Artificial neural network to guide intracorneal ring segments implantation for keratoconus treatment: a pilot study.

BACKGROUND: To analyze the clinical results of an artificial neural network (ANN) that has been processed in order to improve the predictability of intracorneal ring segments (ICRS) implantation in keratoconus. METHODS: This retrospective, comparative, nonrandomized, pilot, clinical study included a cohort of 20 keratoconic eyes implanted with intracorneal ring segments KeraRing (Mediphacos, Belo Horizonte, Brazil) using the ANN (ANN group) and 20 keratoconic eyes implanted with KeraRing using the manufacturer's nomograms (nomogram group). Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA) (visual acuity is expressed in decimal value and in LogMAR value in brackets), manifest refraction, corneal topography, tomography, aberrometry, pachymetry and volume analysis (Sirius System. CSO, Firenze, Italy) were performed during the preoperative visit; and the two groups, ANN group and nomogram group, did not differ significantly preoperatively in all of the parameters evaluated. These preoperative values were compared with the results obtained at the third-month visit. Mann-Whitney test and Wilcoxon test were used for the statistical analyses. RESULTS: The spherical equivalent and the keratometric values decreased significantly in both groups. The CDVA improved from 0.60 ± 0.23 (0.22 LogMAR) pre-operatively to 0.73 ± 0.21 (0.14 LogMAR) post-operatively in the ANN group (p < 0.005), and from 0.54 ± 0.19 (0.27 LogMAR) pre-operatively to 0.62 ± 0.19 (0.21 LogMAR) post-operatively in the nomogram group (p < 0.01), with statistically significant difference between the two groups (p < 0.05), being better in the ANN group. Coma-like aberrations decreased significantly in the ANN group, while in the nomogram group they did not change significantly, but no statistically significant difference was found between the two groups. CONCLUSIONS: ANN to guide ICRS provides an increase in the visual acuity, reduction in the spherical equivalent and improvement in the optical quality of keratoconus patients. ANN gives better results when compared with the manufacturer's nomograms in terms of better corrected vision and reduction of the coma-like aberrations. The constant inclusion of new cases will make the predictability of ANN increasingly better as the software finetunes its learning.

Posterior corneal features in patients with Down syndrome and their relation with keratoconus.

AIMS: To characterise posterior corneal surface features in patients with Down syndrome (DS) and to compare them with healthy and mild keratoconus corneas. METHODS: This restrospective, comparative, non-randomised, clinical study included 123 eyes, divided into three groups (37 eyes of patients with DS, 46 with mild keratoconus and 40 controls), and took place at Vissum Alicante. Only patients with no previous ocular surgery, no corneal scars and no active ocular disease other than keratoconus were included. The Sirius System topographer (CSO, Firenze, Italy) was used in order to analyse posterior corneal surface keratometry, shape and keratoconus screening indices, posterior corneal aberrations, corneal volume and pachymetry. RESULTS: Patients with DS, when compared with healthy controls, have a steeper (mean keratometry 7 mm (KM): -6.30±0.44 vs -6.15±0.22; p<0.05) and more irregular (root mean square per unit of area: 4.5 mm 0.22±0.22 vs 0.09±0.03, p<0.001; posterior vertex of the ectatic area: 33.22±44.29 vs 10.63±2.88, p<0.001) posterior corneal surface, with higher aberrations (high-order aberrations (HOAs): 1.07±1.43 vs 0.15±0.06, p<0.001; coma-like: 0.88±1.09 vs 0.13±0.07, p<0.001) and thinnest pachymetry (497.68±26.88 vs 538.95±31.67, p<0.001). At the same time, no statistically significant difference was found between patients with DS and patients with mild keratoconus (p>0.05) in KM (-6.38±0.34), HOA (0.56±0.36), coma-like (0.51±0.34) and pachymetry (500.56±36.83). CONCLUSIONS: Posterior corneal surface of patients with DS is steeper, more irregular and shows more higher order aberrations, as well as reduced volume and thinner pachymetry than patients with healthy corneas. Additionally, posterior corneal surface in patients with DS shows similar characteristics to those found in mild keratoconus.

Femtosecond-assisted laser in situ keratomileusis for high myopia correction: Long-term follow-up outcomes.

