Corneal Apex Research Articles

A three-dimensional morpho-volumetric similarity study of Down syndrome keratopathy vs. keratoconus

BackgroundTo compare and contrast morpho-volumetric features between Down syndrome (DS) cornea and non-DS keratoconic cornea by three-dimensional (3D) modelling.MethodsForty-three subjects (43 eyes) with DS and 99 patients matching their age and sex (99 eyes) with keratoconus (KC) were included in this single-center cross-sectional study. Main outcome measures were high-order aberrations (HOA), central corneal thickness (CCT), spherical equivalent refraction, and morpho-volumetric parameters established using a 3D corneal model, such as deviation of anterior and posterior corneal apices (Dapexant/Dapexpost) and minimum thickness points (Dmctant/Dmctpost) from corneal vertex, areas of the anterior and posterior surfaces (Aant/Apost), sagittal area passing through the anterior and posterior corneal apices (Aapexant/Aapexpost) and minimum thickness point (Amctpost) and corneal volume of the complete cornea (Vtotal).ResultsAge, gender, spherical equivalent refraction, CCT and Vtotal were similar between the net on-DS KC and DS groups (P > 0.05), while non-DS KC group had higher HOA than the DS group (P < 0.05). Dapexant, Aant, Apost and Aapexant showed higher values in the DS group than in the non-DS KC group, whereas Dapexpost showed a reduction in the DS group when compared with the non-DS KC group (P < 0.05).ConclusionsThis study demonstrated that anterior and posterior corneal apex dynamics were specifically different in DS subjects, as the anterior apex tends to displace more prominently when compared to that from the non-DS KC group, while the posterior apex appears to be more stable than that in non-DS KC, which also support the theory that DS patients suffer from a specific keratopathy, distinctively different to KC but strongly related to it, and probably showing a diversity of corneal phenotypes in all cases of DS.

Pentacam findings after implantation of intrastromal corneal rings in keratoconus

Introduction Intrastromal corneal ring segment implantation is a minimally invasive procedure. Its main goals are to flatten and regularize the cornea, to improve uncorrected and corrected visual acuity, and to delay or even prevent a keratoplasty. ICRSs effect correlates directly to its thickness and inversely to its distance to the visual axis. Patients and methods A retrospective observational study involving 44 eyes of 44 patients was initiated. The files and pentacam printouts of 44 patients were retrospectively extracted and evaluated. The preoperative and postoperative ocular findings and pentacam parameters of anterior and posterior corneal surfaces, in addition to the pachymetry data, were recorded and analyzed. Results Forty-four patients with keratoconus were evaluated in this study. Evaluation of anterior corneal surface showed significant flattening of all keratometry readings (P &lt; 0.001) with significant improvement of corneal astigmatism (P = 0.03), corneal asphercity (P &lt; 0.001), the inferior-superior asymmetry (P = 0.019) and the front elevation (P = 0.005) The posterior corneal surface showed significant improvement in back elevation (P &lt; 0.001), and the back surface asphercity showed significant prolate shift (P = 0.01). The thinnest location was significantly upward displaced towards the corneal apex. kera 355° showed a significant flattening of all keratometry readings with significant improvement of corneal astigmatism and corneal asphercity of the anterior corneal surface and the back surface asphercity showed significant prolate shift (P = 0.001). The ICRS showed a significant flattening of km (P = 0.030) and corneal asphercity of the anterior corneal surface (P = 0.046). Conclusion The intracorneal ring implantation led to improvement of the tomographic corneal parameters which was more significant at the anterior corneal surface.

Repeatability and correlation of corneal biomechanical measurements obtained by Corvis ST in orthokeratology patients

