Customized Ablation Area PTK as a Technique for Salzmann's Degeneration and Other Focal Stromal Pathologies

Case Report

A 26-year-old woman presented with Salzmann's nodules associated with symptoms of recurrent erosions for the past year. She had a history of frequent visits to the clinic due to discomfort and pain caused by clearly visible erosions located inferonasally in the left cornea, approximately 4 and 2 mm in arcuate and radial length, respectively, in an area overlying Salzmann's nodules. Attempts to treat with repeated contact bandage lenses, lubrication, and punctal plugs showed no improvement. Consequently, surgical treatment with custom PTK was chosen.

Technique

To create the custom ablation profile, a measurement of the white-to-white distance was performed using the GALILEI Placido and dual-Scheimpflug analyzer (Ziemer Group). The nodular lesion area was delineated with gentian violet ink and a slit-lamp image of the patient's cornea was taken.

The image of the delineated nodules was entered into the ImageJ image processing software, which we used to measure the nodules' exact shape, size, and location. First, the dual-Scheimpflug white-to-white measurement was used to set a scale on the ImageJ software, creating a “pixel aspect ratio” (Figure 1A). With this scale and using the pupil as the reference point, the outer nasal diameter (green) and inner nasal diameter (red) were measured and their respective angles were measured from the horizontal (Figure 1A). The maximum depth of the lesion from the peripheral unaffected Bowman's layer and the height of the lesion protruding from the peripheral unaffected epithelial surface were obtained using Zeiss Cirrus HD optical coherence tomography (OCT) (136 µm) (Carl Zeiss Meditec AG) (Figure 1B) and were used to determine the depth of the excimer ablation. Subsequently, all determined dimensions, including the distances and their angles and the depth of the lesion, were input into the CAM software (SCHWIND eye-tech-solutions GmbH) to plot the exact size and location of the area to be ablated, using the positive axis and the counterclockwise direction as the starting point.

Figure 1. (A) Slit-lamp photograph of the affected eye imported into ImageJ software. The horizontal black line corresponds to white-to-white (WTW) measurement, which has been derived from the Scheimpflug image and used in the ImageJ software to set the “pixel aspect ratio.” The green and red lines correspond to the outer and inner diameters of the lesion, respectively, and their angles; the nasal angles alpha and theta represented above, were automatically calculated on the ImageJ software and referenced to the horizontal WTW measurement. (B) A section of the cube mode (4 × 4 mm) of Zeiss Cirrus optical coherence tomography (Carl Zeiss Meditec AG) of the affected cornea showing the Salzmann's nodular lesion. The maximum depth of the protruding lesion to the level of the unaffected Bowman's layer was measured. OND = outer nasal diameter; IND = inner nasal diameter; α = angle of OND from horizontal; Ø = angle of IND from horizontal

Corneal topography was performed using the Peramis dual-Placido and pyramidal aberrometry system (SCHWIND eye-tech-solutions), and data for static cyclotorsion control were extracted for the treatment. The topographic data points over the peripheral nodular lesion were not complete and the decision was to avoid doing a corneal wavefront-guided photorefractive keratectomy and instead perform a customized, lesion-guided PTK with fluid-assisted smoothing. The ablation was centered on the pupil centroid to ensure the same centration reference as the image analysis software, so the pupil and treatment offset were chosen as zero. The generated ablation profile (Figure 2) was then programmed into the AMARIS excimer laser (SCHWIND eye-tech-solutions GmbH).

Figure 2. (A) Display screen of the customized ablation area phototherapeutic keratectomy setting of the CAM software (SCHWIND eye-tech-solutions GmbH) showing the input parameters of the ablation profile matching the target lesion. The pupil and treatment offset were chosen as zero to ensure the same centration as the image analysis software. (B) Display screen showing the generated ablation profile.

The eye was anesthetized using topical proparacaine hydrochloride 0.5% drops. The nodules were marked with gentian violet ink and transepithelial PTK was performed in one round, sectorially ablating the area of the pathology only. The fading of the ink markings confirmed the correspondence of the laser ablation profile with the position of the nodules on the cornea. Transepithelial PTK was performed along the entire depth of the lesion, deducting the largest height of the lesion protruding from the level of the unaffected epithelial surface, as determined by Zeiss Cirrus HD OCT (136 – 16 µm = 120 µm). The rest of the ablation was performed using 0.1% methylcellulose masking fluid to smooth out the protruding irregular surface, eventually translating it down to the level of Bowman's layer (Figure 3). The customized ablation area PTK procedure, except for the fluid masking, is detailed in Video 1 (available in the online version of this article).

