Effect of Astigmatism Treatment With Three Excimer Lasers After Photorefractive Keratectomy.

OBJECTIVES: To compare astigmatism correction after photorefractive keratectomy (PRK) using three excimer laser devices, Alcon Wavelight EX500, Schwind Amaris 1,050, and Technolas Teneo317 M2. METHODS: This retrospective study included 414 eyes from 414 subjects with a history of PRK performed using Alcon Wavelight (n=172), Schwind Amaris (n=122), and Technolas (n=120). Uncorrected & corrected distance visual acuity (UDVA & CDVA), and refractive status (spherical equivalent (SE) and vector analysis (J0 and J45)) were postoperatively recorded at the 6-month and 12-month examinations. RESULTS: The mean CDVA and J45 at 6-month and 12-month showed no statistically significant difference among the three different excimer lasers (P>0.05). There was a statistically significant difference in mean UDVA and J0 at 6-month and 12-month after PRK among the three groups, with no statistically significant difference between Alcon Wavelight and Schwind Amaris lasers, while both of the prior lasers showed a significant difference with the Technolas laser. The highest and lowest changes in the magnitude of J0 in 6-month and 12-month follow-ups were seen for the Alcon Wavelight and Technolas groups, respectively. Both Schwind Amaris and Technolas had a small hyperopic SE while the Alcon Wavelight's SE was minimally myopic. This difference in SE between Alcon Wavelight and both Schwind Amaris and Technolas reached statistical significance. CONCLUSION: While all three lasers performed well in reducing preoperative astigmatism; however, the Alcon Wavelight and Schwind Amaris were more effective in correcting astigmatism than the Technolas. The difference between the Alcon Wavelight and Schwind Amaris did not reach statistical significance.

Comparison of corneal biomechanical parameters in healthy corneas with symmetric and asymmetric bow-tie topographic pattern with inferior and superior steepening.

PURPOSE: To compare the corneal biomechanical parameters in healthy corneas with symmetric and asymmetric bow-tie topographic patterns. METHODS: In this cross-sectional study, 144 eyes were divided based on inferior-superior asymmetry value (I-S) into symmetric (zero I-S: - 0.50 to + 0.50 D) and asymmetric bow-tie topographic patterns with inferior (positive I-S: + 0.51 to + 1.4 D) or superior (negative I-S: - 2.5 to - 0.51 D) steepening. The biomechanical assessment was performed using Corvis ST and ocular response analyzer (ORA). A general linear model univariate analysis was used to compare the parameters, while the central corneal thickness, intraocular pressure, and age were considered covariates. RESULTS: Only the peak distance (PD) at the highest concavity phase (P = 0.007) and tomographic biomechanical index (TBI, P = 0.001) showed statistically significant differences between the three groups. For TBI, this difference was statistically significant between the positive I-S group separately with the zero I-S group (P < 0.001), and with the negative I-S group (P = 0.022). For PD, the significant difference was between the negative I-S group separately with zero I-S (P = 0.019), and positive I-S groups (P = 0.018). There was a statistically significant correlation between the I-S value with PD (r = 0.281, P = 0.001) and TBI (r = 0.170, P = 0.044). CONCLUSIONS: Most corneal biomechanical parameters are not statistically significant compared to the zero I-S group. However, superior steepening is associated with a stiffer response based solely on the shorter PD values seen in this group, and the group with the inferior steepening shows the highest or more suspicious values based on TBI.

Recurrent Keratoconus: Corneal Transplants for Keratoconus Develop Tomographic Ectatic Changes.

