Treatment of Corneal Erosion Syndrome: Standard or Phototherapeutic Keratectomy?
Irrespective of underlying pathology, the symptoms of corneal erosion are severe pain, photophobia, excessive tearing, and redness. Often, blurred vision (usually improving between recurrent episodes) accompanies these symptoms. Persistent and hard-to-heal syndromes as well as central erosions may lead to permanent decrease in vision.1-6
In most cases, the disease is caused by past corneal injury, corneal dystrophy or degeneration; its course can be affected by the patient's general condition (ie, hormonal fluctuations of the menstrual cycle; pregnancy; menopause; or concomitant occurrence of other abnormalities including diabetes, herpes simplex infection or autoimmune disorders). Recurrent corneal erosions have also been mentioned in ocular disorders (ie, palpebral dysfunction, Meibomian gland dysfunction, tear film disturbances, degenerations after thermal or chemical injuries, keratitis and loss of limbal stem cells). Conversely, erosions do not always have an underlying cause; these are idiopathic erosions.1,3,6-9
Recurrent corneal erosion syndrome is characterized by easy escape of the corneal epithelium from its surface, caused by poor epithelial adhesion to the anterior limiting lamina. Normal epithelial adhesion depends on several structures seen between the basal cells layer, the basement membrane, Bowman's membrane and the stroma (ie, hemidesmosomes, lamina densa, lamina lucida, anchoring filaments, laminin, fibronectin and type IV and VII collagen). The basement membrane complex abnormality is believed to cause the recurrent corneal erosions. Histologic examinations revealed a decrease in hemidesmosomes and resulting basement membrane disadhesion.1,6,8,10
MANAGEMENT
Managing recurrent corneal erosion still poses problems. Some treatment options described in the literature do not prevent subsequent episodes. Pharmacological agents (eg, ointments, lubricating eye drops, cycloplegics) or pressure patching are not effective in every patient. Antiseptic and hyperosmotic ointments and mechanical debridement of the corneal epithelium are frequently used as temporary measures, however, they fail as a prophylactic treatment for recurrent erosions.4-6,11-13
Nighttime and bedtime ointment application is recommended to prevent contact between the corneal epithelium and the eyelids. Lubricating agents should be continued for longer—even longer than 3 months—due to regression of acute symptoms. Available hyperosmotic agents, when added to the ocular ointment, may decrease corneal edema, which help restore the adhesion complex. Such regeneration may take time, and therefore lubricating agents should be used for 6 to 12 months following the most recent episode of erosion.6,13
Biochemical investigation suggests that excessive matrix metalloproteinase (MMP) activity plays a role in the pathogenesis of recurrent corneal erosion syndrome. Thus, application of MMP inhibitors is a promising therapy for the erosion healing process.14 Topical steroids increase the risk of infection; they are only recommended in selected cases under meticulous specialist supervision.
Another form of prophylaxis is a bandage contact lens to relieve subjective discomfort. Its prophylactic action is insufficient in preventing future episodes of erosions, however. There is also the threat of potential complications (eg, neovascularization and infection),5,6
TREATMENT OPTION
Surgery becomes a treatment option when (1) pharmacological agents or contact lenses are unsuccessful, (2) prophylactic measures fail to prevent frequent recurrences, (3) subjective complaints are hard to relieve, and (4) complications occur. Select the surgical method depending on the (1) frequency and severity of recurrence, (2) etiology and location of erosions, and (3) the patient's preferences.
According to Reidy,5 mechanical debridement of the epithelium and ointment with pressure patching is associated with an 18% erosion recurrence rate. Superficial keratectomy, microcoagulation or cauterization of Bowman's membrane does not yield satisfactory results. Healing may be compromised in patients with a long history of recurrent corneal erosion syndrome leading to irregular astigmatism.5,6,11,12,15
In 1983, Buxton12 reported on the outcome of superficial epithelial keratectomy performed in 13 eyes. All eyes had recurrent erosion that was unresponsive to conservative treatment. The corneal epithelium was manually removed—from limbus to limbus—and the Bowman's membrane was polished with a diamond burr. A similar technique produced a recurrence rate of approximately 25%.5,15 Superficial keratectomy is mostly used in hard-to-heal recurrent erosions when other treatment methods have failed; the risk of inflammation and scarring is quite significant.
Puncturing the anterior stroma was first described by McLean et al10 in 1986. The method was based on an observation that recurrent erosion did not occur following deep corneal traumas or in corneas with deeply stuck foreign bodies. In 86% of cases, the authors obtained good results by puncturing the anterior stroma through the loose epithelium to its half-depth beyond the visual axis. Tritten and Herbort16 modified the technique and made micropunctures to one-third of the stromal depth without removing the corneal epithelium. During the following 18 months, 31% of patients experienced a treatment recurrence, sometimes accompanied by scarring that resulted in visual acuity decrease, glare and night vision disturbances.
AVOID THE VISUAL AXIS
Micropunctures seem safer than prolonged bandage contact lens application, however, the treatment should be avoided in the area of the visual axis. A straight needle poses the threat of corneal perforation due to imprecise puncture or lack of patient cooperation. For this reason, Rubinfeld designed a curved needle that is similar to a cystotome. The needle has a built-in limiter that protects against accidental eyeball perforation.17 Reidy performed anterior stromal punctures in 38 patients and reported an erosion recurrence rate of approximately 40%.5
Several researchers have attempted treatment with Nd:YAG,18 argon2 and excimer3,19-21 lasers. A single impulse mode of the Nd:YAG laser was used to treat shallow superficial lesions either after having previously removed the loose corneal epithelium or through the epithelium.18 Focusing the laser on the anterior cornea prevented an excessively deep penetration into the stroma. Long-term effects of Nd:YAG laser therapy on the corneal endothelium are unknown.
