Purpose
To determine the visual and refractive outcomes of 210-degree arc length intrastromal corneal ring segment (ICRS) implantation in eyes with pellucid marginal corneal degeneration (PMCD).
Design
Retrospective, consecutive case series.
Methods
Sixteen consecutive eyes of 10 patients who underwent a single 210-degree ICRS implantation by femtosecond laser for the management of PMCD and completed at least 1 year follow-up were included. A complete ophthalmic examination was performed preoperatively and postoperatively, including uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest spherical and cylindrical refractions, spherical equivalent, and keratometric readings.
Results
The mean follow-up period was 30.7 months (range 12 to 36 months). No intraoperative complication was observed. White deposits around the segments were noted in 2 of 16 eyes (12.5%) at the first postoperative year. The mean UCVA showed significant improvement, from 1.69 ± 1.02 logarithm of the minimal angle of resolution (logMAR) preoperatively to 0.64 ± 0.43 logMAR at the 36th month (n = 11, P < .001). The mean preoperative BSCVA was 0.88 ± 0.68 logMAR; after 36 months, this improved to 0.35 ± 0.34 ( P < .001). At the 36th month, UCVA was improved in all eyes (n = 11, range: gain of 1 to 6 lines), whereas BSCVA was improved in 9 eyes (81.8%, range: gain of 2 to 7 lines) and remained unchanged in 2 eyes (18.1%); UCVA was 20/40 or better in 3 eyes (27%) and BSCVA was 20/40 or better in 8 eyes (72.7%). There was a significant reduction in the spherical equivalent refractive error, from −4.40 ± 1.85 diopters (D) preoperatively to −1.86 ± 0.60 D ( P < .001), and the mean maximum keratometric power decreased from 49.70 ± 4.32 D to 46.08 ± 2.84 D ( P < .001) after 36 months. The mean cylindrical refraction decreased from −4.39 ± 1.86 D preoperatively to −2.38 ± 1.35 D at 36 months ( P < .001).
Conclusion
A single 210-degree arc length ICRS implantation using a femtosecond laser for patients with PMCD provides good visual and refractive outcomes.
Pellucid marginal corneal degeneration (PMCD) is a noninflammatory corneal thinning disorder that is characteristically distinct from other disorders that fall under the same category, including keratoconus and keratoglobus. The topographic pattern of PMCD is defined by a steep contour, usually in the inferior corneal periphery, extending into the center from the inferior oblique corneal meridians, and a flattening in the vertical meridian. As the disorder progresses, the topographic changes makes it impossible to achieve spectacle correction of vision.
Several treatments for PMCD have been explored in the literature, including rigid gas-permeable contact lens implantation, which has been reported to provide adequate results in eyes that are in an early stage of the disorder. Refractive surgery as a treatment option for patients with PMCD and other similar corneal disorders is not recommended as studies show that there is significant potential for poor visual outcomes and the progression of corneal ectasia attributable to the iatrogenic thinning of the cornea.
Intrastromal corneal ring segment implantation has been reported to provide safe and effective outcomes for the treatment of patients with corneal thinning disorders like keratoconus and post-LASIK ectasia. Also, 1 type of intracorneal ring segment (Intacs; Addition Technology, Fremont, California, USA) provided successful outcomes in the management of PMCD. The Keraring (Mediphacos, Belo Horizonte, Brazil) is another type of intrastromal corneal ring segment (ICRS) made of polymethyl-methacrylate with various arc lengths (90 degrees, 120 degrees, 160 degrees, and 210 degrees) that regularizes corneal ectatic distortions by providing the addition of segments in the mid-periphery. The 210-degree arc length ICRS has advantages such as less induction of astigmatism, more corneal flattening, and implantation of a single segment. The purpose of the current study was to determine the visual and refractive outcomes of a single 210-degree arc length ICRS implantation in eyes with PMCD.
Methods
A retrospective analysis was conducted on the outcomes of patients who underwent a single 210-degree arc length ICRS implantation for the management of PMCD from June 16, 2006 to July 18, 2008. Sixteen consecutive eyes of 10 patients (6 female and 4 male) with a diagnosis of PMCD were included. Only patients unsatisfied with spectacle- and contact lens–corrected vision were considered for ICRS implantation. The eyes that had a corneal thickness of 400 μm or less at the location where ICRS inserts were placed (5-mm optical zone) and had a history of eye rubbing and/or vernal keratoconjunctivitis were excluded. All eyes had a clear central cornea and reduced best spectacle-corrected visual acuity (BSCVA) (more than 2 lines), and all patients completed at least 12 months of follow-up. The diagnosis of PMCD was based on slit-lamp findings, including inferior corneal thinning and ectasia above the area of maximum thinning. The diagnosis was verified by corneal topography, which demonstrated a steep contour in the inferior peripheral cornea with high keratometric powers radiating from the inferior oblique meridians toward the center. All patients were informed about the study as well as advantages and disadvantages of the procedure.
