Thin Corneas Research Articles

Features of the Biomechanical Parameters of the Fibrous Capsule of the Eye in Patients after Radial Keratotomy

Objective: to identify the features of biomechanical parameters of the fibrous capsule of the eye in patients after radial keratotomy (RK). Materials and methods. 87 eyes were examined after radial keratotomy, the average age was 59.8 ± 0.83 years. With glaucoma 47 eyes, without — in 40 eyes. Patients were divided into three groups: 17 eyes with a central corneal thickness (CCT) of less than 530 microns; 30 eyes with a CCT of 530–580 microns; 40 eyes with a CCT of more than 580 microns. The control group consists of myopic patients without glaucoma, without PES, over 45 years old. Corneal tomography and biomechanical parameters were measured using Pentacam (Oculus) and CorVis ST, respectively. Results. in the eyes after RK, the corneal stiffness (DA ratio, R) is higher in comparison with the control and increases with an increase in CCT. The stiffness of the fibrous capsule of the eye (SP-A1) after RK is reduced in comparison with the control and increases with an increase in CCT. The SSI analysis showed a higher stiffness of the eyeball than in the control, regardless of the CCT. BGF is higher in the eyes after RK compared to the control with the maximum value for thin corneas. Hyperopic shift (HS) after RK is distinctive for eyes with glaucoma. With a CCT of more than 580 microns, HS is a clinical glaucoma detector, with thin corneas, it is not. Conclusion. The eye after RC is characterized by an increase in the stiffness of the cornea, a decrease in the stiffness of the fibrous capsule of the eye, a general increase in the stiffness of the eyeball and HS.

Long-term outcomes of tailored stromal expansion with refractive lenticule for crosslinking thin corneas.

To assess the long-term safety and stability of visual outcomes following the modified technique of collagen crosslinking (CXL) using refractive lenticule in eyes with thin corneas (<400 µm) and progressive keratoconus. A tertiary eye care hospital in India. Prospective, interventional case series. Eyes with progressive keratoconus and thin corneas (<400 µm) underwent CXL with intraoperative stromal augmentation using a refractive lenticule obtained from small-incision lenticule extraction (SMILE). Preoperative and postoperative evaluation (3 months, and then yearly thereafter) included corneal tomography (Oculus Pentacam), uncorrected and corrected distance visual acuity (UDVA and CDVA, respectively), manifest refraction, and endothelial cell count (specular microscopy), and adverse events, if any, were noted. The patients were followed up for a period of 5 years. Seven eyes were included in the analysis. Mean corneal flattening of -4.29 D was noted from preoperative maximum keratometry (P = 0.018). An improvement in UDVA and CDVA of 0.38 logarithm of minimum angle of resolution (logMAR) and 0.36 logMAR, respectively, was noted at 5 years postoperative visit. Four eyes demonstrated a gain of two lines in CDVA. Mean spherical equivalent improved from -6.85 D preoperatively to -6.05 D at 5 years postoperatively. Clear demarcation line was noted between 230 to 270 µm on anterior segment optical coherence topography. No significant endothelial cell loss was noted postoperatively. Long-term outcomes demonstrated safety and disease stability following lenticule-assisted CXL.

Investigation of the safety and effectiveness of accelerated contact lens-assisted corneal cross-linking (A-CACXL) in thin corneas.

To determine the safety and effectiveness of accelerated contact lens-assisted corneal crosslinking (A-CACXL) as an alternative method in progressive keratoconus patients with thin corneas. In our retrospective study, 31 eyes from 25 patients with progressive keratoconus that with a minimum corneal thickness of 400 µm or less after epithelial debridement underwent A-CACXL with a follow-up 6 months or more were included. The main outcome measures were uncorrected distance(UDVA) and corrected distance(CDVA) visual acuities, manifest sphere(D) and manifest cylinder(D) refraction values, K1(D), K2(D), Kmax(D), mean keratometry(D) values, minimum corneal thickness(μm) and endothelial cell count(cells/mm2). These outcome measurements were statistically analyzed at preoperative and postoperative 1 month, 3 months, and 6 months follow-ups. 31 eyes from 25 patients with the mean follow-up period of 7.7 ± 2.7 months were included. Data revealed a significant increase in CDVA(p = 0.053). There is no statistically significant change in UDVA, K1, mean keratometry, mean manifest sphere value, minimum corneal thickness and endothelial cell count .(respectively p:0.053, p: 0.333, p: 0,129, p:0.490, p: 0,467, p:0.035, p:0.102). There is a statistically significant decrease in the K2, Kmax and mean manifest cylinder values.(respectively p: 0,030, p < 0,001, p < 0,001). A-CACXL method is a safe and effective method to stop keratoconic progression and improve functional vision in patients with thin corneas. However, larger randomised controlled studies are needed to validate these findings.