PurposeTo evaluate the repeatability of the corneal biomechanical measurements obtained by Corvis ST in post-orthokeratology patients and analyze the correlation between the biomechanical and ocular parameters. MethodsFifty-one eyes of 51 myopic subjects were included in this study. The biomechanical parameters were assessed using Corvis ST. Repeatability was assessed using one-way ANOVA based on within-subject standard deviation (Sw), repeatability coefficient (RC), intraclass correlation coefficient (ICC) and correlation of variation (CoV). The correlation was evaluated using Pearson correlation analysis. ResultsAll parameters measured by Corvis ST, except length of flattened cornea at the first and second applanations (A1L and A2L), showed a good intraobserver repeatability after a 3-month follow-up period. The ICC values for A1L and A2L were 0.444 and 0.654, whereas the other parameters were higher than 0.8. Similar trends were obtained for CoV, wherein the CoV values for A1L and A2L were greater than 13 %. The corneal biomechanical parameters were correlated with age, refraction, axial length (AL), steep and flat keratometry before and after orthokeratology, and central corneal thickness (CCT). Following orthokeratology treatment, post-keratometry demonstrated a higher correlation with stiffness parameter at first applanation (SP-A1), velocity of corneal apex at the first applanation (A1V), and radius than pre-keratometry, which showed a weak correlation with SP-A1. ConclusionCorneal biomechanical parameters assessed using Corvis ST demonstrated a good repeatability, except A1L and A2L. The corneal biomechanical parameters were correlated with age, refraction, AL and pre- and post-keratometry. Thus, Corvis ST is a suitable device for investigating biomechanical parameter.

Corneal stroma densitometry evolution in a clinical model of cellular therapy for advanced keratoconus

AbstractPurpose: To report the corneal stromal densitometry (CD) evolution studied by Scheimpflug tomography, anterior segment optical coherence tomography (AS‐OCT), and confocal microscopy changes, in keratoconus patients included in a clinical experience of advanced cell therapy using autologous humans adipose‐derived adult stem cells (ADASCs), and corneal decellularized or ADASCs‐recellularized human donor corneal laminas in advanced keratoconus.Methods: Interventional prospective, consecutive, randomized, comparative series of cases. Fourteen keratoconic patients were randomly distributed into three groups for three types of surgical interventions: group 1 (G‐1), autologous ADASCs 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: 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 mm, 2–6 mm, and 6–10 mm). There was statistical significance higher in G‐3 compared with G‐2 at the central corneal stroma at (0–2 mm, 2‐6 mm). The confocal microscopy findings, as well as 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.

Microglial activation and retinal pigment epithelium alteration in a model of focal LED‐induced phototoxicity. Neuroprotection afforded by bFGF and minocycline

AbstractPurpose: To study the microglial reaction and degeneration of the retinal pigment epithelium (RPE) and its protection with basic fibroblast growth factor (bFGF) administered alone or combined with minocycline (MC) in a model of focal light‐emitting diode (LED)‐induced phototoxicity (LIP) in mice.Methods: In dark‐adapted adult C57 mice (20–25 g), the left eye was dilated and exposed for 45 seconds to a blue LED (400 nm; 500 lux) placed 2 mm perpendicular to the corneal apex (n = 71). Mice were treated with bFGF (0.5 μg) administered alone or in combination with MC (45 mg/kg). bFGF was administered in a single intravitreal injection just after LIP and the MC was daily injected intraperitoneally, starting the day before LIP (n = 10–13 per group). Vehicle or naïve groups were used as controls (n = 6–10 each group). Retinas were immunodetected with anti‐arrestin and anti‐Iba1 antibodies to study cone outer segments (a+OS) and microglial cells (Iba1+cells) and RPEs were immunodetected with anti‐ZO1 to study RPE cells, at 3 and 7 days after LIP. The number of cones and microglial cells was studied within a pre‐fixed area (PFA) of 0.9 mm diameter at the centre of the lesion.Results: Treatment with bFGF alone or in combination with MC was effective in protecting a+OS within the PFA compared to vehicles at 7 days after LIP (p = 0.034 and p = 0.001, respectively). The combined treatment of bFGF and MC was effective in reducing the number of Iba1+cells within the PFA in the outer plexiform layer at 7 days after LIP (p = 0.0003). However, the treatments had no restorative effect on RPE cell survival or morphological integrity at 7 days after LIP (p = 0.6762).Conclusions: Administration of bFGF alone or in combination with MC increased a+OS survival and reduces Iba1+cell activation but does not reduce RPE damage.

Prediction of corneal astigmatism based on corneal tomography after femtosecond laser arcuate keratotomy using a pix2pix conditional generative adversarial network.

