Corneal Optical Density Research Articles

The impact of postoperative nasal oxygen therapy on early-stage corneal edema in cataract patients with dynamic Scheimpflug analyze: A retrospective study.

This study aimed to assess the impact of 6 hours of postoperative nasal oxygen therapy on early-stage corneal edema in patients with nuclear cataracts of grades 3 to 4. A retrospective study involved 49 patients (49 eyes) with grades 3 to 4 nuclear cataracts undergoing phacoemulsification and intraocular lens implantation from September 2021 to September 2022. The oxygen group (27 cases) received postoperative nasal oxygen therapy for 6 hours, while the control group (22 cases) received no additional treatment. Corneal edema was evaluated 24 hours postoperatively using a slit lamp microscope, recording the edema degree. The Pentacam anterior segment analyzer measured central corneal thickness (CCT), corneal volume (CV), and corneal optical density (COD) values preoperatively and 24 hours postoperatively. The study enrolled 49 patients. Preoperatively, there were no significant differences between the 2 groups. The oxygen group and the control group exhibited significant differences in CCT, CV, and corneal optical density values before and after surgery for intragroup comparison (all P < .05). At 24 hours postoperatively, the proportion of grade 0 corneal edema in the oxygen therapy group was 59.3%, compared to 31.8% in the control group, with no statistically significant difference (P > .05). The postoperative logMAR visual acuity in the oxygen therapy group was 0.0969 (0.0969, 0.2218), and in the control group it was 0.0969 (0.2218, 0.3979), with a statistically significant difference (P < .05). In oxygen group, the CCT, CV were 585.00 (553.00, 604.00), 68.0 (61.9, 71.3) respectively, all significantly lower than 603.50 (578.50, 788.25), 73.05 (65.3, 75.73) (all P < .05). Statistically significant differences were found in overall COD, COD within specific depth and thickness ranges, and COD within the anterior layer (120 μm thickness) at 24 hours postoperatively (all P < .05). No significant difference was observed in COD values within the central and posterior layers (60 μm thickness) between the 2 groups (all P > .05). Postoperative nasal oxygen therapy for 6 hours immediately after surgery could alleviate the severity of early-stage corneal edema in patients with nuclear cataracts of grades 3 to 4.

The effect of different potency glucocorticosteroids treatments on tear inflammatory factors and corneal optical density after femtosecond-assisted laser in situ keratomileusis.

To assess the impact of glucocorticosteroids with varying potencies on inflammatory mediators in tears and corneal optical density after femtosecond-assisted laser in situ keratomileusis (FS-LASIK). In a prospective study, 110 patients (220 eyes) who underwent FS-LASIK were divided into 2 groups: 55 patients (110 eyes) received dexamethasone, and another 55 patients (110 eyes) received fluorometholone. Visual acuity, intraocular pressure, and corneal optical density were measured before, 1 week, and 1 month after surgery. Tear fluid samples were also collected to assess expression levels of TNF-α, IL-1α, IL-6, and TGF-β1. One week after the procedure, the dexamethasone group exhibited elevated intraocular pressure (IOP) levels (P > .05) and a decreased expression of TNF-α in tears (P < .001) compared to the fluorometholone group. Within the 0 to 2 mm range from the corneal apex, the anterior corneal layer's optical density in the fluorometholone group surpassed that of the dexamethasone group (P < .05). At 1 month post-surgery, the IOP in the fluorometholone group was higher than that in the dexamethasone group (P < .05). In both the 0 to 2 mm and 2 to 6 mm intervals from the corneal apex, the optical density of the anterior corneal layer was significantly higher in the fluorometholone group compared to the dexamethasone group (P < .05). There was no statistically significant difference in visual acuity between the 2 groups at any postoperative time point. Short-term use of potent corticosteroids after FS-LASIK can swiftly address ocular surface inflammation, enhance corneal wound healing, reduce corneal edema, and accelerate the restoration of corneal transparency, in contrast to prolonged use of milder corticosteroids post-surgery.

Comparison between a new transepithelial PRK vs. conventional alcohol-assisted PRK: Corneal densitometry and aberrometry study.

