Merging PRK and Collagen Crosslinking: An Analysis of Literature and a Guide to Prevalent Protocols

PURPOSE

The purpose of this review was to summarize the different surgical approaches combining photorefractive keratectomy (PRK) and corneal crosslinking (CXL), present each protocol template in a simple format, and provide an overview of the primary outcomes and adverse events.

METHODS

A literature review was conducted as outlined by the Preferred Reporting Items for Systematic Reviews and Meta-Analysis guidelines. Eight different databases were searched. Papers were included if PRK was immediately followed by CXL.

RESULTS

Thirty-seven papers met the inclusion criteria of a total yield of 823. The latest research into simultaneous PRK and CXL has been shown to not only stabilize the cornea and prevent keratoconus progression but also improve the visual acuity of the patient. Improvements in uncorrected distance visual acuity and (spectacle) corrected distance visual acuity were found to be significant when considering all protocols. There were also significant reductions in K1, K2, mean K, Kmax, sphere, cylinder, and spherical equivalent. Random-effects analysis confirmed these trends. Corrected distance visual acuity was found to improve by an average of 0.18 ± 1.49 logMAR (Cohen's D [CD] 0.12; P <0.02). There was also a significant reduction of 2.57 ± 0.45 D (CD 5.74; P <0.001) in Kmax. Cylinder and spherical equivalent were also reduced by 1.36 ± 0.26 D (CD 5.25; P <0.001) and 2.61 ± 0.38 D (CD 6.73; P <0.001), respectively.

CONCLUSIONS

Combining the 2 procedures appears to be of net benefit, showing stabilization and improvement of ectatic disease, while also providing modest gains in visual acuity. Since customized PRK and CXL approaches appear superior, a combination of these would likely be best for patients.

A Novel Procedure for Keratoconus/Corneal Ectasia Treating Epithelial Compensation of Higher-Order Aberrations, Topographic Guided Ablation, and Corneal Cross Linking - The CREATE+CXL Protocol

Purpose

To present the outcomes of a retrospective study in keratoconus/corneal ectasia patients of treating the higher order aberrations compensated for the corneal epithelium in addition to topographic guided ablation followed by corneal cross linking.

Methods

Twenty-seven eyes of 14 patients were treated for keratoconus/corneal ectasia utilizing trans-epithelial topographic guided ablation photorefractive keratectomy (PRK) for treatment of corneal higher order aberrations and lower order astigmatism followed immediately by 15-minute cross linking were examined retrospectively. Six-month results were analyzed via measurement of vision, refraction, residual higher-order aberrations (HOAs), residual lower-order and higher-order aberrations, as well as for loss or gains of lines of best corrected visual acuity.

Results

All eyes save one had reduction in K1, K2, K Max, and K Mean. All eyes had reduction in manifest astigmatism, Contoura measured astigmatism, 57% reduction of higher-order aberrations (HOA), and 53% reduction of higher-order aberrations grouped with lower-order aberrations (Grouped). Nearly all (96.3%) eyes achieved 20/40 vision or better, 20 eyes had 1-7 lines gained of vision, and no eyes had any loss of lines of vision.

Conclusion

Use of the CREATE+CXL protocol combined with 15-minute corneal cross linking results in a significant increase in HOA reduction, as well as a significant improvement in corrected distance visual acuity over past procedures.

Safety and Efficacy of Corneal Minimized-Volume Ablation With Accelerated Cross-Linking in Improving Visual Function for Keratoconus

PURPOSE

To evaluate the safety and efficacy of corneal minimized-volume ablation with accelerated cross-linking in improving visual function in keratoconus eyes.

METHODS

Through a pilot study, 25 eyes of 25 consecutive patients with keratoconus grade I-III were recruited that underwent corneal transepithelial photorefractive keratectomy with "minimized volume" ablation profile and accelerated corneal cross-linking in the same session. Corrected and uncorrected distance visual acuities, manifest refraction, corneal curvature and higher-order aberrations, endothelial cells, and the ocular modulation transfer function were assessed preoperatively and postoperatively, with a minimum follow-up of 6 months. A P value < 0.05 was the threshold of statistical significance.