PurposeThis study aimed to develop a deep learning model to generate a postoperative corneal axial curvature map of femtosecond laser arcuate keratotomy (FLAK) based on corneal tomography using a pix2pix conditional generative adversarial network (pix2pix cGAN) for surgical planning.MethodsA total of 451 eyes of 318 nonconsecutive patients were subjected to FLAK for corneal astigmatism correction during cataract surgery. Paired or single anterior penetrating FLAKs were performed at an 8.0-mm optical zone with a depth of 90% using a femtosecond laser (LenSx laser, Alcon Laboratories, Inc.). Corneal tomography images were acquired from Oculus Pentacam HR (Optikgeräte GmbH, Wetzlar, Germany) before and 3 months after the surgery. The raw data required for analysis consisted of the anterior corneal curvature for a range of ± 3.5 mm around the corneal apex in 0.1-mm steps, which the pseudo-color corneal curvature map synthesized was based on. The deep learning model used was a pix2pix conditional generative adversarial network. The prediction accuracy of synthetic postoperative corneal astigmatism in zones of different diameters centered on the corneal apex was assessed using vector analysis. The synthetic postoperative corneal axial curvature maps were compared with the real postoperative corneal axial curvature maps using the structural similarity index measure (SSIM) and peak signal-to-noise ratio (PSNR).ResultsA total of 386 pairs of preoperative and postoperative corneal tomography data were included in the training set, whereas 65 preoperative data were retrospectively included in the test set. The correlation coefficient between synthetic and real postoperative astigmatism (difference vector) in the 3-mm zone was 0.89, and that between surgically induced astigmatism (SIA) was 0.93. The mean absolute errors of SIA for real and synthetic postoperative corneal axial curvature maps in the 1-, 3-, and 5-mm zone were 0.20 ± 0.25, 0.12 ± 0.17, and 0.09 ± 0.13 diopters, respectively. The average SSIM and PSNR of the 3-mm zone were 0.86 ± 0.04 and 18.24 ± 5.78, respectively.ConclusionOur results showed that the application of pix2pix cGAN can synthesize plausible postoperative corneal tomography for FLAK, showing the possibility of using GAN to predict corneal tomography, with the potential of applying artificial intelligence to construct surgical planning models.

Short and long term corneal biomechanical analysis after overnight orthokeratology.

To investigate the short and long term corneal biomechanical changes after overnight orthokeratology (OK) and compare them with those occurring in subjects not wearing contact lenses. Retrospective case control study enrolling 54 subjects that were divided into three groups 18 subjects each: control group (CG), short term (15 nights) OK (STOK) group, and long term (more than 1y of OK wear) OK (LTOK) group. Corneal biomechanics were characterized using the CorVis® ST system (Oculus), recording parameters such as time [first/second applanation time (AT1, AT2)], speed [velocity of corneal apex at the first/second applanation time (AV1, AV2)], and amplitude of deformation (AD1, AD2) in the first and second corneal flattening, corneal stiffness (SPA1), biomechanically corrected intraocular pressure (bIOP) and corneal (CBI) and tomographic biomechanical indices (TBI). Significantly lower AD1 and standard deviate on of Ambrosio's relational average thickness related to the horizontal profile (ARTh) values were found in the OK groups compared to CG (P<0.05). Likewise, significantly higher values of CBI were found in STOK and LTOK groups compared to CG (P<0.01). No significant differences between groups were found in integrated radius index (P=0.24), strain stress index (P=0.22), tomographic biomechanical index (P=0.91) and corneal stiffness parameter (SPA1, P=0.97). Significant inverse correlations were found between corneal thickness and CBI in STOK (r=-0.90, P<0.01) and LTOK groups (r=-0.71, P<0.01). OK does not seem to alter significantly the corneal biomechanical properties, but special care should be taken when analyzing biomechanical parameters influenced by corneal thickness such as amplitude of deformation, ARTh or CBI, because they change significantly after treatment but mainly due to the reduction and pachymetric progression induced by the corneal molding secondary to OK treatment.

A novel analysis of Scheimpflug total corneal refractive power following corneal cross-linking in mild to moderate keratoconus.

