Keratoconus is an ectatic corneal disorder characterized by progressive corneal thinning that results in corneal protrusion, irregular astigmatism, and decreased vision.1 Significant corneal steepening is observed in the anterior corneal surface of eyes with keratoconus.1,2 Progressive corneal thinning is another finding to detect keratoconus.3 Therefore, cases of moderate and advanced keratoconus can be easily detected and diagnosed by corneal topography, pachymetry, and slit-lamp examination (Vogt striae or Fleischer rings).1 However, surgeons have considered anterior corneal aberration as an effective tool to detect and grade keratoconus because higher amounts of vertical coma and larger coma-like root mean square values have been found in eyes with keratoconus or suspected keratoconus than in normal corneas.4–15 We used the Cooperative Research Thematic Network (RETICS) classification because it includes anterior corneal aberrations, internal astigmatism, corneal bio-mechanical properties and visual limitations.1 The above-mentioned changes in keratoconus cause a displacement of the anterior and posterior corneal surfaces and, therefore, an increased anterior chamber depth, which represents a refractive impact added to these generated changes.16,17
Corneal reshaping techniques based on wedge re-section and suture traction have been reported with irregular results.18 The concept of the corneal remodeling technique is to reshape the structure of the cornea by flattening the radii of curvature by performing semi-lunar or annular keratectomies that are not wedge resection in relation to corneal stage. Corneal remodeling consists of reducing corneal aberrations without increasing the corneal thickness and generating a large optical zone. We previously described this novel technique and presented the initial results of 69 cases.19 In the current study, we present a long-term follow-up analysis of the same group.
Patients and Methods
This study included 69 cases that underwent the corneal remodeling technique. The ethics committee of Universidad Del Norte, Barranquilla, Colombia, approved our work in 2016 and written informed consent was obtained from all patients. The population was classified according to the RETICS classification: grade I with corrected distance visual acuity (CDVA) of 0.9 or better; grade II with CDVA of 0.6 or better and worse than 0.9; grade III with CDVA of 0.4 or better and worse than 0.6 (28 cases); grade IV with CDVA of 0.4 or better (30 cases), and grade Plus with CDVA of worse than 0.2 (11 cases).1
Preoperative examinations included uncorrected distance visual acuity (UDVA) and CDVA using a Snellen chart, manifest spherical and cycloplegic refractions, slit-lamp biomicroscopic and funduscopic examinations, intraocular pressure (non-contact tonometer), corneal tomography (Sirius, CSO, Florence, Italy; and Galilei, Ziemer Ophthalmology Co., Port, Switzerland), central corneal thickness (Ziemer Ophthalmology Co.), horizontal corneal diameter and white-to-white distance (Ziemer Ophthalmology Co.), anterior chamber depth (measured from corneal endothelium to anterior lens by the Galilei device), and corneal endothelial cell density (non-contact specular microscopy, SP-2000P; Topcon, Tokyo, Japan).
Inclusion and Exclusion Criteria
Inclusion criteria for this study were patients with keratoconus grades II, III, IV, and Plus, corneal transparency, and endothelial cell density of greater than 2,000 cells/mm2. Patients were also required to have a reasonable expectation of surgical outcomes and no cataract, glaucoma, or systemic disease.
Procedures were performed under topical anesthesia using proparacaine hydrochloride 5 mg (Alcaine; Alcon Laboratories, Inc., Fort Worth, TX). After placing the speculum (Moria, Antony, France), keratectomy was performed using software designed for the femtosecond laser (Z8; Ziemer Ophthalmology Co.) and arc lengths of 180°, 270°, or 360°. We performed a channel of vertical walls with different widths between the upper and lower parts, with a greater width in the inferior quadrant that decreased progressively according to the degree of keratoconus. The length of resection depended on the degree of keratoconus: the greater the keratoconus is, the greater the length and width of resection are. Figures 1A–1B show a 270° arc length keratectomy. The width could be 300, 400, or 500 µm for keratoconus grades III, IV, and Plus (RETICS classification), respectively. The resection should be wider at the base of the cone.
(A) A 270° keratectomy performed by femtosecond laser. (B) A piece of 270° arc length keratectomy taken off the cornea. (C) Edges are sutured by interrupted stitches. (D) Immediately after the procedure with all stitches placed.
