ORIGINAL ARTICLE


https://doi.org/10.5005/jp-journals-10025-1199
International Journal of Keratoconus and Ectatic Corneal Diseases
Volume 10 | Issue 1-2 | Year 2023

Treatment of High Astigmatism after Penetrating Keratoplasty in Patients with Keratoconus with 800 µm Base Intrastromal Corneal Ring Segments: A Retrospective Study


Roberto Albertazzi1https://orcid.org/0000-0002-9199-0825, Carlos Rocha-de-Lossada2https://orcid.org/0000-0001-7464-2493, Leonardo Ferlini3, Franco A Perrone4

1,3,4Centro de Ojos Quilmes, Quilmens, Buenos Aires, Argentina

2Department of Ophthalmology (Qvision), Vithas Almería; Hospital Regional Universitario de Málaga, Plaza del Hospital Civil, Málaga; Department of Ophthalmology, Virgen de las Nieves University Hospital, Granada, Spain

Corresponding Author: Roberto Albertazzi, Centro de Ojos Quilmes, Quilmens, Buenos Aires, Argentina, Phone: +54 11 5277-9745, e-mail: albertazzzirg@gmail.com

How to cite this article: Albertazzi R, Rocha-de-Lossada C, Ferlini L, et al. Treatment of High Astigmatism after Penetrating Keratoplasty in Patients with Keratoconus with 800 µm Base Intrastromal Corneal Ring Segments: A Retrospective Study. Int J Kerat Ect Cor Dis 2023;10(1–2):13–19.

Source of support: Nil

Conflict of interest: None

Received on: 29 December 2023; Accepted on: 25 February 2024; Published on: 23 April 2024

ABSTRACT

Purpose: To evaluate the efficacy and stability of implantation of 5 mm diameter intrastromal corneal ring segments (ICRS) with a modified base (800 µm) in the treatment of astigmatism after penetrating keratoplasty (PK).

Materials and methods: A retrospective case-series study was performed in a cornea-keratoconus service in Buenos Aires (Argentina). We included patients with a history of keratoconus who underwent PK and had residual high astigmatism (>5.0 diopters [D]) after 2 years. These patients had undergone 800 µm width ICRS implantation between 2002 and 2019, with at least 2 years of postoperative follow-up. The main outcomes were uncorrected and corrected distance visual acuity (UDVA and CDVA, respectively) and topographic astigmatism, evaluated before ICRS implantation and 2 years postoperatively.

Results: Twelve eyes underwent ICRS implantation. The mean topographic astigmatism was 12.9 ± 3.8 D (6.9–19.6) at baseline, which decreased (p < 0.001) to 4.2 ± 2.3 D (0.4–8.8) after ICRS implantation. The baseline UDVA was 1.00 ± 0.21 logarithm of the minimum angle of resolution (LogMAR) (0.6–1.3), whereas the postoperative UCVA was 0.32 ± 0.17 LogMAR (0.1–0.7). The baseline CDVA was 0.63 ± 0.15 LogMAR (0.2–0.8), whereas the postoperative CDVA was 0.12 ± 0.05 LogMAR (0–0.2). The improvement in visual acuity was statistically significant (p < .0.001).

Conclusion: The high postoperative astigmatism after PK in eyes with keratoconus decreased following the implantation of ICRS with an 800 µm base width, improving the UDVA and CDVA and achieving refractive stability for at least 2 years postoperatively. Complications were not detected, although a larger cohort should be evaluated in a multicentric setting to confirm these results.

Clinical significance: This series clinically proves that ICRS with a base of 800 µm can be an effective option for managing high post-PK astigmatism.

Keywords: Astigmatism, Cornea, Intrastromal corneal ring segments, Keratoconus, Penetrating keratoplasty.

INTRODUCTION

Implantation of intrastromal corneal ring segments (ICRS) is effective in modulating the corneal curvature and decreasing corneal astigmatism in conditions, such as keratoconus, pellucid marginal degeneration, or post-refractive corneal ectasia.1,2 Postoperative astigmatism is a common complication that occurs after penetrating keratoplasty (PK) or deep anterior lamellar keratoplasty (DALK), with over one-fifth of the patients developing >5 diopters (D) of astigmatic error postoperatively.3

Arriola-Villalobos et al. reported that the implantation of 5 mm diameter ICRS may be optimal for correcting high astigmatism after PK.4 Recently, a finite element simulation study evaluated the geometric effects of unilateral implantation of ICRS with a combined variation in ring thickness and base and demonstrated that the use of 800 µm base while maintaining the same ring thickness resulted in the strongest peripheral and central flattening.5 A special ICRS model, with a base of 800 µm and an apical diameter of 5 mm, was solicited and produced by Mediphacos (Belo Horizonte, Brazil) over 20 years ago for implantation in selected patients with high astigmatism after PK.