RESULTS

At 8.2 ± 3.6 months postoperatively, the mean corrected and uncorrected distance visual acuities (LogMAR) were 0.07 ± 0.15 and 0.45 ± 0.39, significantly improving from the baseline of 0.24 ± 0.24 (P8m-before = 0.005) and 1.12 ± 0.33 (P8m-before < 0.001), respectively. Spherical equivalent was -2.80 ± 2.72 diopters (D), significantly decreasing from the baseline of -6.61 ± 3.06 D (P8m-before < 0.001), whereas the attempted corrected spherical equivalent was-2.30 ± 1.22 D. Meanwhile, a significant reduction was found in higher-order aberration, along with the postoperative improvement in ocular modulation transfer function. Corneal surface morphological parameters were found with significant decreases postoperatively (index of surface variance: P8m-before = 0.003; index of vertical asymmetry: P8m-before = 0.005; keratoconus index: P8m-before = 0.004; center keratoconus index: P8m-before = 0.003; and index of height decentration: P8m-before < 0.001). Nevertheless, no significant change was found in posterior corneal curvature or endothelial cell density between pre- and post-operative periods.

CONCLUSIONS

Corneal minimized-volume ablation with accelerated cross-linking was an effective and safe option for correction of mild refractive error, leading to significant improvement of visual function in patients with keratoconus.

Topography/wavefront-guided photorefractive keratectomy combined with crosslinking for the treatment of keratoconus: preliminary results

PURPOSE

To evaluate the clinical outcomes of topography/wavefront-guided (TWFG) photorefractive keratectomy (PRK) using a new high-definition aberrometer combined with epithelium-off crosslinking (CXL-Plus).

SETTING

Centro Oculistico Bresciano, Brescia, Italy.

DESIGN

Prospective case series study.

METHODS

Patients with grade I or II keratoconus, according to the Amsler-Krumeich classification, were included in this prospective case series. All cases underwent TWFG PRK using the VISX STAR S4 IR excimer laser and the new iDesign 2.0 system, followed by accelerated epithelium-off CXL. Visual, refractive, ocular aberrometric, and safety outcomes were evaluated during a 6-month follow-up.

RESULTS

Thirty-five eyes of 19 patients were included. A significant improvement was observed in the uncorrected and corrected distance visual acuities (P < .001). Manifest sphere and cylinder were reduced significantly (P ≤ .001), with a total of 20 eyes (57%) and 30 eyes (86%) having a postoperative spherical equivalent within ±0.50 and ±1.00 diopter, respectively. Most corneal irregularity indexes and the level of ocular higher-order aberrations, primary coma, and trefoil (P < .05) were significantly reduced postoperatively. No significant corneal haze or safety issues were observed.

CONCLUSIONS

TWFG PRK, using the iD2 system with simultaneous CXL, regularized the cornea by correcting the spherocylindrical error and minimizing the amount of higher-order aberrations in mild-to-moderate keratoconus.

Postoperative Corneal Epithelial Remodeling After Intracorneal Ring Segment Procedures for Keratoconus: An Optical Coherence Tomography Study

PURPOSE

To assess epithelial corneal remodeling by anterior segment optical coherence tomography (AS-OCT) after intracorneal ring segments (ICRS) implantation in keratoconic eyes.

METHODS

This prospective observational study included patients with keratoconus receiving ICRS of different arc lengths according to their tomographic pattern. AS-OCT and corneal topography (Scheimpflug camera) were performed before and 1, 3, and 6 months after surgery. Corneal pachymetry mapping was performed and total corneal and epithelial thicknesses (3-mm central and 16 points on 6-mm zone) were measured over the pupil center using AS-OCT. Topographic parameters were also assessed.

