Photography of the anterior eye segment according to Scheimpflug's principle: options and limitations - a review

Assessment by the Scheimpflug imaging system of corneal clarity and anterior segment properties in rosacea patients

OBJECTIVE

To evaluate the effects of rosacea on ocular surface changes such as alterations in dry eye parameters, corneal densitometry, and aberrations, in comparison with healthy controls.

METHODS

A total of 88 eyes of 44 patients diagnosed with rosacea and 88 eyes of 44 healthy controls were enrolled in this cross-sectional study. All participants underwent a comprehensive dermatologic and ophthalmic examination and Tear Break-Up Time (TBUT) and Schirmer-1 tests were performed. The rosacea subtype and Demodex count and OSDI scores of all participants were recorded. Corneal topographic, densitometric, and aberrometric measurements were obtained using the Scheimpflug imaging system.

RESULTS

The mean age of the 44 patients was 41.2 ± 11.0 years of whom 31 (70.5%) were female. The mean TBUT and Schirmer-1 test values were significantly decreased and OSDI scores were significantly increased in the rosacea group compared to healthy controls (p < 0.01 for all). The most common subtype of rosacea was erythematotelangiectatic rosacea (70.4%). The severity grading of rosacea revealed that 18 (40.9%) patients had moderate erythema. The median (min-max) Demodex count was 14.0 (0-120) and the disease duration was 24.0 (5-360) months. The comparison of the corneal densitometry values revealed that the densitometry measurements in all concentric zones, especially in central and posterior zones were higher in rosacea patients. Corneal aberrometric values in the posterior surface were also lower in the rosacea group compared to healthy controls. The topographic anterior chamber values were significantly lower in the rosacea group.

STUDY LIMITATIONS

Relatively small sample size, variable time interval to hospital admission, and lack of follow-up data are among the limitations of the study. Future studies with larger sample sizes may also enlighten the mechanisms of controversial anterior segment findings by evaluating rosacea patients who have uveitis and those who do not.

CONCLUSION

Given the fact that ocular signs may precede cutaneous disease, rosacea is frequently underrecognized by ophthalmologists. Therefore, a comprehensive examination of the ocular surface and assessment of the anterior segment is essential. The main priority of the ophthalmologist is to treat meibomian gland dysfunction and Demodex infection to prevent undesired ocular outcomes.

Effect of smoking on corneal and lens clarity: a densitometric analysis

PURPOSE

To assess the effect of chronic cigarette smoking on corneal and lens densitometry measurements using Pentacam HR and to compare the results obtained with those in non-smokers.

MATERIALS AND METHODS

This cross-sectional comparative study included 40 chronic-smokers and 40 age-matched healthy non-smokers between 18-40 years. After general ophthalmic examination, the Pentacam HR imaging system was used to evaluate corneal and lens densitometry measurements of smokers and non-smokers.

RESULTS

The mean corneal densitometry values were not statistically significantly different in all the concentric zones and layers in the eyes of the smokers and non-smokers (p > 0.05, for all). However, the mean values of zone 1, zone 2, zone 3 and average lens densitometry measurements of the smokers were statistically significantly higher compared to non-smokers (p < 0.05, for all). Additionally, significant positive correlations were detected between the number of pack-years smoked and lens densitometry measurements.

CONCLUSION

Lens densitometry measurements of smokers were significantly increased while corneal densitometry measurements were not significantly altered compared to non-smokers. Smoking may contribute to cataractogenesis and smoking and age-related changes may act synergistically to cataract development among smokers.

The Evolution of Diagnostics for Keratoconus: From Ophthalmometry to Biomechanics

PURPOSE

To enumerate the various diagnostic modalities used for keratoconus and their evolution over the past century.

METHODS

A comprehensive literature search including articles on diagnosis on keratoconus were searched on PUBMED and summarized in this review.

RESULTS

Initially diagnosed in later stages of the disease process through clinical signs and retinoscopy, the initial introduction of corneal topography devices like Placido disc, photokeratoscopy, keratometry and computer-assisted videokeratography helped in the earlier detection of keratoconus. The evolution of corneal tomography, initially with slit scanning devices and later with Scheimpflug imaging, has vastly improved the accuracy and detection of clinical and sub-clinical disease. Analyzing the alteration in corneal biomechanics further contributed to the earlier detection of keratoconus even before the tomographic changes became evident. Anterior segment optical coherence tomography has proven to be a helpful adjuvant in diagnosing keratoconus, especially with epithelial thickness mapping. Confocal microscopy has helped us understand the alterations at a cellular level in keratoconic corneas.

CONCLUSION

Thus, the collective contribution of the various investigative modalities have greatly enhanced earlier and accurate detection of keratoconus, thus reducing the disease morbidity.

Corneal Stromal Densitometry Evolution in a Clinical Model of Cellular Therapy for Advanced Keratoconus

PURPOSE

The aim of this study was to report the corneal densitometry (CD) evolution studied by Scheimpflug tomography, anterior segment optical coherence tomography (AS-OCT), and confocal microscopy changes, in patients with advanced keratoconus included in a clinical experience of advanced cell therapy using autologous humans adipose-derived adult stem cells (ADASCs) and corneal decellularized and ADASCs-recellularized human donor corneal laminas.

METHODS

This study is an interventional prospective, consecutive, randomized, comparative series of cases. Fourteen patients with keratoconus were randomly distributed into 3 groups for 3 types of surgical interventions: group 1 (G-1), autologous ADASC implantation (n = 5); group 2 (G-2), decellularized human corneal stroma (n = 5); and group 3 (G-3), autologous ADASCs + decellularized human corneal stroma (n = 4). Participants were assessed with Scheimpflug-based Oculus Pentacam CD module, AS-OCT (Visante; Carl Zeiss), and confocal microscopy (HRT3 RCM Heidelberg).

RESULTS

A significant improvement of 1 to 2 logMAR lines in all visual parameters in the 3 groups was obtained. The central and total CD were statistically significantly higher in G-2 compared with G-1 and G-3 compared with G-1 at the studied annular zones centered on the corneal apex (0-2, 2-6, and 6-10 mm). There was statistical significance higher in G-3 compared with G-2 at the central corneal stroma at 0-2 and 2-6 mm. The confocal microscopy findings and the AS-OCT reflected the densitometry changes.

CONCLUSIONS

The intrastromal implantation of ADASCs produced very subtle changes in CD at the level of the central corneal stroma. However, the intrastromal implantation of decellularized corneal laminas increases it slightly, but with lower values than the implantation of recellularized laminas with ADASCs.

Analysis of corneal topographic and densitometric properties in patients receiving systemic isotretinoin therapy

PURPOSE

To evaluate dry eye parameters, corneal topographic features, corneal densitometric changes, and anterior segment parameters in patients receiving systemic isotretinoin treatment.

METHODS

This prospective cross-sectional study included 66 eyes of 33 patients who were started on oral isotretinoin therapy for severe acne vulgaris. All patients were evaluated in terms of ocular surface tests such as tear break-up time (TBUT) and Schirmer-1 and were asked to fill in the ocular surface disease index (OSDI) questionnaire. Corneal densitometric and topographic measurements were obtained using the Scheimpflug imaging system.