To describe and compare corneal densitometry, subjective refraction, visual acuity, and corneal higher order aberrations (HOA) after corneal refractive surgery using either alcohol-assisted photorefractive keratectomy (aaPRK) or single-step transepithelial PRK (tPRK). We conducted a retrospective and observational study. We analyzed 120 right eyes from 120 healthy consecutive myopic patients who underwent aaPRK or tPRK to correct myopia of up to 6 diopters and astigmatism of up to 2 diopters. The WaveLight EX500 excimer laser (Alcon Laboratories, Inc.) was used in all cases. Visual acuity, subjective refraction, and Pentacam AXL® measurements were performed at the preoperative visit and at 6-months follow-up visit. Pentacam AXL® software was used to assess corneal optical density in various annuli for different corneal depths and anterior corneal HOA (6 mm area of analysis). Preoperative spherical equivalent values were similar between groups preoperatively (-3.07 ± 1.52 and -3.38 ± 1.46 in the aaPRK and tPRK groups, respectively). There were no statistically significant differences in visual acuity and postoperative refraction between groups. Postoperative corneal densitometry did not show statistically significant differences in any of the areas studied and both surgical procedures obtained similar results. However, analysis of HOA showed statistically significant differences between the techniques (1.42 ± 0.39 and 1.80 ± 0.62 for the aaPRK and tPRK groups, respectively; p = 0.000). Both aaPRK and single-step tPRK gave comparable visual, refractive, and corneal density outcomes. Some differences were observed in HOA but were not clinically relevant.

Could Automated Objective Measurements Acquired at the Preoperative Stage Estimate the Corrected Distance Visual Acuity after Corneal Cross-Linking in Keratoconus?

Objective markers describing corneal optical density (COD), thinnest corneal thickness (TCT), and anterior (ARC) and posterior (PRC) surface radii over the 3 mm thinnest region of the cornea were investigated to provide a model for estimating corrected distance visual acuity (CDVA) after corneal cross-linking (CXL) in keratoconus. CDVA, COD, TCT, ARC, and PRC were monitored (using Pentacam™) over 1 year in patients with (1) keratoconus treated with routine CXL (2) relatively stable untreated keratoconus, and (3) age/gender-matched controls. In group 1 (n = 77), the median logMAR CDVA (mode, interquartile range) improved significantly (p < 0.01) from 0.26 (0.22, 0.12-0.65) to 0.07 (0.00, 0.02-0.21). The mean (±standard deviation, 95% confidence interval) COD (in 0-100 grey scale units) in the 0-2 mm central anterior corneal region (0-2 ant), TCT (µm), ARC (mm), and PRC (mm) changed significantly (p < 0.01), from 21.2 (± 3.70, 20.4-22.0), 454 (± 40.0, 446-462), 6.49 (± 0.71, 6.33-6.65), and 4.81 (± 0.65, 4.66-4.96) to 31.5 (± 9.19, 29.5-33.6), 423 (± 49.3, 412-434), 6.78 (± 0.80, 6.60-6.98), and 4.74 (± 0.64, 4.59-4.88), respectively, but remained stable in groups 2 (n = 23) and 3 (n = 24). Significant relationships (p < 0.01) were uncovered between postop CDVA and preop values of COD, TCT, ARC, and PRC. Multilinear regression revealed significant correlations between CDVA at 1 year and preop COD, TCT, ARC, and PRC (r2 = 0.533, r20-2ant = 0.126, r2TCT = 0.321, r2ARC = 0.506, r2PRC = 0.467). Including preop CDVA further enhanced this correlation (r2 = 0.637, r2LogMAR CDVApreop = 0.566). CXL improved CDVA, increased COD and ARC, and reduced TCT and PRC. The chance of correctly estimating the CDVA at 1 year after CXL using preoperative markers of COD, TCT, ARC, and PRC is 53%, improving to 64% with the inclusion of preoperative CDVA. Objective measurements taken at the preoperative screening stage may be useful to estimate the likely postoperative CDVA when preoperative CDVA measures are unreliable or unobtainable. ClinicalTrials.gov identifier, NCT06522789.

Impacts and Correlations on Corneal Biomechanics, Corneal Optical Density and Intraocular Pressure after Cataract Surgery.