RESULTS

A total of 68 keratoconic eyes were analyzed (Amsler-Krumeich stages 1 to 4) in four groups of 17 eyes: 210° ICRS, 320° ICRS, double 160° ICRS, and single 160° ICRS. Corneal pachymetry mapping revealed that epithelial thickness increased significantly in the internal zones juxtaposed to the ICRS without smoothing during the postoperative period (P < .05). Mean maximum epithelial thickness increased from 67 ± 6 to 79 ± 7 µm for 210° ICRS, 66 ± 9 to 82 ± 4 µm for 320° ICRS, 63 ± 6 to 78 ± 7 µm for double 160° ICRS, and 62 ± 5 to 77 ± 5 µm for single 160° ICRS (P < .0001). Significant epithelial thickening at the apex of the cone was observed in all groups (P < .05).

CONCLUSIONS

Significant epithelial thickening occurs after ICRS implantation adjacent to the ICRS to compensate for the ridge created with a thickening of epithelium over the cone due to regularization of the stromal surface. [J Refract Surg. 2021;37(6):404-413.].

Scheimpflug vs Scanning-Slit Corneal Tomography: Comparison of Corneal and Anterior Chamber Tomography Indices for Repeatability and Agreement in Healthy Eyes

Purpose

To evaluate and compare the repeatability and agreement of Scheimpflug vs scanning-slit tomography of the cornea and the anterior chamber in terms of keratometric and tomographic indices in healthy eyes.

Methods

The 20 eyes of 10 healthy participants underwent 3 consecutive measurements using both Scheimpflug-tomography and scanning-slit tomography, diagnostic devices. Multiple corneal and anterior chamber tomographic parameters were recorded and evaluated to include corneal keratometry and its axis; corneal best-fit sphere (BFS), pachymetry mapping, angle kappa, anterior chamber depth (ACD), pupil diameter, and location. Repeatability for each device was assessed using the within each subject standard deviation of sequential exams, the coefficient variation (CV) and the intraclass correlation coefficient (ICC). Agreement between the two devices was assessed using Bland-Altman plots with 95% limits of agreement (LoA) and correlation coefficient (r).

Results

Both devices were found to have high repeatability (ICC>0.9) both in keratometric and other tomographic measurements. Scheimpflug tomography's repeatability though appeared superior in the average keratometry values, anterior and posterior BFS, thinnest corneal pachymetry value and location (p<0.05). Agreement: Statistically significant inter-device differences were noted in the mean values of K1, K2, BFS, ACD and thinnest corneal pachymetry (p<0.05). Despite the agreement differences noted, the two devices were well correlated (r>0.8) in respective measurements with Scheimpflug delivering consistently lower values than the scanning-slit tomography device.

Conclusion

Scheimpflug-tomography repeatability was found to be superior to that of scanning-slit tomography in this specific study, in most parameters evaluated. Inter-device agreement evaluation suggests that reading from the two devices may not be used interchangeably in absolute values, yet they are well correlated with Scheimpflug delivering consistently lower values in most.

Cylinder Axis Agreement: Unexpected Scenarios

Background

The purpose of this retrospective study was to evaluate cylinder axis agreement between manifest refraction (MR), cycloplegic refraction (CR), Allegro Oculyzer ІІ and Allegro Topolyzer-Vario.

Methods

We included 82 patients (32 males and 50 females, 28.1 ± 8.7 years old), with 156 eyes scheduled for wavefront optimized laser refractive surgery, photorefractive keratectomy (PRK) in 50 eyes and laser-assisted in situ keratomileusis (LASIK) in 106 eyes, for correction of simple, myopic, hyperopic or mixed astigmatism. Cylinder axis was determined under manifest and cycloplegic refractions and using Allegro Occulyzer ІІ and Allegro Topolyzer-Vario platforms. Cylinder axis agreement was assessed by intraclass correlation coefficient, Pearson correlation coefficient and by the method described by Bland and Altman.

