Journal Club Cornea PTK and CXL for Keratoconus.pptx

Journal club about comparison of PTK vs CXL and PTK for Keratoconus

1. Journal Club - Dr Abeer Rehman, Al-Shifa Trust Eye Hospital

2. Study Title and Authors Topography-guided photorefractive keratectomy combined with accelerated corneal collagen cross-linking versus cross-linking alone for progressive keratoconus: a long-term prospective cohort study Zhihao Dai, Ziyuan Liu, Yu Zhang, Yufei Yuan, Yan Liu, Yuexin Wang, Shuo Yu and Yueguo Chen  

3. Study Details Location/ Time Department of Ophthalmology, Peking University Third Hospital, Beijing, China  Duration - between October 2015 and March 2021 Submitted - 22 May 2024    Published 12 August 2024  Journal Frontiers in Medicine   Type Original Research - Retrospective observational study DOI 10.3389/fmed.2024.1420264 Aim  To comprehensively compare the long-term outcome of the combined topography guided photorefractive keratectomy (TG-PRK) with accelerated corneal cross-linking (ACXL) and ACXL alone in eyes with progressive keratoconus. The analysis focused on the changes in the detailed corneal aberrometric values. 

4. Introduction - Keratoconus Keratoconus is a progressive, often bilateral corneal ectasia, often asymmetric, influenced by genetic and environmental factors (e.g., eye rubbing, nocturnal pressure). The disease involves paracentral corneal thinning and steepening, leading to irregular astigmatism and visual loss.

5. Corneal Cross-Linking (CXL) increases corneal rigidity and effectively halts disease progression. Standard “Dresden Protocol” : 0.1% riboflavin + UVA 3 mW /cm² for 30 min. Accelerated CXL (ACXL) uses higher irradiance (e.g., 9–18 mW /cm²) for shorter duration with similar outcomes. CXL alone stabilizes keratoconus but does not improve vision. Introduction - CXL

6. PRK, Photorefractive keratectomy (PRK), is a type of laser eye surgery that reshapes the cornea to correct vision problems like nearsightedness , farsightedness, and astigmatism The outer layer of the cornea is removed before an excimer laser reshapes the surface to improve how the eye focuses light “Topography-guided " treatment analyzes the individual peaks and valleys of cornea and programs the laser to reshape the surface more precisely than standard PRK. Topography-guided PRK (TG-PRK) combined with CXL—known as the “Athens Protocol” —improves both corneal shape and visual acuity. Previous studies show better visual outcomes with combined TG-PRK + ACXL compared to ACXL alone, but limited analysis of detailed corneal higher-order aberrations (HOAs). This study aims to compare long-term outcomes of TG-PRK + ACXL vs. ACXL alone, focusing on detailed aberrometric changes and visual quality. Introduction - PRK

7. Introduction - PRK

8. Materials and Methods - Overview Design: Single- center , prospective cohort study conducted at Peking University Third Hospital (Oct 2015–Mar 2021), approved by the institutional ethics committee (IRB No. 00006761). Participants: 42 patients (45 eyes) diagnosed with progressive keratoconus . Grouping: Patients stratified by Kmax severity : Severe : Kmax ≥55 D Mild–Moderate : Kmax <55 D Within each subgroup, randomized into TG-PRK + ACXL or ACXL-only groups (2:1 ratio).

9. Inclusion and Exclusion Criteria Inclusion Minimum corneal thickness >450 μ m, or postoperative stromal bed >350 μ m. Exclusion: Other ectasias (e.g., pellucid marginal degeneration), prior corneal surgery, ocular/systemic diseases (e.g., diabetes, autoimmune), pregnancy/lactation, or inability to follow up.

10. Progression Definition of Progression: ≥1 D increase in Kmax within 12 months 1 D change in astigmatism ≥30 μ m decrease in thinnest corneal thickness (TCT)

11. Clinical Examination Comprehensive assessment performed preoperatively and at last follow-up, including: UDVA , CDVA (converted to logMAR ), manifest refraction Corneal topography , pachymetry , aberrometry , and densitometry Corneal haze graded via slit-lamp using Hanna et al. scale Primary outcome: Corneal aberrometry results at last follow-up Secondary outcomes: Visual acuity, refraction, corneal tomography, pachymetry, densitometry, and complications Instrumentation: All corneal imaging performed with Pentacam HR (Oculus GmbH, Germany) Parameters analyzed : ARC, PRC, BAD-D, ISV, IVA, KI, CKI, IHA, IHD, K1, K2, Kmax , CCT, TCT, AT Aberrometry details: Reconstructed from Scheimpflug tomography using Zernike polynomials over 2, 4, and 6 mm diameters Refractive index: 1.3375 Analyzed metrics: RMS of total, lower-order, and higher-order aberrations; coma , trefoil , and spherical aberration Densitometry: Measured for total corneal thickness, focusing on central (0–2 mm) and intermediate zones

12. Corneal Parameters SV (Index of Surface Variance): Measures overall irregularity of the anterior corneal surface — higher values indicate more distortion. IVA (Index of Vertical Asymmetry): Quantifies difference between superior and inferior corneal curvature. KI (Keratoconus Index): Ratio of upper to lower corneal curvature radii; elevated in keratoconus. CKI (Central Keratoconus Index): Compares peripheral to central curvature, reflecting central steepening. IHA (Index of Height Asymmetry): Measures elevation asymmetry between corresponding corneal points. IHD (Index of Height Decentration): Quantifies decentration of corneal elevation pattern from geometric center . BAD-D (Belin/Ambrósio Deviation): Composite index combining pachymetric , curvature, and elevation data to detect corneal ectasia. ARC / PRC (Anterior / Posterior Radius of Curvature): Describe steepness of anterior and posterior corneal surfaces. K1, K2, Kmax : Flat, steep, and maximum keratometric readings; indicate corneal refractive power and astigmatism. CCT / TCT / AT: Central, thinnest, and apex corneal thickness — used to monitor corneal structure and stability.