PURPOSE: The purpose of this study was to evaluate postoperative Scheimpflug imaging changes during the first 5 years after penetrating keratoplasty (PK) in patients with keratoconus (KC). METHODS: This retrospective, interventional case series includes 31 eyes of 31 patients who underwent their first PK with a history of KC. Postoperative Scheimpflug imaging was performed 3 months after the removal of the last suture (baseline) and then repeated 3 and 5 years after the PK. Demographic data, donor and host trephination diameter, and Scheimpflug imaging (Pentacam HR, Oculus, Germany) parameters indicative of ectasia were analyzed to evaluate postoperative graft changes that occur after PK. RESULTS: The maximal keratometry (Kmax) progressed significantly between baseline (53.5 ± 6.1 D) and postoperative year 3 and year 5 [56.5 ± 6.1 diopter (D) and 58.8 ± 7.9 D, P < 0.001]. Significant changes were also observed for the anterior best fit sphere and posterior best fit sphere ( P < 0.001 for 3 and 5 years compared with baseline). Kmax increased by at least 2 Ds for 74.2% of patients and up to 7 Ds or more for 25.8% of the patients. A significant inverse correlation was observed for host trephine size and progression of Kmax (r = -0.52, P = 0.01), which indicated that larger host trephination size was associated with a smaller increase in postoperative Kmax. CONCLUSIONS: Tomographic graft changes indicative of ectasia were observed within 3 to 5 years after PK in patients with KC. These changes were observed more frequently and sooner after corneal transplants than previously reported.

Reliability analysis of successive Corvis ST® measurements in keratoconus 2 years after accelerated corneal crosslinking compared to untreated keratoconus corneas.

PURPOSE: To assess the reliability of successive Corvis ST® measurements (CST, Oculus, Wetzlar, Germany) in keratoconus (KC) ≥ 2 years after accelerated corneal crosslinking (9 mW/cm2, 10 min, 5.4 J/cm2) compared to untreated KC corneas. METHODS: Three successive CST measurements per eye were performed in ≥ 2 years after CXL (CXLG, n = 20 corneas of 16 patients) and a control group consisting of non-operated, ABC-stage-matched KC corneas according to Belin's ABCD KC grading (controls, n = 20 corneas, 20 patients). Main outcome measures included maximal keratometry (Kmax), the Belin/Ambrósio-Enhanced-Ectasia-Deviation-Index BAD-D; the biomechanical parameters A1 velocity, deformation amplitude (DA) ratio 2 mm, Ambrósio relational thickness to the horizontal profile (ARTh), integrated radius, stiffness parameter A1 (SP-A1), and the Corvis Biomechanical Factor (CBiF, the linearized term of the Corvis Biomechanical Index). Mean values, standard deviations, and Cronbach's alpha (CA) were calculated. RESULTS: Both groups were tomographically comparable (BAD: 11.5 ± 4.7|11.2 ± 3.6, p = 0.682, Kmax: 60.5 ± 7.2|60.7 ± 7.7, p = 0.868 for controls|CXLG, paired t-test). A1 velocity (mean ± SD: 0.176 ± 0.02|0.183 ± 0.02, p = 0.090, CA: 0.960|0.960), DA ratio 2 mm (6.04 ± 1.13|6.14 ± 1.03, p = 0.490, CA: 0.967|0.967), integrated radius (12.08 ± 2.5|12.42 ± 1.9, p = 0.450, CA: 0.976|0.976), and CBiF (4.62 ± 0.6|4.62 ± 0.4, p = 0.830, CA: 0.965|0.965) were also comparable (controls|CXLG). ARTh was significantly higher in controls (177.1 ± 59, CA: 0.993) than after CXL (155.21 ± 65, p = 0.0062, CA: 0.993) and SP-A1 was significantly higher after CXL (59.2 ± 13, CA: 0.912) than in controls (52.2 ± 16, p = 0.0018, CA: 0.912). CONCLUSION: ARTh and SP-A1 differed significantly between controls and CXLG. Biomechanical measurements were generally of excellent reliability in both groups. CXL seems to affect biomechanical measurements of human corneas over more than 2 years.

EpiSmart Crosslinking for Keratoconus: A Phase 2 Study.

