Fernando Faria-Correia

Scheimpflug imaging for laser refractive surgery.

Purpose of review To review the principles and clinical applications of Scheimpflug corneal and anterior segment imaging with special relevance for laser refractive surgery. Recent findings Computerized Scheimpflug imaging has been used for corneal and anterior segment tomography (CASTm) in different commercially available instruments. Such approach computes the three-dimensional image of the cornea and anterior segment, enabling the characterization of elevation and curvature of the front and back surfaces of the cornea, pachymetric mapping, calculation of the total corneal refractive power and anterior segment biometry. CASTm represents a major evolution for corneal and anterior segment analysis, beyond front surface corneal topography and single point central corneal thickness measurements. This approach enhances the diagnostic abilities for screening ectasia risk as well as for planning, evaluating the results, managing complications of refractive procedures, and selecting intraocular lens power, type, and design. In addition, dynamic Scheimpflug imaging has been recently introduced for in-vivo corneal biomechanical measurements and has also been used for anterior segment imaging of femtocataract surgery. Summary Scheimpflug imaging has an important role for laser refractive surgery with different applications, which continuously improve due to advances in technology.

Scheimpflug-Based Tomography and Biomechanical Assessment in Pressure-Induced Stromal Keratopathy

PURPOSE To report the tomographic and biomechanical findings before and after treatment of a case of pressure-induced stromal keratopathy (PISK), which was misdiagnosed as diffuse lamellar keratitis (DLK). METHODS A case report of a referred patient with supposed diagnosis of DLK after LASIK in the right eye. Scheimpflug-based corneal tomography and biomechanical assessment were provided by the Pentacam HR and CorVis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany). RESULTS A layer of corneal opacity beneath the flap with a presumably fluid-filled interface area was observed on slit-lamp biomicroscopy. Scheimpflug image from Pentacam revealed a hyperreflective area underneath the flap interface. Goldmann applanation tonometry was 12 mm Hg, whereas CorVis intraocular pressure was 53.5 mm Hg with deformation amplitude of 0.42 mm. Two days after starting oral and topical ocular hypotensive therapy, CorVis intraocular pressure was 14 mm Hg and deformation amplitude was 1.02 mm. CONCLUSIONS Ocular hypertension in PISK was associated with lower deformation response, along with steepening and thickening of the cornea.

Integration of Scheimpflug-Based Corneal Tomography and Biomechanical Assessments for Enhancing Ectasia Detection

PURPOSE To present the Tomographic and Biomechanical Index (TBI), which combines Scheimpflugbased corneal tomography and biomechanics for enhancing ectasia detection. METHODS Patients from different continents were retrospectively studied. The normal group included 1 eye randomly selected from 480 patients with normal corneas and the keratoconus group included 1 eye randomly selected from 204 patients with keratoconus. There were two groups: 72 ectatic eyes with no surgery from 94 patients with very asymmetric ectasia (VAE-E group) and the fellow eyes of these patients with normal topography (VAE-NT group). Pentacam HR and Corvis ST (Oculus Optikgeräte GmbH, Wetzlar, Germany) parameters were analyzed and combined using different artificial intelligence methods. The accuracies for detecting ectasia of the Belin/Ambrósio Deviation (BAD-D) and Corvis Biomechanical Index (CBI) were compared to the TBI, considering the areas under receiver operating characteristic curves (AUROCs). RESULTS The random forest method with leave-one-out cross-validation (RF/LOOCV) provided the best artificial intelligence model. The AUROC for detecting ectasia (keratoconus, VAE-E, and VAE-NT groups) of the TBI was 0.996, which was statistically higher (DeLong et al., P < .001) than the BAD-D (0.956) and CBI (0.936). The TBI cut-off value of 0.79 provided 100% sensitivity for detecting clinical ectasia (keratoconus and VAE-E groups) with 100% specificity. The AUROCs for the TBI, BAD-D, and CBI were 0.985, 0.839, and 0.822 in the VAE-NT group (DeLong et al., P < .001). An optimized TBI cut-off value of 0.29 provided 90.4% sensitivity with 96% specificity in the VAE-NT group. CONCLUSIONS The TBI generated by the RF/LOOCV provided greater accuracy for detecting ectasia than other techniques. The TBI was sensitive for detecting subclinical (fruste) ectasia among eyes with normal topography in very asymmetric patients. The TBI may also confirm unilateral ectasia, potentially characterizing the inherent ectasia susceptibility of the cornea, which should be the subject of future studies. [J Refract Surg. 2017;33(7):434-443.].