Surgical Procedure
All surgeries were performed under topical anesthesia. A reference point for centration (pupil center) was chosen and marked under the operating microscope preoperatively. A 5-mm marker was used to locate the exact ring tunnel. Then a disposable vacuum ring was inserted to prevent movement of the eye and reduce the incidence of decentration. The 60-kHz IntraLase femtosecond laser (Abbott Medical Optics Inc, Santa Ana, California, USA) was used for femtosecond-assisted tunnel creation. The entry incision had a length of 1 mm in all cases and it was placed and centered on the steepest corneal axis. The planned tunnel depth was 70% of the corneal thickness, with an inner diameter of 4.8 mm and an outer diameter of 5.6 mm. The corneal thickness at the location site where the ICRS was placed ranged from 432 to 556 μm and the mean actual depth used to create the tunnel was 341.12 ± 24.5 μm (standard deviation; range from 302 to 389 μm). Femtosecond channel creation was achieved using 1.30 μJ of energy and was completed in approximately 15 seconds. The single 210-degree arc length Keraring intrastromal corneal ring segments (Mediphacos, Belo Horizonte, Brazil) were implanted with the manufacturer’s forceps following tunnel creation. The segment thickness was determined based on spherical equivalent values according to the nomogram ( Table 1 ). The Keraring segment thickness ranges from 0.15 mm to 0.35 mm, with 0.05-mm increments. The thicknesses of the segments used in the 16 eyes were 0.15 mm in 1 eye (6.2%), 0.20 mm in 7 eyes (43.7%), 0.25 mm in 6 eyes (37.5%), 0.30 mm in 1 eye (6.2%), and 0.35 mm in 1 eye (6.2%). Lomefloxacin 0.3% (Okacin; Novartis Pharma AG, Basel, Switzerland) and dexamethasone 0.1% (Dexa-Sine SE; Alcon-Thilo, Frieburg, Germany) eye drops were prescribed 4 times a day for 2 weeks after surgery.
| SE (Diopters) | Segment Thickness (μm) |
|---|---|
| Up to −2.00 | 150 |
| −2.25 to −4.00 | 200 |
| −4.25 to −6.00 | 250 |
| −6.25 to −8.00 | 300 |
| >−8.00 | 350 |
Follow up Evaluation
A complete ophthalmic examination was performed preoperatively and for months 12, 18, 24, and 36 postoperatively, including uncorrected visual acuity (UCVA), BSCVA, manifest spherical and cylindrical refractions, and keratometric readings using the Orbscan II (Bausch & Lomb, Rochester, New York, USA). Visual acuity readings were converted to logMAR values for statistical analysis. Vectorial analysis of the cylindrical correction was made by means of the Alpins method, which was based on the refractive data.
Statistical Analysis
Statistical analysis was carried out using SPSS version 10 for Windows (SPSS Inc, Chicago, Illinois, USA). For comparison between preoperative and postoperative data, paired t test was used for data with normal distribution and Wilcoxon test was used for data without normal distribution. A 2-tailed probability of 5% or less was considered statistically significant.
Results
The mean age of the patients was 43.8 ± 9.3 years (standard deviation; range 38 to 56 years). All Keraring segments were implanted successfully, as demonstrated in Figure 1 , with no problems associated with channel creation or segment implantation. The mean follow-up period was 30.7 ± 9.1 months (range 12 to 36 months). All eyes had inferior PMCD and none of the patients had a history of eye rubbing and/or vernal keratoconjunctivitis.
