Thin Corneas Research Articles

Corneal cross-linking in patients with keratoconus: up to 13years of follow-up.

To evaluate long-term safety and efficacy of corneal collagen cross-linking (CXL) in patients with keratoconus up to 13years. In this mono-centre exploratory study, we included all consecutive patients who underwent CXL in our cornea centre from 01/01/2007 to 12/30/2011 and met the inclusion criteria. CXL was performed in all patients according to the Dresden protocol. Evaluation included best-corrected visual acuity (BCVA), topographic keratometry by Scheimpflug corneal tomography and endothelial cell count (ECC). Follow-up measurements were taken up to 13years after treatment were compared with baseline values. The study enrolled 168 eyes. The mean age of our patients was 26.3years ± 7.8years. A complete topographic dataset was available 1year postoperatively for 142 eyes, 5years postoperatively for 105 eyes, 10years postoperatively for 61 eyes and 13years postoperatively for 9 eyes. BCVA increased statistically significant after 1year, 5years and 10years and non-significantly after 13years. All keratometric parameters with exception of posterior astigmatism showed a statistically significant decrease after 1year, 5years and 10years. After 13years, the decrease was statistically significant only in Kmax, K2 and thinnest cornea. No significant changes in ECC were detected. Three eyes received Re-CXL, none of the eyes received penetrating keratoplasty and no infections occurred in this cohort. CXL can slow down or even stop the progression of keratoconus in the majority of cases. The effect is long-lasting with excellent safety.

Динамика кератотопографических и биомеханических параметров роговицы после проведения акселерированного ультрафиолетового кросслинкинга с использованием защитного лоскута донорской роговицы в лечении прогрессирующего кератоконуса при «тонкой роговице»

Purpose. To analyze changes in the biomechanical and topographic parameters of the patient's cornea using the Corvis st (OCULUS, Germany) and Pentacam (OCULUS, Germany) device before and after accelerated ultraviolet crosslinking of the cornea using a donor cornea protective flap in the treatment of progressive keratoconus with "thin cornea" and compare the obtained data with the results after classical accelerated crosslinking. Material and methods. According to the proposed technology, 26 patients (26 eyes) were operated on with a diagnosis of progressive keratoconus 2nd stage with corneal pachymetry less than 400 µm, mean value 390 ± 40 µm. Comparison group – patients diagnosed with progressive keratoconus 2nd stage with corneal pachymetry over 400 µm, mean value 450 ± 40 µm, comparable in age and gender, being operated on using the technology of classical accelerated crosslinking. In addition to standard research methods, before and after surgery, patients underwent an assessment of the biomechanical and topographic parameters of the patient's cornea using the Corvis st (OCULUS, Germany) and Pentacam (OCULUS, Germany) devices. Results. The results obtained in both groups were comparable in all parameters: there was a decrease in keratometric parameters in the first months after the operation, with their further stabilization during the entire period of observation. The pachymetry value remained stable, no significant changes in UCVA and Correctable Visual Acuity were detected. Evaluation of specific keratotopographic indices (ISV, IVA, KI, CKI, IHD) showed their decrease both in the main and control groups, and Rmin tended to increase. The value of the inscribed radius tended to decrease, which indicates an increase in the stiffness of the cornea after classical accelerated crosslinking and crosslinking of the proposed technology. Conclusion. Application of the technology of accelerated ultraviolet crosslinking using a protective flap of the donor cornea in the treatment of progressive keratoconus with "thin cornea" leads to an increase in the rigidity of the cornea and stabilization of the ectatic process of the cornea in the postoperative period, just as with the classical technology of accelerated crosslinking. Keywords: progressive keratoconus, "thin cornea", accelerated ultraviolet crosslinking using a donor cornea protective flap, keratopotographic parameters of the cornea, biomechanical parameters of the cornea.

Рефракционная хирургическая коррекция зрения у пациентки с клинически тонкой роговицей на фоне миопии высокой степени

The article evaluates the clinical effectiveness of implantation of a phakic intraocular lens model (IOL) Visian ICL in a patient with a combination of high myopia and clinically thin cornea on the example of a clinical case. Implantation of a personalized posterior chamber phakic IOL is a clinically effective, safe and predictable method for the surgical correction of high myopia, including in patients with clinically thin corneas, when keratorefractive intervention is contraindicated. Keywords: myopia, phakic IOL ICL, intraoperative difficulties.