OBJECTIVE: Report the outcomes of laser in situ keratomileusis (LASIK) for high myopia correction after long-term follow-up. METHODS: Retrospective, consecutive, clinical study including 70 eyes that underwent LASIK using a 500 Hertz (Hz) repetition rate excimer laser and femtosecond technology for flap creation. Visual, refractive, corneal aberrations, and correlation among the variables were evaluated during 3 years. In addition, 34 eyes were followed during 5 years. RESULTS: Significant improvement of 17 logMAR lines was observed in uncorrected vision at 5 years (p < 0.01). This was consistent with spherical equivalent reduction that came from mean preoperative -7.79 diopters (D) to 5 years postoperative -0.24 D (p < 0.01). Significant induction of primary spherical aberration and coma aberration was also found (p < 0.01) at 3 months with levels of 0.61 µm and 0.47 µm, respectively, with no further changes at 5 years (p > 0.05). Pearson correlation showed that the amount of high-order aberrations at 3 months postoperativeley was significantly correlated with the changes in the keratometry throughout the 5 years (delta K) (R2 0.242 p = 0.05). Finally, preoperative corneal asphericity showed an inverse correlation with the delta K (R2 -308 p = 0.01). CONCLUSIONS: Results from this study suggests that LASIK for high myopia correction using 500 Hz repetition rate excimer laser provides stable visual, refractive and aberrometric results after 5 years of follow-up. A more prolate cornea and the amount of higher-order aberrations induced after LASIK are factors that negatively impact in the long-term stability of the procedure.

Laser flap enhancement 5 to 9 years and 10 or more years after laser in situ keratomileusis: Safety and efficacy.

PURPOSE: To study the safety and efficacy of refractive enhancement by flap lifting 5 and 10 years after laser in situ keratomileusis (LASIK). SETTING: Vissum Alicante, Spain. DESIGN: Retrospective case series. METHODS: Eyes with a flap lift at least 5 years after primary LASIK with a 3-month follow-up were evaluated. The primary outcome measures were safety and the complication rate. Moderate epithelial ingrowth was managed with Nd:YAG laser treatment. RESULTS: The primary LASIK procedure was myopic in 45 eyes, hyperopic in 22 eyes, and presbyopic in 3 eyes. The mean time from primary LASIK to the flap lift was 12.3 years ± 3.45 (SD). In 57 eyes, the primary LASIK flap was created at least 10 years before the enhancement. The mean pre-lift spherical equivalent was -1.29 ± 1.23 diopters (D) in the myopia group and +0.65 ± 1.72 D in the hyperopia group. Three months later, 88% of eyes and 74% of eyes, respectively, had an uncorrected distance visual acuity of 20/20 or better; 100% achieved at least 20/25. No eye lost 2 lines or more of corrected distance visual acuity. In the myopia group, the efficacy index was 0.94 and the safety index was 0.98 at 6 months. Mild epithelial ingrowth developed in 31.43% of eyes and clinically significant epithelial ingrowth in 11.42% of eyes; 4.28% required a relift for severe epithelial ingrowth. CONCLUSIONS: Late flap lift for refractive enhancement 10 years or more after LASIK provided good efficacy and safety with fast visual recovery. The rate of surgical intervention for significant postoperative epithelial ingrowth was low.

Invasive Pharmacology Outcomes with Different Corneal Cross-Linking Protocols: A Review.

Collagen corneal cross-linking (CXL) is an invasive pharmacological treatment strategy used for corneal ectatic disorders and is currently the only treatment capable of halting the progression of the disease. In the past 20 years, the conservative management of progressive corneal ectasia has changed, thanks to this procedure that produces strengthening of the corneal tissue through the photochemical reaction generated by the combined action of riboflavin and ultraviolet A radiation. Many modified protocols have been implemented to halt the progression of the disease and to delay or prevent visual loss and surgical procedures such as corneal transplantation. Because of the variety of different protocols that are currently used, the results that are being reported are very variable, and could generate some confusion in relation to the true efficacy of the procedure. The aim of this review was to provide an overview of the aforementioned protocols that are designed to maintain the efficacy of CXL in halting the progression of the disease but avoiding the major limitations of the procedure.

Clinical Outcomes of a New Asymmetric Intracorneal Ring Segment for the Treatment of Keratoconus.

