Study on corneal biomechanical properties in eyes with diabetic retinopathy / 中华眼底病杂志

Objective:To observe the changes in the biomechanical properties of the cornea of diabetic retinopathy (DR), and analyze its relationship with the degree of DR.Methods:A retrospective study. From September 2020 to February 2021, 83 patients with type 2 diabetes (T2DM) combined with DR treated in the Department of Ophthalmology, The First Affiliated Hospital of Zhengzhou University, 83 eyes (DR group), 30 patients with T2DM without DR recruited from the outpatient clinic 30 eyes (NDR group) and 30 eyes of non-diabetes patients (NDM group) were included in the study. All left eyes were chose as the study eye. Among the 83 eyes in the DR group, 39 eyes were non-proliferative DR (NPDR) and 44 eyes were proliferative DR (PDR). Based on this, they were divided into NPDR group and PDR group. There was no statistically significant difference in age ( t=1.10) and sex ratio ( χ2=0.46) among patients in the DR group, NDR group, and NDM group ( P>0.05); body mass index ( t=3.74), glycosylated hemoglobin ( t=35.02) and the length of the eye axis ( t=5.51), the difference was statistically significant ( P<0.05). The eye response analyzer (ORA) was used to measure the corneal hysteresis (CH), corneal resistance factor (CRF), Goldman related intraocular pressure (IOPg), and corneal compensatory intraocular pressure (IOPcc). The corneal topography was used to measure the central corneal thickness (CCT) of the examined eye. The differences of CCT, IOPcc, IOPg, CH, CRF among multiple groups were compared by one-way analysis of variance. Multiple linear regression was used to analyze the relationship between CH, CRF and related influencing factors in DR patients. Results:There were statistically significant differences in CCT, IOPcc, IOPg, CH, and CRF among the eyes of the DR group, NDR group, and NDM group ( F=3.71, 5.60, 9.72, 9.02, 21.97; P<0.05). Pairwise comparisons were between groups, CH, CRF: the difference between the DR group and the NDM group and the NDR group was statistically significant ( P<0.05); CCT: the difference between the DR group and the NDM group was statistically significant ( P<0.05), and The difference in the NDR group was not statistically significant ( P>0.05). CCT, CH, CRF: the difference between the NDR group and the NDM group was not statistically significant ( P>0.05). The results of multiple linear regression analysis showed that CCT and IOPcc in DR patients were independent influencing factors of CH [CCT: β=0.01, 95% confidence interval ( CI) 0.01-0.03, P=0.013; IOPcc: β=-0.15, 95% CI -0.25--0.05, P=0.005]; Age, CCT, IOPcc were independent influencing factors of CRF [Age: β=-0.06, 95% CI -0.09--0.03, P<0.001; CCT: β=0.01, 95% CI 0.00-0.02, P=0.049; IOPcc: β=0.16, 95% CI 0.07-0.25, P=0.001]. The comparison of CCT, CH, CRF, adjusted CH, and adjusted CRF of the eyes in the NDR group, NPDR group, and PDR group were statistically significant ( F=3.76, 5.36, 12.61, 6.59, 10.41; P<0.05). Pairwise comparison between groups, CH, CRF, adjusted CH, adjusted CRF: the difference between the NPDR group, the PDR group and the NDR group was statistically significant ( P<0.05), and the difference between the PDR group and the NPDR group was not statistically significant ( P>0.05); CCT: The difference between NPDR group and NDR group, PDR group and NPDR group was not statistically significant ( P>0.05), and the difference between PDR group and NDR group was statistically significant ( P<0.05). Conclusion:The CH and CRF of eyes with T2DM and DR are elevated; CCT and IOPcc are independent influencing factors of CH, and age, CCT and IOPcc are independent influencing factors of CRF.

