Post-refractive Surgery Research Articles

High-dose dietary riboflavin and direct sunlight exposure in the treatment of keratoconus and post-refractive surgery ectasia of the cornea

High-dose dietary riboflavin and direct sunlight exposure in the treatment of keratoconus and post-refractive surgery ectasia of the cornea

Comparison of Color Light-Emitting Diode Corneal Topographer and Dual Rotating Scheimpflug-Placido Topographer.

Purpose To compare measurements of anterior and posterior keratometric values, using a color light-emitting diode corneal topographer and a dual rotating Scheimpflug–Placido topographer. Methods Anterior and posterior corneal index measurements were performed using a color light-emitting diode corneal topographer (Cassini) and a dual rotating Scheimpflug–Placido topographer (Galilei G4) and then compared. The paired t-test, intraclass correlation coefficients (ICCs), and Bland–Altman plots were used to evaluate the agreement between measurements. Results Sixty postrefractive surgery eyes and 60 normal eyes were evaluated. Both the color light-emitting diode corneal topographer and the dual rotating Scheimpflug–Placido topographer provided highly repeatable corneal measurements (ICC > 0.969). The agreement levels between the 2 devices for anterior corneal power, astigmatism magnitude, and J0 and J45 values were ICC > 0.906 for the total group. However, the ICC values for posterior corneal power, astigmatism magnitude, and J0 and J45 values were lower than 0.681 for the total group. Conclusions The anterior keratometric values obtained by the color light-emitting diode corneal topographer and the dual rotating Scheimpflug–Placido topographer showed high agreement levels, but the posterior keratometric values showed lower agreement levels.

Corneal tomographic features of postrefractive surgery ectasia.

The purpose of this study was to evaluate the tomographic features of postrefractive surgery eyes. This was a retrospective evaluation of clinical data. Three patients with post-LASIK (laser-assisted in situ keratomileusis) and two patients with post-SMILE (small incision lenticule extraction) ectasia were imaged with Scheimpflug imaging (SI, Pentacam) and optical coherence tomography (OCT, RTVue). Curvature and wavefront aberrations of the air-epithelium interface (A-E) and epithelium-Bowman's layer interface (E-B) were derived. OCT of normal and keratoconic eyes from an earlier study were compared with the data of the ectasia eyes. Curvature and aberrometry of the A-E interfaces were statistically similar between SI and OCT. However, OCT revealed a steeper and more aberrated E-B interface than A-E though correlation between them was inferior to the correlation for keratoconic eyes. Furthermore, the magnitude of differences between the A-E and E-B interfaces was greater in the ectasia eyes than the keratoconic eyes. OCT could possibly assist better in selecting appropriate treatment plan for postrefractive surgery ectasia eyes than conventional tomographers.

Corneal collagen crosslinking in patients treated with dextran versus isotonic hydroxypropyl methylcellulose (HPMC) riboflavin solution: a retrospective analysis

BackgroundCorneal collagen crosslinking (CXL) is a widely used treatment for halting the progression of keratoconus. Although initial studies of CXL were performed with a riboflavin solution containing dextran, recent protocols for CXL have indicated the use of a riboflavin solution containing isotonic hydroxypropyl methylcellulose (HPMC). This study was performed to investigate differences in visual outcomes and Scheimpflug (Pentacam) analysis in patients who have undergone epithelium-off CXL with riboflavin solution containing either 20% dextran versus 1.1% HPMC.MethodsAll patients in this non-randomized, non-masked, retrospective cohort analysis were treated at Edward S. Harkness Eye Institute, Columbia University Medical Center, New York, NY, USA. Thirty-seven eyes of 33 patients were crosslinked with a dextran solution and 19 eyes of 19 patients crosslinked with an isotonic HPMC solution, both using an epithelium-off 30-min, 3 mW/cm2 protocol. All patients had a diagnosis of keratoconus or post-refractive surgery ectasia. Best spectacle corrected visual acuity (BSCVA) and Pentacam parameters were compared at all follow up visits (1, 6, 12, and 24 months). Differences between groups treated with HPMC and dextran were compared using student’s t-test. Differences between treated eye and fellow eye were calculated and compared between HPMC and dextran groups using paired t-test.ResultsPatients treated with a dextran solution had significantly greater improvement in BSCVA at 1, 6, and 24 months (p < 0.05) compared to the isotonic HPMC-treated group. Kmax increased in both groups at 1 month; however, HPMC-treated patients had a greater increase compared to dextran-treated patients (p = 0.01). Kmax decreased in both groups at 6 and 12 months, although this finding was only significant in the HPMC-treated group at 12 months.ConclusionsOur data suggest that crosslinking with the dextran solution may result in significantly better visual outcomes (demonstrated by visual acuity) compared to the isotonic HPMC riboflavin solution. Dextran solutions may have other potential advantages intrinsic to its biochemical properties facilitating more efficient crosslinking. Further research and long-term evidence regarding the use of dextran versus HPMC riboflavin solutions in collagen crosslinking is necessary.