PURPOSE: The aim of this study was to assess changes in visual acuity after epithelium-on ("epi-on") corneal crosslinking after a diagnosis of keratoconus. METHODS: Subjects with corneal ectatic diseases were enrolled in a prospective, randomized, controlled, open-label, multicenter trial. Subjects were randomized to 1 of 3 treatment groups and treated with an epi-on crosslinking system including riboflavin/sodium iodide and pulsed UVA exposure (EpiSmart, CXL Ophthalmics, Encinitas, CA). The UVA treatment groups were 2.4 J/cm 2 over 20 minutes, 3.6 J/cm 2 over 20 minutes, and 3.6 J/cm 2 over 30 minutes. The primary end point was logarithm of the minimum angle of resolution corrected distance visual acuity (CDVA). Secondary end points were logarithm of the minimum angle of resolution uncorrected distance visual acuity (UCVA), maximum corneal curvature (Kmax), and minimum corneal thickness. Data were assessed 6 and 12 months post-operatively, using t -tests for differences from baseline. RESULTS: Two thousand two hundred twenty-eight subjects were treated with epi-on crosslinking. One thousand nine hundred twenty-two subjects had a diagnosis of keratoconus; other treated eyes had postsurgical and other ectasias. At 6 and 12 months, the subjects with keratoconus demonstrated significant improvements in CDVA, UCVA, and Kmax; minimum corneal thickness was unchanged. One hundred ninety-five subjects (8.7%) reported at least 1 adverse event (AE). A mild corneal epithelial defect was reported in 31 cases (1.4%) and was the only AE reported in >1% of subjects. There were no serious AEs related to the treatment. CONCLUSIONS: EpiSmart epi-on crosslinking resulted in mean improvements in CDVA, UCVA, and Kmax at both 6 and 12 months and an excellent safety and efficacy profile in subjects with keratoconus, with few significant side effects. Differences between UVA treatment groups were not significant.

Acute Hydrops with Total Corneal Edema in a Very Young Child with Keratoconus: The Youngest Age Reported Case.

Purpose: To present the youngest age ever reported for acute corneal hydrops with total corneal edema in a child with advanced bilateral keratoconus. Methods: Patient presentation in ophthalmic clinic. The patient underwent various clinical tests and examinations including anterior segment optical coherence tomography (AS-OCT) and Scheimpflug corneal tomography. Results: A 5-year-old girl presented with uncorrected distance visual acuity (UDVA) of 0.4 in the right eye and nonmeasurable UDVA associated with severe photophobia in her left eye of a 3-day duration. Intraocular pressure using the iCare tonometer was 14 and 5 mmHg in the right and left eyes, respectively. An old corneal hydrops scar and posterior subcapsular cataract (PSC) in the right eye and a total limbus to limbus corneal hydrops in the left eye were observed on slit-lamp examinations. Scheimpflug corneal tomography was possible in the right eye but, due to excessive irregularity and scaring, was not possible in the left eye. Corneal thinning and scarring were evident in the anterior segment optical coherence tomography in the right eye and very edematous cornea associated with stromal cleft and epithelial bullae in the left eye. A management plan consisting of topical hypertonic solution and ointment was started to reduce her symptoms. Conclusion: Acute corneal hydrops may be the presenting sign of keratoconus; however, extensive hydrops involving the total cornea area at a very young age is very rare and has not been previously reported in the literature.

Pachymetric Assessment After EpiSmart® Epithelium-on Cross-Linking for Keratoconus and Post-Surgical Ectasia.

Purpose: To assess the change in corneal pachymetry after a novel epithelium-on (EpiSmart®) corneal crosslinking procedure (CXL). Methods: Eyes treated as part of the open-label, non-controlled arm of the study "Collagen Crosslinking with Ultraviolet-A in Asymmetric Corneas" (NCT01097447) were examined at baseline, 3-, 6- and 12-months post-CXL. Thinnest pachymetry readings based on Pentacam (OCULUS GmbH, Wetzlar, Germany) were recorded. Results: A total of 101 eyes met the study inclusion criteria. Thinnest pachymetric readings at baseline averaged 451 ± 50 microns. The mean (± SD) minimum thickness was 450 ± 46 microns at 3 months, 452 ± 47 microns at 6 months, and 451 ± 48 microns at 12 months post-CXL. The changes from baseline (mean ± SE) at 3, 6, and 12 months post-CXL were -1.2 ± 1.5 microns, 0.5 ± 1.6 microns, and 0.4 ± 1.6 microns, respectively. Student's t-tests showed no statistically significant change in pachymetry from baseline for any exam period. Conclusion: This study demonstrated that, after EpiSmart® epithelium-on CXL, there was no substantial corneal thinning observable on Scheimpflug tomography out to 12 months.