Enhanced combined tomography and biomechanics data for distinguishing forme fruste keratoconus

PURPOSE To evaluate the performance of the Ocular Response Analyzer (ORA) (Reichert Ophthalmic Instruments, Depew, NY) variables and Pentacam HR (Oculus Optikgeräte GmbH, Wetzlar, Germany) tomographic parameters in differentiating forme fruste keratoconus (FFKC) from normal corneas, and to assess a combined biomechanical and tomographic parameter to improve outcomes. METHODS Seventy-six eyes of 76 normal patients and 21 eyes of 21 patients with FFKC were included in the study. Fifteen variables were derived from exported ORA signals to characterize putative indicators of biomechanical behavior and 37 ORA waveform parameters were tested. Sixteen tomographic parameters from Pentacam HR were tested. Logistic regression was used to produce a combined biomechanical and tomography linear model. Differences between groups were assessed by the Mann-Whitney U test. The area under the receiver operating characteristics curve (AUROC) was used to compare diagnostic performance. RESULTS No statistically significant differences were found in age, thinnest point, central corneal thickness, and maximum keratometry between groups. Twenty-one parameters showed significant differences between the FFKC and control groups. Among the ORA waveform measurements, the best parameters were those related to the area under the first peak, p1area1 (AUROC, 0.717 ± 0.065). Among the investigator ORA variables, a measure incorporating the pressure-deformation relationship of the entire response cycle was the best predictor (hysteresis loop area, AUROC, 0.688 ± 0.068). Among tomographic parameters, Belin/Ambrósio display showed the highest predictive value (AUROC, 0.91 ± 0.057). A combination of parameters showed the best result (AUROC, 0.953 ± 0.024) outperforming individual parameters. CONCLUSIONS Tomographic and biomechanical parameters demonstrated the ability to differentiate FFKC from normal eyes. A combination of both types of information further improved predictive value. [J Refract Surg. 2016;32(7):479-485.].

Enhanced Screening for Ectasia Susceptibility Among Refractive Candidates: The Role of Corneal Tomography and Biomechanics

Progressive “iatrogenic” ectasia or keratectasia is a very severe complication of laser vision correction procedures. This is more common after LASIK, in which the lamellar cut promotes a larger biomechanical impact than the excimer laser ablation. However, ectasia has been also reported after surface ablation. Considering the severity of such complication, prevention is the best approach. Preoperative abnormal topography has been classically considered as the most important risk factor for ectasia development. Other risk factors are young age, high myopic corrections, low residual stromal bed and thin cornea. Multiple laser retreatments and thick flaps are additional risk factors, as are postoperative trauma or intense eye rubbing. However, there are mysteries related to the cases that develop ectasia with no identifiable risk factors, and also to the cases of successful LASIK that remain stable despite of multiple risk factors (including abnormal topography). Corneal ectasia may occur due to two distinct mechanisms: 1. preoperative abnormal (weak) corneal stroma; and 2. severe biomechanical impact (weakening) from the procedure. While these mechanisms are distinct, there is an association and overlapping between the level of susceptibility of any cornea and the biomechanical impact of the procedure. Corneal tomography and biomechanical assessment provide an advanced understanding of the cornea that augments the sensitivity to identify a very mild (forme fruste keratoconus) form of ectasia, that may still present with relatively normal front surface topography. Such an enhanced screening approach not only augments the sensitivity to detect susceptible cases, but also provides higher specificity for a cornea with irregular topography, considered as a keratoconus suspect, that may be suitable for laser vision correction.

Ectasia Detection by the Assessment of Corneal Biomechanics.