PURPOSE: To report visual, refractive, and corneal aberrations after implantation of a new asymmetric intracorneal ring segment (ICRS). METHODS: This was a prospective, multicenter clinical study including 30 eyes of 26 patients with keratoconus. All cases were implanted with an ICRS, named the VISUMRING (VR), which had an arc length of 353 degrees and 2 asymmetric sections that can be customized in base width, length, and thickness. Ophthalmic evaluation included uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), refraction, topography, and anterior corneal aberrations using the Sirius System (CSO, Firenze, Italy). Mean follow-up period was 14.7 ± 7.9 months. RESULTS: Significant improvement of both UDVA and CDVA was observed after 1 year. UDVA improved from 0.08 ± 0.22 to 0.22 ± 0.16 and CDVA from 0.24 ± 0.29 to 0.43 ± 0.18 (P = 0.01). A significant reduction of more than 7 D in the spherical equivalent from -12.38 ± 3.77 D to -5.00 ± 3.26 D (P < 0.05) was noted 1 year after the procedure. In terms of higher-order aberrations, a slight reduction that was not statistically significant in the higher-order and coma-like aberrations was noted at 1 year from 4.32 and 3.82, to 4.12 and 3.55, respectively. Regarding complications, 5 of the 30 cases needed to have the VR explanted throughout the follow-up period due to severe corneal melting. CONCLUSIONS: VR ICRS improves vision and refraction and induces major corneal flattening in patients with keratoconus. Further design enhancement is needed to increase the reduction of the asymmetric corneal aberrations and reduce the extrusion rate.

Keratoconus Corneal Posterior Surface Characterization According to the Degree of Visual Limitation.

PURPOSE: To characterize posterior corneal surface features in patients with keratoconus and healthy controls and correlate them with the severity of the disease according to visual limitation. METHODS: Retrospective, comparative, clinical study including 477 cases, 374 keratoconic eyes and 103 healthy corneas. Patients were classified according to the degree of visual limitation. The corneal posterior surface including shape indices and keratoconus screening indices was evaluated using the rotating Scheimpflug camera and Placido disc topographer. RESULTS: Dioptric power of the posterior corneal surface increases linearly as corrected distance visual acuity deteriorates (r > 0.700; P < 0.001). A significant correlation was also observed between shape indices root mean square per unit of area (RMS/A) (posterior surface irregularity) and corrected distance visual acuity (r = -0.750; P < 0.001). In addition, keratoconus screening indices such as posterior corneal aberrations and posterior ectasia vertex (KVb) also showed significant correlation with the degree of visual limitation (r = -0.687; P < 0.001 and r = -0.789; P < 0.001, respectively). Receiver operating characteristic curves demonstrate that RMS/A and KVb showed highest discriminating capabilities between normal and mild keratoconus cases with an area under the curve of 0.96 and 0.97, respectively, with a sensitivity and specificity of more than 93% for the RMS/A and 89% and 84% for the KVb. CONCLUSIONS: Posterior corneal surface characteristics correlate with the degree of visual impairment and can be used for classifying patients with keratoconus. RMS/A, KVb, and posterior corneal aberrations are the most representative variables of visual function deterioration and are also useful to differentiate normal from mild keratoconus cases.

Corneal Epithelial Thickness Intrasubject Repeatability and its Relation With Visual Limitation in Keratoconus.

PURPOSE: To evaluate intra-subject repeatability of anterior segment optical coherence tomography (AS-OCT) combined with placido disc MS-39 (CSO, Firenze, Italy) and correlate epithelial thickness measurements and the degree of visual limitation in keratoconus patients. DESIGN: Reliability analysis and cross-sectional study. METHODS: Setting: Vissum, Alicante, Spain. SUBJECTS: Total of 167 eyes, of which 107 were from keratoconus patients and 60 were healthy. PROCEDURES: Three repeated consecutive epithelial thickness measurements were taken: central 3.0 mm and the nasal, temporal, superior, and inferior regions at 3.0-6.0 mm and 6.0-8.0 mm. MAIN OUTCOME MEASURES: Intrasubject repeatability of epithelial indices was assessed and correlated to the degree of best-corrected visual acuity (BCVA). RESULTS: The intraclass correlation coefficient was ≥0.90, indicating highly repeatable measurements for both keratoconus and healthy eyes. In multivariate analysis, epithelial indices associated with worse BCVA were as follows: thinner 3 mm central (P = .04), thicker 8 mm superior (P < .001), and thinner 8 mm inferior (P < .001). Thickness central 3 mm decreased as keratoconus grading increased (P = .002). The superior-inferior ratio at 8 mm significantly increased as keratoconus grading increased (P < .001). In multivariate analysis thinner 3 mm central (R2 = 6.19%, P = .04), greater superior-inferior 8 mm ratio (R2 = 8.37%, P = .004), greater superior-inferior 6mm ratio (R2 = 2.67%, P = .02), and steeper K2 (R2 = 21.51%, P < .001) were associated with keratoconus with a combined area under the curve of 0.92. CONCLUSION: High repeatability of epithelial thickness measurements may be achieved in both keratoconus and healthy eyes with the MS-39. There is a significant correlation between epithelial thickness measurements and BCVA. These measurements may be of additional value in discriminating between keratoconus and healthy eyes.