Long-Term Outcome of Corneal Collagen Crosslinking with Riboflavin and UV-A Irradiation for Keratoconus*

Purpose To evaluate long-term outcomes of corneal collagen crosslinking (CXL) using riboflavin and UV-A irradiation and to determine when to repeat CXL. Methods In this retrospective consecutive interventional case series 131 eyes of 131 patients (95 male, 36 female, mean age 29.7 ± 11.4 years) between 2006 and 2016 received standard CXL (Dresden protocol, epithelium-off) for progressive keratoconus. Corrected distance visual acuity (CDVA) and corneal tomography (K1, K2, K max) were repeatedly recorded 1 year (n = 103 eyes) to 10 years (n = 44) postoperatively. Only one eye per patient was included. Paired t-test or Wilcoxon matched-pairs signed rank test was used for parametric and nonparametric data, respectively. Results 1–3 years preoperatively, median K2 significantly increased by 1.1 D (p < 0.001). Postoperatively, median K2 increased by 0.1 D after 1 year, then decreased over the remaining postoperative period by 0.85 D (p = 0.021). K max fluctuated without significant change. Median apical corneal thickness decreased by 16 µm (p = 0.012) after 5 years and then returned to preoperative values. Mean CDVA showed a significant improvement (decrease in logMAR 0.08 after 10 years, p = 0.010). CXL non-responders, defined by a postoperative increase in K max>2 D, increased from 16% after 5 to 33% after 10 years. Risk factors for non-response were young age, high astigmatism (>4.3 D), thin cornea (<480 µm), poor initial visual acuity (CDVA ≥0.3 D), and atopic dermatitis. 4 eyes were re-treated 3–4 years after first CXL without complications and keratoconus stabilized thereafter. Conclusions CXL can slow or stop keratoconus progression. However, as the number of responders declines after 5 years, especially patients with risk factors may require re-treatment.

Epithelium-off corneal cross-linking versus transepithelial diluted alcohol and iontophoresis-assisted corneal cross-linking in keratoconus patients with thin corneas

Epithelium-off corneal cross-linking versus transepithelial diluted alcohol and iontophoresis-assisted corneal cross-linking in keratoconus patients with thin corneas

Comparison of safety and efficacy of silicone hydrogel contact Lens-assisted CXL and accelerated CXL in keratoconus patients with thin corneas.

To evaluate the efficacy and safety of silicone hydrogel contact lens-assisted corneal cross-linking (CL-CXL) and compare 12-month visual and topographic outcomes with accelerated CXL using hypo-osmolar riboflavin (A-CXL) in keratoconus patients with thin corneas (below 400 μm with epithelium). This retrospective study included 27 eyes of 27 keratoconus patients who underwent CL-CXL (n = 14) or A-CXL (n = 13). Uncorrected and corrected distance visual acuity (UDVA and CDVA) and data obtained from corneal topography were analyzed at baseline and again at 6- and 12-month follow-ups. Corneal demarcation line depth (DLD) was measured at one month, and changes in the corneal endothelial cell density (ECD) at 12 months were also assessed. Mean UDVA improved significantly in both groups at 12 months (all p < 0.05). Maximum keratometry (K-max) decreased by 1.04 ± 1.90 D in the CL-CXL group and by 0.87 ± 1.89 D in the A-CXL group at 12 months, which was not statistically significant (all p>0.05). Total corneal higher-order aberrations (HOAs) analysis showed a significant improvement in only the CL-CXL group at 12 months (p = 0.041). Average DLD was 227.18 ± 65.60 μm in the CL-CXL group and 245.30 ± 66.84 μm in the A-CXL group (p = 0.275). No significant change in ECD was found in either group (all p>0.05). Mean changes in UDVA, CDVA, K-max, K-mean, HOAs, and ECD were not statistically significant between the groups (all p>0.05). Silicone hydrogel CL-assisted CXL seems as effective as A-CXL in halting keratoconus progression in thin corneas with no side effects during the one-year follow-up period.