This study aimed to evaluate the efficacy and safety of this ICRS model in managing high astigmatism post-PK and its stability during a long follow-up period.

MATERIALS AND METHODS

Study Design

This was a retrospective single-center serial case study designed to review the electronic clinical charts of patients who underwent specialized keratoconus treatment at a private clinic in Quilmes (Buenos Aires, Argentina) between 2002 and 2019. The study adhered to the tenets of the Declaration of Helsinki, and written informed consent was obtained from each patient. The patients were informed that clinical data, pictures, and/or videos could be used for scientific purposes. The patients also received information regarding the surgical characteristics associated with the study. The ethics committee of our clinic reviewed and approved this study.

Patient Population and the Inclusion and Exclusion Criteria

We included eyes of patients with a history of keratoconus who developed high astigmatism (>5.0 D) after PK surgery and underwent ICRS implantation using the model with an 800 µm base width and 5 mm apical diameter. The patients included in this study had at least 2 years of postoperative follow-up. ICRS implantation can be performed only after an interval of a minimum of 2 year after PK. Graft suture should be removed at least 6 months before ICRS implantation. Patients with collagen corneal cross-linking and those who underwent any refractive corneal procedures or intraocular lens implantation (phakic or pseudophakic) were excluded. Patients with other corneal lesions, such as diffuse corneal keratitis or corneal ulcer, corneal abscess, limbus insufficiency, dendritic or pseudo-dendritic keratitis, or filamentous keratitis, were also excluded.

Parameters and Follow-up

All eyes who underwent ICRS implantation were considered clinically discharged at the 6-month follow-up. The patients underwent at least one routine annual follow-up after this period. The following data were collected from the medical records of the patient: age, sex, ICRS characteristics, and ICRS implantation site. The ocular fundus was evaluated using a binocular ophthalmoscope and posterior segment ophthalmic coherence tomography (OCT). Visual acuity was evaluated using the Snellen scale and expressed as the logarithm of the minimum angle of resolution (LogMAR) for statistical analysis. Corneal keratometry (K1: the flattest meridian; K2: the steepest meridian) and topographic astigmatism were measured using Tomey MS4 (Nagoya, Japan). These parameters were compared with the baseline values (i.e., before ICRS implantation) and those at 2 years postoperatively.

Slit-lamp evaluation was performed (with and without fluorescein staining) to rule out ICRS postoperative complications, such as keratitis, corneal melting, ICRS migration, and/or extrusion. Since we also evaluated the safety index, defined as the ratio between the postoperative corrected distance visual acuity (CDVA) and preoperative CDVA, the patients could not lose more than two lines of CDVA in the postoperative follow-up period.

We also evaluated the efficacy index, defined as the ratio between the postoperative uncorrected distance visual acuity (UDVA) and preoperative CDVA. We subsequently compared the percentage of patients in each level of preoperative CDVA and postoperative UDVA. Furthermore, we evaluated the level of surgically induced astigmatism (SIA) that developed after ICRS implantation.

If any patients had a longer follow-up period, this was registered and described to evaluate the long-term stability. The occurrence of complications (intraoperative and/or postoperative) was also reviewed in each clinical record. Anterior segment OCT (Optovue Corneal Advance, Fremont, CA, USA) was performed only in some recent cases as this technology was not available at the beginning of our study period.

ICRS Characteristics

The ICRS used in these procedures was a model developed by Mediphacos Ltd. The design is similar to the Ferrara type, which has a flat design made of acrylic material (polymethyl methacrylate). The width of the base was 800 µm with an apical diameter of 5.0 mm. The thickness was 150 or 200 µm, and the arc lengths were 90°, 120°, or 150°. The ICRS devices and their implantation sites were selected according to the severity of astigmatism and the axis of preoperative refraction; corneal topography was the primary consideration.

Surgery

The ICRS implantation surgery was performed using the manual corneal tunnel creation technique by the same surgeon with experience in anterior segment surgery. None of the surgeries were femtosecond laser-assisted cataract surgeries. The depth of the stromal tunnel was always performed at 180 µm from the corneal endothelium. This was calculated by subtracting 180 µm from the total corneal thickness, which was measured using ultrasonic pachymetry from the incision site. The incision was created using a surgical diamond knife after adjusting for depth in each patient. The corneal incision was always made at the steep axis (previously marked) in the superior site. Corneal dissection was performed using a 5 mm circular spatula. The stromal tunnel was created, followed by the careful implantation of the ICRS. Excessive force was avoided since the circumferential wound in corneas with PK can be fragile. Figure 1 shows the procedure for selecting the ICRS, based on a concept determined as “Anchor Point.”