To detect an earlier improvement in mild to moderate keratoconus following corneal cross-linking (CXL) with total corneal refractive power (TCRP) using ray tracing method. A total of 40 eyes of 30 consecutive patients who underwent CXL for progressive keratoconus were retrospectively enrolled. The following keratometric parameters provided by Pentacam HR, including maximum keratometry (Kmax), steepest keratometry (Ksteep), 3 mm zonal TCRP centered over corneal apex (TCRPapex,zone 3 mm), zonal mean keratometry and TCRP centered over corneal cone (Kmcone,zone and TCRPcone,zone 1, 2, 3 mm) were evaluated preoperatively and 1, 3, 6, and 12mo postoperatively. Groups 1 and 2 were defined based on Kmax at postoperative 1mo as improved (the initial improvement group) or worsen (the initial deterioration group) compared to the preoperative level. In the overall group, only keratometric parameters based on ray tracing method displayed significant improvement early at 3mo postoperatively, in which TCRPcone,zone 1 mm and 2 mm exhibited the largest flattening (0.57 D and 0.53 D, respectively). In Group 1, only Kmax, Kmcone,zone 2 mm and TCRPcone,zone 2 mm showed significant improvement initially at 1mo postoperatively, in which Kmax exhibited the largest improvement (1.05 D), followed by TCRPcone,zone 2 mm (0.82 D). In Group 2, only keratometric parameters based on ray tracing method and Kmcone,zone 3 mm showed slight but not significant improvement early at 3mo, in which TCRPcone,zone 3 mm displayed the most improvement (0.19 D), followed by TCRPcone,zone 2 mm (0.15 D). The findings indicate that a 2 mm zonal TCRP centered over Kmax could earlier detect keratometric improvement by CXL compared to other commonly used parameters in mild to moderate keratoconic eyes.

The Shape of Corneal Deformation Alters Air Puff-Induced Loading.

Purpose: To determine the dynamic modification of the load exerted on the eye during air-puff testing by accounting for the deformation of the cornea. Methods: The effect of corneal load alteration with surface shape (CLASS) was characterized as an additional component of the load produced during the concave phase where the fluid outflow tangential to the corneal surface creates backward pressure. Concave phase duration (t CD ), maximum CLASS value (CLASS max ), and the area under CLASS-time curve (CLASS int ) are calculated for 26 keratoconic (KCN), 102 normal (NRL), and 29 ocular hypertensive (OHT) subjects. Tukey’s HSD tests were performed to compare the three subject groups. A p-value less than 0.05 was considered statistically significant. Results: Accounting for CLASS increased the load by 34.6% ± 7.7% at maximum concavity; these differences were greater in KCN subjects (p < 0.0001) and lower in OHT subjects (p = 0.0028) than in NRL subjects. t CD and CLASS int were significantly longer and larger, respectively, for KCN subjects than those in the NRL and OHT groups (p < 0.0001). Conclusion: Load characterization is an essential step in assessing the cornea’s biomechanical response to air-puff–induced deformation. The dynamic changes in the corneal surface shape significantly alter the load experienced by the corneal apex. This implies a subject-specific loading dynamic even if the air puff itself is identical. This is important when comparing the same eye after a surgical procedure or topical medication that alters corneal properties. Stiffer corneas are least sensitive to a change in load, while more compliant corneas show higher sensitivity.

Efficacy and safety of accelerated corneal collagen cross-linking in patients with keratoconus

AIM: To study the efficacy and safety of accelerated collagen cross-linking in keratoconus. METHODS: Medical records of keratoconic corneas underwent accelerated collagen cross-linking at King Chulalongkorn Memorial Hospital, Thailand between April 2015 and August 2018 were reviewed. Preoperative and postoperative data at 1y of visual acuity, auto-refraction, corneal topography, higher-order aberrations (HOA), topometric indices and corneal densitometry were evaluated. Age of 24-30 (mean age 23.43±7.26)y, maximum keratometric value (Kmax) of 55 D, and baseline best corrected visual acuity (BCVA) of 20/40 (or 0.3 in LogMAR unit) were used as cut-off values to highlight the cross-linking effects. The effect of age, preoperative Kmax and BCVA were analyzed. The association between the change of corneal densitometry and other factors including preoperative Kmax, Kmean, manifest refraction spherical equivalent (MRSE), visual acuity, thinnest pachymetry, the change in Kmax, and the change of those parameters were also analyzed. P&lt;0.05 was considered statistically significant. RESULTS: One hundred and fifty-five patients (185 eyes) were included. Male to female ratio was 3:31. According to Amsler-Krumeich classification, stage 1 and 2 were dominant (37.84% and 35.14% respectively). At 1y, mean LogMAR uncorrected visual acuity (UCVA) improved by 0.1 (P&lt;0.05). The number of eyes of which postoperative BCVA improved more than 0.2 LogMAR was higher in the worse baseline BCVA group (preoperative BCVA ≥0.3) compared to the better baseline BCVA group (preoperative BCVA &lt;0.3) (78.26% vs 21.74%, P&lt;0.05). Mean Kmax decreased from baseline by 2.36 diopters (D) (P&lt;0.05). Seventy-three percent of the eyes of which Kmax reduced more than 2.0 D had preoperative Kmax ≥55 D. Q-value showed less prolate by 0.06 (P&lt;0.05). Corneal HOA at 6 mm from corneal apex decreased by 0.40 (P&lt;0.05). Corneal densitometry at 0-6 mm zone increased at 1mo and persisted 1y postoperatively (P&lt;0.05). The relationship of the increase in densitometric value and the decrease of thinnest pachymetry at 1y were in linear fashion. Index of surface variance, index of vertical asymmetry, keratoconus index, index of height decentration decreased at 1y (P&lt;0.05). Success rate at 1y was 90.24%. Postoperative corneal haze was found 11.35%, 30.27%, 15.67%, 10.27% and 2.16% at 1wk, 1, 3, 6mo and 1y respectively. No eyes developed corneal edema. There was one case of sterile keratitis. CONCLUSION: Accelerated collagen cross-linking in keratoconus was effective to flatten, reshape the cornea, improved visual acuity, HOA and topometric indices. Great Kmax reduction was found in advanced keratoconus. The magnitude of Kmax reduction is also greatest among previous reports.