The influence of altitude on the differences between Goldmann tonometry and Pascal dynamic contour tonometry: An ecological meta-analysis.

A meta-analysis found that including atmospheric pressure as altitude in generalized linear models reveals higher differences between Goldmann tonometry and Pascal dynamic contour tonometry at higher altitudes, with the difference increasing in thinner corneas. To examine the difference in intraocular pressure (IOP) measurements by using Goldman applanation tonometry (GAT) and dynamic contour tonometer (DCT) tonometry in published literature and determine the influence of central corneal thickness (CCT), age, and altitude on that difference. Articles that compare GAT and DCT were selected for an extensive literature review, and the location and altitude of the research centers were found online. CCT and age were analyzed as covariates, when available. A total of 157 studies including 24,211 eyes of 20,214 patients were included in the study. The results showed that the difference between DCT and GAT was higher at higher altitudes above sea level and increased with thinner corneas. However, the results were different in eyes with corneal transplants, where altitude and CCT had less influence, and in those post-refractive surgery where age was found to influence the difference. Theoretical correction formulas using altitude, CCT, and age were derived from this meta-analysis, but their accuracy and usefulness in clinical practice need validation. The findings suggest that there is a higher risk of underestimating IOP when the Goldmann tonometer is used at a higher altitude, particularly in eyes with glaucoma, thinner corneas, or corneal refractive surgery. Further research is needed to validate the accuracy of the correction formulas derived from this meta-analysis in clinical practice.

Biomechanical properties of cornea and ocular aberrations in myopic eyes.

To study the correlation of corneal topography, corneal biomechanical properties, and ocular aberrations with the magnitude of refractive error in myopic eyes. All myopic patients attending the clinic for refractive surgery were recruited. Data recorded included visual acuity, axial length (AL), central corneal thickness (CCT), manifest refraction spherical equivalent (MRSE), topography (Pentacam - Oculus), corneal biomechanical factors [ocular response analyzer (ORA)], and optical aberrations (iTrace). They were further categorized into group 1 (suitable for femto-LASIK) and group 2 (unsuitable for femto-LASIK). Sixty eyes (30 myopes) of mean age 22.78 ± 2.71 years were enrolled. A negative correlation of refractive error was noted with AL (ρ = -0.9; P < 0.001), total aberrations (ρ = 0.53; P < 0.001), and lower-order aberrations (LOA) (ρ = 0.54; P < 0.001). A strongly positive correlation was noted between CCT and corneal hysteresis (CH) (ρ = 0.63; P < 0.001), CCT and CRF (ρ = 0.56; P < 0.001), CH and corneal resistance factor (CRF) (ρ = 0.83; P < 0.001), and Goldmann equivalent intraocular pressure (IOPg) and corneal compensated intraocular pressure (IOPcc) (ρ = 0.78; P < 0.001). An increase in higher-order aberrations (HOAs) as well as lower-order aberrations (LOAs) was noted with increasing sim-K [HOA (r = 0.73, P = 0.001); LOA (r = 0.601, P = 0.014)] and increasing CRF [HOA (r = 0.5, P = 0.006); LOA (r = 0.732, P = 0.001)] in group 2. The amount of refractive error, axial length, central corneal thickness, and sim-K were significantly different in the two groups. Increasing degree of myopia is associated with an increase in axial length, total aberrations, and lower-order aberrations. Corneal biomechanical parameters have a strong correlation with each other. Lower corneal biomechanics are noted in high myopes as they have weaker and thinner corneas. Corneal biomechanics and ocular aberrations do not differ significantly between cases suitable for femto-LASIK and cases unsuitable for femto-LASIK.