The study aimed to investigate the extended effects and interrelations of corneal biomechanics, corneal optical density (COD), corneal thickness (CT), and intraocular pressure (IOP) following cataract surgery. Sixteen eyes were analyzed prospectively. The Corneal Visualization Scheimpflug Technology (Corvis ST) device assessed corneal biomechanics, while the Pentacam AxL® (Pentacam) measured COD and CT. Postoperative data were collected around six months after surgery, with a subgroup analysis of data at nine months. The Pearson correlation was used to examine the relationship between surgical-induced changes in corneal biomechanics and COD. At six months, significant postoperative differences were observed in various biomechanical indices, including uncorrected IOP (IOPuct) and biomechanics-corrected IOP (bIOP). However, many indices lost statistical significance by the nine-month mark, suggesting the reversibility of postoperative corneal changes. Postoperative COD increased at the anterior layer of the 2-6 mm annulus and incision site. The changes in COD correlated with certain biomechanical indices, including maximal (Max) deformative amplitude (DA) and stiffness parameter (SP). In conclusion, despite significant immediate postoperative changes, corneal biomechanics, COD, and IOP experienced a gradual recovery process following cataract surgery. Clinicians should maintain vigilance for any unusual changes during the short-term observation period to detect abnormalities early.

Corneal Stroma Analysis and Related Ocular Manifestations in Recovered COVID-19 Patients.

The purpose of this study was to assess the impact of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) on corneal stroma characteristics, ocular manifestations, and post-recovery refractive surgery outcomes after varying recovery durations. Fresh corneal lenticules from patients with post-coronavirus disease 2019 (COVID-19; recovered within 135days) and healthy controls (HCs) after small incision lenticule extraction (SMILE) surgery were obtained for experimental validation of SARS-CoV-2 susceptibility, morphological changes, and immune response of the corneal stroma. Corneal optical density (CD) was measured using the Pentacam HR. Corneal epithelium thickness (ET) and endothelium parameters were evaluated by wide-field optical coherence tomography (OCT) and non-contact specular microscopy (SP-1P), respectively. All the patients were assessed after SMILE surgery until 3 month of follow-up. The cornea was susceptible to SARS-CoV-2 with the presence of SARS-CoV-2 receptors (CD147 and ACE2) and spike protein remnants (4 out of 58) in post-recovery corneal lenticules. Moreover, SARS-CoV-2 infection triggered immune responses in the corneal stroma, with elevated IL-6 levels observed between 45 and 75days post-recovery, which were then lower at around day 105. Concurrently, corneal mid-stromal nerve length and branching were initially higher in the 60D to 75D group and returned to control levels by day 135. A similar trend was observed in CD within zones 0 to 2 and 2 to 6 and in the hexagonal cells (HEX) ratio in endothelial cells, whereas ET remained consistent. Notably, these changes did not affect the efficacy, safety, or predictability of post-recovery SMILE surgery. SARS-CoV-2 induces temporal alterations in corneal stromal morphology and function post-recovery. These findings provided a theoretical basis for corneal health and refractive surgery management in the post-COVID-19 milieu.

Monitoring the transition from corneal ulceration to healed scar using a Scheimpflug tomography-based densitometry.

To compare corneal haze between active ulcer and healed scarring using a Scheimpflug densitometry. A prospective longitudinal study enrolled 30 patients (30 eyes) with ulcerative keratitis (UK). Each subject's corneal optical density (COD) was measured with a Scheimpflug corneal densitometry, Pentacam® AXL (Oculus GmbH, Wetzlar, Germany), at the active ulcerative and complete scarring stage. The COD data were analyzed through distinct methods (inbuilt, sorted annular partitions, and ulcer-matching densitometric maps). We compared different CODs to select the better index for clinically monitoring the transition from corneal ulceration to healed scar. The CODs of the periphery (P = 0.0024) and outside of the active ulcer (P = 0.0002) significantly decreased after scarring. Partitioning the cornea into different depths and annular zones, the anterior layer, center layer, and the 2-6mm annular zone had a more remarkable COD decrease after scar formation. The 3rd-sorted COD in the anterior layer revealed the highest area under the receiver-operating characteristic curves (0.709), in which 90% of subjects had COD reduction during the ulcer-to-scar transition. Aside from subjective judgment based on clinical signs, the Scheimpflug tomography-based densitometry could provide objective and efficient monitoring of the corneal opacity evolution in UK patients. Because the 3rd-sorted annular COD is a better index than the inbuilt or mapping CODs in differentiating active ulcers from healed scars, this COD could be a clinically promising parameter to monitor the progression of UK patients.

The Impact of Standard Cross-Linking on the Corneal Optical Density-Age Relationship in Keratoconus After Mechanical Stripping of the Epithelium.

