|Ahead of print publication
Deep phototherapeutic keratectomy for Schnyder corneal dystrophy
Ching-An Chen1, Hsiao-Fan Tung2, Yu-Ling Liu2, Chang-Ping Lin3
1 Department of Ophthalmology, Kaohsiung Medical University Hospital, Kaohsiung, Taiwan
2 Department of Ophthalmology, Changhua Christian Hospital, Changhua, Taiwan
3 Department of Ophthalmology, Changhua Christian Hospital, Changhua; Champion Eye Clinic, Kaohsiung, Taiwan
|Date of Submission||14-Sep-2021|
|Date of Acceptance||26-Feb-2022|
|Date of Web Publication||04-May-2022|
Champion Eye Clinic, No. 267, BO'AI 1st Road, Sanmin Dist., Kaohsiung City 80743
Source of Support: None, Conflict of Interest: None
We report a case of Schnyder corneal dystrophy (SCD) treated with deep phototherapeutic keratectomy (PTK). A 33-year-old man presented with a 5-year history of blurred vision and corneal haze in both eyes. Slit-lamp examination revealed needle-like subepithelial crystalline depositions and prominent arcus lipoides bilaterally. Similar clinical findings were observed in the patient's father. A diagnosis of SCD was made on the basis of the clinical presentation. PTK was performed using a multizone, multipass, and shoot and check technique with the WaveLight EX500 excimer laser. After 22 months of follow-up, the best-corrected visual acuity had increased from 0.5 to 0.9 in the right eye and from 0.3 to 0.9 in the left eye. SCD is rare but has a unique ocular presentation, which facilitates the diagnosis. PTK can increase patients' visual acuity and eliminate the need for aggressive management through penetrating keratoplasty or deep anterior lamellar keratoplasty.
Keywords: Multizone, multipass, phototherapeutic keratectomy, Schnyder corneal dystrophy
| Introduction|| |
Schnyder corneal dystrophy (SCD) is a rare autosomal dominant progressive disease manifesting as needle-shaped crystalline depositions over the anterior corneal stroma, early-age arcus lipoides, panstromal haze, and hypercholesterolemia.,,, Fewer than 20,000 cases have been documented in the literature.
The most common symptoms are glare and decreased photopic vision with age, whereas scotopic vision may remain intact., In typical cases, a diagnosis can be made solely on the basis of a slit-lamp examination. However, approximately 50% of patients with SCD have crystalline depositions., Therefore, for cases without crystals, genetic tests and modern imaging techniques, such as anterior segment optical coherence tomography (AS-OCT) and in vivo confocal microscopy, may be required.
Phototherapeutic keratectomy (PTK) has been reported to be effective in the treatment of SCD. Most studies have indicated that PTK was applied for superficial lesions with an ablation depth of approximately 100 μm.,,,, Herein, we report a case of SCD with a deep ablation depth in which most of the lesions were cleared, and we highlight the benefits and risks of such deep PTK.
| Case Report|| |
A 33-year-old man with a 5-year history of progressively decreasing visual acuity and corneal opacity in both eyes was referred to our hospital. The patient reported having statin-treated hypercholesterolemia with elevated low-density lipoprotein but normal triglyceride levels.
Upon examination, his best uncorrected visual acuity was 0.5 in the right eye, and it could not be corrected. His best-corrected visual acuity (BCVA) was 0.3 corrected with −3.00/−0.75 × 12 in the left eye. A slit-lamp examination revealed a central discoid lesion with needle-like crystalline deposits under the epithelium and anterior stroma [Figure 1]. Prominent arcus lipoides in both eyes were also noted [Figure 1]. The central corneal thickness was 582 and 571 μm in the right and left eyes, respectively. AS-OCT revealed hyperreflective opacities in the anterior corneal stroma concentrated over the central cornea. Diffuse posterior optical shadow and thick hyperreflective epithelial basement membrane were also observed [Figure 2]. AS-OCT indicated that the depth of the lesion was 120 and 133 μm in the right and left eyes, respectively.