Fig. 1: Description of procedure for selecting the ICRS, based on a concept determined as “Anchor Point.” Anchor Point is the topographic point that marks an abrupt change of curvatures; the green zones are the transition between high (blue) and low (red) heights

Statistics

Descriptive statistical results and graphics were analyzed and obtained using the XLMiner Analysis ToolPak software (Frontline Systems Inc., Incline Village, NV, USA). The values are expressed as mean, standard deviation, and range. The paired t-test was used to compare the differences between the means. Statistical significance was set at p < 0.05. The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Results

Between 2002 and 2019, 12 patients (13 eyes) underwent implantation of the special ICRS model at our hospital; however, one case was excluded from our analysis as the patient was lost to follow-up and did not meet the minimum required follow-up period of 2 years. The pre- and postoperative characteristics of the remaining 11 patients (one woman and 10 men, 12 eyes) are presented in Table 1. Figures 2 and 3 present complementary information, including a descriptive diagram and the pre- and postoperative topographic images of the PK eyes 2 years after ICRS implantation. The mean age of the 11 patients was 31.4 ± 6.3 years (24–42 years). The mean duration between PK and the ICRS implantation for each eye was 33.6 ± 5.9 months (25–45 months), and the mean topographic astigmatism decrease was 8.3 ± 3.7 D (3.7–14.7 D). None of the patients developed intraoperative complications, and no postoperative complications were detected during the follow-up period.

Table 1: Description of cases that underwent ICRS implantation after penetrating keratoplasty for managing high residual astigmatism
  1 2 3 4 5 6 7 8 9 10 11 12
Cases
Eye OD OS OS OS OD OS OD OD OS OD OD OS
Time 38 30 28 32 30 25 41 45 37 29 37 32
Preoperative
K1 34.72 40.38 45 36.52 38.33 37.29 37.31 39.19 33.92 38.58 43.01 42.53
Merid 105 120 7 156 62 180 132 70 100 60 103 55
K2 54.35 58.65 57 48.5 51.8 47.92 50.02 51.13 50.36 46.15 57.15 49.51
Ang 15 30 97 66 152 90 42 160 10 150 13 145
Astig 19.63 18.27 12 11.98 13.46 10.63 12.71 11.94 16.44 7.57 14.14 6.98
Postoperative
K1 39.63 41.9 43.44 41.03 39.54 39.06 42.15 43.04 37.28 35.43 48.56 42.39
Merid 55 130 131 166 65 179 142 60 20 60 96 59
K2 44.54 49.52 43.91 45.44 48.02 44.97 45.65 46.32 39.91 44.21 56.1 45.21
Ang 145 40 41 76 155 89 52 150 110 150 6 149
Astig 4.91 7.62 0.47 4.41 8.48 5.91 3.29 3.28 2.63 3.78 7.54 2.82
↓ Astig 14.72 10.65 11.53 7.57 4.98 4.72 9.42 8.66 13.81 3.79 6.6 4.16
*Time, time between penetrating keratoplasty and ICRS implantation; ↓Astig, astigmatism decrease; Ang, angle; Astig, astigmatism; Merid, meridian

Fig. 3: Pre- and postoperative topographic images of PK eyes 2 years after ICRS implantation. A diagram depicting the site of ICRS implantation, their characteristics, the number of segments used per patient, including manifest refraction, spherical equivalent (SE), and the date of each surgery is also shown. ICRS, Intrastromal corneal ring segments; PK, Penetrating keratoplasty

Fig. 2: Pre- and postoperative topographic images of PK eyes 2 years after ICRS implantation. A diagram depicting the site of ICRS implantation, their characteristics, the number of segments used per patient, including manifest refraction, spherical equivalent (SE), and the date of each surgery is also shown. ICRS, Intrastromal corneal ring segments; PK, Penetrating keratoplasty

The visual performance and topographic astigmatism outcomes are given in Table 2. Statistically significant differences were observed in all the evaluated parameters. The safety index was 3.30. Regarding the variation in the lines of CDVA, none of the patients lost any line of vision. Moreover, 91.7% (11 eyes) of patients gained three or more lines of vision, whereas 8.3% (one patient, one eye) gained one line; none gained two lines. The efficacy index (mean postoperative UDVA/postoperative CDVA) was 2.08. The SIA of the whole sample is represented in Figure 4. Representative images of the procedures in two patients are shown in Figure 5.