Refractive surgery: the most cost-saving technique in refractive errors correction.

To compare the lifetime and annual economic burden of spectacles, contact lenses, and refractive surgery in correction of refractive errors. This is a cross-sectional study with convenience sampling which 120 patients were interviewed in a tertiary referral hospital in the Iranian health care system. The bottom-up based cost of illness approach was estimated using a face-to-face interview to assess the direct and indirect cost of different refractive errors correction of any correction technologies. Correction with spectacle imposes a total direct cost of US dollar (US$) 342.5 (±8.41) per year and US$9373.5 (±230.1) per lifetime to each patient. These figures for the contact lenses were obtained US$198.3 (±0.12) and US$5203.1 (±256.3) and for refractive surgery were obtained US$19.1 (±1.2) and US$568.1 (±64.6), respectively. Overall, based on age-adjusted prevalence rates, astigmatism had the highest share of refractive errors economic burden with a lifetime direct cost of slightly less than US$5.49 billion, while hyperopia and myopia imposed less than US$5.24 and 4.2 billion on patients, respectively. The annually imposed cost on each individual Iranian patient with refractive errors is US$308.5. Based on 18mo post refractive surgery course observation, which is generalized to whole life, refractive surgery significantly imposed much less cost compared with spectacles and contact lenses. Refractive errors among Iranians result in considerable economic burden. Using the refractive surgery instead of other two correction methods has the ability to reduce this economic loss in the future.

Repeatability of automatic measurements by a new anterior segment optical coherence tomographer combined with Placido topography and agreement with 2 Scheimpflug cameras

To evaluate the repeatability of automatic measurements by a new anterior segment optical coherence tomographer (AS-OCT) combined with Placido topography and their agreement with those provided by 2 rotating Scheimpflug cameras. G.B. Bietti Foundation IRCCS, Rome, Italy. Evaluation of a diagnostic test instrument. Unoperated eyes and eyes with previous myopic excimer laser surgery were analyzed. Three consecutive scans were acquired with an AS-OCT device (MS-39) and 1 with 2 rotating Scheimpflug cameras (Pentacam HR and Sirius). The following parameters were evaluated: simulated keratometry, posterior and total corneal power, total corneal astigmatism, corneal asphericity, thinnest corneal thickness, central epithelial thickness, corneal diameter, and aqueous depth. Repeatability was assessed using test-retest variability, the coefficient of variation (CoV), and the intraclass correlation coefficient; agreement was assessed by the 95% limits of agreement. The study comprised 96 unoperated eyes and 43 eyes with previous myopic excimer laser surgery. High repeatability was achieved in both groups, as shown by a CoV less than 1.0% for most parameters. The repeatability of epithelial thickness was slightly lower than that of the whole corneal thickness, although the CoV was still good (1.87% in unoperated eyes; 3.28% in post-refractive surgery eyes). Moderate repeatability was found for total corneal astigmatism measurements, with a CoV greater than 20.0%. Agreement with Scheimpflug cameras was high for aqueous depth and thinnest corneal thickness and moderate for most other parameters. The high repeatability of automatic measurements by the new AS-OCT device supports its use in clinical practice.