RESULTS

The mean age of the patients was 19.9 ± 1.6 years, and 21 (63.6%) of the participants were female. The mean OSDI score was significantly higher in the third month than before treatment (20.05 ± 19.38, vs. 26.96 ± 22.94, p = 0.00, respectively). The mean values of the TBUT test were significantly lower in the third month than before treatment (9.06 ± 4.40 sec, vs. 10.71 ± 4.61 sec, p = 0.02, respectively). Mean scores of the Schirmer 1 test showed no statistically significant difference between before treatment and the third month (16.08 ± 8.40 mm, vs. 16.08 ± 8.50 mm, p = 1, respectively). There was no statistically significant difference between before treatment and the third month in the majority of the densitometry measurements in concentric zones. However, the difference tended to be significant between the groups concerning posterior zone 0-2 mm (11.01 ± 0.85 GSU vs. 10.62 ± 0.89 GSU, p = 0.006). The RMS LOAs (front), RMS Total (Total), RMS LOAs Total (Total), RMS HOAs Total (Total), K_max, CCT, and CoV values were significantly higher in the third month than before treatment (p < 0.05 for all).

CONCLUSIONS

The dermatology specialists should be aware of the ocular complications of systemic isotretinoin therapy. Therefore, a complete ophthalmologic examination for the prompt apprehension and management of ocular involvement is essential in patients under isotretinoin therapy to increase ocular comfort and adherence to the therapy.

Comparison between the CASIA SS-1000 and Pentacam in measuring corneal curvatures and corneal thickness maps

PURPOSE

To compare the intra-device repeatability and inter-device reproducibility between two anterior segment imaging instruments, the CASIA SS-1000 (Tomey Corp., Nagoya, Japan) and Pentacam (OCULUS, Arlington, WA) in measuring anterior segment parameters.

METHODS

Single-center, prospective clinical trial. Participants ≥20 years of age were included. One eye was randomly selected, each imaged by three CASIA SS-1000 devices and three Pentacam devices by three different examiners. Each photographer operated a pair of devices, one CASIA SS-1000 and one Pentacam. The image order for each participant was determined by a random permutation table. Three images were taken from each device. A total of 18 images were taken for each eye. Ratios of the standard deviations, referenced as (CASIA/Pentacam), were calculated to compare the repeatability and reproducibility of the two imaging instruments.

RESULTS

In all, 66 participants with a mean age of 46.4 years (±21.7) were enrolled in the study. All repeatability ratios and intra-device variability were less than 1 (anterior corneal curvature: flat = 0.86, steep = 0.85; posterior corneal curvature: flat = 0.43, steep = 0.61; and map: thinnest = 0.22; central = 0.24, 2 mm = 0.26, 4 mm = 0.27, and 6 mm = 0.30). All reproducibility ratios, which measure the inter-device variability, were less than 1 (anterior corneal curvature: flat = 0.58, steep = 0.73; posterior corneal curvature: flat = 0.25, steep = 0.31; and pachymetry map: thinnest = 0.20; central = 0.20; 2 mm = 0.20; 4 mm = 0.19; and 6 mm = 0.22). A ratio of less than 1 indicates that the CASIA SS-1000 has more consistent measurements.

CONCLUSIONS

The CASIA SS-1000 was found to have better repeatability and reproducibility compared to the Pentacam for both corneal curvature and pachymetry maps. This greater consistency may require further study to determine whether the decreased variability can be translated into improved clinical results.

Assessing and compensating for the confounding factors in Scheimpflug-based corneal densitometry

Scheimpflug-based corneal densitometry is a clinically verified method for assessing corneal transparency. Nevertheless, the estimates of corneal densitometry appear to be correlated with age and eye biometry parameters, such as the anterior chamber depth or the pupil size, and that ensues a convoluted conditional estimation problem, where it is difficult to interpret the results. This study aims at devising a methodology for compensating for such confounding factors by using, as a research platform, a commercially available Scheimpflug camera that allows exporting images in a dynamic fashion, allowing averaging the results from multiple acquisitions. Two approaches are considered, one based on appropriately normalizing the line densitometry signal and one based on image histogram equalization. Then, three parameters for describing corneal densitometry are derived including the mean value of backscatter and the scale and shape parameters of the Weibull distribution estimated in regions of interest encompassing parts of corneal stroma. The results show that, unlike the non-normalized measures, the proposed approaches lead to parameters that are not correlated with age nor the eye biometry.

Inter-changeability Between Anterior Segment Optical Coherence Tomography and Scheimpflug Imaging in the Evaluation of Corneal Opacity

Purpose

To compare the results of corneal evaluation, either the total corneal thickness and corneal opacity depth by both technologies AS- OCT and Scheimpflug imaging by Sirius Scheimpflug placido topography.

Methods

sixty-eight eyes of sixty- eight consecutive patients with corneal opacities were examined by both AS-OCT and Sirius Scheimpflug imaging. Corneal thickness and corneal opacity depth were measured and compared determining the interchangeability using Bland–Altman plotting.

Results

Total corneal thickness was (470.32±62.10) and (463.47±56.47) by AS. OCT and Sirius Scheimpflug imaging, respectively (P value = 0.8).

While the actual measurement of corneal opacity, corneal opacity depth was (135.39±119) and (85.45±128) by AS-OCT and Siris Scheimpflug imaging respectively with P value (0.004).

Conclusion

AS-OCT and Scheimpflug imaging Sirius may be used interchangeably for measuring both total corneal thickness, while in the determination of corneal opacity depth. the AS-OCT is superior to Scheimpflug imaging in the accuracy of determination of actual boundaries of the corneal opacity.

Effect of light backscattering from anterior segment structures on automated flare meter measurements

BACKGROUND

To evaluate effect of maximal anterior cortical lens density, iris scatter and anterior chamber depth on laser flare photometry.

METHODS

Patients diagnosed with clinical uveitis were enrolled in the study. Clinical flare gradings were recorded upon the Standardization of Uveitis Nomenclature. Aqueous flare was measured with an automated device (Kowa FM-700). Back-scattering from anterior cortical lens and anterior iris surface was calculated from Scheimpflug images. A curvilinear regression model was used to calculate estimated values for each clinical grade. These values were used to split cases in Group I (laser flare photometry lower than estimated) and Group II (laser flare photometry higher than estimated). Mean anterior chamber depth, pupil aperture, maximal anterior cortical lens density and iris scatter values were compared between two groups. A stepwise multiple regression analysis was performed to determine the effect of clinical flare gradings and ocular parameters on aqueous flare measurements.

RESULTS

The study included 228 eyes of 114 cases. Scheimpflug images were obtained from 105 eyes. Estimated aqueous flare measurements (in photons/milliseconds) were 4.87, 8.50, 14.81, 25.83, 45.04 and 136.93 for 0, 0.5+, 1+, 1.5+, 2+ and 3+ clinical flare respectively. Group II had higher maximal anterior cortical lens density than Group I (96.6 ± 37.1 vs 77.9 ± 17.1 pixel unit, p = 0.001). The measured aqueous flare was significantly related to clinical flare, maximal anterior cortical lens density and pupil aperture (adjusted R2: 0.480, p < 0.001).

CONCLUSION

The back-scattered light from anterior cortical lens could affect laser flare photometry measurements. This effect might be quantified by Scheimpflug imaging.

