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PTK proves to be an option for Schnyder’s crystalline dystrophy
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PHILADELPHIA — Phototherapeutic keratectomy (PTK) can be effective at improving visual symptoms in patients with Schnyder’s crystalline dystrophy (SCD), according to Christopher J. Rapuano, MD, of Wills Eye Hospital here. Dr. Rapuano reported on four cases in which PTK was shown to be a useful therapeutic alternative to lamellar or penetrating keratoplasty in a recent issue of Cornea, The Journal of Cornea & External Disease.
SCD is characterized by bilateral and usually symmetric deposition of fine, needle-shaped polychromatic cholesterol crystals in the central cornea. According to Dr. Rapuano’s report, the deposits are predominately located in the anterior one-fifth of the stroma and Bowman’s membrane, and are accompanied by a prominent arcus senilis and a diffuse, gray stromal haze.
SCD with age
---Schnyder’s crystalline dystrophy in a 50-year-old white man. Note the significant central crystals before excimer laser PTK.
In previous studies, the progression of SCD with age has been described such that patients younger than 23 had only mild subepithelial crystalline deposits or a central disc-like opacity. Patients 23 to 38 years of age had the additional findings of arcus lipoides and slightly decreased visual acuity, and patients older than 38 developed centrally dense panstromal haze and prominent arcus lipoides.
“Although some authors believe that both factors affect vision, we believe that in patients with mild to moderate stromal haze the superficial cholesterol crystals primarily affect visual acuity due to diffraction of light resulting in a blurred image, glare and photophobia,” Dr. Rapuano said. “It is of interest that the visual axis is spared until late in the disease because of relative lucency of the center of the disciform crystalline deposits in many patients.”
All four eyes in Dr. Rapuano’s series had the central crystalline form of SCD, and all underwent PTK at Wills Eye Hospital from March 1992 to December 1998. The surgical plan was to remove less than one-third of the corneal thickness, leaving at least 250 mm. All procedures were performed with Ar-F lasers, which were calibrated to achieve a fluence of 160 mJ/cm2 at a pulse rate of 5 to 6 Hz. The mean ablation rate was 0.26 mm/pulse, with a range of 0.24 to 0.28.
Case studies
---Fifteen months after excimer laser PTK, the patient’s central crystals are much improved as were his glare, photophobia and night driving.
The first case in the series, a 47-year-old male, was referred because of decreased visual acuity and marked photophobia in both eyes. Upon examination by slit lamp, it was discovered that both corneas had crystalline deposits in the anterior stroma. The patient underwent PTK in the left eye because the visual changes were more prominent in that eye. Ultrasound pachymetry 6 weeks after surgery was 570 mm. Final follow-up of the eye after 7 months showed best corrected visual acuity (BCVA) to be 20/30– in a dark room, 20/50– in a lit room. According to Dr. Rapuano, slit lamp findings showed no recurrence of cholesterol crystals in the central area and mild central haze.
The second case in the series, a 54-year-old male, was referred to Dr. Rapuano because of corneal clouding, decreased vision and photophobia in his right eye. This patient had had penetrating keratoplasty (PKP) for SCD in his left eye 11 years earlier. A slit lamp examination indicated that he had a dense central panstromal disc-like opacity and arcus senilis in his right eye. A less dense midperipheral panstromal haze was present in the central cornea. His left eye also showed visual changes upon slit lamp examination, including early recurrence of cholesterol crystals in the central anterior stroma of the corneal transplant and a 1+ nuclear sclerotic cataract.
Three months after PTK, his BCVA in a dark room was 20/40– and in a lit room was 20/60– in the right eye; and the manifest refraction was +4 sphere. Slit lamp examination showed less dense subepithelial central haze and a recurrence of crystal deposits in the periphery of the ablated area. Thirty-six months after surgery, his visual acuity in his right eye with a contact lens was 20/25 in a dark room and 20/50– in a lit room. BCVA with a contact lens in his left eye was 20/40– in a dark room. In the left eye, there was a subepithelial central scar with recurrence of superficial cholesterol crystals in the graft. Subjectively, the patient reported that the vision in his right eye, in which he had received PTK, was better in terms of photophobia and glare compared with his left eye in which he had received PKP.
The third case in the series, a 50-year-old male, was referred because of decreased visual acuity for night driving and marked bilateral photophobia. The patient underwent PTK in his left eye, and 3 months later developed a “lacy, reticular subepithelial opacity” in the periphery of the ablation zone. It was treated with prednisolone acetate 1% four times per day. The post-excimer haze improved and the steroid drops were tapered over several months. Slit lamp examination after 11 months showed no recurrence of cholesterol crystals; however, there was persistence of a less dense central opacity and a mild lacy reticular subepithelial scar in the periphery of the ablation zone.
PTK also was performed in the patient’s right eye, and the epithelial defect healed within 4 days. Similar to the fellow eye, the right eye developed a subepithelial reticular opacity in the periphery of the ablation zone, and similarly responded well to a tapering of prednisolone acetate 1%. According to Dr. Rapuano, the patient reported a significant improvement in his night driving vision and photophobia in both eyes.
For Your Information:
- Christopher J. Rapuano, MD, can be reached at Wills Eye Hospital, 900 Walnut St., Philadelphia, PA 19107; (215) 928-3180; fax: (215) 928-3854.
Reference:
- Paparo LG, Rapuano CJ, Raber IM, Grewal S, Cohen EJ, Laibson PR. Phototherapeutic keratectomy for Schnyder’s crystalline corneal dystrophy. Cornea. 2000;19(3):343-347.