Effect of accelerated corneal crosslinking on ocular response analyzer waveform-derived parameters in progressive keratoconus / Efeito do crosslimking corneano acelerado nos parâmetros derivados da forma de onda do analisador de resposta ocular no ceratocone progressivo

ABSTRACT Purpose: To evaluate the effect of accelerated corneal crosslinking on corneal biomechanics with an ocular response analyzer in patients with progressive keratoconus. Methods: In this retrospective study, 50 eyes of 45 patients with progressive keratoconus who underwent accelerated corneal crosslinking were evaluated with ocular response analyzer waveform parameters before and one year after corneal crosslinking. Paired two-tailed Student's t-test was performed to compare the parameters before vs. after corneal crosslinking. Results: Mean patient age was 17.6 ± 3.6 (range 9-25) years. A significant increase was observed in p1 area, p2 area, h2, and dive2 values. No significant difference in corneal hysteresis, corneal resistance factor, or other waveform-derived parameters was observed at one year postoperatively. Conclusion: For estimating the effect of accelerated corneal crosslinking on corneal biomechanics, parameters such as p1 area, p2 area, h2, and dive2 are more sensitive than corneal hysteresis and corneal resistance factor. These results may help us to find out which corneal crosslinking method is most effective for stiffening the cornea.

RESUMO Objetivo: Avaliar o efeito do cross-linking corneano acelerado na biomecânica corneana com analisador de resposta ocular em pacientes com ceratocone progressivo. Métodos: Neste estudo retrospectivo, 50 olhos de 45 pacientes com ceratocone progressivo submetidos à cross-linking corneano acelerado foram avaliados com os parâmetros da forma de onda do analisador de resposta ocular antes e um ano após o tratamento com cross-linking corneano. O teste t de Student pareado bicaudal foi realizado para comparar os parâmetros antes e depois do cross-linking corneano. Resultados: A média de idade dos pacientes foi de 17,6 ± 3,6 (variação de 9 a 25) anos. Um aumento significativo foi observado nos valores de p1area, p2area, h2 e dive2. Nenhuma diferença significativa foi encontrada na histerese da córnea, fator de resistência da córnea ou outros parâmetros derivados da forma de onda foi observada em um ano de pós-operatório. Conclusão: Para estimar o efeito do cross-linking corneano acelerado na biomecânica corneana, parâmentros como p1area, p2area, h2 e dive2 são mais sensíveis que histerese da córnea e fator de resistência corneana. Esses resultados podem nos ajudar a descobrir qual método cross-linking corneano é mais eficaz no enrijecimento da córnea.

Biomecánica corneal y glaucoma / Corneal biomechanical properties and glaucoma

Este trabajo tiene como objetivo conocer los avances más novedosos relacionados con el estudio de las características biomecánicas de la córnea y su posible relación en el diagnóstico del glaucoma. Se realizó una búsqueda en la plataforma Infomed, específicamente en la Biblioteca Virtual de Salud, con el objetivo de conocer los avances más novedosos relacionados con el estudio de las características biomecánicas de la córnea y su posible relación en el diagnóstico del glaucoma. La biomecánica corneal es la facultad de resistencia y flexión simultánea de las moléculas de colágeno en las diferentes capas de la córnea. Trata del equilibrio y de la deformación del tejido corneal sometido a cualquier acción exterior. La histéresis corneal, junto con el factor de resistencia corneal, son medidas que pueden ser proporcionadas por el analizador de respuesta ocular. La existencia de un bajo valor de estas dos medidas pudiera considerarse como un factor de riesgo de progresión en el glaucoma(AU)

The purpose of this work is to know the more novel advances related with the study of the biomechanic characteristic of the cornea and its possible relationship in the diagnosis of the glaucoma. A search was made in Infomed platform, particularly in the Virtual Library of Health, to find out the most advanced in the study of the corneal biomechanical properties and its possible relation with the diagnose of glaucoma. Corneal biomechanical is the power of the resistance and flexion simultaneity of collagen molecules of the different corneal layer. It is the balance and deformity of the corneal tissue submitted to an external action. Corneal hysteresis and corneal resistance factor are two corneal biomechanical properties measured by the Ocular Response Analyzer. The existence of a low value of these two properties may be considered as progression factors in glaucoma(AU)

Association between corneal volume change and corneal biomechanical property before and after small incision lenticule extraction in myopia / 中华实验眼科杂志