Keratoconus: Diagnosis and Staging.

ABSTRACT: The advent of refractive surgery and corneal cross-linking for ectatic disease has further highlighted the need to recognize early or subclinical ectatic disease. Historical systems depend on anterior corneal changes that occur late in the disease course and are commonly associated with visual loss. Tomographic imaging allows for the acquisition of posterior corneal surface data and corneal thickness distribution. This led to the development of modalities to diagnose early or subclinical keratoconus and to screen patients for refractive surgery.This article reviews the modern methods for assessing changes in posterior corneal surface and pachymetric distribution, now accepted by the major cornea societies to be the hallmarks of ectatic disease. Screening tools utilized by the commonly used tomographic imaging devices are discussed, and the difference between screening for ectasia and diagnosing keratoconus is highlighted. The Belin ABCD staging and classification system and the ABCD Progression Display are reviewed as a new grading and monitoring system that can be used for earlier intervention and prevention of visual loss in keratoconus.

Implications of Diagnostic Drops on Scheimpflug Tomography: The Proper Order for Clinical Testing.

PURPOSE: The purpose of this article was to study the impact of instillation of 1% fluorescein and mydriatics on measurements made by Scheimpflug imaging. METHODS: This was a cross-sectional study of patients who had measurements of corneal shape (maximum keratometry and best fit sphere of anterior and posterior corneal surfaces), pachymetry (at the pupil center, corneal apex, and thinnest location), and anterior chamber parameters (depth, volume, and angle of anterior chamber and corneal volume) using the Pentacam HR before and after the instillation of fluorescein and mydriatics. Group A had baseline measurements that were repeated 1.5 hours after the instillation of 1% fluorescein and 0.8% tropicamide+ 5% phenylephrine eye drops. Group B had baseline measurements that were repeated 10 minutes after the instillation of 1% fluorescein, and group C had baseline measurements that were repeated 1.5 hours after the instillation of mydriatics. RESULTS: Overall, 131 eyes of 131 patients were studied: 87 in group A, 28 in group B, and 16 in group C. Significant differences and wide variations were noted in corneal pachymetry and anterior chamber parameters in all 3 groups. The highest magnitude and range of difference was observed in pachymetry at the pupil center (17 ± 53.5 µm) and in anterior chamber volume (26.7 ± 69.8 mm 3 ). Corneal shape measurements of anterior and posterior corneal surfaces were not significantly affected by either fluorescein or mydriatics. Pupillary dilation also affected the ability of the Pentacam to accurately trace the pupil margin in 19.5% of cases. CONCLUSIONS: For consistent and accurate measurements, it is important that Scheimpflug imaging be performed before other tests which may need the instillation of fluorescein or mydriatics.

Corneal Stability and Visual Acuity 1 Year After Corneal Cross-linking Assessed Using the ABCD Keratoconus Staging System.

PURPOSE: To assess corneal stability and corrected distance visual acuity (CDVA) 3, 6, and 12 months following corneal cross-linking (CXL) using the ABCD keratoconus staging system. METHODS: This prospective longitudinal study included 31 eyes with keratoconus receiving CXL based on the standard Dresden protocol. CDVA, refraction, and Scheimpflug tomography with the Pentacam HR (Oculus Optikgeräte GmbH) were evaluated before and after surgery. Geometric and functional changes were assessed using the actual values and staging of each element of the ABCD keratoconus staging system. A, B, C, and D refer to the anterior and posterior radii of curvature in a 3-mm zone centered on the cor-neal thinnest point, minimum corneal thickness, and CDVA, respectively. RESULTS: There were no significant changes in the actual values of anterior radius of curvature (P = .497) and CDVA (P = .082), whereas posterior radius of curvature (P = .007) and corneal thinnest point (P < .001) showed significant changes statistically. Pairwise comparison showed only a statistically significant steepening in posterior radius of curvature at 3 months after CXL compared to the preoperative radius (P = .002) and a significant decrease in corneal thinnest point at 3 (P < .001) and 6 (P = .028) months after CXL compared to baseline assessment. Staging of each element of the ABCD keratoconus staging system indicated no change between baseline and 3, 6, and 12 months after CXL. CONCLUSIONS: The geometric and functional parameters included in the ABCD keratoconus staging system showed stability of corneal status and CDVA 1 year after CXL. [J Refract Surg. 2021;37(10):700-706.].