Correlation Between Central Corneal Thickness and Intraocular Pressure with the Goldmann Applanation Tonometer

Purpose: The aim of this review is to investigate the correlation between central corneal thickness (CCT) and Intraocular pressure with the Goldmann applanation tonometer (GAT).&#x0D; Materials and Methods: A literature search using Medline database was conducted for the years 1946 to 2022 to explore the relationship between central corneal thickness and Intraocular pressure measured by the Goldmann applanation tonometer. The search was restricted to studies published in English language. The first 80 articles were reviewed and five relevant studies were selected in this analysis.&#x0D; Findings: Impacts of central corneal thickness on Intraocular pressure were investigated in five studies. Overestimation of intraocular pressure is associated with thick cornea while underestimation of intraocular pressure was associated with thin cornea&#x0D; Implications to Theory, Practice and Policy: Central corneal thickness can affect the result of Intraocular pressure measurement with the Goldmann applanation tonometer (GAT) . Assessment of central corneal thickness (CCT) is necessary for correct interpretation of IOP measurements obtained with the Goldmann applanation tonometer (GAT).

A COMPARATIVE STUDY OF CORRELATION BETWEEN CENTRAL CORNEAL THICKNESS AND INTRAOCULAR PRESSURE IN PRIMARY OPEN-ANGLE GLAUCOMA WITH HEALTHY CONTROL SUBJECTS

Objective: The objective of the study is to compare the central corneal thickness (CCT) of primary open-angle glaucoma (POAG) patients with healthy subjects. Methods: A prospective, hospital-based, cross-sectional study conducted on total 100 consecutive subjects of age 40–60 years, 50 subjects of POAG, and 50 healthy controls presenting to the eye OPD in study period August 2021 to July 2022, at Department of Ophthalmology, Sardar Patel Medical College and Associated Group of Hospital, Bikaner, Rajasthan. Results: Mean age was 49.56±7.17 years in Group A and 52.36±7.86 years in Group B (p&gt;0.05). 40% had 6/9 vision followed by 34% had 6/6 vision in Group A and 44% had 6/9 vision followed by 40% 6/12 vision in Group B (p&lt;0.05). All cases in Group A had intraocular pressure (IOP) of 10–20 mmHg and 60% had IOP of 21.1–25.0 mmHg. (p&lt;0.05). Mean CCT was 545.2±38.51 μm in Group A and 519.35±40.52 μm in Group B (p&lt;0.05). Conclusion: Patients with thin corneas are more likely to develop POAG.

A double-crosslinked nanocellulose-reinforced dexamethasone-loaded collagen hydrogel for corneal application and sustained anti-inflammatory activity

In cases of blinding disease or trauma, hydrogels have been proposed as scaffolds for corneal regeneration and vehicles for ocular drug delivery. Restoration of corneal transparency, augmenting a thin cornea and postoperative drug delivery are particularly challenging in resource-limited regions where drug availability and patient compliance may be suboptimal. Here, we report a bioengineered hydrogel based on porcine skin collagen as an alternative to human donor corneal tissue for applications where long-term stability of the hydrogel is required. The hydrogel is reinforced with cellulose nanofibers extracted from the Ciona intestinalis sea invertebrate followed by double chemical and photochemical crosslinking. The hydrogel is additionally loaded with dexamethasone to provide sustained anti-inflammatory activity. The reinforced double-crosslinked hydrogel after drug loading maintained high optical transparency with significantly improved mechanical characteristics compared to non-reinforced hydrogels, while supporting a gradual sustained drug release for 60 days in vitro. Dexamethasone, after exposure to crosslinking and sterilization procedures used in hydrogel production, inhibited tube formation and cell migration of TNFα-stimulated vascular endothelial cells. The drug-loaded hydrogels suppressed key pro-inflammatory cytokines CCL2 and CXCL5 in TNFα-stimulated human corneal epithelial cells. Eight weeks after intra-stromal implantation in the cornea of 12 New-Zealand white rabbits subjected to an inflammatory suture stimulus, the dexamethasone-releasing hydrogels suppressed TNFα, MMP-9, and leukocyte and fibroblast cell invasion, resulting in reduced corneal haze, sustained corneal thickness and stromal morphology, and reduced overall vessel invasion. This collagen-nanocellulose double-crosslinked hydrogel can be implanted to treat corneal stromal disease while suppressing inflammation and maintaining transparency after corneal transplantation. Statement of significanceTo treat blinding diseases, hydrogel scaffolds have been proposed to facilitate corneal restoration and ocular drug delivery. Here, we improve on a clinically tested collagen-based scaffold to improve mechanical robustness and enzymatic resistance by incorporating sustainably sourced nanocellulose and dual chemical-photochemical crosslinking to reinforce the scaffold, while simultaneously achieving sustained release of an incorporated anti-inflammatory drug, dexamethasone. Evaluated in the context of a corneal disease model with inflammation, the drug-releasing nanocellulose-reinforced collagen scaffold maintained the cornea's transparency and resisted degradation while suppressing inflammation postoperatively. This biomaterial could therefore potentially be applied in a wider range of sight-threatening diseases, overcoming suboptimal administration of postoperative medications to maintain hydrogel integrity and good vision.