Corneal Densitometry and In Vivo Confocal Microscopy in Patients with Monoclonal Gammopathy—Analysis of 130 Eyes of 65 Subjects

Background: Corneal imaging may support an early diagnosis of monoclonal gammopathy. The goal of our study was to analyze corneal stromal properties using Pentacam and in vivo confocal cornea microscopy (IVCM) in subjects with monoclonal gammopathy. Patients and methods: In our cross-sectional study, patients with monoclonal gammopathy (130 eyes of 65 patients (40.0% males; age 67.65 ± 9.74 years)) and randomly selected individuals of the same age group, without hematological disease (100 eyes of 50 control subjects (40.0% males; age 60.67 ± 15.06 years)) were included. Using Pentacam (Pentacam HR; Oculus GmbH, Wetzlar, Germany), corneal stromal light scattering values were obtained (1) centrally 0–2 mm zone; (2) 2–6 mm zone; (3) 6–10 mm zone; (4) 10–12 mm zone. Using IVCM with Heidelberg Retina Tomograph with Rostock Cornea Module (Heidelberg Engineering, Heidelberg, Germany), the density of hyperreflective keratocytes and the number of hyperreflective spikes per image were manually analyzed, in the stroma. Results: In the first, second and third annular zone, light scattering was significantly higher in subjects with monoclonal gammopathy, than in controls (p ≤ 0.04). The number of hyperreflective keratocytes and hyperreflective spikes per image was significantly higher in stroma of subjects with monoclonal gammopathy (p ≤ 0.012). Conclusions: Our study confirms that increased corneal light scattering in the central 10 mm annular zone and increased keratocyte hyperreflectivity may give rise to suspicion of monoclonal gammopathy. As corneal light scattering is not increased at the limbal 10–12 mm annular zone in monoclonal gammopathy subjects, our spatial analysis provides evidence against the limbal origin of corneal paraprotein deposition. Using IVCM, stromal hyperreflective spikes may represent specific signs of monoclonal gammopathy.

Correlation Between Degree of Lens Opacity and the Phacoemulsification Energy Parameters Using Different Imaging Methods in Age-Related Cataract

Purpose

To compare the correlation between degree of lens opacity and the phacoemulsification energy parameter in patients with age-related cataract as determined by slit lamp, 25-MHz ultrasound biomicroscopy (UBM), and Scheimpflug imaging (Pentacam) and to evaluate the application of these three methods to measuring lens opacification.

Methods

This observational study was conducted in 319 patients (381 eyes) with different types of age-related cataract. The average age of patients was 67.3 ± 11.4 years. The degree of lens opacity acquired by slit lamp, 25-MHz UBM, and Pentacam was determined by the Lens Opacity Classification System III (LOCSIII), pixel units calculated by ImageJ, and lens density, respectively. We primarily analyzed and compared the correlation between lens opacity and the cumulative dissipated energy (CDE) values of phacoemulsification.

Results

Cortical, nuclear, and posterior subcapsular (PSC) cataracts were evaluated as follows: LOCSIII grades 3.31 ± 1.42, 3.29 ± 1.49, and 0.91 ± 0.83; pixel units 120.91 ± 22.8, 93.2 ± 15.9, and 99.7 ± 13.0; and lens density 51.8 ± 31.2, 21.2 ± 6.10, and 53.3 ± 35.3, respectively. The CDE values were 12.1 ± 12.4, 13.5 ± 9.11, and 3.93 ± 1.96. In cortical cataract, there was a linear correlation among LOCSIII, pixel units, and CDE value (r = 0.560, r = 0.832, and r = 0.582, respectively; both P < 0.05), but lens density had no correlation with other parameters. In nuclear cataract, there was a linear correlation among LOCSIII, lens density, and CDE value (r = 0.747, r = 0.865, and r = 0.906, respectively; both P < 0.05), but pixel units had no correlation with other parameters. In PSC, only pixel units and LOCSIII showed a correlation.

Conclusions

The various imaging methods offered different advantages in terms of determining lens opacity, a feature related to types of age-related cataracts. Choosing the most suitable imaging method to evaluate lens opacification based on the type of age-related cataract is important for accurately predicting the phacoemulsification parameters for cataract surgery.

Translational Relevance

Determining the appropriate phacoemulsification strategy depends on quantitative analysis of the degree of lens opacity to reduce intraoperative and postoperative complications and to obtain the optimal postoperative visual outcome.

Intraocular lens power calculation in eyes with previous corneal refractive surgery

Intraocular lens (IOL) power calculation after corneal refractive surgery (CRS) becomes an expanding challenge for ophthalmologists as more and more cataract surgeries after CRS are required. These patients typically also have high expectations as to visual performance. Conventional IOL power calculation schemes frequently provide inaccurate results in these cases. This review aims to summarize and recommend currently available IOL power calculation methods for eyes with the most common CRS methods: radial keratotomy (RK), photorefractive keratectomy (PRK), laser in situ keratomileusis (LASIK), and small incision lenticule extraction (SMILE). To this end, biometry measuring methods and IOL formulas will be explained and combinations of both are proposed. In synopsis, it is evident that the latest generation of vergence formulas exhibit favorable IOL power prediction accuracy in post-CRS eyes, even though the predictive precision of methods in eyes without CRS is not attained. Ray tracing computation, intraoperative aberrometry, and machine learning–based formulas hold potential to further improve refractive outcomes in post-CRS eyes.

Detection of shallow anterior chamber depth from two-dimensional anterior segment photographs using deep learning

BACKGROUND

The purpose of this study was to implement and evaluate a deep learning (DL) approach for automatically detecting shallow anterior chamber depth (ACD) from two-dimensional (2D) overview anterior segment photographs.

METHODS

We trained a DL model using a dataset of anterior segment photographs collected from Shanghai Aier Eye Hospital from June 2018 to December 2019. A Pentacam HR system was used to capture a 2D overview eye image and measure the ACD. Shallow ACD was defined as ACD less than 2.4 mm. The DL model was evaluated by a five-fold cross-validation test in a hold-out testing dataset. We also evaluated the DL model by testing it against two glaucoma specialists. The performance of the DL model was calculated by metrics, including accuracy, sensitivity, specificity, and area under the receiver operating characteristic curve (AUC).

RESULTS

A total of 3753 photographs (1720 shallow AC and 2033 deep AC images) were assigned to the training dataset, and 1302 photographs (509 shallow AC and 793 deep AC images) were held out for two internal testing datasets. In detecting shallow ACD in the internal hold-out testing dataset, the DL model achieved an AUC of 0.86 (95% CI, 0.83-0.90) with 80% sensitivity and 79% specificity. In the same testing dataset, the DL model also achieved better performance than the two glaucoma specialists (accuracy of 80% vs. accuracy of 74 and 69%).

CONCLUSIONS

We proposed a high-performing DL model to automatically detect shallow ACD from overview anterior segment photographs. Our DL model has potential applications in detecting and monitoring shallow ACD in the real world.

TRIAL REGISTRATION

http://clinicaltrials.gov , NCT04340635 , retrospectively registered on 29 March 2020.

Analysis of corneal densitometry and endothelial morphometry in patients with psoriasis

BACKGROUND

To evaluate corneal endothelial properties and corneal densitometry values in patients with psoriasis and to compare the results with those of healthy controls.

METHODS

This prospective, comparative, and cross-sectional study included 106 eyes of 53 patients who were diagnosed with psoriasis and 106 eyes of 53 age-gender matched healthy controls. All patients were evaluated in terms of ocular surface tests such as Schirmer-1 and tear break-up time (TBUT). Corneal endothelial measurements were performed using noncontact specular microscopy. Corneal tomographic and densitometric measurements were obtained using the Scheimpflug imaging system. Measurements were also evaluated according to the psoriasis area and severity index (PASI) score.