Initial Healing Effects of Platelet-Rich Plasma (PRP) Gel and Platelet-Rich Fibrin (PRF) in the Deep Corneal Wound in Rabbits

Platelet concentrates (PCs), including platelet-rich plasma (PRP) gel and platelet-rich fibrin (PRF), are autologous blood-derived biomaterials containing numerous growth factors. This study aimed to evaluate the initial healing effects of PRP gel and PRF on deep corneal wounds. Thirty-three eyes from New Zealand white rabbits were divided into four groups: group 1, lamellar keratectomy (LK); group 2, LK + commercial porcine small intestinal submucosal membrane (SIS); group 3, LK + SIS + PRP gel; and group 4, LK + SIS + PRF. Postoperative clinical and histological findings were observed for eight weeks. Group 1 showed no neovascularization during the observation period, and incompletely recovered with a thin cornea. Group 2 showed active healing through neovascularization, and a thick cornea was regenerated through the sufficient generation of myofibroblasts. Although group 3 showed a healing effect similar to that of group 2, angiogenesis and subsequent vessel regression were promoted, and corneal opacity improved more rapidly. In group 4, angiogenesis was promoted during initial healing; however, the incidence of complications, such as inflammation, was high, and myofibroblasts were hardly generated in the corneal stroma, which adversely affected remodeling. In conclusion, while PRP gel is a safe surgical material for promoting remodeling through vascular healing and myofibroblast production in deep corneal wounds, the use of PRF is not recommended.

Managing a middle-aged patient with bilateral neglected keratoconus

The Orbscan's benefits include providing a thickness map and being noncontact for keratoconus screening. However, several developing countries have delayed keratoconus management due to a lack of resources and qualified examiners. Here we report a case of underdiagnosed and mistreated by high astigmatism, leading to a neglected case of keratoconus. A 34-year-old woman is bothered by her developing blurred eyesight and habit of scratching her eyes. The streak retinoscopy examination revealed the right eye was 5/20 cc S+7.75 C-6.00 Axis 150 became 5/15 and 5/20 cc S+7.25 C-6.00 Axis 80 became 5/15 for the left eye. The Placido test revealed irregular lines. The Schirmer test showed dry eyes. Slit-lamp examination revealed irregular thin cornea, Munson sign, Rizzuti's sign, and Vogt's striae were positive. The manual keratometer showed remarkably high corneal powers. The corneal topography showed characteristics of keratoconus. Scleral contacts with AS-OCT guiding were inserted into both eyes. Each eye's final BCVA improved to 5/12 and 5/6.5, respectively. The patient attained better visual performance and comfort. Detecting keratoconus by corneal topography and scleral contact lens fitting improved visual acuity. A skillful practitioner and accessible sources are essential to prevent these neglected cases.

Mapping of corneal birefringence in thin and asymmetric keratoconus corneas with ultrahigh-resolution polarization-sensitive OCT.

To evaluate phase retardation (PR) across healthy eyes and eyes with thin corneas (<500 μm) and with asymmetric and bilateral keratoconus (KC). Narayana Nethralaya Eye Hospital, Bangalore, India. Observational cross-sectional. There were 4 eye groups: healthy eyes (Group 1; n = 10 eyes), eyes with thin corneas and no clinical disease (Group 2; n = 10 eyes), eyes with asymmetric KC (Group 3; n = 5 eyes), and eyes with clinical KC (Group 4; n = 15 eyes). All eyes were imaged with polarization-sensitive optical coherence tomography (PS-OCT), MS-39, and Corvis-ST. Using PS-OCT, PR was analyzed in annular regions. The anterior (A-E) and Bowman (E-B) wavefront aberrations, epithelial Zernike indices (EZI), total corneal thickness, Corvis biomechanical index (CBI), total biomechanical index (TBI), and Belin-Ambrósio overall deviation index (BAD-D) were analyzed. Only CBI, TBI, BAD-D, A-E and E-B aberrations, EZI, and total corneal thickness distributions of Groups 1 (n =10), 2 (n =10), and 3 (n =5) were similar ( P > .05) but not CCT ( P < .05). PR distributions clearly showed that the eyes in Groups 1, 2, and 3 had a normal corneal birefringence unlike Group 4 (n = 10) eyes ( P < .05). The PR map was similar to the preferred orientations of collagen fibers seen in X-ray diffraction ex vivo studies of corneal stroma. PR distributions may eliminate the uncertainty associated with the stromal status of thin and asymmetric KC corneas. Group 2 and 3 eyes appeared as healthy because of normal corneal birefringence at the time of imaging, but a longitudinal follow-up of these eyes with PS-OCT may assist in early detection of onset of disease.