Comparison of Mean Corneal Power of Annular Rings and Zones Using Swept-Source Optical Coherence Tomography.

This study aims to investigate differences in the mean corneal power of annular zones (corneal power measured over the inner annular zone of difference diameters) and rings (corneal power measured over a ring of different diameters) centered on the corneal apex using the swept-source optical coherence tomography technique. The mean anterior axial curvature (AAC), posterior axial curvature (PAC), and total corneal power (TCP) centered on the corneal apex with the annular rings (0–2 mm, 2–4 mm, 4–6 mm, and 6–8 mm) and zones were assessed using the ANTERION device. The paired-sample t-test was used for data comparison. For the 0–2 mm comparison, the AAC, PAC, and TCP values of rings and zones were interchangeable. For the 2–4 mm comparison, the AAC of the rings was lower than that of the zones (p = 0.004), and the TCP values of the rings were higher than that of the zones (p < 0.001). For the 4–6 mm comparison, the AAC of the rings was lower than that of the zones (p < 0.001), and the PAC and TCP values of the rings were higher than that of the zones (both p < 0.001). For the 6–8 mm comparison, the AAC of the rings was lower than that of the zones (p < 0.001), and the PAC and TCP values of the rings were higher than that of the zones (both p < 0.001). Comparisons between AAC and TCP in each sub-region showed significant differences both in the rings (p < 0.001) and the zones (p < 0.008). Differences in the AAC, PAC, and TCP measured at different diameters (2–4 mm, 4–6 mm, and 6–8 mm) of the rings and zones, centered on the corneal apex, should be noticed in clinical practice. As the diameter increases, the difference between the rings and the zones in terms of AAC, PAC, and TCP increase as well. Clinicians should also pay attention to differences between AAC and TCP for the rings and the zones within the same annular region.

Multiscale mechanical model based on patient-specific geometry: Application to early keratoconus development

Keratoconus is a pathology of the cornea associated with a tissue thinning and a weakening of its mechanical properties. However, it remains elusive which aspect is the leading cause of the disease. To investigate this question, we combined a multiscale model with a patient-geometry in order to simulate the mechanical response of healthy and pathological corneas under intraocular pressure. The constitutive behavior of the cornea is described through an energy function which takes into account the isotropic matrix of the cornea, the geometric structure of collagen lamellae and the quasi-incompressibility of the tissue. A micro-sphere description is implemented to take into account the typical features of the collagen lamellae as obtained experimentally, namely their orientation, their stiffness and their dispersion, as well as the their unfolding stretch, at which they start to provide a significant force. A set of reference parameters is obtained to fit experimental inflation data of the literature. We show that the most sensitive parameter is the unfolding stretch, as a small variation of this parameter induces a major change in the corneal apex displacement. The keratoconus case is then studied by separating the impact of the geometry and the one of the mechanics. We computed the evolution of the SimK (a clinical indicator of cornea curvature) and elevation maps: we were able to reproduce the reported changes of SimK with pressure only by a mechanical weakening, and not by a change in geometry. More specifically, the weakening has to target the lamellae and not the matrix. The mechanical weakening leads to elevations close to early stage keratoconus, but our model lacks the remodeling component to couple the change in mechanics with changes in geometry. Still, these findings indicate that new methods for early diagnosis of keratoconus should focus on the detection of a mechanical weakening, and that stiffening treatments should be appropriate.