Visual acuity results at the preoperative and postoperative examinations are summarized in Table 2 . The mean UCVA showed statistically significant improvement, from 1.69 ± 1.02 logMAR (range 0.4 to 3) preoperatively to 0.64 ± 0.43 (range 0.1 to 1.3, P < .001) at the 36th postoperative month. The mean preoperative BSCVA was 0.88 ± 0.68 (range 0.18 to 2). After 36 months, this improved to 0.35 ± 0.34 (range 0 to 1, P < .001). At the 36th month, UCVA was improved in all eyes (range gain of 1 to 6 lines), whereas BSCVA was improved in 9 of 11 eyes (81.8%, range gain of 2 to 7 lines) and remained unchanged in 2 of 11 eyes (18.2%). The mean line gains between preoperative and month-36 UCVA and BSCVA measurements was 2.4 ± 2.1 lines and 3.3 ± 1.8 lines respectively ( Figures 2 and 3 ) . At the 36th month UCVA was 20/40 or better in 3 of 11 eyes (27%) and 20/25 or better in 1 of 11 eyes (9%), while none of the eyes had a UCVA of 20/20 or better. BSCVA was 20/40 or better in 8 of 11 eyes (72.7%), 20/25 or better in 2 of 11 eyes (18.2%), and 20/20 or better in 1 eye (9%).
| N | Preoperative 16 | 12 Months 16 | 18 Months 14 | 24 Months 13 | 36 Months 11 | P Value a (Preoperative to 36 Months) — |
|---|---|---|---|---|---|---|
| UCVA (logMAR), mean±SD | 1.69±1.02 | 0.83±0.55 | 0.78±0.55 | 0.75±0.54 | 0.64±0.43 | <.01 |
| Range | 0.4 to 3 | 0.3 to 1.3 | 0 to 1.3 | 0.1 to 1.3 | 0.1 to 1.3 | — |
| BSCVA (logMAR), mean±SD | 0.88±0.68 | 0.41±0.45 | 0.35±0.30 | 0.34±0.32 | 0.35±0.34 | <.01 |
| Range | 0.18 to 2 | 0.18 to 2 | 0 to 1 | 0 to 1 | 0 to 1 | — |
| SE (D), mean±SD | −4.40±1.85 | −1.89±1.07 | −1.89±0.66 | −1.86±0.69 | −1.86±0.60 | <.01 |
| Range | −0.50 to −9.00 | 0.00 to −4.75 | −0.50 to −3.25 | −0.50 to −3.25 | −0.50 to −2.50 | — |
| Spher (D), mean±SD | −2.43±1.92 | −0.75±0.82 | −0.80±0.63 | −0.79±0.55 | −0.72±0.61 | <.01 |
| Range | +2.00 to −7.00 | 0.00 to −2.25 | 0.00 to −2.25 | 0.00 to −2.00 | 0.00 to −2.00 | — |
| Cylinder (D), mean±SD | −4.39±1.86 | −2.35±1.00 | −2.32±1.03 | −2.25±1.18 | −2.38±1.35 | <.01 |
| Range | −2.00 to −8.50 | −1.00 to −4.25 | −1.00 to −4.00 | −1.00 to −5.00 | −1.00 to −5.25 | — |
| Kmax (D), mean±SD | 49.70±4.32 | 46.53±3.14 | 46.51±3.30 | 45.96±2.60 | 46.08±2.84 | <.01 |
| Range | 45.20 to 61.70 | 43.90 to 54.70 | 43.10 to 54.7 | 42.80 to 51.00 | 42.90 to 51.00 | — |
| Kmin (D), mean±SD | 43.00±4.28 | 41.44±3.28 | 41.32±3.53 | 40.82±2.22 | 40.42±1.87 | .03 |
| Range | 39.4 to 46.3 | 38.40 to 45.10 | 38.20 to 45.40 | 38.30 to 45.20 | 38.20 to 44.00 | |
| Thinnest (μm), mean±SD | 463.22±57.65 | 469.00±51.15 | 454.91±31.18 | 450.90±31.54 | 455.40±22.19 | .84 |
a Paired t test was used for data with normal distribution, Wilcoxon test was used for data without normal distribution.
Refractive results are summarized in Table 2 . There was a significant reduction in the spherical equivalent refractive error, from −4.40 ± 1.85 diopters (D) (range −0.50 to −9.00 D) preoperatively to −1.86 ± 0.60 D (range −0.50 to −2.50 D, P < .001) at the 36th month; also, the mean maximum keratometric power decreased from 49.70 ± 4.32 D (range 46.00 to 61.70 D) to 46.08 ± 2.84 D (range 42.90 to 51.00 D, P < .001) after 36 months. Figures 4 and 5 show the topographic changes of the same eye from the preoperative period to the 24th postoperative month.
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