Effect of Age Under 20-60 years on Central Corneal Thickness

The measurement of central corneal thickness is an important measure for the diagnosis of corneal pathologies. 510–520 microns is the standard central corneal thickness. Optical or ultrasound techniques are used for the measurement of thickness CCT. Objectives: To evaluate the effect of age on central corneal thickness in normal population visiting The University of Lahore Teaching Hospital, Raiwind road Lahore. Methods: Descriptive study design was used. Data was obtained from The University of Lahore Teaching Hospital, Raiwind road Lahore. The sample size of patients was 147 with ages ranging from 20 to 60 years. All genders were included in the data collection. Data were collected through convenient sampling technique by using researcher administrative performa and study was finalized in three months after the approval of synopsis. Data entry and analysis were done using computer software SPSS version 25.0. CCT was measured by non-contact Pachymeter (Canon TX-20P) and values were represented in the form of frequency tables and bar charts. Results: CCT drops over time, resulting in thinner corneas in older people. The dependence of CCT on age is greater in men. Mean CCT in male individuals were 538.66 µm and in females mean CCT was 540.37µm. In this study mean central corneal thickness values of right and left eyes were also compared. In males right mean CCT value was 537.94 µm and left mean CCT was 539.39µm. In females the mean CCT value of right was540.28µm and left mean CCT value was 540.47µm. Conclusions: The Central Corneal Thickness decreases with age. Men have thinner corneas than females in every age group.

Visual Outcomes of Small-Incision Lenticule Extraction (SMILE) in Thin Corneas.

We aimed to find out whether thin (≤500 μm) or normal (>500 μm, control) corneal thickness would impact efficacy and safety outcomes of small-incision lenticule extraction (SMILE). We retrospectively analyzed medical records of adult patients who had undergone SMILE. A total of 57 eyes were included in the “thin corneas” group and 180 eyes in the “control” group. At one month after surgery, rates of patients with uncorrected distance visual activity (UDVA) ≥ 0.8 were significantly higher in patients from the control group compared to the “thin corneas” group (87 vs. 71%, respectively p < 0.01), though rates were comparable at 3 months (87 vs. 76%, respectively, p > 0.05). SMILE had comparable safety in patients with thin and normal corneas. Procedure result predictability was comparable between groups. Regression analysis demonstrated that cap thickness impacted posterior corneal biomechanics, and the volume of removed tissue had a higher influence in patients with thin corneas. Moreover, an increase in cap thickness was associated with better final BCVA. Further study is needed for the evaluation of the impact of thin corneas on SMILE outcomes and planning. Our study also indicates that patients with thin corneas might require a different approach to nomogram calculation.

Current clinical practice in corneal crosslinking for treatment of progressive keratoconus in four Nordic countries.

To evaluate clinical practice in the diagnosis and treatment of progressive keratoconus with corneal crosslinking (CXL) in four Nordic countries. A questionnaire was sent to all centres at which keratoconus patients are evaluated and CXL is performed in Sweden, Denmark, Norway and Iceland. Nineteen of 20 centres participated. CXL is performed approximately 1300 times per year in these four Nordic countries with a population of around 21.7 million (2019). In most cases, progression is evaluated using the Pentacam HR, and the maximum keratometry reading (Kmax ) is considered the most important parameter. The most frequently used treatment protocol in Scandinavia is the 9mW/cm2 epi-off protocol, using hydroxylpropyl methylcellulose riboflavin (HPMC-riboflavin). The participants deemed the following areas to be in most need of improvement: adaptation of the CXL protocol to individual patients (5/19), the development of effective epi-on treatment protocols (4/19), optimal performance of CXL in thin corneas (4/19), improvement of the definition of progression (2/19), and diagnosis of the need for re-treatment (2/19). We concluded that the diagnosis of progressive keratoconus and the diagnostic equipment used are similar. Treatment strategies are also similar but are suitably different to provide an interesting basis for the comparison of treatment outcomes. The high degree of participation in this survey indicates the possibility of future scientific collaboration on CXL focusing on the areas deemed to need improvement. It would also be of interest to evaluate the possibility of creating a Nordic CXL Registry. The high number of CXL treatments performed ensures sufficient statistical power to solve many questions. Such a registry could be an important contribution to evidence-based care and would allow for longitudinal evaluation.