Comparison of Keratoconus Cone Location of Different Topo/tomographical Parameters.

Purpose: To compare the corneal cone location on different maps and instruments, and their agreements, with elevation maps.Methods: In 90 left eyes with bilateral keratoconus, the apex of cone location was determined based on the maximum simulated keratometry (Kmax) location on the anterior sagittal curvature map by Pentacam HR, the maximum curvature on the mean curvature map by ATLAS 9000, most elevated point of the island of positive elevation relative to the best fit sphere on the front and back corneal elevation maps by Pentacam HR, and thinnest point on the thickness map by Pentacam HR and Orbscan, and the thinnest points on pachymetry and epithelial thickness maps by RTVue OCT.Results: There was a significant difference among the location on different maps along the x- and y-axes (p < .001). The lowest agreement with the cone apex on both front and back elevation maps was for the anterior sagittal curvature map and the highest agreement for the Pentacam thickness map. The majority of keratoconus cone apexes were displaced in the inferotemporal direction on the different maps except for the epithelial thickness maps.Conclusions: Despite the variability between different devices and methods; the thickness map on the Pentacam HR showed the highest correlation with the front and back elevation maps, while the RTVue epithelial thickness map showed the poorest correlation. Based on this study, epithelial thickness maps and anterior curvature maps should be utilized with caution to determine the location of the cone.

Outcomes of Conductive Keratoplasty Combined with Corneal Crosslinking in Advanced Ectatic Corneal Disease.

PURPOSE: To assess the effectiveness of a novel treatment for patients with advanced corneal ectasia and loss of visual acuity (VA). Conductive keratoplasty (CK) is performed to improve VA followed by epithelium-on (epi-on) corneal crosslinking (CXL) to stabilize the cornea after CK. METHODS: Retrospective, exploratory cohort study. Patients with keratoconus or postsurgical ectasia and best spectacle-corrected distance VA (CDVA) ≤ 20/40 were included. Conductive keratoplasty was performed (ViewPoint CK System, Refractec, Inc., Bloomington, MN); followed a day later by epi-on CXL (CXLUSA/CXLO, Bethesda, MD/CXLO Encinitas, CA). Measures included uncorrected distance visual acuity (UDVA) and CDVA, as well as refractive and tomographic measures and tomographic indices. RESULTS: Data from 50 eyes of 45 patients were analyzed. Mean follow-up was 15.1 ± 12.2 months (range: 2 to 51). Overall, UDVA and CDVA improved postoperatively. Subjective refraction and tomographic metrics did not show consistent changes, but changes in tomographic indices were associated with treatment follow-up time. At the 1-year visit, mean UDVA significantly improved over baseline (P = 0.009) by approximately 3 lines; mean CDVA improved significantly (P = 10-5) by approximately 2 lines. No eye lost lines of CDVA. Change in the Index of Surface Variance (ISV) was associated with treatment, and the D-Index trended over follow-up time. CONCLUSION: Conductive keratoplasty with a proprietary epi-on CXL treatment improved vision in patients with advanced ectasia This CK/epi-on CXL treatment offers the possibility of improved VA for patients with compromised vision due to ectasia.

Evaluating keratoconus progression prior to crosslinking: maximum keratometry vs the ABCD grading system.