High-dose dietary Riboflavin and direct sunlight exposure in the treatment of keratoconus and post-refractive surgery ectasia

High-dose dietary Riboflavin and direct sunlight exposure in the treatment of keratoconus and post-refractive surgery ectasia

Calculation of Unknown Preoperative K Readings in Postrefractive Surgery Patients

Purpose To determine the unknown preoperative K readings (Kpre) to be used in history-based methods, for intraocular lens (IOL) power calculation in patients who have undergone myopic photorefractive keratectomy (PRK). Methods A regression formula generated from the left eyes of 174 patients who had undergone PRK for myopia or for myopic astigmatism was compared with other methods in 168 right eyes. The Pearson index and paired t-test were utilized for statistical analysis. Results The differences between Kpre and those obtained with the other methods were as follows: 0.61 ± 0.94 D (range: −3.94 to 2.05 D, p < 0.01) subtracting the effective treatment, 0.01 ± 0.86 D (range: −2.61 to 2.34 D, p = 0.82) with Rosa's formula, −0.02 ± 1.31 D (range: −3.43 to 3.68 D, p = 0.82) with the current study formula, and −0.43 ± 1.40 D (range: −3.98 to 3.12 D, p < 0.01) utilizing a mean K (Km) of 43.5 D. Conclusions These formulas may permit the utilization of history-based methods, that is, the double-K method in calculating the IOL power following PRK when Kpre are unknown.

Assessment of meibomian glands and tear film in post‐refractive surgery patients

Corneal refractive surgery may impact meibomian gland and tear film in post-refractive surgery patients. To compare ocular surface parameters between post-refractive surgery patients and normal controls. Cross-sectional single centre study. A total of 120 eyes of 120 subjects were divided into three groups: (i) 60 controls and 60 patients underwent corneal refractive surgery at least 12 months ago; (ii) 30 post-laser in-situ keratomileusis (LASIK) patients and (iii) 30 post-laser epithelial keratomileusis (LASEK)/photo-refractive keratectomy (PRK) patients. Tear meniscus height, non-invasive keratographic tear film break-up time and meibography were measured using the Keratograph® 5M. Fluorescein break-up time, ocular surface staining, examination of lid margins and meibomian glands, Schirmer's test and Ocular Surface Disease Index questionnaire were performed. Ordinary logistic regression was performed to evaluate the impact of clinical variables including refractive surgery on the meiboscores. In post-LASIK patients, ocular surface parameters including Ocular Surface Disease Index scores, fluorescein break-up time and staining scores, except Schirmer's scores, were significantly worse than those in controls (P < 0.050). Ocular surface staining scores in post-LASEK/PRK patients was higher than that in the controls (P = 0.001). In post-refractive surgery patients, grade of meibomian gland parameters and meiboscores were worse than those of controls (all P < 0.050). Histories of refractive surgery were associated with high meiboscore (β = 1.100, P = 0.043 for LASIK and β = 1.039, P = 0.042 for LASEK/PRK). Corneal refractive surgery may adversely affect the ocular surface, and a reduction of functional meibomian glands can contribute to chronic tear film dysfunction after corneal refractive surgery.

Calculation of IOL power after refractive surgery

The purpose of this article is to identify and describe the methods used nowadays to calculate intraocular lens (IOL) power in post refractive surgery patients. All the reasons why the standard way of calculating IOL power do not work in post refractive surgery patients are analysed. Moreover, other formulas that can calculate the IOL power are described. The importance for the surgeon to understand the advantages and limitations of each method is stressed. The necessity of new, even more accurate methods to exist is also pointed out.

The Effect of Corneal Refractive Surgery on Glaucoma.