|Figure 1: Preoperative slit-lamp images of (a) right and (b) left eyes revealing needle-shaped crystals (white arrow) and arcus lipoides (asterisk). The crystals were located in the anterior stroma. Postoperative slit-lamp images of (c) right and (d) left eyes at the 22-month follow-up revealing mild corneal haze without crystal recurrence|
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|Figure 2: Preoperative cross-sectional anterior segment optical coherence tomography of (a) right and (b) left eyes revealing hyperreflective opacities in the anterior stroma concentrated over the central cornea (white arrow). Diffuse optical shadow was observed under the opacities (arrow). Irregular corneal epithelial basement membrane protruding into epithelium (thin arrow). Postoperative anterior segment optical coherence tomography of (c) right and (d) left eye at 22-month follow-up revealing no crystal recurrence|
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The patient reported that his father and paternal grandmother had had similar symptoms of blurred vision and corneal opacity. Hypercholesterolemia and subepithelial central opacity with metallic reflection and arcus lipoides had been observed in his father. Records of examinations of other family members were unavailable. A standard three-generation pedigree was obtained through the patient's medical history [Figure 3]. A diagnosis of SCD was made on the basis of family history and clinical presentation. Due to the typical signs and device limitations, we did not perform confocal microscopy, a genetic test, or a lipid panel.
On the basis of the slit-lamp evaluation, the images from AS-OCT, and the pachymetry map obtained from the Pentacam system (Oculus Inc., Wetzlar, Germany), we concluded that PTK was the optimal treatment because it is conservative and would enable the elimination of most of the central opacity and the retention of a safe residual stromal bed.
We performed transepithelial PTK using a WaveLight EX500 excimer laser (Alcon Laboratories, Fort Worth, TX, USA). A multizone, multipass technique was used to prevent the creation of a deep crater with a sharp edge, which may have inhibited epithelial growth [Table 1]. With broad-beam excimer lasers, PTK can be stopped at any time, and a homogenous ablation surface can be retained. However, with flying-spot excimer lasers, the intended ablation depth must be accessed through multiple passes. After each pass, we observed the surface using balanced salt solution (BSS; Alcon Laboratories) irrigation, which helped us identify the residual density of the opacity. When further ablation was necessary, we dried the surface with a wedge sponge and continued the ablation process. The process was repeated until the density of the residual opacity was satisfactory. Mitomycin C (MMC) 0.04% was applied for 20 s, and the surface was rinsed with BSS and covered with a contact lens.
|Table 1: Diameter (mm) of ablation and depth (μm) of phototherapeutic keratectomy in each pass|
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Postoperatively, a slit-lamp examination revealed a substantial decrease in crystal deposition. The residual corneal thickness was 352 and 351 μm in the right and left eyes, respectively. The epithelial defect was healed by the 3rd postoperative day. After surgery, treatment with 0.5% levofloxacin ophthalmic solution (Santen Pharmaceutical, Co., Ltd., Osaka, Japan) four times daily till the epithelial was healed, 0.1% fluorometholone (Patron Pharmaceutical, Co., Ltd., Taiwan) four times a day was initiated, tapered to three times daily after dispensed the second bottle of fluorometholone, and gradually tapper to twice daily, and discontinued after four bottles of fluorometholone. After 22 months of follow-up, BCVA was 0.9 corrected with − 1.00/−2.00 × 25 in the right eye and 0.9 corrected with − 1.50/−1.00 × 175 in the left eye. Faint central stromal haze without recurrent corneal crystals was noted [Figure 1] and [Figure 2].