Background The relationship between corneal central thickness (CCT) and corneal biomechanical property does not reflect the effective amount of ablated tissue because CCT measures only the change in a single point.Corneal volume (CV) is a representative parameter of corneal morphology,and it can fully reflect corneal thickness and tissue distribution.Objective This study was to investigate the correlation between volumetric corneal changes and corneal biomechanical properties after small incision lenticule extraction (SMILE).Methods A prospective series cases-observational study was carried out.This study protocol was approved by Ethic Committee of Tianjin Eye Hospital,and written informed consent was obtained from each patient prior to entering the cohort.Sixty-seven right eyes of 67 myopia or myopic astigmatism patients who received SMILE in Tianjin Eye Hospital from June 2014 to July 2015 were included in this study.Before and 3 months after surgery,the CV at 3,3-5,5-7 and 7-10 mm (CV3,CV3-5,CV5-7,CV7-10) was measured by Pentacam anterior segment analysis system,and corneal hysteresis (CH) and corneal resistance factor (CRF) were obtained by ocular response analyzer (ORA).The changes of CV (ACV),CH (ACH) and CRF (ACRF) were calculated,and the correlations between ACV and ACH or ACRF were analyzed.Results CV3,CV3-5 and CV5-7 values after SMILE were significantly lower than those before SMILE (t =36.24,20.38,16.17,all at P＜ 0.001).The CH values before and after SMILE were (10.06± 1.11) mmHg and (8.10± 1.05) mmHg (1 mmHg =0.133 kPa),and the CRF values before and after SMILE were (10.40 ± 1.38) mmHg and (6.91 ± 1.19) mmHg,respectively,showing significant reduces after SMILE than before SMILE (t =16.71,27.41,both at P＜0.001).Positive correlations were seen between the CV values at different corneal areas and CH value or CRF value.Moderate positive correlations were found between CV3 and CH or CRF (r =0.571,0.569;both at P＜0.001) before surgery,and 3 months after surgery,a weak positive correlation was seen between ACV3 and ACH (r =0.394,P ＜ 0.001) or a moderate positive correlation between ACV3 and ACRF (r=0.501,P＜0.001).Conclusions The CV value is gradually increased from the central cornea to periphery cornea.The CV change is associated with CH and CRF changes after SMILE,and CV3 probably is a useful parameter for the evaluation of corneal biomechanics after refractive surgery.

Detection of the early keratoconus based on corneal biomechanical properties in the refractive surgery candidates.

Context: Subclinical keratoconus is contraindication to refractive surgery. The currently used methods of preoperative screening do not always allow differentiating between healthy eyes and those with subclinical keratoconus. Aim: To evaluate biomechanical parameters of the cornea, waveform score (WS), and intraocular pressure (IOP) as potentially useful adjuncts to the diagnostic algorithm for precise detection of the early keratoconus stages and selection of refractive surgery candidates. Settings and Design: Department of Ophthalmology and prospective cross‑sectional study. Patients and Methods: Patients enrolled in the study were diagnosed with refractive disorders. We assessed parameters of corneal biomechanics such as corneal hysteresis (CH), corneal resistance factor (CRF), Goldman‑correlated IOP (IOPg), corneal compensated IOP, WS, and keratoconus match index (KMI). They were classified into one of three groups based on the predefined KMI range: Group 1 (from 0.352 to 0.757) – 45 eyes, Group 2 (from −0.08 to 0.313) – 52 eyes, and Group 0 ‑ control group (from 0.761 to 1.642) – 80 eyes. Results: In both study groups, IOPg, CRF, and CH were decreased when compared to control (P < 0.0001). In control group, there was positive correlation between CH and KMI (P < 0.05), with no correlations in any of the two study groups. CRF correlated positively with KMI in control (P < 0.0001) and in Group 2 (P < 0.05). Conclusions: CH and CRF, together with WS and IOPg, consist a clinically useful adjunct to detect subclinical keratoconus in patients referred for refractive surgery when based on KMI staging.

The latest progress of corneal biomechanical measurement and its clinical application / 医学研究生学报

Cornea is a very important component of the human eyeball wall.It maintains the physiological structure of eyeball and provides protection for eye content and it is an important part of refractive media.As human inhomogeneous viscoelastic material, the cornea possesses many biomechanical properties such as the elastic, viscosity and non linear elastic.Currently, ocular response an-alyzer and corneal visualization scheimpflug technology are often used in vivo measurement and analysis to assist in the diagnosis and treatment of clinical diseases such as keratoconus, and to assess the feasibility and prognosis of refractive surgery.The latest progress of corneal biomechanical measurement and its clinical application are reviewed in this paper.