Results

Intraclass correlation coefficient and Pearson correlation coefficient showed statistically significant cylinder axis agreement between manifest refraction, cycloplegic refraction, Allegro Oculyzer ІІ and Allegro Topolyzer-Vario (p <0.001). Despite statistically significant cylinder axis agreement between the four measuring tools, 4 of 156 eyes (2.5%) showed unexpected discrepancy between Allegro Oculyzer ІІ and Allegro Topolyzer-Vario cylinder axis.

Conclusion

Although cylinder axis shows statistically significant agreement between manifest refraction, cycloplegic refraction, Allegro Oculyzer ІІ and Allegro Topolyzer-Vario, unexpected discrepancies occur.

Ten-Year Outcomes of Progressive Keratoconus Management With the Athens Protocol (Topography-Guided Partial-Refraction PRK Combined With CXL)

PURPOSE

To report the safety and long-term efficacy of topography-guided partial-refraction PRK combined with corneal cross-linking (CXL) (the Athens Protocol), refractive, topographic, and pachymetric changes of keratoconic eyes treated were studied.

METHODS

Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), refraction, keratometry, qualitative and quantitative assessment of corneal keratometric, and pachymetric properties recorded by topography and tomography were evaluated for 10 years postoperatively.

RESULTS

A total of 144 eyes were followed up for a mean 128 ± 4 months (range: 120 to 146 months). Mean UDVA markedly improved at 1 year (0.19 ± 0.17 to 0.53 ± 0.21 decimal) with further improvement to 0.55 ± 0.19 decimal at 10 years. CDVA increased from 0.59 ± 0.21 to 0.80 ± 0.17 decimal at 1 year and further to 0.81 ± 0.19 decimal at 10 years. Corneal thickness decreased from 468.74 ± 35.05 to 391.14 ± 40.07 μm at 1 year (P < .01) and up to 395.42 ± 32.21 μm at 10 years. Steep keratometry decreased from 50.57 ± 2.80 to 45.87 ± 2.70 diopters (D) (P < .01) at 1 year and to 44.00 ± 3.22 D at 10 years. Maximum keratometry decreased from 53.43 ± 2.97 to 46.17 ± 1.18 D at 1 year and 44.75 ± 2.14 D at 10 years (P < .01). A total of 94.4% demonstrated ectasia stabilization and 3.5% showed progressive "overcorrection" or "hyperopic" shift.

CONCLUSIONS

The Athens Protocol confirms long-term safety and efficacy for corneal ectasia and visual function. Most parameters had little change after 1 year, through year 10. [J Refract Surg. 2019;35(8):478-483.].

Long-Term Stability With the Athens Protocol (Topography-Guided Partial PRK Combined With Cross-Linking) in Pediatric Patients With Keratoconus

PURPOSE

To evaluate the safety, efficacy, and stability of topography-guided partial PRK combined with corneal cross-linking (CXL) (the Athens Protocol [AP]) in pediatric patients with keratoconus over a 4-year follow-up period.

METHODS

This prospective study included 39 keratoconic eyes of 21 patients younger than 18 years with clinical and imaging evidence of keratoconus progression. Partial topography-guided excimer laser ablation in conjunction with high-fluence CXL was performed in all patients according to the AP. Uncorrected distance visual acuity, corrected distance visual acuity, refraction, keratometry, endothelial cell density, topography, and tomography using both Scheimpflug and optical coherence tomography (OCT) were evaluated for 4 years postoperatively.

RESULTS

At 4 years postoperative, there was significant improvement in mean uncorrected distance visual acuity from 0.51 ± 0.31 (decimal) to 0.65 ± 0.26 (decimal; P < 0.05). Mean corrected distance visual acuity improved from 0.71 ± 0.22 (decimal) preoperatively to 0.81 ± 0.19 (decimal; P < 0.05), respectively. Mean flat keratometry (K1) and mean steep keratometry (K2) readings reduced from 44.95 ± 3.71 D and 49.32 ± 5.05 D, respectively, preoperatively to 43.14 ± 2.95 D and 46.28 ± 4.87 D, respectively, (P < 0.05) at 4 years. The mean anterior maximum keratometry (Kmax) reading reduced from 56.81 ± 2.94 D preoperatively to 48.11 ± 3.17 D at 48 months. The mean index of height decentration was 0.105 ± 0.054 μm preoperatively and 0.049 ± 0.024 (P < 0.05) at 4 years postoperative. Mean preoperative corneal thickness at the thinnest point was 436.7 ± 42.6 μm preoperatively, 392.50 ± 45.68 μm at 12 months postoperative, and 418.42 ± 17.01 μm at 4-year follow-up. Late-onset deep corneal haze, a potential intrinsic complication of this technique in pediatric patients, was encountered in 2 cases at least 1 year after the procedure.