The edges of the removed area were closed by 10-0 interrupted nylon sutures placed approximately 25° apart (Figure 1C). Sutures were passed at 90% depth of the crescentic trench, and the suture tension was adjusted by using double slip knots. The slip knots were locked down with overlying square knots (Figure 1D). The loose ends were trimmed with a sharp blade and the suture was then rotated to bury the knot in the suture track. A bandage lens was inserted at the end of the procedure for the patient's comfort.
Postoperative prophylaxis with moxifloxacin and dexamethasone three times a day for 1 week and prednisolone twice a day for 1 month was administered. The postoperative examinations were performed at 1 day, 1 week, and 3, 6, 12, 24, and 36 months. Corneal tomography, corneal aberration examinations, and endothelial counting were performed at 6 months. Figure 2 demonstrates the long-term postoperative results in one patient. The sutures were removed no earlier than 12 months postoperatively, based on the appearance of their tension on slit-lamp and topography readings.
Long-term results of slit-lamp examination without sutures.
Main Outcome Measures
The improvement of CDVA, sphere and cylinder refraction, and higher order aberrations (HOAs) were the main outcome measures.
Data were collected at 1 day (n = 69) and 3 (n = 69), 6 (n = 69), 12 (n = 69), 24 (n = 51) and 36 (n = 32) months postoperatively and analyzed in a database using Microsoft Excel 2015 software (Microsoft Corporation, Redmond, WA). Data were analyzed according to the arc length: 180°, 270°, and 360°. Preoperative and postoperative data at 36 months of follow-up were compared using the Student's paired t test. Outcomes measured were analyzed for final results. Data were expressed as mean ± two standard deviations. A P value of less than .05 was considered to be statistically significant.
The age of the population was 30.83 ± 12.65 years (range: 16 to 48 years). There were 151 men and 18 women. The mean follow-up time was 29.81 ± 6.22 months (range: 12 to 36 months).
Table 1 shows preoperative and 12- and 36-month postoperative UDVA, CDVA, sphere and cylinder refraction, and anterior chamber depth for 180°, 270°, and 360° arc lengths, respectively. UDVA and CDVA showed an improvement between 12 and 36 months postoperatively. Sphere refraction presented more hyperopic values at 12 months than at 36 months. Cylinder refraction showed higher values at 12 months than at 36 months. Most of the compared parameters were moderately to statistically significant (P < .05 to < .0000001).
Visual Outcomes and Anterior Chamber Depth
At 36 months postoperatively, 57.2% presented with UDVA of 20/100 or worse and 42.8% achieved between 20/80 and 20/40. After performing photorefractive keratectomy (PRK) in 3 cases, 14.3% presented with UDVA of 20/100 or worse, 57.2% achieved between 20/80 and 20/40, and 28.5% achieved 20/30 or better with an arc length of 180° and 45.4% presented with UDVA of 20/100 or better, 45.4% achieved between 20/80 and 20/40, and 9.2% achieved 20/30 or better with an arc length of 270°. After performing PRK in 4 cases, 9.2% of the cases presented with UDVA of 20/100 or worse, 45.4% achieved between 20/80 and 20/40, and 45.4% achieved 20/30 or better. For an arc length of 360°, 64.3% presented with UDVA of 20/100 or worse and 35.7% achieved between 20/80 and 20/40. After performing PRK in 7 eyes, 28.5% of the cases presented with UDVA of 20/100 or worse, 57.2% achieved between 20/80 and 20/40 and 14.3% achieved 20/30 or better.
Table 2 shows preoperative and postoperative HOAs for 180°, 270°, and 360° arc lengths; HOAs decreased 14% and coma decreased 17%. Figure 3 shows the pre-operative and postoperative corneal tomography in a representative case.
HOAs and Coma
Preoperative and postoperative corneal tomography in a representative case. (A) Corneal tomography of the right eye of an 18-year-old man with refraction of −5.00 diopters (D) cylinder at 35°. UDVA was 20/100 and CDVA was 20/50. The flattest meridian was 46.25 D at 22° and the steepest meridian was 51.50 D at 112°. The corneal remodeling technique assisted by femtosecond laser was planned using a 270° keratectomy, with a gap of 500 µm. Eighteen months after surgery, the refraction in the right eye was +2.50 −1.00 × 175°. UDVA was 20/50 and CDVA reached 20/20; the flattest meridian was 40.00 D at 0° and the steepest was 45.00 D at 90°. (B) Postoperative corneal tomography map.