Ocular anterior segment and corneal parameters evaluation in celiac disease

This observational case–control study evaluated the anterior ocular segment parameters of patients with celiac disease with a Scheimpflug imaging system and compared them with those of a healthy controls group, highlighting potential differences related to the underlying pathogenetic mechanisms of the disease. Seventy celiac patients and 70 healthy subjects were assessed with a comprehensive ophthalmological evaluation, including clinical history, Snellen best-corrected visual acuity, axial length (AL) measurements with IOLMaster, and anterior segment tomographic evaluation with Pentacam HR. The measurements of all keratometry values, astigmatism, steep axis, anterior and posterior Q value (asphericity), pupil diameter, pupil center, corneal apex, the thinnest point, corneal volume, anterior chamber depth from the epithelium, anterior chamber depth from endothelium, anterior chamber volume, and iridocorneal angle were also appraised. The two study groups were comparable and similar for gender, age, and AL, with no statistically significant differences regarding all analyzed tomographic parameters. Thus, ocular anterior segment parameters of celiac patients are not significantly different from those of healthy subjects, suggesting no underlying pathogenetic implications of celiac disease affecting the assessed structures. Nevertheless, a routine ophthalmological examination for all celiac patients should be recommended throughout their lifetimes due to the potential ocular manifestations of the disease.

Five-year follow-up of corneal morphology and corneal refractive power changes after uneventful DMEK.

To investigate changes of corneal thickness spatial profile (CTSP), corneal volume (CV) distribution, and total corneal refractive power (TCRP) over a course of 60months after uneventful Descemet membrane endothelial keratoplasty (DMEK). In our prospective, comparative study, sixty DMEK cases without intraoperative and postoperative complications and with complete 60-month follow-up were included (group 1). CTSP at corneal apex (CCT) and at 2mm, 4mm, 6mm, and 8mm rings, CV in 3mm, 5mm, 7mm, and 10mm zones, and TCRF in 2mm, 4mm 6mm, and 8mm zones were evaluated preoperatively and at 3, 6, 12, 24, and 60months postoperatively. The 60-month results were compared to an age-matched group of uncomplicated pseudophakic eyes (group 2; n = 20). The CCT and CTSP at 2, 4, and 6mm increased significantly at 60months compared to 3-month outcomes (P < 0.001). Similarly, CV increased significantly in 3mm, 5mm, and 7mm zones at 60months compared to 3months outcomes (P < 0.001). The TCRP showed in all zones a significant decrease at 3months (P < 0.001) followed by a continuous and significant increase at 60months (P < 0.001). The 60-month CCT and CTSP at 2mm were similar to group 2 (P ≥ 0.094). Sixty months after uneventful DMEK, CT within the central 2mm zone and CV at 3mm zone were similar to uncomplicated pseudophakic eyes. A continuous and statistically significant increase of TCRP was observed in all measured zonesafter the 3-month examination.

Central corneal thickness and its determinants in a geriatric population: a population-based study.

To determine the distribution of central corneal thickness (CCT) and its determinants in an Iranian geriatric population. This population-based study was conducted in 2019 in Tehran, the capital of Iran, using stratified multistage random cluster sampling. The study population was all residents ≥60 years of age. First, preliminary optometric and ocular health examinations were performed including the measurement of uncorrected and best-corrected visual acuity, objective and subjective refraction, anterior and posterior segment examination. The study participants then underwent corneal imaging using Pentacam HR. Out of 3791 invitees, 3310 participated in this study (response rate: 87.3%). The mean CCT and apex corneal thicknesses were 528 µ (95% CI: 526-529) and 529 µ (95% CI: 527-530), respectively. The highest and lowest mean corneal thickness was related to the superior (620 µ: 95% CI: 618-622) and the temporal (591 µ: 95% CI: 590-592) paracentral points, respectively. According to the multiple linear regression model, the CCT was significantly inversely related to keratometry readings (K1 and K2) and had a statistically significant direct relationship with intraocular pressure (IOP), corneal eccentricity (ECC), and corneal volume (CV) (all p values <0.05). The CCT was significantly higher in diabetic patients (p = 0.043). The CCT values in the geriatric Iranian population were lower than the values reported in most previous studies. The CCT is mostly influenced by IOP and corneal parameters (curvature, shape factor, and volume) and is not affected by demographic factors, refractive error, and ocular biometric components.

