Combined Rotating Ultra-High-Resolution Spectral Domain OCT and Scheimpflug Imaging for In Vivo Corneal Optical Biopsy.

PURPOSE: This article introduces the Pentacam® Cornea OCT (optical coherence tomography). This advanced corneal imaging system combines rotating ultra-high-resolution spectral domain OCT with sub- 2-micron axial resolution and Scheimpflug photography. The purpose of this study is to present the first experience with the instrument and its potential for corneal diagnostics, including optical biopsy. METHODS: In this prospective study, the Pentacam® Cornea OCT was used to image the corneas of seven patients. The novel wide-angle pericentric scan system enables optimal OCT imaging performance for the corneal layer structure over the entire width of the cornea, including the limbal regions. A detailed analysis of the resulting images assessed the synergism between the OCT and Scheimpflug photography. RESULTS: The Pentacam® Cornea OCT demonstrated significantly improved image resolution and ability to individualize corneal layers with high quality. There is a synergism between the OCT high-definition signal to individualize details on the cornea and Scheimpflug photography to detect and quantify corneal scattering. The noncontact exam was proven safe, user-friendly, and effective for enabling optical biopsy. CONCLUSIONS: Pentacam® Cornea OCT is an advancement in corneal imaging technology. The ultra-high-resolution spectral domain OCT and Scheimpflug photography provide unprecedented detail and resolution, enabling optical biopsy and improving the understanding of corneal pathology. Further studies are necessary to compare and analyze the tomographic reconstructions of the cornea with the different wavelengths, which may provide helpful information for diagnosing and managing corneal diseases.

Keratoconus and Corneal Ectasia with Relatively Low Keratometry.

INTRODUCTION: The study aims to demonstrate and estimate the prevalence of clinical corneal ectasia and keratoconus (KC) in patients with relatively low keratometry (low-K KC). METHODS: In a retrospective, analytical, and non-interventionist study, one eye was randomly selected from 1054 patients from the original Tomographic Biomechanical Index (TBIv1) study and the external validation (from Rio de Janeiro, Brazil, and Milan, Italy clinics). Patients were stratified into three groups. Group 1 included 736 normal patients, and groups 2 and 3 included 318 patients with clinical KC in both eyes, divided into low-K KC (90 patients) and high-K KC (228 patients), respectively. All patients underwent a comprehensive ophthalmological evaluation along with Pentacam and Corvis ST (Oculus, Wetzlar, Germany) examinations. Cases with maximum mean zone 3 mm keratometry (Kmax zone mean 3 mm) lower than 47.6 diopters (D) were considered as low-keratometry keratoconus, and cases with Kmax zone mean 3 mm higher than 47.6 D were regarded as high-keratometry keratoconus. RESULTS: Ninety (28.30%) of the 318 KC group presented ectasia with low-keratometric values (low-Kmax). The average age in the normal group was 39.28 years (range 6.99-90.12), in the low-Kmax KC group it was 37.49 (range 13.35-78.45), and in the high-Kmax KC group it was 34.22 years (range 12.7-80.34). Mean and SD values and median (range), respectively, of some corneal tomographic and biomechanical parameters evaluated from the low-Kmax KC group were as follows: Belin-Ambrósio enhanced ectasia display (BAD-D) 3.79 ± 1.62 and 3.66 (0.83-9.73); Pentacam random forest index (PRFI) 0.78 ± 0.25 and 0.91 (0.05-1); corneal biomechanical index (CBI) 0.58 ± 0.43 and 0.75 (0-1); TBI 0.93 ± 0.17 and 1 (0.35-1); and stiffness parameter at A1 (SP-A1) 86.16 ± 19.62 and 86.05 (42.94-141.66). CONCLUSION: Relatively low keratometry, with a Kmax lower than 47.6 D, can occur in up to 28.30% of clinical keratoconus. These cases have a less severe presentation of the disease. Future studies involving larger populations and prospective designs are necessary to confirm the prevalence of keratoconus with low keratometry and define prognostic factors in such cases.

Investigation of How Corneal Densitometry Artefacts Affect the Imaging of Normal and Keratoconic Corneas.