Laser-assisted refractive procedures have become very popular in the last two decades. As a result, a “generation” of patients with altered corneal properties is emerging. These patients will require both cataract extraction and glaucoma follow-up in the future. Since the glaucoma examination largely depends on the corneal properties, the reshaped postrefractive surgery cornea poses a challenge in the diagnosis, follow-up, and management of the glaucomatous patient. In order to overcome this problem, every patient who is planned to undergo corneal refractive surgery must have a thorough glaucoma examination in order for the ophthalmologist to be able to monitor their patients for possible glaucoma development and/or progression. Some examinations such as tonometry are largely affected by the corneal properties, while others such as the evaluation of the structures of the posterior pole remain unaffected. However, the new imaging modalities of the anterior segment in combination with the most recent advances in tonometry can accurately assess the risk for glaucoma and the need for treatment.

Progress in Modern Cataract Surgery – New Steps and Algorithms for Precise Measuring and Intraocular-lens Calculations

In standard cataract surgery, one of the major goals is to reach target refraction. Based on keratometry measurements, axial length and anterior chamber depth, most of the intraocular lens calculation formulae are suitable to achieve this aim. Further evaluation of corneal refractive parameters like anterior and posterior corneal surface by Scheimpflug devices led to a significant enhancement of precision in astigmatic and post-refractive surgery cases.

The Enigmatic Cornea and Intraocular Lens Calculations: The LXXIII Edward Jackson Memorial Lecture

To review the progress and challenges in obtaining accurate corneal power measurements for intraocular lens (IOL) calculations. Personal perspective, review of literature, case presentations, and personal data. Through literature review findings, case presentations, and data from the author's center, the types of corneal measurement errors that can occur in IOL calculation are categorized and described, along with discussion of future options to improve accuracy. Advances in IOL calculation technology and formulas have greatly increased the accuracy of IOL calculations. Recent reports suggest that over 90% of normal eyes implanted with IOLs may achieve accuracy to within 0.5 diopter (D) of the refractive target. Though errors in estimation of corneal power can cause IOL calculation errors in eyes with normal corneas, greater difficulties in measuring corneal power are encountered in eyes with diseased, scarred, and postsurgical corneas. For these corneas, problematic issues are quantifying anterior corneal power and measuring posterior corneal power and astigmatism. Results in these eyes are improving, but 2 examples illustrate current limitations: (1) spherical accuracy within 0.5 D is achieved in only 70% of eyes with post-refractive surgery corneas, and (2) astigmatism accuracy within 0.5 D is achieved in only 80% of eyes implanted with toric IOLs. Corneal power measurements are a major source of error in IOL calculations. New corneal imaging technology and IOL calculation formulas have improved outcomes and hold the promise of ongoing progress.

Comparison of the visual acuity after photorefractive keratectomy using Early Treatment Diabetic Retinopathy Study Chart and E-chart

PurposeTo compare the visual responses of post refractive surgery's patients using Early Treatment Diabetic Retinopathy Study Chart (ETDRS) and E-chart with and without color filters. MethodsThe uncorrected Logarithm of the Minimum Angle of Resolution Visual Acuity (LogMAR VA) of 70 patients with a mean age of 26.2 ± 3.76 years (from 19 to 34 years) who had undergone Photorefractive Keratectomy (PRK) (the range of post operation refractive error: ±0.5 D) was measured under the light conditions of with and without asymmetrical glare by using red, green, and yellow filters and ETDRS chart and E-chart. ResultsIn both light conditions of with and without glare, the mean visual acuity of the three filters in the right and left eyes was significantly better with the E-chart versus the ETDRS chart (P < 0.0001). Only in the glare light condition, the mean visual acuity of the left eye showed no significant difference between the two charts using the red filter (P = 0.30). ConclusionsVisual acuity measurements were different with ETDRS chart and E-chart. These two charts cannot be used interchangeably.

Cornea donors who have had prior refractive surgery: data from the Eye Bank Association of America.