RESULTS

The mean TBUT and Schirmer 1 test values were significantly lower in the psoriasis group than in the healthy controls (p = 0.02, p < 0.001, respectively). While the mean endothelial cell density was significantly lower in patients with psoriasis than the healthy controls (2389.9±314.9 cells/mm² vs. 2512.4±289.7 cells/mm², p = 0.02), the mean average endothelial cell area, standard deviation of cell area, coefficient of variation of cell area were significantly higher in patients with psoriasis (426.6±62.7 µm² vs. 403.2±46.1 µm², p = 0.01; 206.4±52.3 µm² vs. 183.2±43.8 µm², p = 0.006; and 48.1±6.3% vs. 45.7±6.7%, p = 0.04, respectively). Most of the densitometry measurements in concentric zones were higher in patients with psoriasis than in healthy controls, but none of the differences reached statistical significance.

CONCLUSIONS

A regular eye examination is crucial in patients with psoriasis because corneal structural and functional changes, particularly endothelial alterations, are of utmost importance in planning intraocular surgeries in patients with psoriasis.

Reliability and agreement of the central and mid-peripheral corneal thickness measured by a new Scheimpflug based imaging

Background

To assess the intra-observer repeatability and inter-observer reproducibility of central corneal thickness (CCT) and mid-peripheral corneal thickness (MPCT) measurements using a new Scheimpflug imaging instrument (Scansys) and compare the agreement with the rotating Scheimpflug corneal tomographer (Pentacam HR).

Methods

The same well-trained operator performed the measuring using the two devices, after which Scansys measurements were repeated by another operator. Both instruments required three consecutive measurements per subject. Corneal thickness measurements were obtained by each instrument, including CCT, thinnest corneal thickness (TCT), pupil corneal thickness (PCT), and MPCT. Test-retest repeatability (TRT), within-subject coefficient of variation (CoV), and intra-class correlation coefficient (ICC) were used to evaluate repeatability and reproducibility. A paired t-test was used to compare the differences between Scansys and Pentacam, and the agreement was compared with Bland-Altman plots.

Results

This study enrolled 112 healthy subjects. The CoV were <0.91% and 0.55% for repeatability and reproducibility, respectively. The ICC was close to 1 in all measurements. For intra-observer repeatability in the CT_2mm region, TRT was <10.30 µm. Moreover, TRT was <15.26 µm within the CT_5mm region. The paired t-test showed significant differences in all corneal thickness measurements (P<0.001). The central region and CT_2mm agreement were high, but the largest range of 95% limits of agreement (LoA) appeared in the CT_nasal-5mm.

Conclusions

The new Scheimpflug imaging instrument showed excellent intra-observer repeatability and inter-observer reproducibility for corneal thickness measurements. The agreement analysis suggested that Scansys and Pentacam could be interchangeably used between the central region and CT_2mm, except CT_5mm.

Current Developments in Corneal Topography and Tomography

Introduction: Accurate assessment of the corneal shape is important in cataract and refractive surgery, both in screening of candidates as well as for analyzing postoperative outcomes. Although corneal topography and tomography are widely used, it is common that these technologies are confused. The aim of this study was to present the current developments of these technologies and particularly distinguish between corneal topography and tomography. Methods: The PubMed, Web of Science and Embase databases were the main resources used to investigate the medical literature. The following keywords were used in various combinations: cornea, corneal, topography, tomography, Scheimpflug, Pentacam, optical coherence tomography. Results: Topography is the study of the shape of the corneal surface, while tomography allows a three-dimensional section of the cornea to be presented. Corneal topographers can be divided into large- and small-cone Placido-based devices, as well as devices with color-LEDs. For corneal tomography, scanning slit or Scheimpflug imaging and optical coherence tomography may be employed. In several devices, corneal topography and tomography have been successfully combined with tear-film analysis, aberrometry, optical biometry and anterior/posterior segment optical coherence tomography. Conclusion: There is a wide variety of imaging techniques to obtain corneal power maps. As different technologies are used, it is imperative that doctors involved in corneal surgery understand the science and clinical application of devices for corneal evaluation in depth.

Radiation-Induced Lens Opacity and Cataractogenesis: A Lifetime Study Using Mice of Varying Genetic Backgrounds

Recent epidemiological findings and reanalysis of historical data suggest lens opacities resulting from ionizing radiation exposures are likely induced at lower doses than previously thought. These observations have led to ICRP recommendations for a reduction in the occupational dose limits for the eye lens, as well as subsequent implementation in EU member states. The EU CONCERT LDLensRad project was initiated to further understand the effects of ionizing radiation on the lens and identify the mechanism(s) involved in radiation-induced cataract, as well as the impact of dose and dose-rate. Here, we present the results of a long-term study of changes to lens opacity in male and female adult mice from a variety of different genetic (radiosensitive or radioresistant) backgrounds, including mutant strains Ercc2 and Ptch1, which were assumed to be susceptible to radiation-induced lens opacities. Mice received 0.5, 1 and 2 Gy 60Co gamma-ray irradiation at dose rates of 0.063 and 0.3 Gy min-1. Scheimpflug imaging was used to quantify lens opacification as an early indicator of cataract, with monthly observations taken postirradiation for an 18-month period in all strains apart from 129S2, which were observed for 12 months. Opacification of the lens was found to increase with time postirradiation (with age) for most mouse models, with ionizing radiation exposure increasing opacities further. Sex, dose, dose rate and genetic background were all found to be significant contributors to opacification; however, significant interactions were identified, which meant that the impact of these factors was strain dependent. Mean lens density increased with higher dose and dose rate in the presence of Ercc2 and Ptch1 mutations. This project was the first to focus on low (<1 Gy) dose, multiple dose rate, sex and strain effects in lens opacification, and clearly demonstrates the importance of these experimental factors in radiobiological investigations on the lens. The results provide insight into the effects of ionizing radiation on the lens as well as the need for further work in this area to underpin appropriate radiation protection legislation and guidance.

Analysis of Corneal Densitometry and Endothelial Cell Function in Fuchs Uveitis Syndrome

OBJECTIVES

To evaluate corneal densitometry and endothelial cell properties in patients with unilateral Fuchs uveitis syndrome (FUS), and to compare results with unaffected contralateral eyes and healthy control subjects.

METHODS

A total of 90 participants were included in this prospective cross-sectional study. Forty-five affected eyes of patients with FUS were regarded as group 1 (FUSa), 45 fellow eyes were regarded as group 2 (FUSf), and 45 healthy-control eyes were regarded as group 3. Corneal densitometry was measured with densitometry software of Scheimpflug Corneal Topography (Pentacam HR, Oculus GmbH, Wetzlar, Germany), whereas endothelial cell measurement was evaluated with specular microscopy (Tomey, EM4000, GmbH, Germany).

RESULTS

The mean corneal densitometry values were higher in the midstromal (zones; 2-6, 6-10 mm), posterior (all zones), and total thickness (zones; 2-6, 6-10 mm) layers in the FUSa compared with FUSf and control eyes (P<0.05 for all comparisons). The mean values of average cell area and cell size characteristics (minimum, maximum, SD, and coefficient of variation) were higher; endothelial cell density and percentage of hexagonal cells were lower in the FUSa than in the other two groups (P<0.05 for all comparisons). There was a significantly strong correlation between specular microscopy parameters and posterior corneal densitometry values in the FUSa group.

CONCLUSIONS

Impairment of endothelial cell function in affected eyes of patients with FUS resulted in increased values of corneal densitometry, especially posterior layer.