Table 2: Refractive efficacy in eyes with high astigmatism after penetrating keratoplasty implanted with intracorneal ring segments (ICRS) of 800 mm base width
Parameters Preop Postop Change p
K1 (D) 38.89 ± 3.3
(33.92–45.0)
41.12 ± 3.3
(35.43–48.56)
↑2.22 ± 2.77
(3.15–5.55)
0.007
K2 (D) 51.87 ± 4.0
(46.15–58.65)
46.15 ± 3.8
(39.91–56.10)
↓5.72 ± 3.8
(1.05–13.09)
<0.001
Astigmatism (D) 12.97 ± 3.8
(6.98–19.63)
4.59 ± 2.3
(0.47–8.84)
↓8.38 ± 3.7
(3.79–14.72)
<0.001
UDVA (LogMAR) 1.00 ± 0.21
(0.6–1.3)
0.32 ± 0.17
(0.1–0.7)
↓0.67 ± 0.16
(0.4–0.9)
<0.001
CDVA (LogMAR) 0.63 ± 0.15
(0.2–0.8)
0.12 ± 0.05
(0–0.2)
↓0.50 ± 0.14
(0.1–0.7)
<0.001
*UDVA = Uncorrected distance visual acuity; CDVA = Corrected distance visual acuity

Fig. 4: Double angle plot of the surgically induced astigmatism in 11 patients (12 eyes) with a mean of 3.33x ± 8.21x and 2.54y ± 6.70y standard deviation

Fig. 5: Topographic astigmatism of case 1, followed up for 15 years after ICRS implantation in a PK eye. PK = Penetrating keratoplasty; ICRS = Intrastromal corneal ring segments

Regarding long-time stability, one patient with 15 years of follow-up after ICRS implantation was noted in the records. This patient has the longest follow-up in our clinical records, and the records showed that the patient’s astigmatism decreased and remained stable over time.

DISCUSSION

The present study retrospectively reviewed the clinical records of patients with a history of keratoconus and severe post-PK astigmatism. These patients underwent implantation of ICRS models designed with a wider base (800 µm). The implants elicited a statistically significant decrease in the mean astigmatism (8.3 ± 3.7 D) and improved CDVA with a mean of 0.12 ± 0.05 LogMAR within 2 years of follow-up. All eyes gained lines of CDVA and UDVA during this period.

Recently, a computational simulation concluded that ICRS with a base width of 800 µm can create a greater flattening effect than models with 600 µm.5 In this study, we selected a special ICRS model with a base width of 800 µm to decrease post-PK astigmatism and maintain stability over time. This study was designed to critically review the clinical records of patients who underwent implantation of this particular ICRS model. The retrospective analysis of these patients revealed that the first procedure was performed in 2004, and the outcomes among all evaluated patient records were consistent with the computational simulation.

Approximately, 20% of patients may develop astigmatism of 5.0 D or more after PK.6,7 Furthermore, a systematic review by Liu et al. reported that femtosecond laser-assisted PK did not improve the outcome when compared with conventional PK in terms of decreasing postoperative astigmatism.8 These data emphasize the challenge in managing post-PK astigmatism, especially in patients with a history of keratoconus, where corneal biomechanics are potentially unstable over time.

A recent review described various factors that could lead to post-PK astigmatism and described the techniques for decreasing and correcting this postoperative complication.9 Implanting ICRS in patients with PK for astigmatism management is considered a viable option. Regarding safety, the mechanical stromal dissection described in this study can induce an excessive torque that results in corneal graft dehiscence, as previously reported.10 Nonetheless, this complication was not observed in this study. Complications, such as night halos, stromal neovascularization, and sterile deposits in the channels, have also been described in previous research.5 However, dysphotopsia was not assessed in this study.

This study provides clinical evidence supporting the effectiveness of the 800 µm base ICRS. Therefore, this model should be considered for implantation in patients with a history of keratoconus who develop high astigmatism after PK. Theoretically, the optimal treatment would include asymmetric ICRS with variable thickness and base width.5 Our retrospective analysis demonstrated that the 800 µm base ICRS significantly decreased astigmatism in patients with high preoperative astigmatism (up to 19.38 D), and the decrease was stable for at least 2 years postoperatively. Furthermore, one patient experienced 15 years of postoperative stability.