Metal-Organic Frameworks as Drug Delivery Platforms for Ocular Therapeutics.

Metal-organic frameworks (MOFs) have been evaluated as potential nanocarriers for intraocular incorporation of brimonidine tartrate to treat chronic glaucoma. Experimental results show that UiO-67 and MIL-100 (Fe) exhibit the highest loading capacity with values up to 50-60 wt %, whereas the performance is quite limited for MOFs with narrow cavities (below 0.8 nm, for example, UiO-66 and HKUST-1). The large loading capacity in UiO-67 is accompanied by an irreversible structural amorphization in aqueous and physiological media that promotes extended release kinetics above 12 days. Compared to the traditional drawbacks associated with the sudden release of the commercial drugs (e.g., ALPHAGAN), these results anticipate UiO-67 as a potential nanocarrier for drug delivery in intraocular therapeutics. These promising results are further supported by cytotoxicity tests using retinal photoreceptor cells (661W). Toxicity of these structures (including the metal nodes and organic ligands) for retinal cells is rather low for all samples evaluated, except for HKUST-1.

Corneal Morphologic Characteristics in Patients With Down Syndrome.

Importance: Literature suggests corneal morphologic characteristics compatible with keratoconus are present in a high percentage of patients with Down syndrome (DS), suggesting the need to perform a detailed examination of the anterior segment to try to avoid serious visual impairment in this group of patients. Objective: To characterize the abnormal features of the cornea in patients with DS and compare these with a control group. Design, Setting, and Participants: Multicenter case-control study at Vissum Alicante, Alicante, Spain, and the Ophthalmology and Pediatric Department, Cairo University, Cairo, Egypt. Data collection took place between May 2013 and May 2016. Data were analyzed between June 2016 and August 2016. The study included 321 eyes of 217 participants from 2 groups: 112 participants in the DS group and 105 healthy participants in the control group. Interventions: Patients were evaluated using Placido disc/Scheimpflug camera topographer (Sirius, CSO). Visual, refractive and anterior, and posterior corneal characteristics were assessed and compared in both groups. Main Outcomes and Measures: Keratoconus diagnosis. Incidence of corneal morphologic irregularities similar to keratoconus in patients with DS. Results: In the DS group, mean (SD) age was 14.88 (15.76) years, 54 (48%) were women, 66 (59%) were white, and 46 (41%) were Arab. In the control group, mean (SD) age was 40.29 (14.66) years, 54 (51%) were women, and all were white. Clinical assessment of corneal topography showed that 71.3% (95% CI, 45.2-97.4) of patients in the DS group showed characteristics compatible with keratoconus. Differences were found in steepest keratometry of 47.35 diopters (D) in patients with DS vs 43.70 D in control individuals (difference, 3.65 D; 95% CI, 3.23-4.35 D; P <.001) and in corneal pachymetry of 503 µm in patients with DS vs 545 µm in control individuals (difference, 42 µm; 95% CI, 38.8-56.7 µm; P <.001). Conclusions and Relevance: Patients with DS have steeper and thinner corneas and more corneal aberrations than those without genetic alterations and normal corneas. The findings suggest a detailed corneal study should be considered in such patients to detect keratoconus and implement treatment as appropriate to try to avoid serious visual impairment in this group of patients.

Clinical outcomes with a diffractive trifocal intraocular lens.