Figure 3. Schematic of the Salzmann's nodular lesion targeted by the customized ablation area phototherapeutic keratectomy (PTK). Customized ablation area PTK is first performed without fluid masking at a depth of ‘b’ and the lesion is then smoothed out with fluid masking at a depth of ‘a–b’. a = depth from the highest point of the lesion to the level of the peripheral unaffected Bowman's layer; b = maximum height of the lesion protruding from the level of the unaffected epithelial surface; BL = Bowman's layer

A bandage contact lens (Acuvue Oasys; Johnson & Johnson base curve = 8.4 mm) was applied and the patient was instructed to instill one drop of moxifloxacin and topical prednisolone acetate 1% four times a day for 1 week. The bandage contact lens was removed after 4 days. On day 10, the antibiotic was discontinued and the patient was given loteprednol 0.5% four times a day and it was gradually tapered over 5 weeks. Hyaluronic acid lubrication was prescribed as needed. The patient was examined at day 1, day 2, day 4, 1 week, and 1, 3, and 6 months postoperatively.

Results

The patient had complete epithelial recovery the next day, and the contact lens was removed on day 4. Corrected distance visual acuity was 20/20 preoperatively, 20/20 at 1 week, and 20/20 at 1, 3, and 6 months. Manifest refraction was +2.25 −2.25 × 180° preoperatively and +2.00 −2.25 × 180° postoperatively.

Preoperatively, the Peramis dual-Placido and pyramidal aberrometer system could not map the peripheral nodular change (Figures 4A–4B), so a customized ablation area PTK was selected over a topography-guided ablation. When evaluated with the GALILEI platform, central corneal topography, including cor-neal astigmatism and regularity before and after surgery did not change, but the peripheral irregularity improved (Figures 4B–4C). OCT was performed at 1 week, 1 month, and 3 months postoperatively. The lesion flattened significantly, and there was almost complete resolution of the lesion after custom ablation area PTK, as shown by OCT (Figure 5).

Figure 4. (A) Placido rings of the Peramis dual-Placido and pyramidal aberrometer platform (CSO) projected on the cornea preoperatively, showing lack of data acquisition over the inferonasal peripheral nodular lesion. (B) The color-coded instantaneous curvature map of the Peramis platform showing a measurement deficit over the lesion. (C) Preoperative instantaneous curvature map of the cornea using the GALILEI dual-Placido and Scheimpflug system (Ziemer). Moderate peripheral irregularities could be seen inferonasally at the site of the corneal lesion. (D) Instantaneous curvature map at 6 months postoperatively showing no change centrally, but smoothing of the irregularities inferonasally.

Figure 5. (A) A 3-month postoperative section of the cube mode (4 × 4 mm) of Zeiss Cirrus optical coherence tomography (Carl Zeiss Meditec AG) showing complete resolution of the lesion. (B) Slit-lamp photograph of the cornea at 3 months postoperatively.

Discussion

The clinical diagnosis of the lesion observed in the patient being treated was Salzmann's nodular degeneration, although peripheral hypertrophic subepithelial corneal degeneration, a related clinical entity that is often bilateral, might still be a plausible diagnosis in the differential diagnosis.^9,10 Historically, Salzmann's degeneration and related lesions have been treated by surgical peeling,¹¹ with one report combining surgical debridement with non-custom PTK laser^5,6 and another report describing non-custom PTK-only treatment using a small optical zone manually decentered on the lesion.⁶ In our specific case, the lesion did not penetrate Bowman's layer, as shown on corneal OCT. An alternative therapeutic modality would be to peel the nodular lesion using a toothed forceps and a hockey blade. However, in view of the concomitant recurrent erosions, we believed a PTK was needed to minimize the risk of epithelial erosions postoperatively, and hence our rationale for the customized ablation area PTK.

Using the customized ablation area PTK approach for the treatment of Salzmann's nodules accompanied by recurrent erosion syndrome demonstrated excellent postoperative results with no complications. Compared to traditional full-diameter PTK,⁵ application of a customized ablation area allows a defined treatment of the pathology and avoids unnecessary epithelial and stromal ablation, contributing to faster visual recovery, potentially better visual outcomes, and less refractive impact, mainly for peripheral lesions because central deep lesions may still induce an unpredictable refractive change. Customized ablation area PTK makes use of the precision imparted by pupil tracking and iris registration as opposed to manually decentered small-diameter PTK⁶ or the use of the polyvinyl alcohol disc with a punched out hole, hence making sure the entire lesion has been ablated with minimal removal of unaffected adjacent tissue. Additionally, focal PTK would be a good alternative to conventional PTK in cases with recurrent erosion without associated focal lesion when the area of erosion could be determined preoperatively.

We believe customized ablation area PTK is a promising tool in treating focal anterior corneal pathologies and recurrent erosion syndrome, whether it is due to a focal pathology or not. It can be made readily available for surgeons to apply on all commercially available laser platforms by incorporating it into the laser software.