 2. Corneal GP lens fitting below a bleb.
Figure 3. Scleral notch.
Figure 4. Scleral lens with a notch fitting around a bleb.
Scleral lenses are designed to be fit without movement, so even though the lens is locked in place there is no physiological consequence. Notches that are less than 4.00mm deep into the lens will usually not affect fit; however, anything more may result in the formation of air bubbles underneath the lens.
Compliance and Care
When fitting contact lenses for visual correction for patients who have blebs, extra caution and care is required to avoid complications, which include blebitis and endophthalmitis. Compliance and follow up are critical to reduce risk of contact lens-related bleb complications. Patients should fully understand the extra risks involved with wearing contact lenses under these circumstances. Assessment of the patient's history of compliance after his trabeculectomy will help you determine how compliant the patient may be with contact lens wear. Frequent follow up is essential to evaluate lens fit and the condition of the lens. Continuously monitor the bleb for staining or damage secondary to lens wear. The patient should use a lens replacement schedule and a care system that keeps the lenses free of deposits, which can increase the risk of infection and complications.
Contact Lenses for Bleb Leaks
A conjunctival bleb leak is a serious complication of trabeculectomy. The use of antifibrotic agents such as 5-FU and MMC have significantly increased the incidence of bleb leaks (Mandal, 2009; Khaw et al, 2003; Schwartz et al, 2002). Although antifibrotic agents prevent excessive scarring to prevent filtering failure, they may also contribute to thinning of conjunctival and Tenon's tissue, which predisposes the bleb to a leak. The incidence of leaks when antifibrotics are used is estimated to be 5 percent to 30 percent (Mandal, 2009; Schuman et al, 1996; Ticho and Ophir, 1993; Katz et al 1995). Complications of bleb leaks are serious and can include hypotony, choroidal effusion, blebitis, and endophthalmitis. Patients may be asymptomatic of a bleb leak; however, they may complain of excessive watering in the affected eye. Diagnosis of a bleb leak is confirmed by a positive Seidel's sign.
Initial treatment of a leaking bleb is to slow or stop aqueous flow through the leak to give the epithelium a chance to seal the wound. First, if tolerated, prescribe aqueous suppressants such as a beta blocker and/or carbonic anhydrase inhibitor. This may seem counterintuitive, especially if the patient's eye pressure is already hypotonous. However, aqueous suppression will reduce the amount of aqueous that is able to flow through the leak and is continuously disrupting epithelial healing.
Secondly, pressure at the leak site with the use of pressure patch or with a soft lens will slow or stop aqueous flow and reduce mechanical aggregation from the lid to allow epithelial restoration. Soft contact lenses have a definite visual and cosmetic advantage over pressure patching for patients. A study by Blok et al (1990) reported an 80 percent success rate using large-diameter (20.5mm) soft lenses to successfully treat leaking blebs after a mean treatment period of 2.2 months. The patients in the study reported the lenses to be comfortable, and complications occurred in only one eye (Blok et al 1990). In another study Shoham et al (2000) demonstrated a 92 percent success rate using 17.50mm soft bandage contact lenses to manage leaking blebs following trabeculectomy.
There are three contact lens characteristics to consider when fitting a bandage soft lens to treat a bleb leak. The first is lens diameter, which is dependent on the location of the bleb, leak location, and bleb size. If the bleb and the location of the leak are proximal to the limbus, then a standard bandage soft contact lens with approximately 14.00mm diameter may work (Figure 5). A larger-diameter contact lens with a diameter of approximately 20.00mm may be needed for larger blebs or if the wound is 2.00mm or greater from the limbus (Figure 6). Secondly, the soft bandage contact lens should have a low modulus, which will help it more easily drape up and over the bleb, especially if the bleb is significantly elevated. Finally, choose a lens that has a high Dk to reduce the risk of hypoxic-related complications, as the lenses will be worn on an extended wear basis.
Figure 5. A 14.00mm soft lens draping over a bleb leak.
Figure 6. A 20.00mm soft lens over a bleb leak.
Besides aqueous suppressants, prescribe an antibiotic drop to reduce the risk of an infection. Frequent follow ups are necessary to monitor for contact lens-related bleb complications. Educate patients on the symptoms of complications, especially blebitis and endophthalmitis, and advise them to return immediately if they should occur. Removal of the contact lens during checks is necessary to check IOP and to clean the contact lens. Applying an artificial tear before lens removal will minimize epithelial disruption to the wound, especially if the lens has tightened down secondary to extended wear. Lenses that have deposits that are not removable should be immediately replaced to reduce the risk of complications.
If a bandage contact lens fails to help repair a leaking bleb, then consider surgical options such as conjunctival-Tenon's advancement flap or hinged partial thickness scleral flap (Mandal, 2001).
Previously, filtering blebs were a contraindication for any type of contact lens wear. However, there is evidence that patients who have blebs can wear contact lenses for visual correction, especially for aphakia or if corneal irregularity warrants their use. There is also evidence that bandage soft contact lenses can help effectively manage a leaking bleb.
The aging population will increase the number of glaucoma patients, and this may increase the demand for patients who may benefit visually or medically from contact lenses after trabeculectomy. Careful patient selection, fitting, and evaluation will minimize contact lens complications for this select group of patients. CLS
For references, please visit www.clspectrum.com/references.asp and click on document #170.