CONCLUSIONS

Long-term results of the AP seem to be safe and effective in pediatric patients, with marked improvement in visual function and keratometric symmetry indices.

Management of progressive keratoconus with partial topography-guided PRK combined with refractive, customized CXL - a novel technique: the enhanced Athens protocol

Purpose

To report a novel application of partial topography-guided photorefractive keratectomy combined with topographically customized, higher fluence, and variable pattern corneal cross-linking applied on the same day of the treatment of keratoconus.

Methods

A topography-guided partial photorefractive keratectomy treatment of maximum 30 µm over the thinnest cone area was applied initially followed by a 7 mm, 50 µm phototherapeutic keratectomy treatment to address epithelial removal. 0.02% Mitomycin C was applied for 20 seconds and then the exposed stroma was soaked with 0.1% riboflavin solution for 5 minutes. The cornea was then treated with a customized, variable-pattern and 20 mW/cm² fluence for a total of 5-10 J, and up to 15 J of energy was delivered with the KXL-II device employing an active tracker. The center of the pattern that received the 15 J was topography-matched with the thinnest area of the cone. Visual acuity, refractive error, cornea clarity, keratometry, topography, pachymetry with a multitude of modalities and endothelial cell density were evaluated over 36 months.

Results

Keratoconus was stabilized in all cases. The severity of keratoconus stage by Amsler- Krumeich criteria improved from an average of 3.2 (1-4) to 1.8 (0-3). Uncorrected distance visual acuity changed from preoperative 20/80 to 20/25 at 6 months. A maximum astigmatic reduction of 7.8 D (5.3-15.6), and a significant cornea surface normalization (an index of height decentration improvement from 0.155 [±0.065] to 0.045 [±0.042]) were achieved by 1 month and remained relatively stable for 36 months postoperatively. Two cases delayed full reepithelialization for up to 9 days.

Conclusion

This paper introduces a novel technique in order to maximize the refractive normalization effect along with ectasia stabilization in young keratoconus patients. This may facilitate the use of less tissue ablation, in comparison to utilizing a homogeneous UV light beam for corneal cross-linking in Athens Protocol cases. It broadens the number of potential candidate cases that would have been limited to employ this technique due to tissue thickness limitations.

Primary Topography-Guided LASIK: Refractive, Visual, and Subjective Quality of Vision Outcomes for Astigmatism ⩾2.00 Diopters

PURPOSE

To evaluate the outcomes of primary topography-guided laser in situ keratomileusis (LASIK) in eyes with subjective refractive astigmatism of 2.00 diopters (D) or greater.

METHODS

This was a prospective study in consecutive eyes with cylinder of 2.00 D or greater that had LASIK using the Alcon WaveLight EX500 excimer laser and T-CAT/Contoura software (Alcon Laboratories, Inc., Fort Worth, TX). The accuracy, efficacy, safety, cylinder vector analysis, higher order aberrations, and patients' subjective quality of vision were assessed. Eyes with naturally occurring topographic irregular astigmatism were not excluded.

RESULTS

The mean cylinder was -2.55 D preoperatively and -0.34 D postoperatively; 81% and 95% of eyes were within ±0.50 and ±0.75 D of intended cylinder after LASIK, respectively. The correction index and index of success were 1.00 and 0.13, respectively. The efficacy and safety indexes were 0.98 and 1.04, respectively. The preoperative corneal topography irregularity index, anterior corneal higher order aberrations, and refractive astigmatism magnitude were mildly correlated to postoperative residual astigmatism. Mean ocular and corneal coma were not increased postoperatively. Patients had significant improvements after LASIK in both subjective uncorrected quality of vision and night vision disturbances compared to spectacle- and contact lens-corrected vision before LASIK.