PURPOSE: To evaluate the correlation between changes in maximum keratometry (Kmax) and ABC values from the ABCD Progression Display (Pentacam) in progressive keratoconus (KC) and to evaluate whether the ABC changes were able to detect progression earlier than Kmax. SETTING: Humanitas Clinical and Research Center, Rozzano, Milan, Italy. DESIGN: Retrospective study. METHODS: Kmax, ABC values, and thinnest point (ThCT) were recorded at the day of corneal crosslinking (CXL) (T0) and previous follow-up (T-1). In patients without earlier progression in Kmax, follow-up examination (T-2) was used to determine whether any of the ABC parameters reached statistical significance for progression. RESULTS: Seventy-six eyes of 63 patients scheduled for CXL with documented progression (Kmax increase of >1.00 diopter) were included. There was a significant, albeit moderate, correlation between the change in Kmax between T0 and T-1 and the change in both A (ρ = 0.391) and B values (ρ = 0.339). There was no significant correlation between the change in Kmax between T0 and T-1 and the change in either C or ThCT. In patients with T-2 examinations, 16 (51.6%) of 31 patients showed a statistically significant change on the ABCD progression display that was not detected with Kmax. CONCLUSIONS: This study showed a significant, but moderate, correlation between the change in Kmax and the change in A and B values in progressive KC. Moreover, more than half of the cases showed documented progression earlier with the ABCD progression display than that detected by standard Kmax changes. This study suggests possible changes in progression criteria to allow for earlier intervention.

Comparative analysis of two different types of intracorneal implants in keratoconus: A corneal tomographic study.

OBJECTIVE: To evaluate changes in visual acuity and corneal tomographic outcomes at 6 months after femtosecond-laser assisted implantation of two different types of intracorneal implants in keratoconus. METHODS: A total of 39 keratoconus eyes implanted with two segments KeraRing (n = 22 eyes) or MyoRing (n = 17 eyes) were enrolled. Tomographic data (Pentacam system, Oculus) were analyzed and correlated with enhancement in uncorrected (UDVA) and corrected distance visual acuity (CDVA). The tomographic indices were front maximum keratometry (Kmax), corneal asphericity (Q-value) on both surfaces, average pachymetric progression indices (PPI), maximum Ambrosio relational thickness (ARTmax), Belin-Ambrósio enhanced ectasia total deviation index (BAD-D), index of surface variance (ISV), vertical asymmetry (IVA), height asymmetry (IHA) and height decentration (IHD). RESULTS: LogMAR UDVA and CDVA improved 2.1 (p = 0.003) and 0.7 (p = 0.074) lines with KeraRing, and 8 and 2.5 lines with MyoRing (p = 0.001). The highest and lowest mean differences in the tomographic indices between both groups were related to ISV and IHD, respectively. Changes in all indices differed significantly between two groups except for changes in front corneal astigmatism, ARTmax, ISV, IVA, IHD and IHA (p > 0.05). Correlation of changes in CDVA with changes in other parameters was statistically significant only for IHD in the KeraRing group, while changes in in UDVA were significantly correlated with changes in spherical equivalent, back Q-value, ISV, IVA, and IHA only in the MyoRing group. CONCLUSION: Both implants promote corneal shape regularization and an enhancement in UDVA in keratoconus. A considerable flattening effect and reduction in prolateness in the front corneal surface were observed with MyoRing.

Extreme corneal flattening following collagen crosslinking for progressive keratoconus.

PURPOSE: To study the clinical, tomographic and densitometric features of eyes that showed >5 D of corneal flattening following collagen crosslinking (CXL) for progressive keratoconus and to identify preoperative predictive factors for such a response. METHODS: This was a retrospective case control study of 548 eyes with progressive keratoconus which had undergone epithelium-off CXL (Dresden protocol) with a follow-up of 1 to 10 years. Eyes that showed ⩾5 D corneal flattening in maximum keratometry (Kmax) following CXL (group A) were compared with one eye of the remaining patients in the same cohort (group B). Changes in refraction and visual acuity, Kmax and thinnest pachymetry were compared between both groups. Univariate and multivariate regression analysis identified preoperative risk factors for unusual corneal flattening. RESULTS: Forty three eyes in group A were compared with 502 eyes in group B. At the time of maximum flattening, group A showed more flattening (-7.6 ± 3.2 D) and thinning (-53.7 ± 45.2 µ) than group B (-1.69 ± 2.9 D and -26.6 ± 36.7 µ, respectively). Multivariate analysis based on parameters suggested by a univariate regression analysis identified pre-op Kmax to be the most significant predictor of intense corneal flattening. A subgroup analysis of K-matched eyes revealed that the duration of time following CXL was a significant risk factor for extreme corneal flattening following CXL. CONCLUSION: An intense corneal flattening >5 D in Kmax was documented in 7.85% of a cohort of keratoconus patients who underwent CXL. High preoperative Kmax and the duration of time following CXL were significant predictors of this response which was accompanied by significant corneal thinning.