Lenticule Intrastromal Keratoplasty for the Correction of Iatrogenic High Hyperopia.

The aim of this study was to evaluate the safety, efficacy, and predictability of lenticule intrastromal keratoplasty (LIKE) for the correction of iatrogenic high hyperopia. Three patients (4 eyes) were referred to our department because of overcorrection of myopia induced by femtosecond laser-assisted in situ keratomileusis. All eyes exhibited hyperopia (between +4.00 and +8.00 D) and thin corneas ranging from 307 to 378 μm. Because of the regression of the use of laser ablation to correct high hyperopia and thin corneas, we initially adopted LIKE to correct iatrogenic high hyperopia in all 4 eyes. The uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), manifest refraction, corneal topography, and anterior segment optical coherence tomography findings were recorded during each follow-up evaluation. No postoperative complications, such as interface haze and opacification, were observed in the 4 eyes during each follow-up evaluation, with an average follow-up of 9.50 months. All eyes had significantly improved UDVA postoperatively. A total of 3 eyes achieved an UDVA of 20/25 or better while the other 1 eye had an UDVA of 20/40 postoperatively. In addition, 2 of the 4 eyes had a postoperative UDVA equal to or better than preoperative CDVA. No eyes lost any CDVA lines. All 4 eyes were within ±0.50 D of the spherical power (intended target of 0). The central corneal thickness and curvature of the anterior corneal surface in all 4 eyes increased postoperatively. Anterior segment optical coherence tomography revealed that the lenticule was transparent, with no wrinkles or offsets, during each follow-up evaluation. LIKE for the correction of iatrogenic hyperopia has good efficacy and safety. Although an extremely thin cornea after overcorrection may not be suitable for hyperopic laser enhancement, LIKE is a good choice because of its good predictability and ability to restore the normal corneal structure.

Early, Forme Fruste keratoconus and normal thin cornea, evaluation of sensitive parameters by combined Placido Scheimpflug topography.

To determine the sensitive indices distinguishing forme-fruste keratoconus (FFKC) and early keratoconus (early KC) from thin normal corneas, and their cutoff values using Sirius topography. 156 eyes with normal thin corneas < 500 um (group 1), 99 eyes with early KC (group 2) and 41 eyes with FFKC (group 3), were assessed retrospectively for: corneal keratometric indices, pachymetry indices, corneal aberrations, elevation indices; thinnest corneal point elevation, Q value, root mean square (RMS) withRMS/ area (RMS/A); and KC summary indices of front and back surfaces; surface asymmetry index (SIf, SIb), elevation at KC vertex (KVf, KVb), Baiocchi-Calossi-Versaci index (BCVf, BCVb) and summation of its vector (BCV). Cutoff values were calculated. Keratometry indices were significantly different between early KC and thin normal cases (apex front curvature had the highest area-under-the-ROC-curve (AUROC) (0.926) in early KC, while only apex curvature and coordinates were significant in FFKC cases. Pachymetry indices did not show any significance in differentiating either early KC or FFKC from normal thin corneas. KC summary indices were highly significant among the 3 groups. The highest AUROC was observed with KVb in early KC (0.987) and with KVf in FFKC (0.831). Vertical coma and vertical trefoil showed the highest significance of all aberration parameters differentiating the 3 groups. Thinnest point elevation, RMS and RMS/A showed the highest AUROC in differentiating early KC and FFKC cases from thin normal corneas. Comparing early KC and FFKC to thin normal corneas, Sirius provided high precision in prediction.

