Refractive surgery options have continued to advance, not only improving outcomes for normal corneas, but also corneas that have limitations. Common corneal limitations include irregular astigmatism, high levels of refractive correction (>12 D of myopia or 6.00 D of astigmatism), thin corneas (< 450 µm), previous refractive surgery treatments, keratoconus (KCN), or those that have ocular surface disease (OSD).
Here, I discuss the refractive surgery options for corneas that have limitations.
Laser Keratorefractive Procedures
LASIK involves the highest amount of corneal tissue alteration. Myopic patients who have undergone LASIK in one eye and SMILE in the other expressed a preference for vision from their LASIK eye over their SMILE eye.1
Photorefractive keratectomy (PRK) and SMILE should be considerations in patients who have thin corneas or higher levels of correction, as both result in low levels of corneal tissue alteration when compared to LASIK, and are ultimately believed to have better biomechanical strength.1 PRK, in particular, is beneficial when corneal thickness is the major limitation, due to the procedure’s decreased amounts of percent tissue altered, with recommendations to stay below 40%. (See “PTA Equation,” below.)
Additionally, SMILE and PRK have less of an effect on postoperative tear production,2 making the procedures an attractive option for patients who have OSD.
Also, due to the lack of the need for a flap, PRK or SMILE may be better indicated for patients who may be at risk for trauma to the head/eyes due to no risk for flap dislodgement with these techniques. Such patients may include athletes, such as football or basketball players.
When deciding among the three techniques above, each has its considerations and should be customized to the patient being treated.
Topography-guided excimer laser treatments (TGT) have been used off-label for the treatment of abnormal corneas resulting from complications from previous refractive surgery.
TGT can treat corneas that have high amounts of higher-order aberrations, such as cases of decentered ablation zones, small ablation zones, or asymmetric astigmatism.3 Studies have demonstrated positive outcomes when TGT has been used for the treatment of irregular astigmatism, decentered ablations, and small ablation zones resulting from previous refractive surgery.3,4,5,6 Further, several studies have revealed positive outcomes on patients who have undergone previous keratoplasty, stable KCN after corneal cross-linking (CXL), and prior radial keratotomy (RK).7,8,9
Sequential techniques after CXL have been reported when treating patients who have KCN or post-refractive surgery ectasia.10,11,12 Further, 10-year follow-up data from the Athen’s protocol demonstrated long-term stability and safety in patients who had progressive KCN treated with sequential CXL and TGT.13 Contoura Vision (Alcon) is currently the only FDA-approved TGT in the United States.
Phakic IOLs (P-IOLS)
P-IOLs may be a safer option than laser keratorefractive procedures for patients who have high myopia (>12 D), thin corneas (<450 µm), severe OSD, or certain systemic diseases, such systemic lupus erythematosus.
KCN patients who have high refractions and undergo a laser keratorefractive procedure are at risk of corneal ectasia with the potential for a high percentage of corneal tissue altered, as well as induction of higher-order aberrations affecting visual quality, given high-tissue ablation.
Patients who have systemic diseases, such as autoimmune conditions, and who undergo laser keratorefractive procedures may experience delayed healing, increased inflammation, and exacerbations of OSD.
Three phakic IOLs are FDA approved: the Visian Implantable Collamer Lens (ICL) (Staar Surgical), the EVO Visian ICL (Staar Surgical), and the Verisyse (Johnson & Johnson Vision).
The Visian ICL is a posterior chamber IOL FDA approved to treat myopia ranging from -3.00 D to -16 D with reduction of myopia of up to -20 D. (A toric option is also available that can treat a range of 1.00 D to 4.00 D of astigmatism.)
The EVO Visian ICL contains several holes to enable aqueous flow, and has shown a decreased rate of cataract formation, IOP stability, and positive visual outcomes.
The Verisyse is an iris claw anterior chamber phakic IOL FDA approved for the treatment of spherical myopia that ranges from -5.00 D to -20 D with less than 2.5 D of astigmatism.
A caveat: P-IOL implantation requires a clear corneal incision, so it would potentially be contraindicated in patients who have a shallow anterior chamber depth (< 3.0 mm), glaucoma, an existing cataract, a low endothelial cell count, or in those who are younger than age 21.
Refractive Lens Exchange
This is now a feasible option in cases of abnormal corneas, such as those that have undergone prior RK, laser refractive surgery, or have KCN. These IOLs: Akreos AO (model AO60, Bausch + Lomb); Akreos AO Microincision lens (Akreos) MICS; model MI60 (Bausch + Lomb); enVista MX60E (Bausch + Lomb); enVista MX60ET (Bausch + Lomb); RayOne Aspheric (RA0600C, Rayner USA), the SofPort Advanced Optics Aspheric Lens (Bausch + Lomb), and, most recently, the IC-8 Apthera IOL (Bausch + Lomb) used off label.