Features of the Biomechanical Parameters of the Eye Fibrous Membrane and the Index of the Biomechanical Glaucoma Factor in Various Clinical Situations

Objective: to analyze the biomechanical parameters of the eye fibrous membrane and the biomechanical glaucoma factor (screening index for low-pressure glaucoma) studied by the Oculus Corvis ST device in various clinical situations.Patients and Methods: the study included 382 eyes, 181 eyes with glaucoma (47 %), 201 eyes without glaucoma (53 %). Patients were divided into groups: without glaucoma, with glaucoma (POAG, NTG, PEG), with keratotomy, depending on the CCT and axial length. Corneal tomography and biomechanical parameters were measured using Pentacam (Oculus) and Corvus ST, respectively.Results in patients without glaucoma, the stiffness of the eye increases with age (increasing SSI). Even higher SSI in the PEX group. Higher BGF values compared to the control. With PEG, the CCT is thinner, p = 0.005, bIOP is higher than p = 0.038, SSI is higher than p = 0.00 than in the control. With NTG, the CCT is thinner, p = 0.002, bIOP is lower than p = 0.000, DA ratio, R is higher (p = 0.000) than in the control. In all groups, BGF is higher than in the control (POAG p = 0.016, PEG and NTG p = 0.000). With ketatotomy, DA ratio, R and SP-A1 p = 0.000, lower than with myopia, and SST is higher, p = 0.000, BGF is almost twice as high. With a thin cornea, the DA ratio, R, SP-A1 (p = 0.000) and SSI p = 0.044 are lower than in the control, BGF is higher than p = 0.000. With a axial length of more than 24.00 mm below the DA ratio p = 0.034, BGF above p = 0.000.Conclusion: with age, with different CCT, with increasing axial length, with different forms of glaucoma and keratotomy, the indicators of the fibrous membrane of the eye change.

Brittle cornea syndrome: A tale of three brothers

Brittle cornea syndrome (BCS) is a genetic connective tissue disorder with discernible ocular features such as blue scleral and thin cornea that predominantly presents in younger children. We herein describe cases of three siblings with BCS, two of whom presented to us with open globe injuries following trivial trauma. Clinical examination of the other eye in both showed diffusely thin corneas and blue sclera. A systemic evaluation revealed sensorineural hearing loss and hyperextensible joints. The third sibling was screened and found to have features concurrent with BCS. This report highlights the challenges faced in the management of ocular injuries and consecutive complications in these patients.

Имплантация кольца myoring для коррекции миопии высокой степени у пациента с нистагмом

Purpose. Analysis of clinical and functional results and quality of life after implantation of MyoRing in a patient with high myopia and nystagmus. Material and methods. Patient M., 29 years old, was implanted a myoRing using a femtosecond laser to correct high myopia. Uncorrected visual acuity (UCVA) on the operated eye before surgery was 0.03, corrected visual acuity (CVA) 0.5, spherical refractive component –10.25 D, cylindrical component –4.00 D. Keratometry OD 41.5 × 45.25 × 174°. Corneal hysteresis (CH) was 7.3 mm Hg and corneal resistance factor (CRF) was 6.6 mm Hg. The thickness of cornea in center was 513µm. The data on higher-order aberrations were in line with the generally accepted norm. Observation period – 2 years. Results. 2 years after the operation, visual acuity without correction at OD 0.6, with correction – 0.7. The spherical component was 0.75 D, cylindrical component was –1.25 D. Keratometry OD 30.5 × 31.5 × 171°. Corneal hysteresis was 8.5 mm Hg, corneal resistance factor was 6.9 mm Hg. The thickness of cornea in center was 518µm. All higher-order aberrations decreased, except for vertical Coma (Z3/–1), which increased by 0.35µm, horizontal Coma (Z3/+1), which increased by –0.06µm. According to the results of the questionnaire, the patient noted a significant improvement in visual functions in the period from 3 to 12 months. Problems with the quality of vision in conditions of reduced contrast and complaints of halos were present only in the first months (3–4 months) after surgery. Conclusion. The MyoRing implantation method for correction of high myopia in a patient with nystagmus is highly effective, safe, providing a refractive effect on the spherical and cylindrical component of refraction and enhancing the biomechanical properties of cornea. Keywords: myopia and complex myopic astigmatism, thin cornea, MyoRing ring, femtosecond laser.

