Purpose: To evaluate and compare clinical outcomes after femtosecond laser-assisted implantation of 325-degree versus 340-degree arc length intracorneal ring segments (ICRS) in eyes with keratoconus (KCN).
Methods: In this prospective non-randomized interventional case series, 23 eyes of 21 patients diagnosed with KCN, underwent femtosecond laser-assisted implantation of two types of ICRS, which included a 325-degree ICRS (Group 325) and a 340-degree ICRS (Group 340). The primary outcome measures were uncorrected distance visual acuity (UDVA), and the secondary outcome measures included corrected distance visual acuity (CDVA), sphere, cylinder, mean refractive spherical equivalent (MRSE), keratometry, vectorial change in corneal astigmatism, and the location of maximum keratometry relative to the corneal apex. The study groups were compared using the primary and secondary outcome measures obtained at postoperative months six and 12.
Results: Groups 325 and 340 consisted of 10 and 13 eyes, respectively. The two groups were comparable in terms of parameters measured preoperatively. On comparison to the baseline values, both study groups exhibited a significant increase in UDVA and CDVA measured at postoperative month six (Ps < 0.05) and a significant decrease in the sphere, cylinder, spherical equivalent refraction, and keratometry readings measured at postoperative months six and 12 (Ps < 0.05). No significant differences were observed between the two groups in terms of visual, refractive, and keratometric outcomes at any time point. No intraoperative or postoperative complications were observed in any of the study groups.
Conclusion: Both the 325-degree ICRS and the 340-degree ICRS effectively and equally improved visual, refractive, and keratometric outcomes in keratoconic eyes.

2. Romero-Jiménez M, Santodomingo-Rubido J, Wolffsohn JS. Keratoconus: A review. Cont Lens Anterior Eye 2010;33:157-166.

3. Fleming JF, Reynolds AE, Kilmer L, Burris TE, Abbott RL, Schanzlin DJ. The intrastromal corneal ring: Two cases in rabbits. J Refract Surg 1987;3:227–232.

4. Vega-Estrada A, Alio JL. The use of intracorneal ring segments in keratoconus. Eye Vis (Lond) 2016;3:8.

5. Bromley JG, Randleman JB. Treatment strategies for corneal ectasia. Curr Opin Ophthalmol 2010;21:255–258.

6. Gorgun E, Kucumen RB, Yenerel NM. Influence of intrastromal corneal ring segment implantation on cornealbiomechanical parameters in keratoconic eyes. Jpn J Ophthalmol 2011;55:467–471.

7. Shetty RK, Wartluft L, Moster MR. Slit-lamp needle revision of failed filtering blebs using high-dose mitomycin C. J Glaucoma 2005;14:52–56.

8. Nosé W, Neves RA, Burris TE, Schanzlin DJ, Belfort Júnior R. Intrastromal corneal ring: 12-month sighted myopic eyes. 2J Refract Surg 1996;12:20–8.

9. Burris TE, Ayer CT, Evensen DA, Davenport JM. Effects of intrastromal corneal ring size and thickness on corneal flattening in human eyes. Refract Corneal Surg 1991;7:46– 50.

10. Daxer A. Biomechanics of corneal ring implants. Cornea 2015;34:1493–1498.

11. Gharaibeh AM, Muhsen SM, AbuKhader IB, Ababneh OH, Abu-Ameerh MA, Albdour MD. KeraRing intrastromal corneal ring segments for correction of keratoconus. Cornea 2012;31:115–120.

12. Paranhos JD, Ávila MP, Paranhos A, Schor P. Evaluation of the impact of intracorneal ring segments implantation on the quality of life of patients with keratoconus using the NEI-RQL (National Eye Institute Refractive Error Quality of life) instrument. Br J Ophthalmol 2010;94:101–105.

13. Daxer A, Mahmoud H, Venkateswaran RS. Intracorneal continuous ring implantation for keratoconus: One-year follow-up. J Cataract Refract Surg 2010;36:1296–1302.