Assessment of Corneal Haze After PRK and the Effect of Sutureless Amniotic Membrane Graft by Corneal Densitometry

PURPOSE

To assess whether densitometry analysis appropriately monitors the development of haze in myopic patients after photorefractive keratectomy (PRK) when compared to subjective slit-lamp haze grade examinations, and whether sutureless cryo-preserved amniotic membrane reduced postoperative haze development when compared to the standard bandage contact lens.

METHODS

In this retrospective cohort at the Center for Refractive Surgery, Walter Reed National Military Medical Center, a secondary analysis of prospectively collected data was performed. In the prospective study, participants underwent PRK for myopia. Postoperatively, a standard bandage contact lens was applied to the dominant eye and a sutureless cryo-preserved amniotic membrane graft to the nondominant eye. Participants were evaluated at 1, 3, and 6 months postoperatively for haze formation and corneal densitometry using slit-lamp biomicroscopy and Scheimpflug imaging, respectively.

RESULTS

Densitometry measurements at 6 months postoperatively were positively and significantly associated with the presence or absence of haze as assessed by slit-lamp examination in 39 patients (78 eyes; age range: 21 to 44 years). Eyes with increased densitometry measurements had 2.3 to 3.4 times the odds (P ⩽ .014) of having clinical haze on slit-lamp examination. Eyes with the amniotic membrane graft showed a positive correlation with increased corneal densitometry throughout most layers of the cornea.

CONCLUSIONS

Densitometry analysis appears to be a useful tool to supplement slit-lamp examination in monitoring haze development after PRK. The amniotic membrane failed to show a reduction in corneal densitometry in myopic eyes after PRK. [J Refract Surg. 2020;36(5):293-299.].

Changes in the Optical Corneal Densitometry, Visual Acuity, and Refractive Error after the Annular Intracorneal Inlay Implantation

Purpose:

To investigate the changes in the optical corneal densitometry as an objective method in assessing the corneal light back-scattering before and 1 year after the annular intracorneal inlay (AICI) implantation into the keratoconic corneas.

Methods:

Changes in the optical corneal densitometry, visual acuity, refractive, and tomographical status were assessed before and 1 year after the AICI implantation into the corneas with different stages of keratoconus. Optical corneal densitometry was evaluated using the Pentacam-HR in 0–2, 2–6, 6–10, and 10–12 mm rings in the anterior 120 μ, central layers, posterior 60 μ and also the total value were measured for cornea in the Grey Scale Unit criterion.

Results:

Totally, 34 patients with keratoconus were studied; the uncorrected and best corrected visual acuity were increased after the surgery (0.98 ± 0.25 to 0.53 ± 0.30 logMAR, P < 0.001 and 0.26 ± 0.18 to 0.19 ± 0.14, P = 0.007 logMAR, respectively); the spherical equivalent was decreased from −4.45 ± 2.25 to − 2.06 ± 2.01 D (P = 0.004). AICI implantation led to an increase in the amount of optical corneal densitometry in 0–2 mm central, 2–6 mm central, 6–10 mm central, total central, 2–6 mm posterior, and 2–6 mm total rings (all, P < 0.05); however, a decrease was observed in 0–2 mm anterior ring (P = 0.049). Results of statistical analysis showed that the total optical corneal densitometry, anterior total, and posterior total back-scattering did not change after the AICI implantation (all, P > 0.05).

Conclusions:

Our results revealed a significant improvement in the visual function, including refractive error and visual acuity following the AICI implantation. Changes in the optical corneal densitometry were different in distinct regions and layers however, the total amount did not change after the AICI implantation.

Evaluation of lens clarity in children with atopic dermatitis: A densitometric analysis with Pentacam

The association of atopic dermatitis (AD) with a wide variety of ocular complications is known; however, there is no study in the literature that measured lens densitometry in pediatric patients with AD. This study aimed to investigate lens densitometry in children with AD. In order to examine ocular complications in AD, 31 pediatric patients (13 males, 18 females; mean age 12 ± 3 years) with AD and 20 healthy children (9 males, 11 females; mean age 12 ± 2 years), who presented to the dermatology clinic of Istanbul Medipol Mega University between December 2018 and May 2019 were included in this study. The diagnosis of AD was based on the UK Working Party's Diagnostic Criteria for AD. Patients receiving inhaler and systemic steroids were excluded from the study. All children were examined by the same dermatologist and ophthalmologist. The mean values of best-corrected visual acuity, refractive error, and axial length were similar between both groups (P > .05). The lens densitometry values of zone 1, zone 2, and zone 3, as well as the average lens densitometry measurements were found statistically significantly higher in children with AD compared to the controls (P < .05 for all). This is the first study to demonstrate an increase in treatment-independent lens densitometry in children with AD.

The Effect of Corneal Thickness, Densitometry and Curvature on Intraocular Pressure Measurements Obtained by Applanation, Rebound and Dynamic Contour Tonometry

Evaluate the effect of corneal thickness, densitometry and curvature on intraocular pressure (IOP) measurements obtained by Goldmann applanation tonometry (GAT), non-contact tonometry (NCT), rebound tonometry (RT), and dynamic contour tonometry (DCT). A cross-sectional prospective study involving 40 participants was performed. Corneal measurements were obtained using Pentacam (Oculus GMbH, Wetzlar, Germany), densitometry was measured at annuli of 0–2, 2–6, 6–10 and 10–12 mm. The relationship between corneal thickness (central, 4 and 6 mm), corneal astigmatism and corneal densitometry and IOP was examined. There was a significant relationship between corneal thickness (central, 4 and 6 mm) and GAT180, GAT90, RT, and NCT (P < 0.001 for all comparisons) but not for DCT. Higher corneal densitometry (6–10 mm and 10–12 mm zones) was associated with higher IOP from GAT180 and GAT90, and higher densitometry in the 6–10 mm zone correlated with higher IOP from NCT, however corneal densitometry increased with age. Accounting for age, the relationship between corneal densitometry and IOP measurements was not significant. In eyes with greater corneal astigmatism there was a greater difference between GAT90 and GAT180 measurements. IOP measurements may be affected by corneal thickness, densitometry and curvature. DCT was less affected by properties of the cornea compared to other devices.

Biometric Measurement of Anterior Segment: A Review

Biometric measurement of the anterior segment is of great importance for the ophthalmology, human eye modeling, contact lens fitting, intraocular lens design, etc. This paper serves as a comprehensive review on the historical development and basic principles of the technologies for measuring the geometric profiles of the anterior segment. Both the advantages and drawbacks of the current technologies are illustrated. For in vivo measurement of the anterior segment, there are two main challenges that need to be addressed to achieve high speed, fine resolution, and large range imaging. One is the motion artefacts caused by the inevitable and random human eye movement. The other is the serious multiple scattering effects in intraocular turbid media. The future research perspectives are also outlined in this paper.

Comparison of Biometry Measurements Using Standard Partial Coherence Interferometry versus New Scheimpflug Tomography with Integrated Axial Length Capability

Purpose

To compare biometry measurements obtained by a partial interferometer biometer (IOLMaster 500) to the new Scheimpflug tomography with an integrated axial length biometer module (Pentacam AXL).

Patients and Methods

Cataract patients who underwent biometric measurements with the IOL Master 500 and the Pentacam AXL from July to November 2017 were enrolled in this study. Comparisons were performed for axial length (AL), keratometry (K), and anterior chamber depth (ACD). The Pearson correlation coefficient and the 95% limits of agreement (LoA) were calculated. Paired Student’s t-tests and Bland-Altman plots were used to assess the differences between devices.