PURPOSE: To evaluate clinical and visual outcomes, quality of near vision, and intraocular optical quality of patients bilaterally implanted with a trifocal PanOptix intraocular lens. METHODS: In this prospective consecutive case-series study, 52 eyes of 26 bilateral patients (mean age, 60.2 ± 7.4 years) were implanted with the AcrySof IQ Panoptix intraocular lens. Visual acuity, defocus curve, contrast sensitivity (Pelli-Robson test), near activity visual questionnaire, and internal aberrations with Osiris were evaluated. A prototype light-distortion analyzer was used to quantify the postoperative light-distortion indices. The follow-up was 6 months after surgery. RESULTS: Uncorrected, corrected distance, and uncorrected near visual acuities improved with the surgery (p ≤ 0.02). Distance corrected near visual acuity was 0.13 ± 0.10, 0.13 ± 0.13, and 0.13 ± 0.08 at 1, 3, and 6 months after surgery, respectively (p = 0.82). Distance corrected intermediate visual acuities were 0.09 ± 0.13, 0.13 ± 0.15, and 0.12 ± 0.12 at 1, 3, and 6 months, postoperatively. Binocular contrast sensitivity was 1.86 ± 0.15 Log Units. Defocus curve provided a visual acuity equal or better to 0.30 LogMAR between defocus levels of +0.50 to -3.00 D. The near activity visual questionnaire scores improved significantly with the surgery (p < 0.01). CONCLUSION: The AcrySof IQ Panoptix intraocular lens is able to restore visual function with an acceptable intermediate and near vision after cataract surgery with good contrast sensitivity and an improvement in the near activity visual questionnaire.

Descemet Membrane Endothelial Keratoplasty (DMEK) Under Previous DMEK for Secondary Endothelial Graft Failure.

PURPOSE: To describe an alternative treatment option for secondary Descemet membrane endothelial keratoplasty (DMEK) graft failure, using a second DMEK graft without primary graft removal ("DMEK under DMEK"). METHODS: A 72-year-old patient with pseudophakic bullous keratopathy in the left eye underwent an 8.25-mm second DMEK under an 8.5-mm failed DMEK because of previous graft rejection and subsequent secondary failure. RESULTS: Corrected distance visual acuity improved from 0.2 (decimal scale) before surgery to 0.56 (best visual potential due to concomitant preexisting macular damage) from the first month after surgery and up to sixth-month follow-up. Complete corneal transparency was achieved from the first postoperative day and remained until the end of the follow-up. Pachymetry returned to normal values within the first month. No intraoperative or postoperative complications were observed. CONCLUSIONS: A second DMEK graft without peeling or removing the first DMEK graft is an alternative treatment option for DMEK graft secondary failure. This approach is able to achieve full anatomical and functional restoration of the prefailure status. This technique allows a second graft surgery to be easier, faster, and with less intraoperative risks (as a result of a potential difficult host descemetorhexis). Future studies with larger samples and a longer follow-up are necessary to confirm the short and long-term outcomes of this new DMEK under DMEK approach.

Accommodative intraocular lenses: where are we and where we are going.

Presbyopia still remains the last frontier of refractive surgery. Its surgical management is under constant evolution due to the limitations that exist today with respect to its management, which is probably in relation with the multifactorial basis in which presbyopia is clinically developed in the human. Until currently, virtually all surgical techniques that have been proposed for its correction are based on the induction of pseudoaccommodation in the presbyopic eye, including multifocality. However, the real restoration of accommodation is more complex, and it has been tried by the use of different, so called, "accommodative" pseudophakic intraocular lenses (AIOL). Overall, the reported results with these lenses by independent authors have been modest in relation with the restoration of the accommodative power of the eye and these modest benefits are usually lost with time due to the long term changes in the capsular bag. This fact made these lenses to be almost abandoned in the last few years, but there are currently other AIOL models being used with innovative mechanisms of action and different anatomical support outside the capsular bag that offer encouraging preliminary results that could bring a new potential of application to these types of lenses. In this article, we will update the modern refractive surgeon about the fundamentals and provide updated information about the outcomes of AIOLs by reviewing the concept of accommodation, the different attempts that have been accomplished in the past, their demonstrated published results in human clinical trials, and the future alternatives that may arrive in the near future.

The use of intracorneal ring segments in keratoconus.

Keratoconus is a corneal degeneration that usually appears during puberty and may seriously deteriorate the quality of life of the patients. This corneal disease is today the first indication of corneal transplantation in young patients. Until the last decade of the XX century, keratoplasty procedures were the only alternative to treat this pathological condition. In the beginning of the XXI century, intracorneal ring segments implantation was proposed as a therapeutic choice for treating keratoconus patients. Since then, several published articles have reported the benefits of this surgical procedure in treating this type of corneal ectatic disorder. The purpose of the present investigative work is to summarize the characteristic of the intracorneal ring segments and also to review the different features published in the literature in relation to this surgical technique for the treatment of keratoconus patients.