Background: To determine if cross-linking (CXL) treatment modifies any pre-existing association between corneal optical density (COD) and age in keratoconus free of corneal scarring. Methods: COD was monitored in two groups (i) before and after standard CXL treatment for keratoconus (de-epithelization with a crescent blade, n = 69 eyes) and (ii) age/gender-matched cases without any signs of keratoconus (n = 24 eyes). Seven different markers of COD were quantified using a 0-100 grey scale, supplied with Pentacam™ software. Results: Mean age (±sd, range) in Group I (19 females and 50 males) was 24.2 years (±7.2, 11-44) and in Group II (9 females and 15 males), it was 24.7 years (±7.6, 17-45). COD over the apex and along the depth of the cornea (y, arbitrary scale units) was associated with age (x, in years) in Group I at preop (y = 0.08x + 13.12, r s = 0.350 and p=0.003), at 12 months postop (y = 0.08x + 15.15, r s = 0.295 and p=0.014) and in Group II, at the start (y = 0.16x + 11.28, r s = 0.474 and p=0.019) and 12 months later (y = 0.24x + 8.63, r s = 0.600 and p=0.002). The change in COD following CXL was significantly associated with the preop value. Conclusion: CXL initially breaks down the pre-existing relationship between COD and age. This is re-established by 12 months postop. The CXL induced change in COD depends on the preop value but not on the patient's age.

Corneal densitometry and associated factors in an elderly population

ABSTRACT Clinical Relevance Knowing normative corneal optical density (COD) values is important for identifying pathologic corneal changes. Background The aim of this work is to determine the distribution and associated factors of COD in the elderly population. Methods This report is a part of a cross-sectional population-based study conducted on the elderly population (≥60 years) of Tehran, Iran from Jan 2019 to Jan 2020. Using a multi-stage stratified random cluster sampling method, a total of 160 clusters were randomly selected from 22 districts of Tehran city. Study participants underwent a complete ocular examination including measurement of visual acuity, refraction, and slit-lamp biomicroscopy. Corneal densitometry was evaluated using the Pentacam HR. Generalized estimating equation (GEE) models were used to investigate associations of COD with study variables. Results A total of 3633 eyes from 2068 individuals were analysed. Of these, 1256 (60.7%) were female, and the mean age of the individuals was 66.42 ± 5.28 (60 to 95) years. The mean entire COD was 21.96 ± 4.45 greyscale unit (GSU) (95% CI: 21.57–22.34). There was a statistically significant difference in the mean COD between the anterior, central, and posterior layers (p < 0.001); the highest and lowest average COD was related to the anterior and posterior corneal layers, respectively. The lowest and highest mean COD were observed in the 0–2 mm [17.21GSU (95% CI:16.87–17.55)], and 10–12 mm annular zones [31.4 GSU (95% CI: 30.89–31.91)], respectively (p < 0.001). According to the multiple GEE model, the COD had a statistically significant direct relationship with age, central corneal thickness, and mean keratometry, while it was significantly inversely associated with female sex, anterior chamber depth, white-to-white distance, and corneal volume. Conclusion These normal values of COD in the present study could be used as reference data in older adults. The associated factors of COD should be taken into account to avoid misinterpretation of physiologic changes as pathologic processes.

Corneal optical density: Structural basis, measurements, influencing factors, and roles in refractive surgery.

The cornea is the main refractive medium of the human eye, and its clarity is critical to visual acuity. Corneal optical density (COD) is an important index to describe corneal transparency. Intact corneal epithelial and endothelial cells, regular arrangement of collagen fibers in the stroma, and normal substance metabolism are all integral for the cornea to maintain its transparency. In the last two decades, the Pentacam Scheimpflug imaging system has emerged as a breakthrough for the measurement of COD (also called corneal densitometry). It has been found that a wide variety of factors such as age, refractive status, and corneal diseases can affect COD. Different corneal refractive surgery methods also change COD in different corneal regions and layers and affect visual acuity following the surgery. Thus, COD has gradually become a significant indicator to evaluate corneal health, one on which the attention of clinicians has been increasingly focused.