Results

One hundred and sixty-six eyes of 92 patients were analyzed. There were no statistically significant differences in AL (p=0.558) or flat K (p=0.196) values between the IOL Master 500 and Pentacam AXL measurements. Statistically significant differences were found between the two devices with respect to steep K, ACD, and mean K measurements (p<0.001).

Conclusion

Both devices provided similar measurements of AL and flat K, though there were statistically significant differences in ACD, steep K, and mean K measurements.

Clinical Application of 25-MHz Ultrasound Biomicroscopy for Lens Opacity Degree Measurements in Phacoemulsification

Purpose

To evaluate the correlation between lens opacity degrees and phacoemulsification cumulated dissipated energy (CDE) values in patients with age-related cataract by applying 25-MHz panoramic ultrasound biomicroscopy (UBM).

Methods

This observational study was conducted in 227 patients (294 eyes) with age-related cataract. Patient ages ranged from 45 to 91 years. According to the lens images acquired by 25-MHz UBM, the objective indexes of lens opacity degrees were determined by using the ImageJ software. The correlation between lens opacity degrees (pixel units) and CDE values of phacoemulsification were mainly analyzed.

Results

The means of measurements were as follows: preoperative LogMAR corrected distance visual acuity, anterior chamber depth, and central lens thickness was 1.10 ± 0.61, 2.52 ± 0.51, and 4.34 ± 0.60 mm, respectively. The mean 25-MHz UBM-measured lens opacity degree was 101.30 ± 19.70 pixel units, and the mean CDE value was 9.74 ± 9.10. There was a linear correlation between pixel units and the CDE value, as well as LogMAR corrected distance visual acuity (r = 0.38 and 0.50, respectively; both P < 0.05). Age correlated with anterior chamber depth and lens thickness (r = −0.18 and 0.16, respectively; both P < 0.05) but not with pixel units (r = −0.08, P > 0.05).

Conclusion

The 25-MHz UBM has significant advantages in displaying the opacity feature of age-related cataract. The 25-MHz UBM combined with ImageJ software can be used to evaluate the opacity degree of age-related cataract quantitatively and may help predict the phacoemulsification parameters in cataract surgery.

Translational Relevance

Combination of the lens ultrasonic image and image analysis software enables researchers to evaluate lens opacity degree quantitatively and predict the parameters of phacoemulsification surgery.

Comparison of Corneal Power and Corneal Astigmatism of Different Diameter Zones Centered on the Pupil and Corneal Apex Using Scheimpflug Tomography

PURPOSE

Using Scheimpflug tomography to investigate the difference in corneal power and corneal astigmatism between 3- and 4-mm diameter zones centered on the pupil and corneal apex.

METHODS

A total of 90 eyes were included in this study. Axial keratometry, total refractive power, and true net power centered on the pupil and corneal apex in 3- and 4-mm diameter zones were assessed. The paired sample t test and independent sample t test were used for data comparison.

RESULTS

For corneal power and corneal astigmatism for the 3- and 4-mm diameter zones, the flat K values of axial keratometry, total refractive power, and true net power centered on the pupil (3-mm: 43.99 ± 1.69 D, 43.12 ± 1.71 D, 42.53 ± 1.67 D; 4-mm: 44.04 ± 1.67 D, 43.38 ± 1.71 D, 42.61 ± 1.65 D) were significantly higher than those centered on the apex (3-mm: 43.93 ± 1.69 D, 43.05 ± 1.71 D, 42.46 ± 1.67 D; 4-mm: 44.01 ± 1.67 D, 43.34 ± 1.69 D, 42.58 ± 1.65 D; all P < 0.02). However, the steep K and astigmatism magnitude values centered on the pupil (3-mm: 45.71 ± 1.73 D, 45.01 ± 1.73 D, 44.38 ± 1.69 D; 1.72 ± 0.83 D, 1.89 ± 0.86 D, 1.85 ± 0.84 D; 4-mm: 45.78 ± 1.73 D, 45.28 ± 1.74 D, 44.45 ± 1.68 D; 1.73 ± 0.84 D, 1.90 ± 0.85 D, 1.84 ± 0.85 D) were lower than those centered on the apex (3-mm: 45.81 ± 1.74 D, 45.10 ± 1.72 D, 44.50 ± 1.70 D; 1.88 ± 0.90 D, 2.05 ± 0.90 D, 2.04 ± 0.90 D; 4-mm: 45.85 ± 1.73 D, 45.34 ± 1.73 D, 44.51 ± 1.69 D; 1.83 ± 0.88 D, 2.00 ± 0.90 D, 1.93 ± 0.86 D; all P < 0.01). Compared with the 3-mm diameter zone, the corresponding 4-mm diameter zone showed higher corneal power centered on both pupil and corneal apex.

CONCLUSIONS

The difference in corneal power and corneal astigmatism, measured at 3 and 4 mm, centered on the pupil and the corneal apex should be noted in corneal refractive surgery and toric intraocular lens calculation.

Corneal Involvement of Patients with Polymyositis and Dermatomyositis

Purpose: To evaluate corneal parameters in patients with polymyositis (PM) and dermatomyositis (DM) and compare them with those of healthy controls.Methods: A total of 43 PM and 32 DM patients and 93 controls were enrolled in this cross-sectional, observational, case-control study. Corneal parameters were evaluated by Pentacam. Objective clinical tests of dry eye disease (DED) were also performed.Results: All pachymetric measurements and corneal volumes (CVs) proved to be significantly lower both in PM and DM patients. The values of DM patients were closer to control values than those of the PM patients. For tear break-up time and Schirmer-I test values significant differences were observed between patients and controls, with values decreased both in PM and DM patients.Conclusions: PM patients rather than DM patients tend to develop thinner and low-volume corneas as compared to controls. Additionally, a high prevalence of DED among both PM and DM patients was also detected.

Corneal densitometry in high myopia

Background

To investigate corneal densitometry values obtained using Scheimpflug tomography in normal and highly myopic (HM) eyes and to assess the differences in densitometry values between them.

Methods

Highly myopic and normal corneas were examined using the Pentacam Scheimpflug imaging system. Corneal densitometry was automatically performed over a 12-mm diameter area, which was divided on the basis of annular concentric zones (0–2 mm, 2–6 mm, 6–10 mm, 10–12 mm, total diameter) and depth (anterior layer: inner 120 μm; center layer: from 120 μm to the last 60 μm; posterior layer: last 60 μm; total corneal thickness).

Results

A total of 100 normal and 100 HM eyes were enrolled in this study. Upon total corneal thickness densitometry, the HM group was found to have significantly lower values compared with the normal group in 4 annuli, including the 2 mm central zone, 2-6 mm zone, 6–10 mm zone, and 0–12 mm total diameter. Upon anterior layer densitometry, the HM group demonstrated statistically lower values in the 2-6 mm and 6–10 mm zones. Upon densitometry of the central and posterior layers, the HM group was found to have lower values in all annuli.

Conclusions

The densitometry map reveals that light backscatter was lower in most portions of the HM cornea than in the normal cornea.

Corneal Manifestations of Systemic Sclerosis

Purpose: Corneal involvement in systemic sclerosis (SSc) is rare, but due to rich collagen composition cornea is especially vulnerable to connective tissue diseases. Therefore, our aim was to evaluate corneal parameters of SSc patients. Methods: The study included 32 SSc patients and 39 control subjects with no ocular symptoms or ocular surface disorders. All study participants underwent Pentacam evaluation and objective signs of dry eye disease (DED), and clinical parameters were evaluated. Results: All pachymetric values, most of the corneal front surface, corneal volume, as well as anterior chamber depth measurements were significantly lower in the SSc group than in the control group (p < 0.05). Significant negative correlation was found between corneal parameters and age on the one hand, and disease duration on the other. Conclusions: Early recognition of corneal impairment, a possible extraintestinal manifestation of SSc, should be included in the check-up of the disease in order to reduce sight-threatening complications.