To the Editor: We read with interest the article from Steinberg et al entitled “Screening for Keratoconus With New Dynamic Biomechanical In Vivo Scheimpflug Analyses.” We commend the authors for their work and also thank and applaud their scientific spirit by allowing us to further analyze the raw data from the Scheimpflug technology measurements (CorVis ST [CST], OCULUS Optikgeräte GmbH; Wetzlar, Germany) of their patients. In this study, the ability to detect corneal ectasia by CST was tested. Despite the statistically significant differences found for some of the tested parameters, the discriminant ability to detect disease was relatively poor. Also, the analyzed CST parameters failed to detect abnormalities in the cases referred to as having subclinical disease. However, we do have a few comments that should provide a positive insight into this important subject for our field. We agree with the authors that the detection of mild forms of ectatic corneal diseases has gained substantial relevance because these cases are at a very high risk for iatrogenic progressive ectasia (keratectasia) after corneal refractive procedures. However, in addition to refractive surgery, early detection and monitoring of ectasia progression have become of utmost importance because of the paradigm shift in the management of ectatic corneal disease. In addition, despite the evolution of corneal shape analysis, biomechanical understanding is paramount for augmenting the sensitivity in identifying cases with mild disease and characterizing the susceptibility for ectasia progression. In fact, there is a consensus that the pathophysiology of corneal ectasia is related to altered corneal biomechanics. The current understanding is that a focal abnormality in corneal biomechanical properties precipitates a cycle of decompensation and leads to localized thinning and steepening, which clinically define ectasia progression. Furthermore, we would like to offer comments on the criteria that were used in the published article to define the studied populations and on the clinical parameters that were analyzed. In fact, these are the foremost points for studies involving diagnostic technologies. The authors wisely used objective front surface curvature indices [KISA, paracentral inferior–superior (I–S) asymmetry, and the maximum keratometry (Kmax)] for defining the inclusion criteria for each group. This approach avoids problems related to subjectivity and variability of classifications of topographic maps. Another positive aspect of the methods was the inclusion of 1 eye per patient, which avoids selection bias related to the use of both eyes from the same subject. Nevertheless, they did not consider corneal tomographic data and solely considered topometric (front surface) evaluation at a single time point for each patient. In this study, 87 eyes from 87 patients with normal topography maps were compared with 65 eyes from 65 cases with clinical keratoconus. Normal topography was defined as KISA less than 60%, I–S less than 1.4D, and Kmax less than 47D. Even though this is relatively rare, it is possible that some of these cases have mild or susceptible forms of ectasia, because there are reported cases that, despite having normal topography and central corneal thickness, progressed to keratectasia after laser-assisted in situ keratomileusis (LASIK) or photorefractive keratectomy. Considering the preoperative state of stable LASIK cases with longterm follow-up would provide a more robust population for the normal control group. The study also included 42 cases considered as keratoconus suspects, defined as cases with steep (Kmax . 47D) and asymmetric corneas (I–S . 1.4D), but with KISA less than 100%. Interestingly, the stability of LASIK in corneas with such characteristics has been reported because these eyes may be classified as nonkeratoconic by segmental or layered tomographic epithelial thickness mapping. The study also included 27 cases considered as subclinical keratoconus, defined as the eye with normal topography (KISA , 60%, I–S , 1.4 D, and Kmax , 47D) from patients with clinical ectasia detected in the fellow eye. Although these eyes were referred to as forme fruste keratoconus by Klyce, and have been widely used to develop and to test advanced screening algorithms for detecting mild ectatic disease, some of these cases may be true unilateral ectasia. Interestingly, although there is a consensus that true unilateral keratoconus does not exist, secondary induced ectasia caused by a purely mechanical process may occur unilaterally. These concepts are in agreement with the 2-hit hypothesis, which proposes an underlying genetic predisposition coupled with external environmental factors, including eye rubbing and atopy. In addition, the further exclusion of cases with central corneal thickness less than 500 mm and greater than 575 mm may augment the population selection bias, limiting the relevance of the results on the cases referred to as subclinical. Interestingly, the authors noted the relevance of KISA indices for the detection of mild ectatic diseases in a previous report, but they also acknowledged the limitations of such criteria for group selections as part of the discussion. Other topometric metrics such as the Cone Location and Magnitude Index may be of interest to objectively separate normal and ectatic cases. However, longitudinal data are needed to improve the definition of the groups. A closer-to-ideal population for representing cases with mild disease or with ectasia susceptibility would be the preoperative state of cases that developed ectasia after LASIK, which is relatively challenging. Considering the published study, we advise evaluating these patients longitudinally to better stratify normal and ectatic corneas. In addition, future studies should consider integrating tomographic data to further improve criteria to define the groups. Nevertheless, the main comment on the study is related to the clinical parameters from CST that were analyzed. In vivo characterization of corneal biomechanical response during noncontact tonometry using ultrahigh

Scheimpflug lens densitometry and ocular wavefront aberrations in patients with mild nuclear cataract