PURPOSE: To investigate corneal densitometry artefacts found in Pentacam Scheimpflug scans and their potential effect on assessing keratoconic (KC) corneas compared to normal (N) corneas. METHODS: The current study utilises Pentacam data of 458 N eyes, aged 35.6 ± 15.8 (range 10-87), referred to as the "N group", and 314 KC eyes, aged 31.6 ± 10.8 (range 10-72), referred to as the "KC group", where densitometry data were extracted and analysed via a custom-built MATLAB code. Radial summations of the densitometry were calculated at diameters ranging from 0.5 mm to 5.0 mm. The minimum normalised radial summation of densitometry (NRSD) value and angle were determined at each diameter and then linked. KC cone locations and areas of pathology were determined, and a comparison between N and KC groups was carried out both within the averaged area of pathology and over the corneal surface. RESULTS: Joining minimum NRSD trajectory points marked a clear distortion line pointing to the nasal-superior direction at 65° from the nasal meridian. The findings were found to be independent of eye laterality or ocular condition. Consistency was detected in the right and left eyes among both the N and KC groups. The location of the KC cone centre and the area of pathology were determined, and the densitometry output was compared both within the area of pathology and over the whole cornea. When the average densitometry was compared between N and KC eyes within the KC area of pathology, the N group recorded a 16.37 ± 3.15 normalised grey-scale unit (NGSU), and the KC group recorded 17.74 ± 3.4 NGSU (p = 0.0001). However, when the whole cornea was considered, the N group recorded 16.71 ± 5.5 NGSU, and the KC group recorded 15.72 ± 3.98 NGSU (p = 0.0467). A weak correlation was found between the Bad D index and NGSU when the whole measured cornea was considered (R = -0.01); however, a better correlation was recorded within the KC area of pathology (R = 0.21). CONCLUSIONS: Nasal-superior artefacts are observed in the densitometry Pentacam maps, and analysis shows no significant differences in their appearance between N or KC corneas. When analysing KC corneas, it was found that the cone positions are mostly on the temporal-inferior side of the cornea, opposite to the densitometry artefact NRSD trajectory. The analysis suggests that the corneal densitometry artefacts do not interfere with the KC area of pathology as it reaches its extreme in the opposite direction; therefore, weighting the densitometry map to increase the contribution of the inferior-temporal cornea and decreasing that of the superior-nasal area would improve the classification or identification of KC if densitometry is to be used as a KC metric.

Repetibilidade do estudo tomográfico da córnea com Scheimpflug rotacional, em olhos normais, olhos com ceratocone e olhos com ceratocone operados por crosslinking / Repeatability of the tomographic study of the cornea with a rotational Scheimpflug in normal eyes, eyes with keratoconus and eyes with crosslinking for keratoconus

RESUMO Objetivo Avaliar a precisão da tomografia corneana com imagens de Scheimpflug (Pentacam® AXL, OCULUS, Wetzlar, Alemanha) nos padrões de escaneamento com 25 e 50 imagens, verificando sua repetibilidade e reprodutibilidade em olhos normais, com ceratocone e com ceratocone após crosslinking. Métodos Estudo prospectivo, transversal, misto, no qual foram incluídos os pacientes que tinham córneas normais, ou com ceratocone; e não tinham realizado cirurgias corneanas, com exceção do crosslinking. Foram excluídos os pacientes que tivessem realizado outras cirurgias, como implante de anel intracorneano ou transplante de córnea. Foram realizadas três medidas com 25 imagens e três medidas com 50 imagens em cada olho incluído no estudo. Resultados O estudo avaliou 54 olhos de 41 pacientes. Destes, dez (18,52%) olhos eram com córneas normais e sem cirurgia ocular prévia aleatoriamente selecionados de 5 pacientes; 22 (40,74%) olhos aleatoriamente selecionados de 18 pacientes com ceratocone, sem cirurgia ocular prévia; e 22 (40,74%) olhos com ceratocone de 18 pacientes operados por crosslinking. No estudo da repetibilidade, percebemos uma maior variação de valores em todos os índices nos pacientes com ceratocone comparados aos de pacientes com olhos normais, em grande parte dos parâmetros analisados. Conclusão Não houve diferença significativa entre os métodos de escaneamento por 25 e 50 imagens, sendo o escaneamento por 25 imagens mais conveniente. A presença de ceratocone teve impacto negativo na repetibilidade de ambos os tipos de exame, e foi grande a concordância entre os métodos nos três grupos estudados. O coeficiente de repetibilidade permite considerar a relevância clínica dos dados para avaliar a progressão de ceratocone.

ABSTRACT Objective To evaluate the accuracy of corneal tomography with Scheimpflug images (Pentacam® AXL, OCULUS, Wetzlar, Germany) in scanning patterns with 25 and 50 images, by analyzing their repeatability and reproducibility in normal eyes, eyes with keratoconus and with keratoconus after crosslinking. Methods Prospective, cross-sectional, mixed study including patients who had normal corneas, or who had keratoconus, who had not undergone corneal surgery, with the exception of crosslinking. Patients who had undergone surgery for intracorneal ring implantation or corneal transplantation were excluded. Three measurements were performed with 25 images and three measurements were performed with 50 images on each eye included in the study. Results The study evaluated a total of 54 eyes of 41 patients. Of these, 10 (18.52%) eyes had normal corneas, without previous eye surgery, 22 (40.74%) were eyes with keratoconus, without previous eye surgery, and 22 (40.74%) were eyes with keratoconus, with crosslinking for keratoconus. In the study of repeatability, we noticed a greater variation of values in all indices in patients with KC compared to those with normal eyes, in most of the parameters analyzed. Conclusion There is no significant difference between the scanning methods with 25 and 50 images. However, 25 scans has advantages that make it the main method suggested. The presence of keratoconus has a negative impact on the repeatability of both types of examination, and there is great agreement between the methods in the three groups studied. The high repeatability coefficient in some parameters suggests that these data should be used with care in the assessment of keratoconus progression.