Intracorneal Silicone Oil Following Retinal Detachment Surgery With Silicone Oil Tamponade

Silicone oil (SO) is used for the management of complex retinal detachments. But SO may result in a number of complications. We report here on 2 eyes of 2 patients who were admitted to our clinic with intracorneal SO and who underwent complicated vitreoretinal surgery with SO infusion. In both cases, the presence of SO was identified via clinical assessments. The SO bubble was detected in the center of the cornea in the first case. Scheimpflug camera imaging demonstrated sharply demarcated hyporeflective areas into the intrastromal space. In the second case, intrastromal bright and emulsified SO particles were noted by slit-lamp examination. Scheimpflug camera imaging demonstrated sharply demarcated hyperreflective areas into the intrastromal space. SO droplets may be seen in the cornea. Scheimpflug camera imaging may be helpful in understanding the pathogenesis of this condition.

Stabilization Time of Anterior Segment Parameters After Trabeculectomy Surgery

OBJECTIVES

To investigate the postoperative changes in the anterior segment parameters by Scheimpflug imaging method in patients undergoing trabeculectomy surgery.

METHODS

This prospective study included 38 phakic eyes of 38 patients with primary open-angle glaucoma who underwent trabeculectomy. Anterior chamber angle (ACA), anterior chamber depth (ACD), anterior chamber volume (ACV), and central corneal thickness (CCT) of the eyes were measured by performing Scheimpflug imaging in preoperative (baseline) and postoperative periods (1st week and 1st, 3rd, and 6th months after the surgery).

RESULTS

Significant differences were observed in all the anterior segment parameters during the postoperative period (P<0.001 for ACA, ACD, and CCT; P=0.001 for ACV). Compared with preoperative values, ACA, ACD, and ACV values decreased and CCT value increased in the 1st postoperative week (P<0.001 for all the parameters). Compared with the 1st postoperative-week values, ACA, ACD, and ACV values significantly increased and CCT value significantly decreased in the 1st postoperative month (P=0.002 for ACV; P<0.001 for ACA, ACD, and CCT). However, no significant differences were observed between the baseline and 1st postoperative-month values (P>0.05 for all the parameters). Moreover, the changes in the anterior segment parameters were not statistically significant after the 1st postoperative month.

CONCLUSIONS

Our results showed that the changes in the anterior segment parameters observed in the early postoperative period after trabeculectomy returned to their baseline values after approximately 1 month after the surgery and remained stable thereafter.

Lifetime study in mice after acute low-dose ionizing radiation: a multifactorial study with special focus on cataract risk

Because of the increasing application of ionizing radiation in medicine, quantitative data on effects of low-dose radiation are needed to optimize radiation protection, particularly with respect to cataract development. Using mice as mammalian animal model, we applied a single dose of 0, 0.063, 0.125 and 0.5 Gy at 10 weeks of age, determined lens opacities for up to 2 years and compared it with overall survival, cytogenetic alterations and cancer development. The highest dose was significantly associated with increased body weight and reduced survival rate. Chromosomal aberrations in bone marrow cells showed a dose-dependent increase 12 months after irradiation. Pathological screening indicated a dose-dependent risk for several types of tumors. Scheimpflug imaging of the lens revealed a significant dose-dependent effect of 1% of lens opacity. Comparison of different biological end points demonstrated long-term effects of low-dose irradiation for several biological end points.

Imaging Lenticular Autofluorescence in Older Subjects

Purpose

To evaluate whether a practical method of imaging lenticular autofluorescence (AF) can provide an individualized measure correlated with age-related lens yellowing in older subjects undergoing tests involving shorter wavelength lights.

Methods

Lenticular AF was imaged with 488-nm excitation using a confocal scanning laser ophthalmoscope (cSLO) routinely used for retinal AF imaging. There were 75 older subjects (ages 47–87) at two sites; a small cohort of younger subjects served as controls. At one site, the cSLO was equipped with an internal reference to allow quantitative AF measurements; at the other site, reduced-illuminance AF imaging (RAFI) was used. In a subset of subjects, lens density index was independently estimated from dark-adapted spectral sensitivities performed psychophysically.

Results

Lenticular AF intensity was significantly higher in the older eyes than the younger cohort when measured with the internal reference (59.2 ± 15.4 vs. 134.4 ± 31.7 gray levels; P < 0.05) as well as when recorded with RAFI without the internal reference (10.9 ± 1.5 vs. 26.1 ± 5.7 gray levels; P < 0.05). Lenticular AF was positively correlated with age; however, there could also be large differences between individuals of similar age. Lenticular AF intensity correlated well with lens density indices estimated from psychophysical measures.

Conclusions

Lenticular AF measured with a retinal cSLO can provide a practical and individualized measure of lens yellowing, and may be a good candidate to distinguish between preretinal and retinal deficits involving short-wavelength lights in older eyes.

Corneal Densitometry for Quantification of Corneal Deposits in Monoclonal Gammopathies

PURPOSE

To assess the capability of Scheimpflug-based densitometry of the cornea to quantify light chain deposits in patients with active monoclonal gammopathies.

METHODS

This is a case-control study in which data from a leading tertiary university center in myeloma care were analyzed. Ten eyes of 5 patients with monoclonal gammopathy and 26 eyes of 13 healthy controls undergoing clinical evaluation and Scheimpflug-based measurements were included in the study. The main outcome measures were densitometry data of the 4 corneal layers-anterior layer (AL), central layer (CL), posterior layer, and total layer (TL)-in 4 different annuli (central annular zone 0-2 mm, intermediate annular zone 2-6 mm, peripheral annular zone 6-10 mm, and total annular zone 0-12 mm).

RESULTS

In 8 eyes of 4 patients with IgG-based gammopathy, corneal light backscatter was highest in the AL and decreased with increasing corneal depth. The peripheral annular zone showed a higher densitometry value compared with the corneal center. Compared with healthy controls, the AL (P < 0.001), the CL (P < 0.001), and the TL (P < 0.001) had significantly higher corneal light backscatter in patients with gammopathy in the total and the peripheral annular zones. In one patient with predominantly IgA-based disease, corneal light backscatter was not elevated.

CONCLUSIONS

Scheimpflug-based densitometry of the cornea is able to quantify opacification by immunoglobulin G light chain deposits in monoclonal gammopathies. This noninvasive technique can complement presently used in vivo confocal microscopy and corneal photography to objectivize corneal changes. Densitometry might allow monitoring of corneal immunoglobulin deposits in follow-up examinations.

Comparison of corneal measurements in keratoconus using swept-source optical coherence tomography and combined Placido-Scheimpflug imaging

PURPOSE

The aim of this study was to provide a comprehensive comparison of reliability of corneal topographic measurements in keratoconic eyes using swept-source optical coherence tomography (OCT) and a combined Placido-Scheimpflug imaging.

