👁️

Advanced Corneal Thickness Variation Simulation
after Refractive Surgery

Professional Tool for PRK, LASIK, KLEX/SMILE Planning
by Pr. Damien Gatinel
Standard Mode: Uses average corneal parameters (K = 43.0 D, Q = -0.2) for quick calculations. Ideal for routine screening and patient education.

📊 About the Standard Mode

This mode calculates the residual corneal thickness after refractive surgery using population-average corneal parameters. It supports three main techniques: PRK (photorefractive keratectomy), LASIK (laser-assisted in situ keratomileusis), and KLEX/SMILE (small incision lenticule extraction).

Key Parameters Used

  • Mean corneal radius: 7.8 mm (K = 43.0 D)
  • Asphericity (Q): -0.2 (prolate shape)
  • Keratometric index: n = 1.3375 (for K readings)
  • Stromal index: n = 1.376 (for optical calculations)
  • Posterior radius: 6.7 mm

Clinical Guidelines

  • PRK epithelium removal: 50 µm
  • LASIK flap thickness: 100-140 µm (typical)
  • Optical zone: 6.0-7.0 mm (standard)
  • Minimum safe residual bed: 300 µm (PRK), 250-300 µm (LASIK)
  • PTA (Percentage of Tissue Altered): <40% recommended (Santhiago et al.)

⚡ Vertex Distance Settings

🛡️ Safety Limit Settings

Custom Mode: Allows specification of patient-specific corneal parameters including preoperative keratometry and asphericity. Ideal for complex cases and research applications.

🔬 About the Custom Mode

This advanced mode enables precise calculations using patient-specific corneal parameters. You can input the actual preoperative keratometry and asphericity values, and specify the target postoperative asphericity for customized ablation profiles.

Additional Custom Parameters

  • Preoperative keratometry (K): Mean corneal power in diopters
  • Preoperative Q value: Corneal asphericity (-1 to +1)
  • Target postoperative Q: Desired asphericity after surgery
Radius calculation from K:
R (mm) = (n - 1) × 1000 / K
where n = 1.3375 (keratometric index)

Note: Optical calculations use n = 1.376 (stromal index)

Asphericity (Q) Values

  • Q < 0: Prolate cornea (normal, periphery flatter than center)
  • Q = 0: Spherical cornea
  • Q > 0: Oblate cornea (periphery steeper than center)
  • Typical range: -0.4 to 0.0 (most corneas are prolate)

Safety Considerations

  • PTA (Percentage of Tissue Altered): Calculated as (Flap + Ablation) / CCT × 100%
  • Risk threshold: PTA > 40% associated with increased ectasia risk (Santhiago et al.)

🎯 Custom Corneal Parameters

⚡ Vertex Distance Settings

🛡️ Safety Limit Settings

📈 Calculation Results

⚠️ Clinical Disclaimer:

This simulator is an educational and research tool. All surgical decisions must be based on comprehensive clinical examination, actual patient measurements, and professional judgment. Individual variations in corneal biomechanics, healing response, and other factors significantly influence surgical outcomes.

📚 References

Gatinel D, Weyhausen A, Bischoff M. The Percent Volume Altered in Correction of Myopia and Myopic Astigmatism With PRK, LASIK, and SMILE. J Refract Surg. 2020 Dec 1;36(12):844-850. doi: 10.3928/1081597X-20200827-01. PMID: 33295998.

Gatinel D, Saad A, Binder PS. Comparison of the effect of LASIK parameters on the percent tissue altered (1-dimensional metric) versus percent volume altered (3-dimensional metric). J Cataract Refract Surg. 2018 Jul;44(7):897-904. doi: 10.1016/j.jcrs.2018.04.041. Epub 2018 Jun 28. PMID: 29960656.

Gatinel D, Hoang-Xuan T, Azar DT. Three-dimensional representation and qualitative comparisons of the amount of tissue ablation to treat mixed and compound astigmatism. J Cataract Refract Surg. 2002 Nov;28(11):2026-34. doi: 10.1016/s0886-3350(02)01379-2. PMID: 12457680.

Gatinel D, Hoang-Xuan T, Azar DT. Volume estimation of excimer laser tissue ablation for correction of spherical myopia and hyperopia. Invest Ophthalmol Vis Sci. 2002 May;43(5):1445-9. PMID: 11980859.

Gatinel D, Hoang-Xuan T. Modélisation tridimensionnelle et géométrie descriptive des profils de photoablations sphériques et cylindriques pures au laser Excimer [Three-dimensional representation and descriptive geometry of the pure spherical and pure cylindrical profiles of Excimer photoablation]. J Fr Ophtalmol. 2002 Mar;25(3):247-56. French. PMID: 11941250.

Santhiago MR, Smadja D, Wilson SE, Krueger RR, Monteiro ML, Randleman JB. Role of percent tissue altered on ectasia after LASIK in eyes with suspicious topography. J Refract Surg. 2015 Apr;31(4):258-65. doi: 10.3928/1081597X-20150319-05. PMID: 25884581.