Corneal Optical Densitometry in the Evaluation of 2-Year Graft Function Following Endothelial Keratoplasty

This study aimed to assess clinical application of the Scheimpflug corneal tomography for objective evaluation of corneal optical density in eyes undergoing Descemet's stripping endothelial keratoplasty (DSEK). In this prospective study, 39 pseudophakic eyes with bullous keratopathy were enrolled. All eyes underwent primary DSEK. Ophthalmic examination included best corrected visual acuity (BCVA) measurement, biomicroscopy, Scheimpflug tomography, pachymetry, and endothelial cell count. All measurements were taken preoperatively and within a 2-year follow-up period. Gradual BCVA improvement was observed in all patients. After two years, the mean and median BCVA values were 0.18 logMAR. A decrease in central corneal thickness was noted only during the first 3 months postoperatively and was followed by a gradual increase. Corneal densitometry decreased constantly and most significantly in the first 3 months postoperatively. The consecutive decrease in endothelial cell count of the transplanted cornea was most significant during the first 6 months postoperatively. Six months postoperatively, the strongest correlation (Spearman's r = -0.41) with BCVA was found for densitometry. This tendency was maintained throughout the entire follow-up period. Corneal densitometry is applicable for objective monitoring of early and late outcomes of endothelial keratoplasty, showing a higher correlation with visual acuity than pachymetry and endothelial cell density.

Corneal and lenticular clarity in children with inflammatory disease as assessed by Scheimpflug imaging

BackgroundCorneal and lenticular optical properties are not well-documented in pediatric patients with inflammatory diseases. Here we aimed to evaluate corneal and lenticular optical density as well as corneal morphology in children with ocular and/or systemic inflammation by Scheimpflug imaging. MethodsFifty-five eyes of 29 children with non-infectious uveitis, 56 eyes of 28 children with systemic inflammation without uveitis and 60 eyes of 31 healthy children were included. Corneal/lenticular optical density, corneal volume, central corneal thickness, keratometry were analyzed by Pentacam HR. Corneal endothelial cell density, hexagonal cell ratio and coefficient of variation were measured by specular microscope. ResultsThe mean age was 12.0 ± 3.1 years, 11.9 ± 4.0 years and 11.3 ± 3.4 years whereas the female/ratio was 15/14, 15/13 and 14/17 in uveitis, systemic inflammation and control groups respectively. Uveitis type was anterior uveitis in 16 (29.1%) eyes, intermediate uveitis in 32 (58.2%) eyes and panuveitis in 7 (12.7%) eyes. Twenty-two (40%) eyes had active uveitis whereas 33 (60%) eyes had inactive uveitis. Corneal optical density was greater in uveitis group compared with other groups (p = 0.001, Kruskal-Wallis test). Lenticular density and corneal parameters other than optical density were not different between the groups (p > 0.05). Corneal optical density was higher in active uveitis than inactive uveitis (22/33 eyes, p = 0.017). ConclusionChildren with uveitis had decreased corneal clarity compared with systemic inflammation group and healthy controls, while lenticular clarity was similar between the groups. Corneal endothelial parameters did not change significantly based on ocular/systemic inflammation. Scheimpflug imaging provides objective corneal and lenticular optical density measurements.

Clinical efficacy of Fluorometholone versus Loteprednol eye drops after photorefractive keratectomy: A triple-blinded randomized controlled trial.

This study aimed to compare the anti-inflammatory efficacy and safety of 0.1% Fluorometholone (FML) versus (vs.) 0.5% Loteprednol etabonate (LE) following photorefractive keratectomy (PRK). A triple-blinded randomized controlled trial was conducted on both eyes of 100 patients with stable refraction who were candidates for PRK. Both eyes in each subject were randomly allocated to the FML or LE groups. The product to be tested was 0.1% FML eye drops packaged in droppers vs. the 0.5% LE sterile ophthalmic suspension (Lotemax®) packaged in identical droppers. The main clinical outcomes were changes in best-corrected distance visual acuity (BCDVA) and corneal optical density. The second clinical outcomes were a change in intraocular pressure (IOP) after the intervention. There was no significant difference regarding mean corneal optical density changes between the two groups, one (P = 0.55) and three months (P = 0.98) after the intervention. The mean ± SD BCDVA after one month of the intervention was 0.79 ± 0.11 and 0.84 ± 0.11 in LE and FML groups, retrospectively (P = 0.02). There was no significant difference regarding mean BCDVA between the two groups three months after intervention (P = 0.21). The IOP showed no significant difference between the two groups after one (P = 0.18) and three months (P = 0.53) of the intervention. The results of this clinical trial demonstrate that LE and FML treatment was effective with no clinically meaningful effect on IOP following a short course of treatment.

The effect of topical bimatoprost on corneal clarity in primary open-angle glaucoma: a longitudinal prospective assessment.