Purpose To test correlations between Scheimpflug optical densitometry and ocular higher‐order aberrations (HOAs) in patients with mild nuclear cataract. Setting Cornea and Refractive Surgery Department, Hospital de Braga, Braga, Portugal. Design Retrospective single‐center study. Methods In eyes with mild nuclear cataract, lens densitometry was evaluated by Scheimpflug imaging (Pentacam HR), which provided an objective quantification (mean density and maximum density) and grading (nuclear staging score) of the crystalline lens. A visual function analyzer that combines ray‐tracing aberrometry and Placido disk‐based topography (iTrace) was used to evaluate the total ocular and internal HOAs. Results The study comprised 40 eyes of 30 patients. The mean density of the lens nucleus was 8.99% ± 0.76% (SD) (range 7.5% to 10.8%), and the mean maximum density was 27.96% ± 6.97% (range 16.9% to 56.1%). Regarding the score of nuclear staging of the Scheimpflug device, 28 eyes had level 0 and 12 eyes had level 1. Significant positive correlations were found between the mean density and maximum density parameters and the internal HOAs (&rgr; = 0.661, P < .001 and &rgr; = 0.570, P < .001, respectively). Conclusions There were significant correlations between the quantification parameters derived from Scheimpflug lens densitometry and ocular HOAs. The integration of these technologies can help in clinical decision making and in understanding the subjective symptoms of patients with mild nuclear cataracts. Financial Disclosure Dr. Ambrósio is a consultant to Oculus Optikgeräte GmbH, Alcon Surgical, Inc., and Carl Zeiss Meditec AG. None of the other authors has a financial or proprietary interest in any material or method mentioned.

Managing corneal ectasia prior to keratoplasty

The advent of refractive surgery allowed for great advances in the understanding of pathophysiology, diagnosis and treatment of corneal ectatic diseases. The different associations that highlight the importance of this range from the need for early diagnosis in the screening process of candidates for laser vision correction to the impact of refractive surgery technologies on treatment. Keratoconus is still an indication for corneal transplant, and it is expected that about 5–20% of the patients may require it. However, considering technological advances, the current treatment options are diverse and can be customized to each case. This review overviews the fundamental knowledge related to corneal ectatic diseases management and its management prior to keratoplasty. Whereas this is an area of dynamic development of scientific knowledge, we present fundamental concepts, along with information on the most recent studies and future prospects.

Comparison of Dysfunctional Lens Index and Scheimpflug Lens Densitometry in the Evaluation of Age-Related Nuclear Cataracts.

PURPOSE To describe the Dysfunctional Lens Index (DLI) from ray-tracing aberrometry and to test its correlations with logMAR corrected distance visual acuity (CDVA) and lens grading based on the Lens Opacities Classification System III (LOCS III) and the Scheimpflug-based lens density. METHODS The DLI was calculated by the i-Trace Visual Functional Analyzer (Tracey Technologies, Houston, TX). Forty eyes of 30 patients with mild to moderate age-related nuclear cataract were included retrospectively. Nuclear opalescence grading was obtained by slit lamp using the LOCS III, and objective lens densitometry was evaluated by Scheimpflug imaging (Pentacam HR; Oculus Optikgeräte GmbH, Wetzlar, Germany). The average density parameter obtained by Scheimpflug imaging of the nucleus lens was considered. RESULTS The DLI showed a high negative linear correlation with the LOCS III nuclear opalescence score (r = -0.662; P < .01). The average density of the lens nucleus was positively correlated with the LOCS III nuclear opalescence score (r = 0.682; P < .01). The CDVA had a stronger relationship with the DLI parameter (r = -0.702, P < .01) compared to the average density values (r = 0.630, P < .01). CONCLUSIONS The DLI was correlated with the LOCS III nuclear opalescence score and the Scheimpflug-based lens density. The DLI had a stronger correlation with CDVA compared to the LOCS III classification or the Scheimpflug-based lens density. The DLI may improve the preoperative evaluation of nuclear cataract and the monitoring of its progression.

Aplicações clínicas do princípio de Scheimpflug na Oftalmologia

Este artigo apresenta uma revisao dos principios e das aplicacoes clinicas do principio de Scheimpflug na area da imagiologia do segmento anterior. Ao disponibilizar uma imagem tridimensional do segmento anterior, esta tecnologia permite a caraterizacao da elevacao e curvatura das superficies anterior e posterior da cornea, o mapeamento paquimetrico, o calculo do poder refrativo total da cornea e a biometria do segmento anterior. Na subespecialidade de cirurgia refrativa, esta abordagem melhora a capacidade de identificacao de casos com risco de desenvolver ectasia, bem como de planeamento e de avaliacao dos resultados dos procedimentos cirurgicos. Recentemente, esta tecnologia foi introduzida na avaliacao biomecânica in vivo da cornea e na cirurgia de catarata assistida por laser de femtossegundo.