Differences of Corneal Biomechanics Among Thin Normal Cornea, Forme-Fruste Keratoconus, and Cornea After SMILE.

Background: To compare the corneal biomechanics of thin normal cornea (TNC) with thinnest corneal thickness (TCT) (≤500 µm), forme-fruste keratoconus (FFKC) and cornea after small incision lenticule extraction (Post-SMILE) had their central corneal thickness (CCT) matched by Corneal Visualization Scheimpflug Technology (Corvis ST). Methods: CCT were matched in 23 eyes with FFKC, 23 eyes by SMILE in 3 months post-operatively, and 23 TNC eyes. The differences in corneal biomechanics by Corvis ST among the three groups were compared. Results: There was no significant difference in CCT among the three groups, and the biomechanically corrected intraocular pressure (bIOP) did not differ significantly among the three groups (all p > 0.05). There were significant differences in most DCR parameters between pre- and post-operatively (all p < 0.05). Compared with TNC, the values of corneal deflection amplitude during the first applanation (A1DA), length at the first applanation (A1L), corneal deflection amplitude during the second applanation (A2DA), and maximum deformation amplitude (DA) decreased in 3 months after SMILE (all p < 0.05), these values increased in the FFKC (all p < 0.05). Conclusion: The majority of the DCR parameters were different among the three groups. The parameters A1DA, A1L, A2DA, and DA may be different between TNC and Post-SMILE, TNC and FFKC, and Post-SMILE and FFKC.

Predictive factors of posterior corneal shift aftersmall incision lenticule extraction: a 5-year follow-up study.

The aim of this study was to determine risk factors affecting changes in posterior corneal elevation (PCE) and predict the 5-year stability after small incision lenticule extraction (SMILE). This retrospective, longitudinal study enrolled 161 patients post-SMILE. The PCE values were measured at the apex, thinnest, maximal and 24 other prespecified preoperative points and at 6 months, 1 year and 5 years postoperatively. Posterior corneas exhibited time-dependent, region-dependent and angle-dependent changes. For every dioptre increase in the absolute preoperative spherical equivalent (SE), 10-μm decrease in the central corneal thickness (CCT), 10-μm increase in the maximum lenticule thickness (MLT), 10-μm decrease in the residual bed thickness (RBT), 10% increase in the percentage ablation depth (PAD, MLT divided by CCT) and 10% decrease in the percentage stromal bed thickness (PSBT, RBT divided by CCT), PCE exhibited average forward displacements of 0.2-0.4, 0.2-0.7, 0.1-0.2, 0.1-0.3, 0.6-1.0 and 0.5-1.1 μm, respectively (p < 0.05). PSBT was the variable with the highest accuracy in predicting 5-year stability of posterior corneas (area under curve = 0.75). The cut-off values of SE, CCT, MLT, RBT, PAD and PSBT for increased PCE were -8.00 to -8.31 D, 481.0-498.5 μm, 139.5-144.5 μm, 255.5-263.5 μm, 26.9-28.3% and 48.9-52.6%, respectively. Eyes with thinner corneas, higher myopia requiring greater MLT and lower RBT exhibited greater predispositions towards posterior protrusion. The thresholds for preventing forward posterior corneal displacement were 26.9-28.3% for PAD and 48.9-52.6% for PSBT. Prediction of posterior corneal stability is useful for assessing surgical risks post-SMILE.