Biocompatibility and Biomechanical Effect of Single Wall Carbon Nanotubes Implanted in the Corneal Stroma: A Proof of Concept Investigation.

Corneal ectatic disorders are characterized by a progressive weakening of the tissue due to biomechanical alterations of the corneal collagen fibers. Carbon nanostructures, mainly carbon nanotubes (CNTs) and graphene, are nanomaterials that offer extraordinary mechanical properties and are used to increase the rigidity of different materials and biomolecules such as collagen fibers. We conducted an experimental investigation where New Zealand rabbits were treated with a composition of CNTs suspended in balanced saline solution which was applied in the corneal tissue. Biocompatibility of the composition was assessed by means of histopathology analysis and mechanical properties by stress-strain measurements. Histopathology samples stained with blue Alcian showed that there were no fibrous scaring and no alterations in the mucopolysaccharides of the stroma. It also showed that there were no signs of active inflammation. These were confirmed when Masson trichrome staining was performed. Biomechanical evaluation assessed by means of tensile test showed that there is a trend to obtain higher levels of rigidity in those corneas implanted with CNTs, although these changes are not statistically significant (p > 0.05). Implanting CNTs is biocompatible and safe procedure for the corneal stroma which can lead to an increase in the rigidity of the collagen fibers.

Clinical outcomes with a new microincisional diffractive multifocal IOL.

BACKGROUND: To evaluate the refractive outcomes and the optical performance as well as the quality of life in patients implanted with a new diffractive multifocal intraocular lens (IOL). METHODS: Prospective, clinical study including 41 cases of patients who underwent cataract surgery and were divided in two groups: group 1, including 20 eyes implanted with the multifocal IOL SeeLens MF (Hanita Lenses, Israel); group 2, 21 eyes implanted with the Acrysof SA60AT IOL. Visual acuity, defocus curve, intraocular aberrations, contrast sensitivity function and quality of life were assessed during a follow up period of 6 months. RESULTS: Significant improvement was observed in the uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA) in both groups (p < 0.02). The multifocal group showed better results in terms of uncorrected near visual acuity (UNVA) and distance-corrected near visual acuity (DCNVA) (p < 0.01). Comparison of both groups showed better visual acuities for the multifocal IOL group in defocus levels from -3.0 D to -1.50 D (p ≤ 0.01). At 6 months, there was a significant reduction of the internal higher order aberrations (p ≤ 0.04). A significant increase in scotopic contrast sensitivity was detected for 6 cycles/° spatial frequency during follow up (p = 0.04), but no significant changes were observed for the rest of spatial frequencies (p ≥ 0.06). Visual Functioning Index (VF-14) questionnaire showed that patients reported high levels of satisfaction when performing daily tasks. CONCLUSIONS: The SeeLens MF IOL is able to successfully restore distance, near and intermediate visions after cataract surgery. It also provides functional intermediate vision with optimal intraocular optical quality.

Keratoconus progression after intrastromal corneal ring segment implantation in young patients: Five-year follow-up.

PURPOSE: To analyze whether implantation of intrastromal corneal ring segments (ICRS) influences the progression of keratoconus in young patients. SETTING: Vissum Corporation, Alicante, Spain. DESIGN: Retrospective case series. METHODS: Eyes with confirmed progressive keratoconus and ICRS (Intacs or Keraring) were evaluated. The visual, refractive, topographic, and aberrometric outcomes were assessed at 2 preoperative examinations to confirm the progressive nature of each case. The postoperative follow-up was 5 years. RESULTS: The study evaluated 18 eyes in 15 patients with a mean age of 25.75 years ± 3.59 (SD). All the visual, refractive, and topographic measurements worsened between the 2 preoperative examinations, confirming the progressive nature of the cases. Six months postoperatively, there was improvement in the uncorrected and corrected distance visual acuities (P > .05) and all refractive measurements (P < .05) and the mean keratometry (K) was reduced by 4.48 diopters (D) (P < .01). Immediately after the procedure, the visual and refractive variables improved but then worsened. From 6 months postoperatively to 5 years, the mean K value regressed 3.36 D. CONCLUSION: Implantation of ICRS significantly improved the visual, refractive, and topographic parameters in the short term; however, the regression at 5 years suggests that implantation of ICRS does not significantly influence progressive keratoconus in young patients with confirmed progression of the disease. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.