METHODS

A total of 30 eyes of 30 patients were included. The mean age was 31.2 ± 8.4 years. Two consecutive topographic measurements were obtained for one eye of each patient using swept-source OCT (CASIA) and combined Placido-Scheimpflug imaging (TMS-5). Test-retest reliability of CASIA and TMS-5 measurements including central corneal thickness (CCT) and thinnest corneal thickness (TCT), keratometry at steep (Ks) and flat (Kf) axes, average keratometry (Avg K), cylinder, and, best-fit spheres (BFS) of the anterior and posterior corneal surfaces were evaluated.

RESULTS

There was no systematic or scaling bias in any parameter in both devices. Systematic differences between CASIA and TMS-5 were found in posterior corneal Kf, Avg K and BFS, CCT and TCT (p ≤ 0.002); scaling differences between CASIA and TMS-5 were also found in CCT and TCT (p ≤ 0.002). Both machines illustrated adequate reliability. Intraclass correlation coefficients (ICC) ≥0.952 was recorded for all parameters measured with CASIA and ICC ≥ 0.914 was recorded for all parameters on TMS-5. CASIA showed significantly higher ICCs in CCT and TCT, and posterior corneal BFS (p < 0.001).

CONCLUSIONS

This study showed significant differences in posterior corneal surface and corneal thickness measurements between swept-source OCT and combined Placido-Scheimpflug imaging in eyes with keratoconus. Swept-source OCT might be preferred over Placido-Scheimpflug imaging owing to better repeatability of measurements.

Freeform optical design for a nonscanning corneal imaging system with a convexly curved image

Most existing techniques that are typically used by specialists to image the cornea are based on point, slit, or annular scanning due to a narrow field of view. The difficulty in achieving a larger field of view comes from the convex shape of the human eyeball. Field curvature for a refractive imaging system with positive power is typically negative and thus a concave image surface. In order to view the full cornea and sclera with snapshot imaging, we calculate qualified two- and three-mirror solutions from Seidel aberration theory. A three-mirror solution is further optimized as a high-resolution off-axis imaging system using freeform surfaces, which can obtain a full-field tailored image shell without scanning. The lateral resolution on the cornea is about 10 μm with good modulation transfer function (MTF) and spot performance. To ease the assembly, a monolithic design is achieved with slightly lower resolution, leading to a potential mass production solution.

Repeatability and agreement of Scheimpflug-based and swept-source optical biometry measurements

PURPOSE

To evaluate the repeatability and comparability of biometry parameters between a Scheimpflug-based topography with axial length measurement (Pentacam AXL, Oculus, Wetzlar, Germany) and a swept-source optical biometry (IOLMaster 700, Carl Zeiss Meditec AG, Jena, Germany).

METHODS

A total of 50 eyes from 50 adult subjects had biometry measurements in one session three times using the Pentacam AXL and the IOLMaster 700. Keratometry, anterior chamber depth (ACD) and axial length (AL) values were obtained by both devices. Mean keratometry (K_mean) was calculated and the corneal spherocylinder was converted into power vectors (J0, J45). Repeatability was assessed based on intraclass correlation coefficient (ICC). Agreement was evaluated by linear regression analysis and Bland-Altman analysis by calculating the mean difference and 95% limits of agreement (LoA).

RESULTS

Assessment of intraoperator repeatability by means of ICC showed excellent reproducibility of measurements for both devices and all parameters examined ranging from 0.994 to 1.0. IOLMaster 700 exhibited significantly higher K_mean (p<0.001) and AL (p<0.001) values than the Pentacam AXL. Pentacam AXL showed significantly higher ACD (p<0.001) measurements than IOLMaster 700. There was no statistically significant difference of J0 (p=0.115) and J45 (p=0.255) values between Pentacam AXL and IOLMaster 700.

CONCLUSIONS

Both devices provide high reproducible values for all parameters investigated. J0 and J45 values are statistically and clinically interchangeable between Pentacam AXL and IOLMaster 700. All other parameters are statistically different. In clinical practice, the differences for ACD and AL are to small and the values can be used interchangeable. However, K_mean values are clinically and statistically different and cannot be used interchangeable between the two devices.

Repeatability and Agreement of Central Corneal Thickness and Keratometry Measurements between Four Different Devices

Background. To estimate repeatability and comparability of central corneal thickness (CCT) and keratometry measurements obtained by four different devices in healthy eyes. Methods. Fifty-five healthy eyes from 55 volunteers were enrolled in this study. CCT (IOLMaster 700, Pentacam HR, and Cirrus HD-OCT) and keratometry readings (IOLMaster 700, Pentacam HR, and iDesign) were measured. For statistical analysis, the corneal spherocylinder was converted into power vectors (J0, J45). Repeatability was assessed by intraclass correlation coefficient (ICC). Agreement of measurements between the devices was evaluated by the Bland-Altman method. Results. The analysis of repeatability of CCT data of IOLMaster 700, Pentacam HR, and Cirrus HD-OCT showed high ICCs (range 0.995 to 0.999). The comparison of CCT measurements revealed statistically significant differences between Pentacam HR versus IOLMaster 700 (p < 0.0001) and Pentacam HR versus Cirrus HD-OCT (p < 0.0001), respectively. There was no difference in CCT measurements between IOLMaster 700 and Cirrus HD-OCT (p = 0.519). The repeatability of keratometry readings (J0 and J45) of IOLMaster 700, Pentacam HR, and iDesign was also high with ICCs ranging from 0.974 to 0.999. The Pentacam HR revealed significantly higher J0 in comparison to IOLMaster 700 (p = 0.009) and iDesign (p = 0.041); however, no significant difference was between IOLMaster 700 and iDesign (p = 0.426). Comparison of J45 showed no significant difference between IOLMaster 700, Pentacam HR, and iDesign. These results were in accordance with Bland-Altman plots. Conclusion. In clinical practice, the devices analyzed should not be used interchangeably due to low agreement regarding CCT as well as keratometry readings.

Two-Year Course of Corneal Densitometry After Descemet Membrane Endothelial Keratoplasty

PURPOSE

To investigate the 2-year course of corneal densitometry following Descemet membrane endothelial keratoplasty (DMEK) for Fuchs endothelial dystrophy (FED).

DESIGN

Retrospective, interventional case series.

METHODS

Densitometry values (corneal light backscatter in grayscale units) measured by Scheimpflug-based imaging and clinical records of 160 eyes of 160 patients undergoing DMEK for FED were reviewed. Outcome measures included densitometry data in 4 corneal layers (anterior layer [AL], central layer [CL], posterior layer [PL], and total layer [TL]) and 2 annuli (central annular zone 0-2 mm and peripheral zone 2-10 mm), central corneal thickness (CCT), best spectacle-corrected visual acuity (BSCVA), and endothelial cell density (ECD) prior to DMEK and at 1, 3, 6, 12, and 24 months postoperatively.

RESULTS

Corneal densitometry decreased in all 4 layers over 2 years after DMEK surgery. Regarding TL 0-2 mm, the reduction of corneal light backscatter was statistically significant for all follow-up time points compared with preoperative values (P < .001) and compared in between follow-up periods (P ≤ .010). Corneal light backscatter reduction was significantly higher in the center (0-2 mm) than in the periphery (2-10 mm) for all layers at 12 and 24 months (P ≤ .002). ECD and CCT did not correlate with corneal densitometry, whereas BSCVA correlated moderately for TL 0-2 mm (P = .026; r = 0.449) and TL 2-10 mm (P = .001; r = 0.585) at 12 months.

CONCLUSIONS

Corneal light backscatter showed a significant reduction after DMEK surgery in Fuchs endothelial dystrophy over a period of 2 years, more pronounced in the corneal center, apparently in association with visual acuity improvement.