Identification and Management of a Novel PRDM5 Gene Pathologic Variant in a Family With Brittle Cornea Syndrome.

The aim of this study was to report a novel PRDM5 pathologic variant and ophthalmic findings in a family with 3 children diagnosed with brittle cornea syndrome (BCS). Histopathologic findings and surgical outcome of a child with BCS who underwent full-thickness corneal transplant are described. This is an observational case report of a nonconsanguineous Laotian family with 3 siblings diagnosed with BCS. Data collected included visual acuity, cycloplegic refraction, slit-lamp biomicroscopy, dilated fundus examination, corneal pachymetry, corneal topography, and general medical findings. Targeted testing through PRDM5 gene sequencing with copy number variation detection was conducted. The 3 siblings included a 12-year-old boy and 8- and 6-year-old sisters, all of whom presented with myopia, blue-tinted sclerae, thin corneas, and variable corneal scarring. All 3 affected children were found to be homozygous for the PRDM5 gene variant c.1117_1123delinsTTTAATGCTTACAAATGTTTG p.Asp373Phefs*57. Coding sequences of PRDM5 and ZNF469 genes were sequenced in their entirety, and this was the only pathologic variant present in this family. The youngest affected sister developed persistent hydrops with severely decreased vision and underwent penetrating keratoplasty. Histopathology revealed severe corneal thinning, diffuse absence of Bowman layer, and ruptured Descemet membrane scrolls. Three siblings with clinical signs of BCS, including corneal thinning, myopia, and blue sclerae, were found to have a novel PRDM5 gene pathologic variant. This pathologic variant has not been previously reported, although 1 downstream nonsense pathologic variant has been reported as pathogenic. The similar phenotypes in all affected patients support the pathogenicity of this variant. Surgical management of BCS presents unique challenges due to severe tissue fragility.

Assessment of the iCare HOME2, a New IOP Self-Measurement Tonometer.

The iCare HOME2 tonometer generally can be considered reliable for most eyes and clinical settings, although it may produce slightly overestimated or underestimated intraocular pressure readings in thicker and thinner corneas, respectively. To evaluate the accuracy, correlation, and analysis of differences in intraocular pressure (IOP) measurements between the gold standard Goldmann applanation tonometer (GAT) and the new, self-measurement iCare HOME2 tonometer (icare, Vantaa, Finland). In this retrospective study, patients were randomly selected from those who attended for a routine examination in our clinic. After a complete ocular examination, each patient's IOP was measured and recorded with GAT (IOPG) and iCare HOME2 (IOPi). Central corneal thickness (CCT) was measured. Eyes with any corneal morbidity were excluded. Pearson's correlation coefficient was used to determine correlation between paired IOP measurements. Bland-Altman plots were graphed for the analysis of differences for IOP between the instruments. One hundred and thirty-five eyes of 70 patients were included in the study. The mean IOPG was 16.3 ±6.5mm Hg (range 3-56). The mean IOPi was 16.5 ±7.3mm Hg (range 3-55), (P=0.47). A strong, significant positive correlation was found for paired IOP measurements by the two instruments (r=0.94; P<0.0001). A small systematic proportional bias was seen for the paired IOP measurements, meaning that with higher IOPs the iCare HOME2 yielded higher IOP readings than GAT; but this difference was clinically insignificant. The instrument underestimated IOPs with corneas thinner than 522 µm while it overestimated IOPs when corneas were thicker than this. The iCare HOME2 could be a reliable tonometer for most eyes and clinical settings. CCT measurement is recommended in patients who use the instrument.

Parental Corneal Tomographic and Biomechanical Characteristics of Patients With Keratoconus