Оценка ближайших результатов имплантации факичной интраокулярной линзы модели Visian Implantable Collamer Lens (Visian ICL) пациенту с сочетанием миопии высокой степени и клинически тонкой роговицы

The article evaluates the clinical effectiveness of implantation of a phakic intraocular lens model (IOL) Visian ICL in a patient with a combination of high myopia and clinically thin cornea on the example of a clinical case. Implantation of a personalized posterior chamber phakic IOL is a clinically effective, safe and predictable method for the surgical correction of high myopia, including in patients with clinically thin corneas, when keratorefractive intervention is contraindicated. Keywords: myopia, phakic IOL IPCLV 2.0, intraoperative difficulties.

Comparing Pentacam HR Screening Indices in Different Normal Corneal Thicknesses among Refractive Surgery Candidates.

Purpose:To compare Pentacam indices in normal eyes with different corneal thicknesses.Methods:It is a retrospective observational study. Ninety-six normal eyes of 96 patients who were referred for refractive surgery in a tertiary university-based hospital from October 2015 to April 2019 were recruited consecutively. Corneal keratometry as well as Pentacam's software Belin-Ambrósio Enhanced Ectasia Display (BAD) parameters including pachymetry progression indices (PPIs), maximum Ambrosio's relational thickness (ART-max), corneal elevations, normalized deviations, BAD total deviation value (BAD-D), and anterior surface indices were measured by Pentacam HR (Type 70900). The included were classified as thin (26 eyes), average (45 eyes), and thick (25 eyes) corneas with the thinnest point thickness of ≤496 μm, 497–595 μm, and ≥596 μm, respectively. The specificities of all parameters were calculated based on routine cut-off values.Results:The refraction, keratometry, and elevations were not different (P > 0.05). All PPIs (minimum, average, and maximum) of thick corneas were significantly lower than average and thin corneas (P < 0.001). ART-max increased by thickening of the cornea (P < 0.001). BAD-D score and normalized indices of pachymetric parameters decreased with the increase of thickness (P < 0.001), while specificities of all indices increased with corneal thickening. More than 96% of thick corneas were classified as normal PPI-max (24/25), ART-max (25/25), and BAD-D (25/25), while nearly <54% of thin corneas (14/26 for PPI-max, 9/26 for ART-max, and 12/26 for BAD-D) were normal.Conclusions:The pachymetry-related indices and BAD-D were different among normal corneas with various thicknesses. The specificities of PPIs, ART-max, and BAD-D of thin corneas were lower than in thick corneas.

Thinner Central Corneal Thickness is Associated with a Decreased Parapapillary Vessel Density in Normal Tension Glaucoma.

This retrospective cross-sectional study, which enrolled 124 normal tension glaucoma (NTG) eyes and 68 healthy eyes as the control, determined the association between central corneal thickness (CCT) and ocular parameters in NTG. CCT was measured using the Pentacam® system, optical coherence tomography angiography (OCT-A) was adopted to measure the peripapillary and macular area VDs, and spatial data were based on the Garway–Heath map as illustrated in OCT-A. Univariate and multivariate linear regressions were used to statistically analyze for associations between CCT and other factors. In this study, the mean age was similar for both the NTG and control groups. The mean CCT of the NTG group was significantly thinner than that of the control group (533.97 ± 33.11 µm vs. 546.78 ± 38.21 µm; p = .022). Considering all the factors, CCT negatively correlated with visual field (VF) pattern standard deviation (univariate, p = .045). To analyze structural and functional factors separately, we found a significant positive correlation between CCT and whole disc radial peripapillary capillary VD (VDRPC; multivariate, p = .019). To analyze the relationship between all factors and sectoral changes in VDRPC, a significant positive correlation was observed between CCT and inferior temporal VDRPC (univariate, p = .039) and inferior nasal VDRPC (VDRPC IN; univariate, p = .048). In conclusion, this novel study shows that among NTG participants, a thinner cornea correlated with weaker biomechanical properties susceptible to optic nerve tissue displacement, especially in response to mild transient elevation of IOP, leads to compromised ocular microcirculation.