PHOTOTHERAPEUTIC KERATECTOMY
A very precise treatment modality for recurrent corneal erosions is excimer laser photoablation.3,19-23 This treatment allows accurate determination of the stromal puncture area and depth as well as protects against accidental eyeball perforation. Excimer laser photoablation was performed for recurrent erosions of various etiologies, both through the corneal epithelium and after its removal (Figures 1 and 2). Different photoablation diameters and depths have varying degree of success.20,23,24 The ablation depth also depends on the laser parameters. öhman3 compared the outcome of several photoablation depths either performed through the epithelium or after its removal.
örndahl and Fagerholm considered phototherapeutic keratectomy (PTK) better than corneal debridement.21 Jain25 performed PTK using a 7-mm flat beam diameter to a depth of 30 µm and penetrated 6 µm into the Bowman's membrane. All signs and symptoms of erosion were relieved in 69% eyes.
To avoid postoperative glare and night vision disturbances, the photoablation margin should remain beyond the visual axis. Care should also be taken to spare the corneal limbus, as damage could result in stem cell dysfunction.25
It is also possible to (1) combine PRK with PTK or (2) use PRK as a therapeutic procedure to treat recurrent erosion in myopic patients. Therapeutic and refractive effects have been satisfactory,25,26 however, proceed with caution when combining refractive and therapeutic procedures. Photoablation profiles and patient expectations may differ.6
COMBINING PROCEDURES
The success of PTK for the treatment of recurrent erosion is estimated by complete elimination of subjective complaints or longer time intervals between subsequent pain episodes. PTK is successful in patients unresponsive to conventional therapy who suffered from basement membrane dystrophy with recurrent erosion.4,27 Results are not satisfactory in all patients, though.3,20,23,28
The frequency and causes of recurrence are constantly analyzed, and methods to prevent another episode are being identified.1,5,6,8,13 Many factors are responsible for the recurrence of corneal erosion. The frequency of post-PTK recurrence is not determined by the frequency of pretreatment complaints, but they can be affected by the procedure technique.7,19 A too small photoablation zone and too shallow or inadequate photoablation may be responsible for most of post-PTK recurrences. Recurrent erosion are a disperse disease and may develop beyond the photoablation area.24
Literature reports give considerably different recurrence frequencies, rates and time of occurrence after PTK. Within the first year after PTK, the procedure was repeated in 12.5% to 31% of eyes.4 Giessler8 and Morad29 reported recurrences in 8.8% and 17.4% of eyes, respectively.
CARRY OUT METICULOUSLY
The BCVA usually remained unchanged following PTK for recurrent erosion, although refraction and corneal curvature changes were observed. Central photoablation should be carried out meticulously: You do not want to induce a hyperopic shift that may lead to decreased visual acuity or anisometropia.7,22,29
Infections after refractive and therapeutic procedures are rather infrequent, however, it should be considered when reepithelialization of the photoablation area is prolonged. Even with antibiotics, Staphylococcal, Streptococcal, Pseudomonas aeruginosa, and fungal infections may occur. Acute subepithelial infiltrations imitating keratitis may also be found, which most probably develop as an immunological system response to bacterial toxins, bandage contact lenses or applied drugs. Healing difficulties may suggest an Acanthamoeba infection.30-32 Confocal microscopy facilitates diagnosis of the infection's etiology.32,33 Viral infections should also be remembered. Herpes simplex reactivation may be triggered by the laser beam, mechanical epithelial debridement, an injury, pharmacotherapy, stress, or individual susceptibility. The virus may also reactivate spontaneously.34
Typical corneal haze was rarely observed following PTK for recurrent corneal erosion syndrome; it may be determined by the time of reepithelialization of the photoablation surface.28,35 Numerous surgeons consider post photokeratectomy pain undesirable and bothersome for the patient. Post-PTK pain usually subsides within 24 hours,19 and patients with spheroid degeneration and band keratopathy report the least severe pain.4,27 Those with frequent and painful erosions consider postoperative pain as insignificant compared with the benefit of surgery (ie, elimination of recurrences). In my personal experience, most patients mention discomfort rather than pain or moderate pain.
SUMMARY
PTK is now a recognized treatment modality for recurrent corneal erosion. Appropriate patient selection, proper technique, and postoperative care may lead to satisfactory clinical outcome. Despite reports on valuable experimental and clinical investigations concerning PTK, a lot of issues remain to be clarified. PTKs have been performed in my hospital since 1991. We have come to better understand the potential of therapeutic photoablation and observe which corneal disease is more and which less responsive to the treatment.
Ewa Mrukwa-Kominek MD, PhD, is from the department of ophthalmology, Silesian Medical University, in Katowice, Poland, where Professor Ariadna Gierek-Lapinska is the head of the department. Dr. Mrukwa-Kominek states that she has no financial interest in the products or companies mentioned. She may be reached at emrowka@poczta.onet.pl or +48601528850. Dr. Mrukwa-Kominek is a member of the CRST Europe Editorial Board.
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