Determining Progression in Ectatic Corneal Disease.

Before the advent of modern tomographic imaging and corneal cross-linking (CXL), diagnosis and treatment of ectatic disease were limited to disease severity where changes on the anterior corneal surface lead to visual complaints. Rigid contact lenses and/or penetrating keratoplasty addressed late stage disease, as identifying early or subclinical disease was not possible, or its need appreciated. The emergence of CXL as a viable treatment to alter the natural progression of keratoconus heightened the need for improved diagnostics.Several methods have been described in the literature to evaluate and document progression in keratoconus, but there has been no consistent definition of ectasia progression. Newer imaging techniques (ie, tomography) allowed the detection of earlier ectatic disease, before visual loss and subjective complaints. The Belin ABCD classification/staging system was introduced on a Scheimpflug imaging system [Pentacam, (Oculus GmbH, Wetzlar, Germany)] to address previous shortcomings. The ABCD system utilizes 4 parameters: Anterior ("A") and posterior ("B" for Back) radius of curvature taken from a 3.0 mm optical zone centered on the thinnest point, "C" is minimal Corneal thickness, and "D" best spectacle Distance visual acuity. The first 3 parameters (A, B, C) are machine-generated objective measurements that can be used to determine progressive change.The staging system is not limited to a specific commercial entity and can be incorporated in any tomographic imaging system. The ABCD Progression Display graphically displays each parameter and shows when statistical change above measurement noise is reached. This should allow the clinician the ability to diagnose progressive disease at a much earlier stage than was previously possible, with the confidence that earlier intervention could prevent visual loss.

ABCD: A new classification for keratoconus.

Recent advances in the diagnosis and treatment of ectatic corneal disease have mandated a more modern staging system. The new Belin ABCD keratoconus staging system incorporates anterior and posterior curvature centered on the thinnest point of the cornea, thinnest pachymetry values and distance visual acuity in grades from 0-4. By including posterior curvature and thickness measurements based on the thinnest point, as opposed to apical, the new staging system better reflects anatomical changes seen in keratoconus and other ectatic diseases.

Scheimpflug Corneal Densitometry Changes After the Intrastromal Corneal Ring Segment Implantation.

PURPOSE: To investigate the changes in corneal backward scattering using Scheimpflug tomography (densitometry) 6 months after intrastromal corneal ring segments (Keraring) implant for keratoconus and to correlate with clinical results. METHODS: Along with standard ophthalmic examination, Scheimpflug tomography using Pentacam HR was performed to document corneal densitometry and corneal shape. A densitometry map was displayed using grayscale units (GSUs) ranging from 0 to 100 (minimum to maximum light scattering) in 4 concentric annuluses: central 2-, 2- to 6-, 6- to 10-, 10- to 12-, and total 12-mm corneal diameter and at 3 different depths: anterior 120 µm, posterior 60 µm, middle (varying accordingly to the total thickness), and total thickness. RESULTS: The changes in mean corneal densitometry values for anterior, central, and posterior layers were 3.82 ± 3.13, 2.70 ± 1.78, and 1.68 ± 1.52 GSU, respectively, and for annuluses of 0 to 2, 2 to 6, 6 to 10, and 10 to 12 mm were 2.96 ± 2.60, 4.53 ± 2.28, 2.09 ± 1.74, and 0.45 ± 3.93 GSU, respectively. The mean values increased for all corneal layers (P < 0.05), except in the peripheral 10- to 12-mm annulus (P> 0.05). The highest increase was in the annulus 2 to 6 mm of the anterior layer (5.72 ± 3.70 GSU). Changes in the mean densitometry showed a significant correlation with the mean of average keratometry changes only for the front corneal surface and changes in the Q-values for both corneal surfaces in the 2- to 6-mm annulus for all layers. CONCLUSIONS: Significant increase in the corneal densitometry mainly in the anterior 2- to 6-mm annulus of the cornea is associated with the position of the ring segment implant. More studies are needed to elucidate the relevance of such findings.