Figure 4 shows the distribution of gained and lost lines of CDVA at 36 months postoperatively. For a 180° arc length, almost 70% of the cases were stable or gained up to two lines of visual acuity. For a 270° arc length, 65% of the cases were stable or gained two or three lines of visual acuity; almost 30% of patients gained four to six lines of visual acuity. For a 360° arc length, 85% of the cases were stable or gained up to three lines of visual acuity; 15% gained five lines of visual acuity. None of the patients lost lines of visual acuity.
Change in Snellen lines of corrected distance visual acuity for (A) 180°, (B) 270°, and (C) 360° arc length keratectomy. postop = postoperative
Regarding intraoperative or postoperative complications, we had to adjust some sutures or place additional sutures in 8 of 69 cases. These adjustments were made for a better distribution of force vectors during the first postoperative days.
No patient presented with mild, moderate, or severe signs of infection or inflammation during the immediate postoperative period.
Reshaping the cornea in keratoconic eyes means reversing the deformation produced by this entity by remodeling the corneal profile. It is not easy to draw parallels between remodeling and visual acuity in corneal remodeling immediately postoperatively because the sutures persist at least 1 year later (Table 1). The real visual performance appears after the removal of the sutures. The visual results obtained at 24 and 36 months postoperatively showed satisfactory changes in UDVA, CDVA, and sphere and cylinder refraction. PRK was performed in some cases to improve postoperative UDVA and CDVA.20
Poor visual acuity and high corneal aberrations are due to the irregular astigmatism generated by the above-mentioned changes rather than to thinning per se of the cornea. In other words, thin corneas do not cause poor visual acuities: topographic asymmetries of keratoconus generate the visual decrease. Because intracorneal rings must increase the corneal thickness to generate the topographic changes in the cornea, corneal remodeling can produce those changes in a more predictable way and generates an optical zone larger than the one used for intracorneal rings.21,22 Taking into account such unpredictability, the corneal segments are used as an orthopedic treatment in ectasia. However, they induce high corneal aberrations due to their position in the usual useful optical zone, which inevitably affects the visual quality of patients.22 The area in which corneal segments are implanted is so narrow that it does not leave a real refractive optical zone.
The progression of keratoconus is accompanied by an increase in the anterior chamber depth and posterior corneal curvature, corneal thinning, and progressive corneal curvature. A decrease of the anterior chamber depth (an average of 400 µm) is observed and also represents a refractive impact. The corneal remodeling procedure can literally remodel the profile of the cornea.
On the other hand, the management of high astigmatism has been reported through the technique of wedge resection. Its application was modestly stated, but the role it might have had in corneal ectasia has never been well defined, nor its applicability, which might be optimized. Nevertheless, refractive regression that was observed with the wedge resection technique has not been detected in most corneal remodeling cases, except one patient who used to rub her eyes.23–26
The first cases were followed up for 48 months, but we have shown analyzed data over 36 months due to the smaller sample size obtained at that time. In all cases, we observed corneal flattening, which is an increase in the radius of corneal curvature. None of the cases presented loss of visual acuity lines and most of them gained up to three lines of CDVA. Likewise, without being the main objective of this procedure, the UDVA in many cases was better than 20/40. This reflects the predictability and safety of the procedure.
Removing the sutures too early could result in poorer outcomes. We have considered that using shorter and more numerous stitches may generate even more refractive predictability.27
In all arc lengths, there was a particular coma reduction (from 17% to 55%) and general decrease in HOAs. In the slit-lamp examination, a semi-lunar wound arc appeared with an 8-mm optical zone. According to the rigidity of healing, this area has a behavior that may be well described as a sort of “new limbo” due to the limbic reinforcement that generates.19
The technique of semi-lunar or annular corneal keratectomy is a safe procedure that produces corneal flattening, reduces the anterior chamber depth and corneal aberrations, and offers a wide optical zone, which allows the performance of complementary refractive techniques. Studies using computer simulation (Finite Element software; Ansys, Inc., Canonsburg, PA) have allowed us to not only ratify the obtained clinical results, but to guide ourselves to the bases of the surgical nomogram28 Different types of lasers can be used for this technique. Different methods of corneal analysis (eg, topographers, pachymeters, and optical coherence tomography) can be complementarily used due to the fact that cross-linking produces corneal stiffness and may be considered a further step in the search for corneal stabilization. It would be expected that the association with the corneal cross-linking treatment could yield a greater corneal stability in the future.29
To date, treating corneal deformation cases with keratoconus has been either a palliative or barely compensatory procedure. We believe corneal remodeling represents a new and effective approach to treat corneal ectasia, but a longer follow-up will be necessary. Even with a certain degree of astigmatism after the procedure, changes in keratometric values allow us to recover a physiological corneal profile. Furthermore, it allows surgeons to be able to perform complementary refractive corrections to achieve an integral treatment of the ectasia.