Positions of the horizontal and vertical centre of rotation in eyes with different refractive errors.

PurposeTo determine how the position of the centre of rotation of the eyeball is related to axial length and refractive error when horizontal and vertical eye movements are performed.MethodsA custom‐built eye tracker was used that determined the centre of rotation of the eye (COR) from lateral displacements of the pupil centre. Horizontal and vertical eye movements were studied in the right eyes, and each measurement performed five times in 59 subjects (32 females) with an average age of 36.6 ± 9.1 years. Spherical equivalent refractive errors ranged from −9.7 to +6.8 D with an average error of −1.5 ± 2.9 D. Axial lengths were measured with the ZEISS IOL Master 500.ResultsThe mean horizontal centre of rotation (COR) of the right eye for a saccade from 0° to ±11.9° was 15.3 ± 1.5 mm behind the corneal apex, while the average vertical COR for the same angle of eccentricity was 12.5 ± 1.4 mm, indicating that the horizontal COR was 2.8 ± 1.7 mm behind the vertical COR. In right eyes, horizontal COR was significantly correlated with axial length (r = 0.28, p = 0.02) but not with the spherical equivalent refractive error (r = 0.39, p = 0.90). Similarly, vertical COR was significantly correlated with axial length (r = 0.25, p = 0.03) but not with the spherical equivalent refractive error (r = 0.17, p = 0.90).ConclusionsWhile it might be expected that the COR is dependent on axial length, the correlation was not strong. Interestingly, the location of the COR was substantially different for horizontal and vertical eye movements which may relate to the flatter curvature of the eyeball in the vertical meridian, compared to the horizontal, as described in previous studies.

Three-dimensional topographic changes of anterior chamber depth following phacoemulsification with intraocular lens implantation in cataract patients

To investigate the three-dimensional topographic changes of anterior chamber depth (ACD) following cataract surgery. Seventy-eight eyes with age-related cataract undergoing phacoemulsification and intraocular lens (IOL) implantation were retrospectively enrolled. Participants were evaluated with Pentacam for ACD topography before and approximately four weeks after the surgery. The absolute changes of ACD (AACD) and the relative changes of ACD (RACD) topography were calculated, and three-dimensional topographic contours were plotted. The influence of age, gender, distance to corneal apex (DCA), temporal-nasal and superior-inferior on AACD and RACD was analyzed. Both AACD and RACD were negatively correlated with the DCA (p < 0.001; p < 0.001) and positively correlated with the age at all DCA (p < 0.05 for all the analyses). Significantly greater AACD and RACD were observed in female subjects (p < 0.05, respectively, at all DCA). AACD was significantly larger in the temporal compared with the nasal region (p < 0.001) and at the superior compared with the inferior region (p < 0.001), but not RACD. Subgroup analysis indicated that the significant difference of the AACD between the temporal and nasal regions was manifested at the DCA of more than 6mm (p < 0.001), and the difference between the superior and inferior regions was observed at 2mm DCA for both AACD (p < 0.001) and RACD (p = 0.001). We depicted the topographic changes of ACD following cataract surgery and found that it was significantly influenced by age, gender, DCA and quadrant location. The research provided the basis for including postoperative ACD topography prediction before cataract surgery in the future.

Repeatability of Corneal Densitometry Measurements using a Scheimpflug Camera in Healthy Normal Corneas.

Purpose:To determine the repeatability of corneal densitometry measured by the Scheimpflug imaging system.Methods:This cross-sectional study was conducted on photorefractive keratectomy candidates. One eye of each participant underwent imaging using Pentacam HR three times, 10 min apart. The repeatability of densitometry measurements was evaluated in four concentric annuli around the corneal apex and in different corneal depths. The repeatability of the measurements was evaluated using the intraclass correlation coefficient (ICC), repeatability coefficient (RC), and coefficient of variation (CV). The difference of repeatability between layers and zones was tested by tolerance index (TI).Results:Sixty eyes of sixty patients with a mean age of 27.76 ± 3.93 years were studied. Half of the participants were female (n = 30, 50%). ICC was above 0.9 in all corneal parts. The posterior layer and central zones showed the least variability of densitometry measurements considering the CV values. The RC was 2.06, 1.17, and 0.92 in anterior, central, and posterior layers, respectively. The RC was 0.88, 0.71, 1.51, and 4.56 in 0–2, 2–6, 6–10, and 10–12 mm circles, respectively. Only the reliability of densitometry in 10–12 mm annulus was statistically lower than the central zone (TI = 0.71).Conclusions:Corneal densitometry measurements provided by the Pentacam had good repeatability. The repeatability of densitometry measurements decreased from the center to the periphery (with an exception for 0–2 mm and 2–6 mm) and from the posterior to the anterior of the cornea. The reliability of the 10–12 mm zone was markedly less than other zones.