To investigate the hereditability of corneal tomographic and biomechanical parameters in keratoconus (KC). Prospective cohort study. This study was conducted at Qingdao Eye Hospital of Shandong First Medical University in Qingdao, China. Forty-four patients with KC and their biological parents (n=88) were recruited as the study group. The control group consisted of 84 healthy adults with matched age and gender. Both eyes of each participant underwent clinical examinations, and 1 eye was selected for statistical analysis. Exclusion criteria were as follows: individuals with glaucoma, ocular surgery, systemic diseases known to affect the eyes, or poor cooperation during examination. Subjects were asked to discontinue soft contact lens (CL) wear for 2 weeks and rigid gas permeable CL wear for 4 weeks before ocular examination. All participants underwent a comprehensive assessment including Pentacam Scheimpflug tomography, Corvis ST, visual acuity, refraction examination, axial length, and slitlamp examination for both eyes. Individuals presenting with KC manifestations in at least 1 eye were classified as having KC. A total of 9 Pentacam indices including keratometry in the flat/steep meridian (K1/K2), maximal keratometry (Kmax), thinnest point pachymetry (TP), and maximum/average Ambrósio relational thickness (ARTmax/ARTave), anterior and posterior surfaces elevation of the cornea (Ef/Eb) and total deviation value (Final D), and 21 biomechanical indices were collected. Associations of these factors with KC were evaluated using multiple comparison and binary logistics regression analyses. Two parents (2.27%) from 2 different families were diagnosed with KC. Parents of patients with KC had thinner corneas with altered corneal biomechanical parameters compared with healthy controls (P < .05). The combined tomographic and biomechanical index demonstrated the highest discriminatory power (area under the receiver operating characteristic curve 0.785) and strong specificity (84.5%). Parental corneal tomographic and biomechanical index, Corvis biomechanical index, and TP were identified as the major influential factors for KC in their offspring by logistic regression analysis, with a 73.3% accuracy in identifying offspring with KC. Parental corneal tomographic and biomechanical properties of patients with KC suggest a possible predisposition to KC. A combination of tomography and corneal biomechanics can be helpful in predicting the incidence rate of KC in the offspring of patients with subclinical KC.

Association between keratoconus and allergic conjunctivitis in children attending a Tertiary Hospital in Nigeria.

Objective: To ascertain an association between keratoconus and allergic conjunctivitis and to know if it is necessary to investigate all patients with allergic conjunctivitis for keratoconus. Methods: A hospital-based prospective study in which the eyes of children presenting with ocular allergic diseases were examined. Social demographics and clinical data were captured in a questionnaire. All the patients underwent keratometry using the autorefractor-keratometer and the pachymeter was used to measure the central corneal thickness. Data analysis was done with IBM SPSS version 28 for Windows. Frequency and chi-square were used as descriptive statistics to determine the association between dependent and independent variables. Inferential statistics using one-way ANOVA and t-test. P - Value at <0.05 was considered statistically significant. Results: 121 children with allergic conjunctivitis were reviewed. Males were 72 and females 49. The visual acuity was 6/ 6-6/ 18 in 116, and mild visual impairment - 6/ 18-6/ 60 in 5. The most common complaint was frequent itching in 109 (90.1%). Keratometry was normal in 120 (99.5%), while probable keratoconus was found by keratometry in only one patient (0.5%). Central corneal thickness was within the normal range in 33 (27.3%) children, 43 (35.5%) had thin corneas, while 45 (37.2%) had cornea thickness of more than 560 microns. Discussion: Pediatric keratoconus tends to be more aggressive than adult keratoconus with an increased risk of corneal opacities and subsequent keratoplasty. As a result of these negative impacts, early detection and prompt treatment are mandatory. Conclusion: The prevalence of keratoconus was not found to be high in this study population, but with facts emerging between the association of allergic conjunctivitis, and increased prevalence of keratoconus, it is pertinent to integrate keratoconus screening as part of the management of allergic conjunctivitis using an appropriate tool such as video keratography and slit lamp biomicroscope. Abbreviations: KC = Keratoconus, CLEK = Collaborative Longitudinal Evaluation of Keratoconus, SAC = Seasonal Allergic Conjunctivitis, PAC = Perennial Allergic Conjunctivitis, VKC = Vernal Keratoconjunctivitis, IOP = Intraocular Pressure, CCT = Central Corneal Thickness, TNF-α = Tumor Necrosis Factor-Alpha, IL = Interleukin.