14. Jadidi K, Mosavi SA, Nejat F, Naderi M, Janani L, Serahati S. Intrastromal corneal ring segment implantation (keraring 355∘) in patients with central keratoconus: 6-month followup. J Ophthalmol 2015;2015:916385.

15. Jabbarvand M, Salamatrad A, Hashemian H, Khodaparast M. Continuous corneal intrastromal ring implantation for treatment of keratoconus in an Iranian population. Am J Ophthalmol 2013;155:837–842.

16. Coskunseven E, Kymionis GD, Tsiklis NS, Atun S, Arslan E, Jankov MR, et al. One-year results of intrastromal corneal ring segment implantation (KeraRing) using femtosecond laser in patients with keratoconus. Am J Ophthalmol 2008;145:775–779.

17. Ganesh S, Shetty R, D’Souza S, Ramachandran S, Kurian M. Intrastromal corneal ring segments for management of keratoconus. Indian J Ophthalmol 2013;61:451–455.

18. Elaziz MS, El Saebay Sarhan AR, Ibrahim AM, Haggag HA. Anterior segment changes after femtosecond laserassisted implantation of a 355-degree intrastromal corneal ring segment in advanced keratoconus. Cornea 2018;37:1438–1443.

19. Monteiro T, Alfonso JF, Franqueira N, Faria-Correia F, Ambrósio R Jr, Madrid-Costa D. Predictability of tunnel depth for intrastromal corneal ring segments implantation between manual and femtosecond laser techniques. J Refract Surg 2018;34:188–194.

20. Torquetti L, Cunha P, Luz A, Kwitko S, Carrion M, Rocha G, et al. Clinical outcomes after implantation of 320-arc length intrastromal corneal ring segments in keratoconus. Cornea 2018;37:1299–1305.

21. Hosny M, El-Mayah E, Sidky MK, Anis M. Femtosecond laser-assisted implantation of complete versus incomplete rings for keratoconus treatment. Clin Ophthalmol 2015;9:121–127.

22. Piñero DP, Alio JL, El Kady B, Coskunseven E, Morbelli H, Uceda-Montanes A, et al. Refractive and aberrometric outcomes of intracorneal ring segments for keratoconus: Mechanical versus femtosecond-assisted procedures. Ophthalmology 2009;116:1675–1687.

23. Krumeich JH, Daniel J. Lebend-Epikeratophakie und tiefe lamelläre Keratoplastik zur stadiengerechten chirurgischen Behandlung des Keratokonus (KK) I-III. Klin Monbl Augenheilkd 1997;211:94–100.

24. Abdellah MM, Ammar HG. Femtosecond laser implantation of a 355-degree intrastromal corneal ring segment in keratoconus: A three-year follow-up. J Ophthalmol 2019;2019:6783181.

25. Sadoughi MM, Einollahi B, Veisi AR, Zare M, Sedaghat MR, Roshandel D, et al. Femtosecond laser implantation of a 340-degree intrastromal corneal ring segment in keratoconus: Short-term outcomes. J Cataract Refract Surg 2017;43:1251–1256.

26. Yousif MO, Said AM. Comparative study of 3 intracorneal implant types to manage central keratoconus. J Cataract Refract Surg 2018;44:295–305.

27. Rocha GA do N, Ferrara de Almeida Cunha P, Torquetti Costa L, Barbosa de Sousa L. Outcomes of a 320- degree intrastromal corneal ring segment implantation for keratoconus: Results of a 6-month follow-up. Eur J Ophthalmol 2020;30:139–146.

28. Alio JL, Vega-Estrada A, Esperanza S, Barraquer RI, Teus MA, Murta J. Intrastromal corneal ring segments: How successful is the surgical treatment of keratoconus? Middle East Afr J Ophthalmol 2014;21:3–9.

29. Huang J, Huang J, Chen Y, Ying GS. Evaluation of approaches to analyzing continuous correlated eye data when sample size is small. Ophthalmic Epidemiol 2018;25:45–54.