Análisis del espesor coroideo en pacientes con queratocono

Objective. To determine and compare choroidal thickness (CT) in keratoconus (KC) patients using Enhanced Depth Imaging (EDI) OCT. Methods. A comparative cross-sectional study including 26 patients with KC and 26 healthy controls assessed with Pentacam and EDI-OCT. CT was measured manually with the Caliper function at thirteen locations at 500 µm regular intervals. Results. The average CT in T6 was 253.96 ± 88.95 μm in the KC group, and of 309.39 ± 94.11 μm in the control group (p &lt;0.041). No significant differences in mean CT were observed in the rest of the points, including the subfoveal CT (M), 351.48 ± 106.3 vs 365.35 ± 114.6 μm, (p = 0.66). No correlation was observed between the mean subfoveal CT (M), the mean CT in the KC group, and the values of K1 (p = 0.977 and p = 0.498 respectively), K2 (p = 0.450 and p = 0.656), corneal asphericity (Q ) (p = 0.986 and p = 0.902), minimal pachymetry (Pachy) (p = 0.408 and p = 0.688), keratoconus index (KI) (p = 0.601 and p = 0.217), vertical asymmetry index (VAT) (p = 0.296 and p = 0.523), staging of KC (TKC) (p = 0.549 and p = 0.08) and corneal apex morphology. Conclusion. Significant lower CT was found in the KC group in T6 (3000 μm temporal to the fovea). No significant difference of CT values in KC patients and healthy subjects was found in the other twelve measurement locations.We found no association between the refractive and keratometric indexes obtained by corneal topography and subfoveal CT.

Distribution of Corneal Geometric Landmarks and Relationship Between Their Distances and Biomechanical Parameters in the Development of Keratoconus.

Purpose: To analyze the changes in coordinates and distances among three typical geometric landmarks of the cornea, namely, the thinnest point (TP), maximum curvature (Kmax), and corneal apex (AP) during the development of keratoconus, and explore the potential relationship between these changes and the abnormalities of corneal biomechanics. Methods: Normal eyes (n = 127), clinical keratoconic eyes (CKC, n = 290), and the eyes of forme fruste keratoconus (FFKC, n = 85) were included; among them, the CKC group was classified into four grades based on the Topographic Keratoconus Classification (TKC) provided by Pentacam. A total of 38 Corvis ST output parameters and three distance parameters of three typical landmarks (DKmax-AP, DTP-AP, and DKmax-TP) based on Pentacam were included. The differences of parameters among the abovementioned six groups (Normal, FFKC, and CKC stage I to CKC stage IV) were analyzed. Spearman’s rank correlation test was performed to choose several dynamic corneal response (DCR) parameters that could best reflect the changes of corneal biomechanical characteristics during the progression of the disease, and the Pearson’s or Spearman’s correlation test was conducted to determine the association between the three distances and the selected DCR parameters in each grade. In addition, by flipping the X coordinate of the left eye on the vertical axis to reflect the direction of the right eye, the coordinates of TP and Kmax in different developmental grades were highlighted. Results: From CKC stage II, the three geometric landmark distances commenced to correlate with the corneal DCR parameters (CBI, SPA1, IR, DA Ratio 2, ARTh, MIR, Radius, Pachy, and DA Ratio 1), which could better represent the changes of biomechanical properties from normal cornea to keratoconus. From normal cornea to CKC stage IV, the coordinates of Kmax were gradually tended to the inferior temporal region from dispersion, while TP was always concentrated in the inferior temporal region. Although DKmax-AP, DKmax-TP, and DTP-AP all showed a gradual decreasing trend with the progress of the disease, the first two did not change significantly, and only DTP-AP significantly approached AP in the later stage of disease development. In addition, from the FFKC group, the corresponding values of DKmax-TP in each disease development group were smaller than DKmax-AP. Conclusions: In the later stage of keratoconus, the relationship between the three typical landmark distance parameters and DCR parameters is stronger, and even the weakening of corneal biomechanical properties may be accompanied by the merger of typical landmark positions.