Mathematical analysis of corneal remodelling after intracorneal ring surgery in keratoconus

Abstract

The newly derived nomogram can produce better results than the conventional nomogram. Moreover, based on this concept, a new nomogram can be integrated into the femtosecond laser software to create topography-guided, customized, elliptical tunnels with modified focal asphericity that allows for customized focal flattening of the irregularly steepened ectatic cornea.

The number of intracorneal ring segments in asymmetric and central cones

“…Some authors initially proposed using two segments of 120° or 160° arc length [ 22 , 23 ] with equal thicknesses that vary based on the targeted correction of myopic SE [ 15 ], while manufacturers initially proposed implantation of two segments with equal arc lengths, with different thickness and distribution of each segment based on SE and topographic pattern [ 13 ]. As equal ring size had more flattening effect in the steep area than in the flat area, thicker segment was always implanted at the steep area regardless of the cylinder axis of refraction [ 24 ]. Similarly, nomograms tend to place the second ring segment based on targeted SE correction and differ the thicknesses of two segments based on eccentricity and astigmatism to be corrected.…”

“…In this aspect, Alió et al was first to report their findings on the implantation of one or two Intacs segments, where they concluded that based on the topographic pattern, best choice was to implant one segment in those cases of inferior steepening and two segments in central cones [ 19 ]. Sharma et al also reported favorable effects of single segment Intacs implantation in keratoconus [ 21 ], particularly in moderate and severe asymmetric keratoconus defined as a difference between the superior and inferior topographic readings of > 5 D and an apex topographic reading of ≥ 52 D [ 24 ].…”

Corneal Cross-Linking for Keratoconus and Post-LASIK Ectasia and Failure Rate: A 3 Years Follow-Up Study

“…ICRS (Intacs® Addition Technology™, Inc.) were implanted four weeks prior to CXL in both groups if the patient had a decreased CDVA (<20/30), contact lens intolerance, and irregular astigmatism on topography. A total of 57 eyes were implanted with ICRS using Intralase femtosecond laser (IntraLase, Abbott Medical Optics Inc., Santa Ana, California, USA) to create the tunnels at 400µm depth (different ring segment arc length and thickness were used following our published algorithm in each case) [ 20 ]. Also, a simultaneous PRK using an excimer laser (ALCON WAVELIGHT® EX500 Alcon Laboratories, Inc.) was performed at the same day prior to CXL if the patient had a CDVA > 20/30, a minimum pre-operative thinnest pachymetry of 480µm and a calculated ablation depth limited to <50µm over the cone.…”

Clinical outcomes after intracorneal ring segment implantation for keratoconus management in corneas with mild apical haze

“…ICRSs flatten the central cornea by acting through ‘arc shortening effect’ on corneal stroma with advantages of proven stability, safety and reversibility. 10 – 12 ICRS, particularly KERARING (Mediphacos Inc., Belo Horizonte, Brazil) has a triangular cross-sectional profile with an arc length ranging between 90° and 325° and inner and outer diameter of 5.40 and 6.60 mm, respectively, and can be implanted in up to 80% of corneal thickness. 13 Previously, ICRS implantation through manual tunnel dissection has been reported to have various complications, including epithelial defects, infectious keratitis, stromal edema, incision extension, persistent wound gaping and corneal perforation.…”

“… 13 The indications for the implantation of these polymethyl methacrylate (PMMA) segments include CDVA less than 0.6 in the decimal scale, intolerance to contact lenses, clear cornea and a minimum pachymetry of 450 µm in the implantation area. 7 , 9 , 10 The presence of corneal opacities is considered an exclusion criterion for the use of ICRSs. 5 , 7 , 8…”