13. Corneal Parameters

14. Surgical Procedure – Epithelium Removal Central 9 mm corneal epithelium was removed after 20% ethanol exposure for 20 s. All surgeries were performed by the same surgeon.

15. Topography-Guided Photorefractive Keratectomy (TG-PRK) Preoperative corneal maps obtained using Topolyzer Vario (Alcon, USA) . Aim: Minimize corneal irregularity , not refractive error correction. Sphere correction set to 0 D ; ablation optical zone: 5.0–6.5 mm ; max ablation depth: ≤ 50 µm . Cylinder correction: customized (0–2.75 D), aligned with preoperative astigmatism axis. Performed using WaveLight EX500 excimer laser with automated cyclotorsion and kappa-angle compensation. No Mitomycin-C used.

16. Accelerated Corneal Cross-Linking (ACXL) Performed immediately after TG-PRK or epithelial debridement. Cornea soaked with 0.1% riboflavin for 10 min, followed by 365 nm UVA exposure at 30 mW /cm² for 4 min . Riboflavin drops reapplied during irradiation to maintain saturation.

17. Postoperative Care Bandage contact lens applied for 7 days until re-epithelialization. Levofloxacin 0.5% eye drops QID until healing. Fluorometholone 0.1% QID, tapered weekly for 4 weeks. Carteolol 2% prescribed to minimize intraocular pressure elevation and steroid response.

18. Statistical Analysis Data analyzed using SPSS 24.0 ; graphs created in Microsoft Excel 2019 . Normality testing: Shapiro–Wilk test and Q–Q plots. Data presentation: Normally distributed → mean ± standard deviation (SD) Non-normal data → median (interquartile range) Comparisons: Pre- vs. postoperative (within groups): Paired t-test Between groups: Student’s t-test Categorical data: Chi-square test Significance threshold: p < 0.05. No patients lost to follow-up; no missing data.

19. Results - Visual and Refractive Outcomes Participants: 28 patients (30 eyes) TG-PRK + ACXL | 14 patients (15 eyes) ACXL alone Follow-up: Mean 44 ± 10 months (31–65 mo ) Corrected Distance VA (CDVA): Significant improvement in TG-PRK + ACXL (p = 0.006) No significant change in ACXL alone (p = 0.432) Uncorrected VA & Refraction: No significant long-term difference in either group Key Point: TG-PRK + ACXL yielded superior visual improvement.

20. Keratometry ( Kmax ): Both groups showed significant decrease (p < 0.05) Greater decline in TG-PRK + ACXL ( Δ Kmax = 3.06 D vs 0.95 D; p = 0.008) Corneal Aberrations: Total, LOAs, HOAs, vertical coma, and spherical aberration significantly decreased at 4 mm & 6 mm zones in TG-PRK + ACXL (p < 0.001) No meaningful change in ACXL alone Interpretation: Combined treatment produced a smoother, more regular corneal surface. Results - Topography and Corneal Aberrations

21. Results - Subgroup, Haze & Safety Severity Subgroups: Severe ( Kmax ≥ 55 D): Significant Kmax improvement in TG-PRK + ACXL (p = 0.024) Mild/Moderate: No between-group difference Densitometry: No significant difference between groups (p > 0.05) Corneal Haze: TG-PRK + ACXL 66.7%, ACXL alone 60%; all resolved by final follow-up No serious or vision-threatening complications Conclusion: TG-PRK + ACXL achieves better visual and topographic outcomes with comparable safety.

22. Discussion overview The study confirmed that TG-PRK + ACXL achieved better long-term outcomes than ACXL alone. Both procedures stabilized keratoconus, but combined treatment improved higher-order aberrations (HOAs) and visual acuity . CXL (Dresden or accelerated protocols) is established as a safe and effective therapy; the accelerated method (30 mW /cm² × 4 min) used here maintained efficacy with shorter exposure.

23. Discussion - Mechanisms and Comparative Findings CXL strengthens and flattens the cornea, but does not fully correct irregular astigmatism. TG-PRK + ACXL further regularized the anterior corneal surface—reducing vertical coma, spherical aberrations, and total HOAs. These findings align with prior studies (Iselin, Alessio) and meta-analyses showing greater Kmax reduction and visual improvement in the combined approach. Benefits were most pronounced in severe keratoconus ( Kmax ≥ 55 D) .

24. Discussion - Safety, Limitations, and Conclusions No serious complications ; transient haze resolved in all eyes. Mitomycin C was avoided to minimize cytotoxicity, as CXL itself limits keratocyte regeneration. Limitations: Small sample size and mild disease spectrum Aberrometry limited to corneal surface (not full-eye optics) Lack of subjective visual quality assessment Conclusion: TG-PRK + ACXL offers superior long-term visual and optical outcomes with comparable safety — especially beneficial for advanced keratoconus .

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