Assessment of Risk Factors for Primary Open-angle Glaucoma

Introduction: primary open-angle glaucoma (POAG) is a chronic and progressive anterior optic neuropathy characterized by perimetric alterations and pathological excavation of the optic disc in the absence of other ocular pathologies or congenital anomalies. It is usually accompanied by an increase in intraocular pressure. Gonioscopic examination confirms that the iridocorneal angle is open. The term "risk factor" is defined as a condition statistically leading to an increased risk of occurrence of an event. The purpose of our work is to list the main risk factors of POAG.&#x0D; Patients and Methods: This is a retrospective study carried out in our ophthalmology department over a period of 4 years between January 2018 and December 2021, involving one hundred patients with POAG followed in glaucoma consultation.&#x0D; Results: These are 100 cases, with an average age of 64.27, with a male predominance. The most found risk factors in our series are: age, intraocular hypertension (IOH), thin cornea, arterial hypertension, diabetes and family history of glaucoma.&#x0D; Conclusion: The identification of the main risk factors of POAG at the individual level is a major data of the management. Knowing these factors helps to monitor patients at risk more carefully and to adjust the treatment more appropriately in patients likely to develop glaucoma or to aggravate already known glaucoma. More efforts are required for early screening and education on POAG in communities, especially in a POAG high-risk population.

Numerical simulation of aqueous flow in a novel posterior chamber phakic intraocular lens versus its counterparts

Phakic intraocular lenses (pIOLs), particularly posterior chamber pIOLs, are becoming important for patients with high myopia and thin corneas. By phakic intraocular, we mean the ocular environmental conditions, where the natural lens is unremoved. A new posterior chamber pIOL, the sine wave phakic refractive lens (SW-PRL), is in the development stage, and its aqueous humor (AH) dynamics and the effects of intraocular geometry on the flow characteristics are not well understood. To analyze the adaptability and functionality of SW-PRL, a comparison study is made with its counterparts, the posterior chamber phakic refractive lens (PC-PRL), PC-PRL combined with peripheral iridotomy [PC-PRL(PI)], and implantable collamer lens with a central hole (ICL V4c). The result demonstrates that SW-PRL has a positive effect on AH flow circulation. Interestingly, there is a relationship between a posterior chamber flow and the type of pIOLs with vault variation. With an increase in vault, the flow between the lens and pIOLs slowed down after ICL V4C implantation but accelerated after PC-PRL (PI) implantation with little change after SW-PRL implantation. On the rear surface of the iris, the wall shear stress (WSS) was lower for PC-PRL(PI), SW-PRL, and ICL V4c (5.6 × 10−4, 6 × 10−3, and 8.2 × 10−3 Pa, respectively) compared to the PC-PRL (0.14 Pa), and on the front surface of lens, the WSS was lower for PC-PRL and SW-PRL (1.16 × 10−5 and 9.7 × 10−6 Pa, respectively) compared to the ICL V4c (8.2 × 10−4 Pa). WSS on the cornea surface was similar for each pIOL. These might provide a fresh viewpoint on the clinical decision of different intraocular lenses.

Expanding indications for corneal cross-linking.

The aim of this study was to summarize the recent developments in corneal cross-linking (CXL) and its indications, including corneal ectasias, refractive surgery and infectious keratitis. Advances in CXL technology, such as the use of higher-intensity LED ultraviolet (UV) light sources and a better understanding of the UV-riboflavin photochemical reaction, have enabled safer and more effective methods of cross-linking thin and ultra-thin corneas, and more effective accelerated transepithelial/'epi-on' CXL procedures that are beginning to supplant the Dresden protocol as the 'gold standard' CXL method. CXL is also being used in combination with laser surgery, not only to expand the patient base who can receive refractive surgery, but also to help rehabilitate vision in patients with ectasia. CXL, and CXL combined with photorefractive keratectomy (PRK), can result in corneal flattening of 1-2 D, and corneal regularization of 4-5 D, respectively. Finally, photoactivated chromophore for keratitis-corneal cross-linking (PACK-CXL) has been shown to be an effective therapy for infectious keratitis, both alone, and in combination with antimicrobial drugs. CXL has evolved from a single technique to treat a single corneal ectasia, keratoconus, to several techniques with several indications, spanning a spectrum of corneal ectasias, as well as visual rehabilitation, refractive procedures and infectious keratitis treatment.

Ocular Biomechanics and Glaucoma.

Biomechanics is a branch of biophysics that deals with mechanics applied to biology. Corneal biomechanics have an important role in managing patients with glaucoma. While evidence suggests that patients with thin and stiffer corneas have a higher risk of developing glaucoma, it also influences the accurate measurement of intraocular pressure. We reviewed the pertinent literature to help increase our understanding of the biomechanics of the cornea and other ocular structures and how they can help optimize clinical and surgical treatments, taking into consideration individual variabilities, improve the diagnosis of suspected patients, and help monitor the response to treatment.