Millions of Americans have undergone refractive surgeries, including radial keratotomy, photorefractive keratectomy, and laser-assisted in situ keratomileusis. Eye Bank Association of America medical standards do not permit corneas from patients who have undergone refractive procedures to be used in penetrating keratoplasty, anterior lamellar keratoplasty, or tectonic grafting procedures. Such corneas, can, however, be used for endothelial corneal transplantation. The objective of this article is to provide an update on current trends for the screening and usage of corneas that have undergone refractive surgery. Several case reports have highlighted the difficulty in using postrefractive surgery corneas in penetrating keratoplasty. However, tissue with anterior stromal flaws, including a history of refractive surgery, has been used in endothelial keratoplasty with equivalent outcomes in topography, endothelial cell count, and visual acuity. Many modalities for proper identification of postmortem donor corneas that have undergone refractive surgery have been studied. Corneas with a history of refractive surgery have found use in endothelial keratoplasty. Multiple objective methods of tissue identification have been investigated to avoid the use of these corneas in penetrating or anterior keratoplasty surgeries.

Prevention of Iatrogenic Keratectasia.

Iatrogenic corneal ectasia is a rare but devastating complication after refractive surgery. While its incidence appears to be declining, it has not been eliminated. Its cause is probably related to a combination of an intrinsic predisposition to ectasia and an additional anatomical destabilising effect from the refractive surgery. Determining which eyes are intrinsically "weak" and exactly how much additional "weakening" an eye can withstand before developing progressive thinning and protrusion are both difficult tasks. The essentially universal availability of corneal topography and the increasing use of corneal tomography have significantly improved our ability to preoperatively diagnose early forms of corneal ectasias, especially keratoconus and pellucid marginal degeneration. Advanced software algorithms have also enhanced the sensitivity and specificity of these technologies. Newer technologies, such as measuring corneal biomechanics and corneal epithelial distribution, will hopefully continue to help us to differentiate normal from abnormal corneas preoperatively. In addition to abnormalities in anterior and posterior corneal curvature, a number of other risk factors for the development of post-refractive surgery ectasia have been proposed, including younger patient age, thinner central corneal thickness, thinner residual stromal bed thickness and high myopia. If the percentage of altered tissue is > 40 %, this is an extremely accurate predictor of corneal ectasia after refractive surgery. While there are a number of effective treatments for iatrogenic corneal ectasia, such as contact lenses, corneal crosslinking, intracorneal rings and corneal transplantation, prevention should be the goal. With newer and better corneal imaging technology to help screen out patients with abnormal corneas along with an improved understanding of exactly how much weakening a given cornea can take, we should be able to minimize this vision threatening complication.

Combined effects of interleukin-1β and cyclic stretching on metalloproteinase expression in corneal fibroblasts in vitro.

BackgroundCorneal tensile strain increases if the cornea becomes thin or if intraocular pressure increases. However, the effects of mechanical stress on extracellular matrix (ECM) remodelling in the corneal repair process and the corneal anomalies are unknown.MethodsIn this study, the combined effects of interleukin-1β (IL-1β) on matrix metalloproteinases (MMPs) in corneal fibroblasts under cyclic stretching were investigated in vitro. Cultured rabbit corneal fibroblasts were subjected to 5, 10 or 15 % cyclic equibiaxial stretching at 0.1 Hz for 36 h in the presence of IL-1β. Conditioned medium was harvested for the analysis of MMP2 and MMP9 protein production using the gelatin zymography and western blot techniques.Results and conclusionsCyclic equibiaxial stretching changed the cell morphology by increasing the contractility of F-actin fibres. IL-1β alone induced the expression of MMP9 and increased the production of MMP2, and 5 % stretching alone decreased the production of MMP2, which indicates that a low stretching magnitude can reduce ECM degradation. In the presence of IL-1β, 5 and 10 % stretching increased the production of MMP2, whereas 15 % stretching increased the production of MMP9. These results indicate that MMP expression is enhanced by cyclic mechanical stimulation in the presence of IL-1β, which is expected to contribute to corneal ECM degradation, leading to the development of post-refractive surgery keratectasia.

ZDRAVLJENJE OKUŽB ROŽENICE S PREČNIM POVEZOVANJEM KOLAGENIH VLAKEN

Corneal collagen cross-linking increases the stability of the cornea through the use of the photosensitive material - riboflavin (vitamin B2) and ultraviolet A radiation. Progressive keratoconus is the most common indication and the frequency of these procedures is increasing worldwide. As cross-links in the cornea are a physiological principle of all connective tissue, additional indications were proposed. These include postrefractive surgery ectasia, bullous keratopathy, and, infectious keratitis.Infectious keratitis can lead to blindness without proper antimicrobial therapy. But even prompt initial management, with appropriate antimicrobial treatment, can be subjected to microorganism sensitivity and resistance.This article presents current data regarding the use of corneal collagen cross-linking in the treatment of corneal infections. This treatment modality may become important, but unanswered questions remain. Larger, prospective comparative studies should give the answers.