- Alió JL, Piñero DP, Alesón A, et al. Keratoconus-integrated characterization considering anterior corneal aberrations, internal astigmatism and corneal biomechanics. J Cataract Refract Surg. 2011;37:552–568. doi:10.1016/j.jcrs.2010.10.046 [CrossRef]
- Wilson SE, Lin DTC, Klyce SD. Corneal topography of keratoconus. Cornea. 1991;10:2–8. doi:10.1097/00003226-199101000-00002 [CrossRef]
- Ambrosio R Jr, Klyce SD, Wilson SE. Corneal topographic and pachymetric screening of keratorefractive patients. J Refract Surg. 2003;19:24–29.
- Piñero DP, Alió JL, Aleson A, Escaf M, Miranda M. Pentacam: posterior and anterior corneal aberrations in normal and keratoconic eyes. Clin Exp Optom. 2009;92:297–303. doi:10.1111/j.1444-0938.2009.00357.x [CrossRef]
- Beuhren J, Këuhne C, Kohnen T. Defining subclinical keratoconus using corneal first-surface higher-order aberrations. Am J Ophthalmol. 2007;143:381–389. doi:10.1016/j.ajo.2006.11.062 [CrossRef]
- Alió JL, Shabayek MH. Corneal higher order aberrations: a method to grade keratoconus. J Refract Surg. 2006;22:539–545. doi:10.3928/1081-597X-20060601-05 [CrossRef]
- Gobbe M, Guillon M. Corneal wavefront aberration measurements to detect keratoconus patients. Cont Lens Anterior Eye. 2005;28:57–66. doi:10.1016/j.clae.2004.12.001 [CrossRef]
- Barbero S, Marcos S, Merayo-Lloves J, Moreno-Barriuso E. Validation of the estimation of corneal aberrations from videokeratography in keratoconus. J Refract Surg. 2002;18:263–270.
- Nilforoushan MR, Speaker M, Marmor M, et al. Comparative evaluation of refractive surgery candidates with Placido topography, Orbscan II, Pentacam and wavefront analysis. J Cataract Refract Surg. 2008;34:623–631. doi:10.1016/j.jcrs.2007.11.054 [CrossRef]
- Schlegel Z, Hoang-Xuan T, Gatinel D. Comparison of and correlation between anterior and posterior corneal elevation maps in normal eyes and keratoconus-suspect eyes. J Cataract Refract Surg. 2008;34:789–795. doi:10.1016/j.jcrs.2007.12.036 [CrossRef]
- Sonmez B, Doan M-P, Hamilton DR. Identification of scanning slit-beam topographic parameters important in distinguishing normal from keratoconic corneal morphologic features. Am J Ophthalmol. 2007;143:401–408. doi:10.1016/j.ajo.2006.11.044 [CrossRef]
- Rao SN, Raviv T, Majmudar PA, Epstein RJ. Role of Orbscan II in screening keratoconus suspects before refractive corneal surgery. Ophthalmology. 2002;109:1642–1646. doi:10.1016/S0161-6420(02)01121-1 [CrossRef]
- Tomidokoro A, Oshika T, Amano S, Higaki S, Maeda N, Miyata K. Changes in anterior and posterior corneal curvatures in keratoconus. Ophthalmology. 2000;107:1328–1332. doi:10.1016/S0161-6420(00)00159-7 [CrossRef]
- Piñero DP, Alió JL, Barraquer RI, Michael R, Jimenez R. Corneal biomechanics, refraction, and corneal aberrometry in keratoconus: an integrated study. Invest Ophthalmol Vis Sci. 2010;51:1948–1955. doi:10.1167/iovs.09-4177 [CrossRef]