Repeatability of Scheimpflug based corneal tomography parameters in advanced keratoconus with thin corneas.

To determine the repeatability limits of corneal tomography parameters in patients with advanced and moderately thin keratoconic corneas to assist in planning thickness-based procedural interventions. Prospective, single-centre, repeatability study. Three tomography scans using the Pentacam AXL were obtained from patients with keratoconus with thinnest corneal thickness (TCT) ≦400 µm (sub-400 group) and compared to those with TCT = 450-500 µm (450-plus group). Eyes with previous crosslinking, intraocular surgery, or acute corneal hydrops were excluded. Eyes were age and gender-matched. The within-subject standard deviations for flat keratometry (K1), steep keratometry (K2), maximal keratometry (Kmax), astigmatism and TCT were used to calculate respective repeatability limits (r). Intra-class correlation coefficients (ICC) were also analysed. The sub-400 group comprised 114 eyes from 114 participants, and the 450-plus group comprised 114 eyes from 114 participants. In the sub-400 group, TCT was amongst the least repeatable parameters (33.92 µm; ICC 0.96), compared with the 450-plus group (14.32 µm; ICC 0.99, p < 0.01). In the sub-400 group, K1 and K2 of the anterior surface were the most repeatable parameters (r 3.79 and 3.22 respectively; ICC 0.97 and 0.98 respectively) compared with the 450-plus group (r 1.17 and 0.92 respectively; and ICC 0.98 and 0.99 respectively, p < 0.01). The repeatability of corneal tomography measurements is significantly reduced in sub-400 keratoconic corneas when compared to 450-plus corneas. Repeatability limits should be carefully considered when surgical interventions are planned for such patients.

Keratoconus tomographic indices in osteogenesis imperfecta

PurposeOsteogenesis imperfecta (OI) is a rare inherited disease affecting collagen-rich tissues. Ocular complications have been reported such as thin corneas, low ocular rigidity, keratoconus, among others. The purpose of this study is to characterize corneal tomographic features in OI patients compared to unaffected patients, with particular focus on commonly studied keratoconus indices.MethodsCross-sectional case–control study including 37 OI patients and 37 age-matched controls. Patients and controls underwent comprehensive ophthalmological examination including corneal Scheimpflug tomography with a Pentacam HR device (Oculus Optikgeräte GmbH, Wetzlar, Germany) to analyse and compare topometric, tomographic, pachymetric and Belin-Ambrósio Enhanced Ectasia Display III (BAD-D) data of both eyes of each patient.ResultsMost OI patients had type I disease (n = 24; 65%) but type III–VII patients were also included. Two patients had clinically overt bilateral keratoconus. OI patients had significantly higher maximum keratometry (45.2 ± 2.1 vs. 43.7 ± 1.2; p = 0.0416), front and back elevation (3.0 ± 3.3 vs. 2.1 ± 1.3, p = 0.0201; 11.1 ± 8.2 vs. 5.0 ± 3.7, p < 0.0001), index of surface variance (25.5 ± 13 vs. 17.4 ± 8.3; p = 0.0016), index of vertical asymmetry (0.21 ± 0.14 vs. 0.15 ± 0.06; p = 0.0215), index of height asymmetry (9.2 ± 14 vs. 6.0 ± 4.5; p = 0.0421), index of height decentration (0.02 ± 0.01 vs. 0.01 ± 0.01; p < 0.0001) and average pachymetric progression (1.01 ± 0.19 vs. 0.88 ± 0.14; p < 0.0001) readings. Thinnest corneal thickness and maximum Ambrósio relational thickness were significantly lower (477 ± 52 vs. 543 ± 26; 387 ± 95 vs. 509 ± 49; p < 0.0001). Two-thirds of OI patients had corneas with a minimum thickness < 500 µm. BAD-D value was significantly higher in OI patients (2.1 ± 1.4 vs. 0.9 ± 0.2; p < 0.0001).ConclusionOI patients showed significant changes in corneal profiles compared with healthy subjects. A high proportion of patients had tomographically suspect corneas when using keratoconus diagnostic indices. Further studies are warranted to assess the true risk of corneal ectasia in OI patients.