To study the effect of topical bimatoprost on the corneal optical density values using a dual Scheimpflug Placido analysis system. This longitudinal case-control study included 18 patients with newly diagnosed primary open-angle glaucoma who received topical bimatoprost as a first-line treatment and 20 healthy individuals (age and sex-matched controls). Corneal densitometry data were obtained using the dual Scheimpflug analyzer at pre-treatment and 1st, 6th, 12th, 18th months of post-treatment. Repeated measures of ANOVA and Pearson correlation tests were used for statistical analysis. There were statistically significant differences between pre-treatment and post-treatment 1st and 6th months corneal densitometry values (p < 0.001, p = 0.007, respectively). However, there was no statistically significant difference between the post-treatment 12th and 18th months (p > 0.05). Corneal densitometry values decreased during the 1st month. Intraocular pressure (IOP) differences were statistically significant between baseline and 1month after treatment (P < 0.001), however not statistically significant between the 1st and 6th, 6th and 12th, 12th and 18th months after treatment (p > 0.05, for all). Corneal densitometry was not correlated with IOP (r = - 0.037, p = 0.44). In the control group, there was no statistically significant difference between baseline and post-baseline 18th-month corneal densitometry measurements (p > 0.05). Topical bimatoprost administration might result in a decrease in corneal densitometry measurement. It is of clinical importance that topical bimatoprost administration can affect corneal transparency and cause a possible alteration in corneal properties.

Simultaneously Monitoring Whole Corneal Injury with Corneal Optical Density and Thickness in Patients Undergoing Cataract Surgery.

To pursue the least corneal implication during cataract surgery, this study aimed to monitor corneal wound injury after cataract surgery with a novel method. The prospective cohort study involved thirty-two patients, who were assessed by a Scheimpflug tomography AxL® (Oculus GmbH, Wetzlar, Germany) via the following two kinds of indices: whole corneal optical density (COD) and corneal thickness (CT), two weeks before and one month after cataract surgery. The results of the COD revealed that corneal annuli 0.0–2.0 mm and 2.0–6.0 mm, and the average and maximal values at the incisional site significantly increased postoperatively. Also, the anterior and central stroma of 0.0–2.0 mm, and all three depths of 2.0–6.0 mm, increased remarkably after the operation. For the CT, all ranges of diameters plus incisional sites showed significant increases postoperatively. Furthermore, we analyzed the differences (delta) of COD and CT between pre- and post-operation, and found significant correlations between the delta of COD and the delta of CT, regarding annuli 0.0–2.0 mm, 2.0–6.0 mm, and 6.0–10.0 mm, but no correlation at the incisional site, with either average density or maximal density, was detected. We concluded that whole COD and CT, especially at the central zones of the cornea (annulus < 6 mm), are both valuable parameters in the assessment of corneal damage post-cataract surgery, and are independent indices at the incisional site.

Corneal nerve repair and optical density in patients with high myopia after three kinds of corneal refractive surgery

Objective: To investigate the repair of subepithelial nerve fibers in different areas of the cornea and the difference of corneal transparency 12 months after small incision lenticule extraction (SMILE), femtosecond laser in situ keratomileusis (FS-LASIK) and excimer laser in situ keratomileusis (LASEK) in high myopia. Methods: A cohort study. From June 2018 to October 2019, 30 patients with high myopia (60 eyes) were selected for corneal refractive surgery in the Department of Ophthalmology, Affiliated Hospital of Qingdao University, including 16 females (32 eyes) and 14 males (28 eyes). According to the mode of operation, the patients were divided into the SMILE group (n=10), FS-LASIK group (n=11) and LASEK group (n=9). The repair of subepithelial nerves in different areas of the cornea was observed by laser confocal microscopy 12 months after operation,and the morphological parameters were analyzed by ACCMetrics software. The parameters included corneal nerve fiber density (CNFD), corneal nerve branch density (CNBD), corneal nerve fiber length (CNFL), corneal nerve fiber total branch density (CTBD) and corneal nerve fiber width. The Pentacam anterior segment analyzer was used to measure the optical density of the cornea in different diameters. The nerve fiber parameters and corneal optical density were compared by random block analysis of variance, and multiple comparisons were performed between groups by the Turkey test. Results: Twelve months after operation, there was no significant difference in the CNFD among the three groups(all P>0.05). The CNBD around the upper corneal incision in the SMILE group, FS-LASIK group and LASEK group was (7.81±7.93), (9.61±7.18) and (21.25±15.55) branches/mm2, respectively. The CTBD was (22.00±16.02), (24.44±11.42) and (54.37±22.13) branches/mm2, respectively. The values in the LASEK group significantly differed from the other two groups (HSD=2.823, -3.010, 3.053, -3.048, P<0.01). The CNFL was (9.19±3.25), (12.88±3.52) and (15.75±2.36) mm/mm2, respectively. The value in the SMILE group was significantly different (HSD=-3.151, -4.418; P<0.0l). The corneal optical density after SMILE was 13.16±0.72 in the 0-6 mm diameter area(HSD=-4.164, -4.489; P<0.01), 16.12±3.18 in the 6-12 mm diameter area(HSD=-3.918, -3.493;P<0.01) and 14.06±1.36 in the total diameter (HSD=-6.031, -5.519;P<0.01), which differed significantly from the other two groups. Conclusions: Twelve months after SMILE for high myopia, the nerve repair around the superior corneal incision is slightly worse than that after FS-LASIK and LASEK, but the nerve repair in other areas has some advantages, and the corneal transparency is better. (Chin J Ophthalmol, 2021, 57:268-276).