| Discussion|| |
SCD is a lipid metabolism disorder that results in the accumulation of cholesterol and phospholipids, which form crystalline depositions over the cornea. The general ocular manifestations of SCD include needle-shaped corneal crystals, early-age arcus lipoides, and panstromal haze. Systemic findings include hypercholesterolemia.,,,,,
Both subepithelial crystals and panstromal haze affect vision in SCD. The depth and density of the lesions dictate which treatment should be applied. AS-OCT is an effective tool for evaluation. Published AS-OCT findings for SCD include hyperreflective corneal opacities located beneath the epithelium and within the anterior stroma.,,,, Some studies have observed a thick hyperreflective corneal epithelial basement membrane., These findings indicate that most SCD lesions are limited to the superficial cornea. Therefore, for most patients with SCD and only subepithelial crystals, PTK is preferable because crystals are the leading cause of impaired vision. For older patients with SCD and severe stromal haze, removal of the superficial crystals is insufficient, and penetrating keratoplasty or deep anterior lamellar keratoplasty would be more appropriate.,,
In our case, most of the lesions were located in the anterior 10%–20% of the corneal stroma; therefore, PTK was proposed, as suggested by Ayres and Rapuano. The multizone, multipass technique is an early broad-beam excimer laser technique often used for severe myopia to reduce ablation depth and smooth the surface. We applied this technique to PTK not only to completely clear the lesion but also to create a smooth ablated surface to facilitate corneal healing.
We also used the shoot and check technique described by Rapuano to eliminate the lesion. After the initial laser ablation, the cornea was examined using a slit lamp, and the patient was repositioned under the laser if more treatment was necessary. Modern excimer lasers are equipped with slit lamps for patient evaluation, so we developed a more practical technique to determine the results of ablation by directly observing under the laser platform. Dry surfaces after laser ablation hamper the identification of the residual opacity. We rinsed the ablated surface with BSS to mimic the tear layer; we subsequently evaluated the residual opacity and determined whether to repeat PTK. BSS does not behave as a masking agent, and no masking agent was used throughout the procedure. We eliminated most of the dense opacity at the optic zone by using the shoot and check technique until satisfactory results were obtained.
Although we aimed to completely eliminate the lesion, a safe residual corneal stromal bed must be preserved. The Food and Drug Administration recommends a residual bed thickness of at least 250 μm after PTK. Our results indicated that 39.5% and 38.5% corneal thickness had been ablated, with a residual thickness of 352 and 351 μm in the right and left eyes, respectively, which are higher values than that recommended by the Food and Drug Administration. However, the ablation depth was still greater than the average values reported in other studies, which can lead to hyperopic shift and corneal stromal haze. As for hyperopic shift, the WaveLight EX500 excimer platform we used may cause a myopic shift in refraction due to an increase in compensatory peripheral ablation. Such a myopic effect would compensate for the hyperopic shift due to deep ablation. As for corneal stomal haze, Park et al. suggested the prophylactic use of MMC for an ablation depth of more than 75 μm to prevent post-PTK haze formation. Therefore, we applied 0.04% MMC for 20 s over the ablated cornea right after the final PTK. After 22 months, BCVA improved to 0.9 corrected with −1.00/−2.00 × 25 in the right eye and 0.9 corrected with −1.50/−1.00 × 175 in the left eye. Data from other studies have indicated that the postoperative BCVA of PTK and penetrating keratoplasty are approximately 0.4 and 0.5, respectively,, which indicates that our results are superior to those of other studies., In our patient, only mild hyperopic shifts with decreased myopia and faint central stromal haze were noted. However, given the considerable increases in visual acuity, the complete removal of lesions, even through deep PTK, would be appropriate because the benefits outweigh the risks.
| Conclusion|| |
SCD is rare but has a unique ocular presentation, which supported the diagnosis. PTK can increase patients' visual acuity and eliminate the need for aggressive management through penetrating keratoplasty or deep anterior lamellar keratoplasty.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given his consent for his images and other clinical information to be reported in the journal. The patient understands that name and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
The authors declare that there are no conflicts of interests of this article.
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[Figure 1], [Figure 2], [Figure 3]