CONCLUSIONS

Topography-guided ablation using the Alcon WaveLight EX500 excimer laser and T-CAT/Contoura software results in excellent accuracy, efficacy, and safety, with improved postoperative subjective quality of vision and reduced night vision disturbances in virgin eyes with refractive astigmatism of 2.00 D or greater, including eyes with topographic naturally occurring irregular astigmatism. [J Refract Surg. 2019;35(2):78-86.].

Recent Innovations in Collagen Corneal Cross-linking; a Mini Review

Background:

The introduction of corneal cross-linking (CXL) with ultraviolet-A (UVA) and Riboflavin photosensitizer (Vit B₂) from Seiler et al., revolutionized the treatment of Keratoconus and other corneal ectatic diseases.

Today, the commonly known epithelium off Dresden protocol is in clinical use for the last 15 years with great success and regarded by many as the golden standard.

Methods:

With several studies demonstrating its simplicity, efficacy and safety this revolutionary method, paved the way for new therapies and strategies in the treatment of corneal ectatic diseases and changed our understanding in corneal biomechanics. Recent scientific and technological advances enabled the creation of various modifications of the initial CXL protocol and the formation of new ones.

Conclusion:

This work highlights the recent advances of CXL, such as the role of oxygen, higher fluence and shorter irradiation times as well as the various clinical applications and updates of this method.

Keratoconus Treatment Algorithm

Keratoconus management has significantly changed over the last two decades. The advent of new interventions such as cornea cross-linking, intrastromal corneal ring segments, and combined treatments provide corneal clinicians a variety of treatment options for the visual rehabilitation of keratoconus patients. This review summarizes current evidence for these treatments and highlights their place in keratoconus management while new promising emerging therapies are being investigated.

Topography-modified refraction (TMR): adjustment of treated cylinder amount and axis to the topography versus standard clinical refraction in myopic topography-guided LASIK

PURPOSE

To evaluate the safety, efficacy, and contralateral eye comparison of topography-guided myopic LASIK with two different refraction treatment strategies.

SETTING

Private clinical ophthalmology practice.

PATIENTS AND METHODS

A total of 100 eyes (50 patients) in consecutive cases of myopic topography-guided LASIK procedures with the same refractive platform (FS200 femtosecond and EX500 excimer lasers) were randomized for treatment as follows: one eye with the standard clinical refraction (group A) and the contralateral eye with the topographic astigmatic power and axis (topography-modified treatment refraction; group B). All cases were evaluated pre- and post-operatively for the following parameters: refractive error, best corrected distance visual acuity (CDVA), uncorrected distance visual acuity (UDVA), topography (Placido-disk based) and tomography (Scheimpflug-image based), wavefront analysis, pupillometry, and contrast sensitivity. Follow-up visits were conducted for at least 12 months.

RESULTS

Mean refractive error was -5.5 D of myopia and -1.75 D of astigmatism. In group A versus group B, respectively, the average UDVA improved from 20/200 to 20/20 versus 20/16; post-operative CDVA was 20/20 and 20/13.5; 1 line of vision gained was 27.8% and 55.6%; and 2 lines of vision gained was 5.6% and 11.1%. In group A, 27.8% of eyes had over -0.50 diopters of residual refractive astigmatism, in comparison to 11.7% in group B (P<0.01). The residual percentages in both groups were measured with refractive astigmatism of more than -0.5 diopters.

CONCLUSION

Topography-modified refraction (TMR): topographic adjustment of the amount and axis of astigmatism treated, when different from the clinical refraction, may offer superior outcomes in topography-guided myopic LASIK. These findings may change the current clinical paradigm of the optimal subjective refraction utilized in laser vision correction.