The IC-8 is a one-piece acrylic UV-blocking extended-depth-of-focus hydrophobic posterior chamber IOL that has a 6 mm internal optical size and is 12.5 mm long. Additionally, it contains a 1.36 mm central aperture surrounded by a non-diffractive 3.23 mm diameter opaque mask, called FilterRing. Further, the IOL’s power range is 10 D to 30 D. Patients who have irregular astigmatism, due to prior RK or moderate KCN, without macular pathology or significant field loss, have demonstrated improvement in visual acuity, as well as good tolerability with the off-label use of the IC-8.
Another option for patients who have corneal limitation is the Light Adjustable Lens (LAL) (RxSight). The reason: The LAL allows for the adjustment of residual spherical and cylindrical error after surgery from -2 D to +2 D and up to 2.5 D, respectively, enabling the patient to be involved in their refractive transformation.
Intrastomal ring segments (ICRS) have been available since the 1980s for the treatment of mild-to-moderate KCN, correcting astigmatism, along with mild myopia. Sequential ICRS implantation followed by phakic IOLs can be a good option to treat refractive error in patients who have irregular astigmatism with myopia, such as those with KCN.14,15
What’s to Come
Refractive surgery continues to advance with the addition of new technology and emerging imaging, expanding the cornea refractive surgeon’s armamentarium. Improved refractive techniques will continue to enhance patient outcomes and allow for the consideration of candidates previously labelled unsuitable for refractive procedures. CP
References:
1. Ma KK, Manche EE. Patient-reported quality of vision in a prospective randomized contralateral-eye trial comparing LASIK and small-incision lenticule extraction. J Cataract Refract Surg. 2023;49(4):348-353.
2. Sambhi RS, Sambhi GDS, Mather R, Malvankar-Mehta MS. Dry eye after refractive surgery: a meta-analysis. Can J Ophthalmol. 2020;55(2):99-106.
3. Shetty R, Lalgudi VG, Kaweri L, Choudhary U, Chabra A, Gupta K, Khamar P. Customized laser vision correction for irregular cornea post-refractive surgery. Indian J Ophthalmol. 2020;68(12):2867-2879.
4. Lin DT, Holland SR, Rocha KM, Krueger RR. Method for optimizing topography-guided ablation of highly aberrated eyes with the ALLEGRETTO WAVE excimer laser. J Refract Surg. 2008;24(4):S439-45.
5. Kymionis GD, Panagopoulou SI, Aslanides IM, Plainis S, Astyrakakis N, Pallikaris IG. Topographically supported customized ablation for the management of decentered laser in situ keratomileusis. Am J Ophthalmol. 2004;137(5):806-11.
6. Wu L, Zhou X, Ouyang Z, Weng C, Chu R. Topography-guided treatment of decentered laser ablation using LaserSight’s excimer laser. Eur J Ophthalmol. 2008;18(5):708-15.
7. Ramamurthy S, Soundarya B, Sachdev GS. Topography-guided treatment in regular and irregular corneas. Indian J Ophthalmol. 2020;68(12):2699-2704.
8. Spadea L, Visioli G, Mastromarino D, Alexander S, Pistella S. Topography-guided trans-epithelial no-touch photorefractive keratectomy for high irregular astigmatism after penetrating keratoplasty: A prospective 12-months follow-up. Ther Clin Risk Manag. 2021;17:1027-1035.
9. Bizrah M, Lin DTC, Babili A, Wirth MA, Arba-Mosquera S, Holland SP. Topography-guided photorefractive keratectomy for postkeratoplasty astigmatism: long-term outcomes. Cornea. 2021;40(1):78-87.
10. Hatch KM, Ling JJ, Wiley WF,et al. Diagnosis and management of postrefractive surgery ectasia. J Cataract Refract Surg. 2022;48(4):487-499.
11. Kanellopoulos AJ, Asimellis G. Keratoconus management: long-term stability of topography-guided normalization combined with high-fluence CXL stabilization (the Athens Protocol). J Refract Surg. 2014;30(2):88-93.
12. Kanellopoulos AJ. Comparison of sequential vs same-day simultaneous collagen cross-linking and topography-guided PRK for treatment of keratoconus. J Refract Surg. 2009;25(9):S812-8.
13. Kanellopoulos AJ. Ten-year outcomes of progressive keratoconus management with the Athens Protocol (topography-guided partial-refraction PRK combined with CXL). J Refract Surg. 2019;35(8):478-483.
14. D’Oria F, Bagaglia SA, Alio Del Barrio JL, Alessio G, Alio JL, Mazzotta C. Refractive surgical correction and treatment of keratoconus. Surv Ophthalmol. 2024;69(1):122-139.
15. Alfonso JF, Lisa C, Fernández-Vega L, Madrid-Costa D, Poo-López A, Montés-Micó R. Intrastromal corneal ring segments and posterior chamber phakic intraocular lens implantation for keratoconus correction. J Cataract Refract Surg. 2011;37(4):706-13.