Effect of Laser-assisted Subepithelial Keratectomy with Mitomycin C on Corneal Optical Density Measured with Confocal Microscopy.

The development of confocal microscopy allows one to obtain high-resolution corneal images like its optical density. Some studies have evaluated the optical density with Scheimpflug cameras in the early post-operative period after photorefractive keratectomy, but no studies have evaluated the long-term evolution of optical density after surface ablation when mitomycin C is used. This work aimed to study the changes in corneal optical density measured with confocal microscopy in eyes treated with laser-assisted subepithelial keratectomy (LASEK) and intraoperative mitomycin C (MMC) to correct myopia. A study of 24 consecutive myopic eyes that underwent LASEK with 0.02% MMC and a control group of 24 healthy nontreated eyes was performed. Optical density was measured using the images by the confocal microscopy of the Heidelberg Retina Tomograph II with the Rostock Cornea Module. An analysis of confocal microscopy images was performed using the ImageJ software to obtain the optical density, in gray-scale units (GSU). The optical density of the stromal bed was evaluated 3 months, 15 months, and 3 years after surgery and was compared with the optical density at the equivalent depth of the stroma in controls. The mean values of optical density for the LASEK group were 81.7 ± 9.7, 78.6 ± 11.7, and 73.6 ± 18.7 GSU at 3 months, 15 months, and 3 years, respectively, and it was 61.8 ± 8.2 GSU for the control group. A statistically higher optical density 3 and 15 months after LASEK with MMC was found compared with controls (P < .001). No significant difference was found in optical density at 3 years post-operatively. Our study suggests that, after LASEK with MMC, the anterior corneal stroma has a higher optical density at 3 and 15 months post-operatively, which gradually returns to normal values 3 years after surgery.

Corneal optical density in Fuchs endothelial dystrophy determined by anterior segment optical coherence tomography.

In this study, we propose a method to grade corneal stromal opacity using optical density measurements by anterior segment optical coherence tomography (AS-OCT) and validate the approach in Fuchs endothelial corneal dystrophy (FECD). A retrospective analysis of human corneal OCT scans was performed on 48 eyes of 32 patients with FECD and 33 control eyes of 21 patients using the Carl Zeiss Cirrus HD-OCT 5000. In addition, corneal edema in fresh rabbit cadaver eyes was artificially induced by distilled water and imaged with the Thorlabs TELESTO-II spectral domain OCT at different time points during saturation. The increase of opacity due to corneal edema was proposed to directly correlate with enhanced reflectivity sites in the OCT images, corresponding to higher optical density. The increase was determined as the image area above a statistically established gray-scale value using ImageJ and correlated with other disease characteristics. Optical densities in human corneas showed significant differences between FECD patients and the control group (p = 0.002). The increased optical densities determined in FECD corneas correlated well with other disease characteristics such as corneal pachymetry or visual acuity. Likewise, rabbit corneas showed a time dependent increase in thickness and in corneal optical density during soaking in distilled water. This study presents corneal optical density by AS-OCT as an objective value for corneal changes in FECD. Complementing other diagnostic tools in FECD the assessment of corneal optical density may identify progression of FECD, gauge novel therapeutic strategies and support risk and benefit analyses for corneal surgery.

Corneal Densitometry in Diabetes Mellitus.