The Short-Term Effect of Prostaglandin Analog Monotherapy on Corneal Biomechanical Properties in Normal Tension Glaucoma Patients

PURPOSE: To evaluate the effects of short-term prostaglandin analogues treatment on the corneal biomechanics of patients with normal tension glaucoma. METHODS: This study included 52 eyes of 52 patients who were diagnosed with normal tension glaucoma. All patients were divided into two groups; one group (27 eyes) received tafluprost while the other group (25 eyes) received travoprost. Intraocular pressure, Biomechanical properties were measured by using goldmann applanation tonometer, ocular response analyzer before treatment and at 8-week after treatment. RESULTS: The mean decrease in intraocular pressure, Goldmann-correlated IOP (IOPg), corneal-compensated intraocular pressure by using Goldmann applanation tonometer, and Ocular response analyzer were statistically significant in total patients, tafluprost, and travoprost group after using prostaglandin analogues (p < 0.001, p < 0.001, p < 0.001, respectively). Corneal hysteresis showed no statistical differences after treatment in total, tafluprost and travoprost group but corneal resistance factor (CRF) showed statistically significant decrease after using prostaglandin analogues in total, tafluprost, and travoprost group (p < 0.001, p = 0.025, p < 0.001). Upon multivariate analysis, the higher initial IOPg and the lower initial CRF checked, the variation of CRF (CRF in baseline – CRF at 8 weeks) got higher (β = 0.134, p = 0.017). CONCLUSIONS: It is needed to carefully monitor and evaluate the effects of prostaglandin analogues on intraocular pressure associated with initial intraocular pressure and the changes of CRF after prostaglandin treatment in normal tension glaucoma patients. CRF is sensitive factor to short-term changes of intraocular pressure after prostaglandin analogues treatment, and it is required to consider the properties of CRF when we evaluate between progression of glaucoma and corneal biomechanical properties.

Change in Corneal Biomechanical Parameters in Diabetes Mellitus

PURPOSE: In this study, we examined the changes in corneal biomechanical parameters in patients with diabetes mellitus (DM). METHODS: Fifty patients with DM were divided into 2 subgroups, 25 diabetic patients with glycated hemoglobin (HbA1c 7%) and compared with the eyes of 80 healthy subjects. Corneal biomechanical parameters were measured using ocular response analyzer (ORA). Differences in corneal biomechanical properties between healthy subjects and diabetic patients were compared. Additionally, differences in corneal biomechanical properties between diabetic patients with HbA1c 7% were compared. RESULTS: Corneal hysteresis, corneal resistance factor and central corneal thickness (CCT) were statistically significantly higher in patients with diabetes compared to healthy subjects. Goldmann tonometer, non-contact tonometer and Goldmann-correlated intraocular pressure (IOPg) were statistically significantly higher in patients with DM compared to healthy subjects, but corneal compensated IOP (IOPcc) was not statistically significantly different between healthy subjects and diabetic patients. However, corneal biomechanical parameters, which were statistically significantly different between healthy subjects and DM patients, were not statistically significantly different between diabetic patients with HbA1c 7%. CONCLUSIONS: Considering that corneal properties are different between diabetic patients and healthy subject, IOPcc measured with ORA is considered clinically useful for measuring IOP as it reflects CCT and biomechanical properties that should be revised. In diabetes, changes in corneal biomechanical properties depend on long-term glucose control rather than short-term glucose control.

Comparison of ocular response analyzer parameters in primary open angle glaucoma and exfoliative glaucoma patients.