The preoperative level of astigmatism and the postoperative decrease in this study were higher than those in other studies.4,1012 Arriola-Villalobos et al.4 presented a series of nine eyes with a mean topographic corneal astigmatism decrease from 7.07 ± 2.52 D to 4.48 ± 2.00 D. Coscarelli et al.13 evaluated a series of 59 eyes with a mean corneal topographic astigmatism that decreased from 3.37 ± 1.51 D to 1.69 ± 1.04 D postoperatively. Stromal dissection was performed in these studies to create the corneal channels mechanically, as described in the present study. Prazeres et al. reported improvements in a series of 14 eyes with high astigmatism (up to 12.5 D), which decreased and remained stable 6 months postoperatively when the surgical procedure was assisted by a femtosecond laser.11 Similar results were reported by Lisa et al. in a larger study with 32 eyes.12 In the present study, the mean topographic astigmatism decreased by 8.3 ± 3.7 D (3.7–14.7 D) 2 years after ICRS implantation.

Arantes et al. evaluated the use of ICRS for astigmatism correction after DALK.13 In the present study, we reviewed the clinical records of patients who developed high astigmatism after DALK and were treated with the 800 µm base ICRS. The clinical records of these patients are currently under review. Preliminary findings are consistent with those of Arantes et al. and suggest that this is a viable option for astigmatism management after DALK (data not shown).

The main limitations of this study are that the ICRS model used are not currently commercially available, and the retrospective design of it. These ICRS devices were requested from and designed by the manufacturer for the management of a specific type of patient. Therefore, obtaining a higher number of patients or performing a multicenter study is difficult. However, the manufacturer can produce this ICRS upon request. The present series obtained patients from a single center, and the same experienced surgeon performed the surgeries on all patients. This may have introduced bias in the results. Therefore, results from more surgeons are necessary to support the efficacy and stability presented in this study. Moreover, since the patients who typically visited this keratoconus clinic were referred by an external ophthalmologist, a longer follow-up period was not available in our clinical records as the patients obtained clinical discharge 6 months after surgery and continued their follow-up care with their original ophthalmologist. Longer follow-up information (>2 years) was available for only four patients who returned to our clinic. There is another aspect to consider since the femtosecond-assisted implantation technique was not used, because it was not available at that time. Although nowadays the use of femtosecond laser could be considered as the gold standard for implanting any type of ICRS, in the implants described in this work, it would be even more important. Nonetheless, the presence of scars that may be found inside the corneal button, generated by the numerous sutures, may increase the presence of stromal bridges in the tunnel. This fact may provoke to use some spatulas to open the tunnel prior to implant the ICRS Therefore, more comprehensive clinical records of all the patients are required to evaluate the long-term stability of the procedure. Nevertheless, our data support future research into specialized ICRS designs to treat patients with high postoperative astigmatism. Furthermore, technological advances in ICRS implantation will enable customized ICRS designs.1417 Likewise, randomized clinical trials and multicenter studies with more sample are still necessary to confirm these satisfactory outcomes.

In summary, high post-PK astigmatism in patients with a history of keratoconus can be successfully improved by implanting an 800- µm base width ICRS. Refractive stability was achieved for at least 2 years postoperatively. Intraoperative and postoperative complications were not detected.

Clinical Significance

  • Theoretically, an ICRS with a wider base (800 µm) could produce the strongest peripheral and central flattening while maintaining the same ring thickness.

  • An ICRS model, with a base of 800 µm and an apical diameter of 5 mm, was implanted in corneas with high post-PK astigmatism from keratoconus patients.

  • Astigmatism decreased, refractive stability was achieved for a minimum of 2 years after surgery, and complications were not detected.

  • This series clinically proves that ICRS with a base of 800 µm can be an effective option for managing high post-PK astigmatism.

Ethical Approval

The study adhered to the tenets of the Declaration of Helsinki, and written informed consent was obtained from each patient.

AUTHOR CONTRIBUTIONS

RA was involved in Conception, data collection, manuscript drafting, critical revision, and statistical analysis. CRdL carried out conception, data collection, manuscript drafting, critical revision and statistical analysis. LF has performed data collection and manuscript drafting. FP has carried out data collection and manuscript drafting.

ACKNOWLEDGMENTS

Authors would like to thank Rodrigo Torres, MD, PhD, for providing scientific input and Manuel Rodríguez-Vallejo PhD, for assisting in data processing and figure design. We would like to thank Editage (www.editage.com) for English language editing.

AVAILABILITY OF DATA AND MATERIALS

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

SUPPLEMENTARY MATERIALS

All the supplementary materials are available on the website of www.ijkecd.com.

ORCID

Roberto Albertazzi https://orcid.org/0000-0002-9199-0825

Carlos Rocha-de-Lossada https://orcid.org/0000-0001-7464-2493

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