Geometrical custom modeling of human cornea in vivo and its use for the diagnosis of corneal ectasia.

AIM: To establish a new procedure for 3D geometric reconstruction of the human cornea to obtain a solid model that represents a personalized and in vivo morphology of both the anterior and posterior corneal surfaces. This model is later analyzed to obtain geometric variables enabling the characterization of the corneal geometry and establishing a new clinical diagnostic criterion in order to distinguish between healthy corneas and corneas with keratoconus. METHOD: The method for the geometric reconstruction of the cornea consists of the following steps: capture and preprocessing of the spatial point clouds provided by the Sirius topographer that represent both anterior and posterior corneal surfaces, reconstruction of the corneal geometric surfaces and generation of the solid model. Later, geometric variables are extracted from the model obtained and statistically analyzed to detect deformations of the cornea. RESULTS: The variables that achieved the best results in the diagnosis of keratoconus were anterior corneal surface area (ROC area: 0.847, p<0.000, std. error: 0.038, 95% CI: 0.777 to 0.925), posterior corneal surface area (ROC area: 0.807, p<0.000, std. error: 0.042, 95% CI: 0,726 to 0,889), anterior apex deviation (ROC area: 0.735, p<0.000, std. error: 0.053, 95% CI: 0.630 to 0.840) and posterior apex deviation (ROC area: 0.891, p<0.000, std. error: 0.039, 95% CI: 0.8146 to 0.9672). CONCLUSION: Geometric modeling enables accurate characterization of the human cornea. Also, from a clinical point of view, the procedure described has established a new approach for the study of eye-related diseases.

Internal, corneal, and refractive astigmatism as prognostic factors for intrastromal corneal ring segment implantation in mild to moderate keratoconus.

PURPOSE: To improve the predictability of the visual and refractive outcomes of intrastromal corneal ring segment (ICRS) implantation in keratoconus patients and highlight the importance of internal astigmatism and its relationship to corneal and refractive astigmatism as prognostic factors. SETTING: Vissum Corporación, Alicante, and Centro de Oftalmología Barrquer, Barcelona, Spain. DESIGN: Retrospective case series. METHODS: Visual, refractive, topographic, and aberrometric variables were evaluated in eyes having ICRS implantation. The eyes were divided into 2 groups according to the relative position of the keratometric axis and refractive axis; that is, coincident axis (0 degree ± 15 [SD]) or uncoincident axis. Internal astigmatism was calculated by vectorial analysis. The relationship between topographic astigmatism and refractive astigmatism was evaluated. The follow-up was 6 months. RESULTS: Of the 127 eyes evaluated, 79 had grade II keratoconus and 48 had grade I keratoconus. Statistically significant differences were found in the relative position of the refractive axis and keratometric axis (P=.017). Internal astigmatism had a significant correlation with the gain in visual acuity in patients with grade II keratoconus (r = -0.455, P=.0001). This relationship was less significant in patients with grade I keratoconus (r = -0.391, P=.021). CONCLUSION: The predictability of visual and refractive outcomes can be significantly increased in grade II keratoconus patients when the relative position of the keratometric and refractive axes; the internal, corneal, and refractive astigmatism; and their combinations are used as prognostic factors. FINANCIAL DISCLOSURE: No author has a financial or proprietary interest in any material or method mentioned.

Intrastromal corneal ring segments: how successful is the surgical treatment of keratoconus?

This review evaluates the outcomes of intrastromal corneal ring segment (ICRS) implantation for the treatment of keratoconus considering a new grading system based on the preoperative visual impairment of the patient. Additionally, a five-year follow-up analysis of patients with stable and progressive keratoconus is performed in order to assess the long term stability of the surgical procedure. Corrected distance visual acuity decreased statistically significantly in patients with mild keratoconus (P < 0.01) but statistically significantly increased in all other grades (P < 0.05). The improvement in visual acuity and the decrease of keratometric and aberrometric values were stable throughout a long period of time in patients with stable keratoconus. In patients with progressive form keratoconus, a significant improvement was found immediately after the procedure, however clinically relevant regression greater than 3 D was observed at the end of the follow up period.