Accuracy of the Barrett True-K formula for intraocular lens power prediction after laser in situ keratomileusis or photorefractive keratectomy for myopia

To compare the accuracy of the Barrett True-K formula with other methods available on the American Society of Cataract and Refractive Surgery (ASCRS) post-refractive surgery intraocular lens (IOL) power calculator for the prediction of IOL power after previous myopic laser in situ keratomileusis (LASIK) or photorefractive keratectomy (PRK). Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, and private practice, Mesa, Arizona, USA. Retrospective case series. The accuracy of the Barrett True-K formula was compared with the Adjusted Atlas (4.0 mm zone), Masket, modified-Masket, Wang-Koch-Maloney, Shammas, and Haigis-L methods to calculate IOL power. A separate analysis of 2 no-history methods (Shammas and Haigis-L) was performed and compared with the Barrett True-K no-history option. Eighty-eight eyes were available for analysis. The Barrett True-K formula had a significantly smaller median absolute refraction prediction error than all other formulas except the Masket, smaller variances compared with the Wang-Koch-Maloney, Shammas, and Haigis-L, and a greater percentage of eyes within ±0.50 diopter (D) of predicted error in refraction compared with the Adjusted Atlas, Masket, and modified Masket methods (all P < .05). In eyes with no historical data, the Barrett True-K no-history formula had a significantly smaller median absolute refraction prediction error and a greater percentage of eyes within ±0.50 D of the predicted error in refraction than the Shammas and the Haigis-L formulas (both P < .05). The Barrett True-K formula was either equal to or better than alternative methods available on the ASCRS online calculator for predicting IOL power in eyes with previous myopic LASIK or PRK.

Repeatability of posterior and total corneal curvature measurements with a dual Scheimpflug–Placido tomographer

To evaluate the repeatability of the Galilei G4 dual Scheimpflug analyzer in measuring simulated keratometric, total, and posterior corneal curvature in normal and post-refractive surgery eyes. Cullen Eye Institute, Baylor College of Medicine, Houston, Texas, USA. Prospective evaluation of diagnostic technology. A single observer performed 3 consecutive measurements in 1 eye of each subject. The following were evaluated in both eyes and in eyes that had previous myopic excimer-laser surgery: (1) simulated keratometric corneal power and astigmatism, (2) total corneal power and astigmatism, and (3) posterior corneal power and astigmatism. Repeatability was assessed by calculating the within-subject standard deviation (Sw), coefficient of variation (CoV), and intra-class correlation coefficient (ICC). The study evaluated 41 normal eyes and 36 post-refractive surgery eyes. In normal eyes, the Sw was 0.08 diopters (D), 0.10 D, and 0.03 D for simulated keratometric, total, and posterior corneal power, respectively. The CoV ranged from 0.16% to 0.40%, and the ICC was 0.992 or more (P < .001) for all corneal powers. In post-refractive surgery eyes, the Sw was 0.09 D, 0.09 D, and 0.02 D for simulated keratometric, total, and posterior corneal power, respectively. The CoV ranged from 0.19% to 0.32%, and the ICC was 0.990 or more (P < .001) for all corneal powers. For posterior corneal astigmatism, the ICC was 0.814 and 0.886 for normal and post-refractive surgery eyes, respectively. In normal corneas and corneas that had undergone myopic excimer laser ablation, the dual Scheimpflug analyzer showed high intra-observer repeatability for simulated keratometric, total, and posterior corneal power measurements and moderate repeatability for posterior corneal astigmatism. Drs. Koch, Weikert, and Wang received research support from Ziemer USA, Inc. No other author has a financial or proprietary interest in any material or method mentioned.