- Ortiz D, Piñero D, Shabayek MH, Arnalich-Montiel F, Alió JL. Corneal biomechanical properties in normal, post-laser in situ keratomileusis, and keratoconic eyes. J Cataract Refract Surg. 2007;33:1371–1375. doi:10.1016/j.jcrs.2007.04.021 [CrossRef]
- Parker J, Van Dijk K, Melles G. Treatment options for advanced keratoconus: a review. Surv Ophthalmol. 2015;60:459–480. doi:10.1016/j.survophthal.2015.02.004 [CrossRef]
- Vega-Estrada A, Alió JL, Brenner LF, et al. Outcome analysis of intracorneal ring segments for the treatment of keratoconus based on visual, refractive, and aberrometric impairment. Am J Ophthalmol. 2013;155:575–584. doi:10.1016/j.ajo.2012.08.020 [CrossRef]
- Ezra EG, Hay-Smith G, Mearza A, Falcon MG. Corneal wedge excision in the treatment of high astigmatism after penetrating keratoplasty. Cornea. 2007;26:819–825. doi:10.1097/ICO.0b013e318093de39 [CrossRef]
- Carriazo C, Cosentino MJ. A novel corneal remodeling technique for the management of keratoconus. J Refract Surg. 2017;33:854–856. doi:10.3928/1081597X-20171004-05 [CrossRef]
- Mortensen J, Ohrström A. Excimer laser photorefractive keratectomy for treatment of keratoconus. J Refract Corneal Surg. 1994;10:368–372.
- Zadnik K, Lindsley K. Intrastromal corneal ring segments for treating keratoconus. Published2014. https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD011150/full
- Alió 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. doi:10.4103/0974-9233.124076 [CrossRef]
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- Shumway CL, Aggarwal S, Farid M, et al. Penetrating keratoplasty using the femtosecond laser: a comparison of postoperative visual acuity and astigmatism by suture pattern. Cornea. 2018;37:1490–1496. doi:10.1097/ICO.0000000000001738 [CrossRef]
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Visual Outcomes and Anterior Chamber Depth
|Arc Length Keratometry||Preoperative||12-Month Postoperative||36-Month Postoperative|
| UDVA (decimal)||0.07 ± 0.08||0.14 ± 0.11||0.20 ± 0.13|
| Sphere refraction (D)||−2.55 ± 1.21||+0.70 ± 3.44||+0.21 ± 3.06|
| Cylinder refraction (D)||−3.29 ± 1.75 × 69°||−3.21 ± 0.87 × 152°||−2.30 ± 0.95 × 139°|
| CDVA (decimal)||0.38 ± 0.12||0.61 ± 0.17||0.69 ± 0.11|
| ACD (mm)||3.92 ± 0.25||3.78 ± 0.29||3.80 ± 0.22|
| UDVA (decimal)||0.03 ± 0.03||0.32 ± 0.28||0.41 ± 0.18|
| Sphere refraction (D)||−1.17 ± 3.27||+0.66 ± 2.58||−0.30 ± 2.19|
| Cylinder refraction (D)||−4.88 ± 2.45 × 52°||−4.81 ± 2.45 × 157°||−3.35 ± 2.01 × 136°|
| CDVA (decimal)||0.42 ± 0.19||0.59 ± 0.24||0.69 ± 0.13|
| ACD (mm)||4.10 ± 0.13||3.83 ± 0.43||3.85 ± 0.32|
| UDVA (decimal)||0.05 ± 0.06||0.04 ± 0.33||0.22 ± 0.18|
| Sphere refraction (D)||−2.70 ±3.03||+1.77 ± 1.83||+1.34 ± 1.06|
| Cylinder refraction (D)||−4.25 ± 1.30 × 100°||−4.96 ± 1.16 × 171°||−3.70 ± 0.74 × 164°|
| CDVA (decimal)||0.34 ± 0.17||0.61 ± 0.28||0.76 ± 0.13|
| ACD (mm)||3.77 ± 0.32||3.38 ± 0.37||3.42 ± 0.41|
HOAs and Coma
|Arc Length Keratectomy||Preoperative HOAs (µm)||Preoperative Coma (µm)||Postoperative HOAs (µm)||Postoperative Coma (µm)|