Chronic hyperglycemia induces morphological and functional changes of the cornea. Corneal clarity is essential for visual function, and the measurement of corneal optical density (COD) might provide further information on diabetes mellitus (DM)-induced alterations. COD of patients with DM and age-matched healthy subjects was measured using the Pentacam HR. Furthermore, central and thinnest corneal thickness and peripheral pachymetry of concentric circles around thinnest corneal thickness were investigated. In DM, information on disease duration, type, presence of diabetic retinopathy and maculopathy, and HbA1c value was recorded. In this study, 76 patients with DM and 65 healthy subjects were included. In patients with DM, the COD values of nearly all corneal layers and zones were reduced in comparison with healthy subjects (P < 0.05). Furthermore, the COD measurements were inversely correlated with the HbA1c value (total COD central layer: r = -0.424, P = 0.044) and stage of diabetic retinopathy (total COD: r = -0.271, P = 0.019). Diabetic patients with maculopathy revealed lower total COD values than patients without maculopathy (16.5 ± 5.6 vs. 21 ± 7.6, P = 0.031), and COD was lower in DM type 1 than in type 2 (16.1 ± 5.1 vs. 20.8 vs. 7.5, P = 0.035). In both groups, the COD values increased with age (patients with DM: r = 0.336, P = 0.003; healthy subjects: r = 0.679, P < 0.001) and decreased with peripheral corneal thickness increase. In patients with DM, COD was significantly reduced in comparison with healthy subjects. These changes were associated to disease-specific factors and measurements of peripheral corneal thickness profiles.

The changes in corneal transparency after orthokeratology with juvenile myopia

Objective: To evaluate the changes of corneal transparency undergoing overnight orthokeratology treatment. Methods: Prospective cohort study. Right eyes of juvenile myopic patients fitted with Ortho-K CL at Qingdao Eye Hospital were enrolled. Corneal optical density values were measured by the Pentacam Scheimpflug system before orthokeratology and at 1 day, 1 week, and 1, 3, 6, and 12 months after wearing. Four concentric radial zones centered on the apex of the cornea (≤2 mm, >2 mm and ≤6 mm, >6 mm and ≤10 mm, and>10 mm and ≤12 mm diameter) were applied. Anterior layer (anterior 120 μm), central layer, and posterior layer (posterior 60 μm) were defined according to corneal depth. The data analysis were used One-Way Repeated Measures ANOVA and LSD test. Results: Forty patients (40 eyes) with myopia (24 male and 16 female, age 10.76±1.74 years) were in enrolled. Corneal optical density value was 13.18±0.23 before orthokeratology, then showed a decreasing trend at the early stage, but there was no statistical difference (within 3months: t=-1.594, -1.472, 0.064, 1.971; P>0.05). The value increased significantly and reached the peak (15.31±0.23, t=7.613, P<0.01) at 6-month, and was still maintained in a high value at 1-year (15.15±0.24, t=7.227, P<0.01). Anterior, central, and posterior layer of corneal optical density values had a downward trend at early stage, and increased significantly in 6-and 12-month (anterior layer t=7.143, 6.177, central layer t=7.508, 6.563, posterior layer t=6.722, 8.533;P<0.01). Only the values decreased significantly in posterior layer at 1-week (baseline 10.21±0.14 vs. 1-week 9.91±0.14, t=-2.348, P=0.024). The corneal optical density value of ≤2 mm diameter began to increase significantly at 1-month (baseline 12.88±0.14 vs. 1-month 13.31±0.19, t=2.158, P=0.037),>2 mm and ≤6 mm diameter at 3-month (baseline 11.71±0.13 vs. 3-month 12.50±0.19, t=3.213, P=0.003), and>6 mm and ≤10 mm diameter at 6-month (baseline 11.40±0.30 vs. 6-month 13.70±0.33, t=7.635, P=0.000). The high values lasted for 1 year at this three areas. However, >10 mm and ≤12 mm diameter had no obvious change in optical density (F=1.668, P>0.05). In addition, the significant reduction of optical density values at early stage were mainly concentrated in the posterior layer of the cornea and the>6 mm and ≤10 mm diameter. Conclusions: Orthokeratology transiently increases corneal transparency of the posterior layer and the>6 mm and ≤10 mm diameter at early stage. However, long-term wearing can cause a decrease of transparency within a 10 mm diameter range. The corneal transparency changes first at the center of the optical zone, then gradually expanding to the periphery, and the anterior, central and posterior layers of cornea are all affected. We speculate orthokeratology affect the corneal oxygen supply and compress cornea mechanically, that leads to corneal stromal remodeling. (Chin J Ophthalmol, 2019, 55:435-441).