Aim: We sought to identify differences in the following measures of the ocular response analyser (ORA) between primary open angle glaucoma (POAG) and exfoliative glaucoma (EXG) patients: Corneal hysteresis (CH), corneal resistance factor (CRF), corneal‑compensated intraocular pressure (IOPcc) and Goldmann‑correlated intraocular pressure (IOPg). We also sought to relate these ORA measures with central corneal thickness (CCT). Materials and Methods: This cross‑sectional study was conducted on a total of 162 individuals (46 EXG patients, 66 POAG patients and 50 healthy subjects without any ocular and systemic disease). ORA measurements were performed, and a minimum of three readings were obtained from each test subject. Groups were compared according to their ORA parameters. Results: The mean CH levels of the EXG, POAG and healthy subjects were 7.6 ± 2.1, 9.1 ± 1.9 and 9.6 ± 1.7 mmHg, respectively. CH was significantly lower in the EXG patients compared to the other groups (P < 0.001).The mean CRF levels of the EXG, POAG and healthy subjects were 9.0 ± 2.0, 10.1 ± 1.7 and 9.8 ± 1.8mmHg, respectively. CRF levels in the eyes of the EXG patients were significantly lower compared to those of either the POAG patients (P = 0.005) or the healthy subjects (P = 0.03), but there was no significant difference in CRF levels between the POAG patients and the healthy subjects (P = 0.59). There was a significant positive correlation between CH and CCT in the EXG patients and healthy subjects (P < 0.001), but this correlation was not present in the POAG patients (P = 0.70). Conclusions: In this study, CH and CRF were found to be significantly reduced in the eyes of EXG patients compared to both the POAG patients and healthy subjects. Reduced CH in EXG patients might result in decreased support of peripapillary scleral structure and increased damage to the optic nerve during IOP increase.

Evaluation of corneal biomechanical properties following penetrating keratoplasty using ocular response analyzer.

Purpose: To evaluate corneal biomechanical properties in eyes that has undergone penetrating keratoplasty (PK). Materials and Methods: Retrospective observational study in a tertiary care centre. Data recorded included ocular response analyzer (ORA) values of normal and post‑keratoplasty eyes [corneal hysteresis (CH), corneal resistance factor (CRF), Goldmann‑correlated intraocular pressure (IOPg), and cornea‑compensated intraocular pressure (IOPcc)], corneal topography, and central corneal thickness (CCT). Wilcoxon signed rank test was used to analyze the difference in ORA parameter between post‑PK eyes and normal eyes. Correlation between parameters was evaluated with Spearman’s rho correlation. Results: The ORA study of 100 eyes of 50 normal subjects and 54 post-keratoplasty eyes of 51 patients showed CH of 8.340 ± 1.85 and 9.923 ± 1.558, CRF of 8.846 ± 2.39 and 9.577 ± 1.631 in post-PK eyes and normal eyes, respectively. CH and CRF did not correlate with post‑keratoplasty astigmatism (P = 0.311 and 0.276, respectively) while a significant correlation was observed with IOPg (P = 0.004) and IOPcc (P < 0.001). Conclusion: Biomechanical profiles were significantly decreased in post‑keratoplasty eyes with significant correlation with higher IOP as compared with that in normal eyes.

Biomechanical Property of Keratoconus Measured by ORA

PURPOSE: To compare the biomechanical properties of keratoconus, keratoconus suspect, and normal subjects measured by ocular response analyzer. METHODS: A total of 72 patients were divided into 3 groups: keratoconus, suspected keratoconus, and normal control subjects. The 3 age-matched groups were evaluated according to age, sex, and visual acuity. Slit lamp examinations, Pentacam, and ocular response analyzer (ORA) examinations were performed. Mean corneal refractive power, central corneal thickness, corneal hysteresis (CH), and corneal resistance factor (CRF) were evaluated and analyzed. RESULTS: Twenty-four eyes were included in each group. The mean age was 23.8 years in keratoconus, 26.0 years in suspected keratoconus and 26.1 years in normal subject groups. Mean corneal refractive power was significantly higher in keratoconus (p < 0.001) and suspected keratoconus (p = 0.001) groups than in the normal subject group. Mean central corneal thickness showed significant differences among the 3 groups (p < 0.05). CH was significantly lower in keratoconus than suspected keratoconus (p = 0.025) and normal subject groups (p = 0.005), but showed no significant difference between suspected keratoconus and normal subject groups. CRF showed significant differences among all 3 groups (p < 0.05). CH and CRF had negative correlations with mean corneal refractive power and positive correlations with central corneal thickness. CONCLUSIONS: CH and CRF measured by ORA were significantly different between keratoconus and normal subject groups and had significant correlations with mean corneal refractive power and central corneal thickness. CRF may be a useful method to differentiate between suspected keratoconus and normal cornea patients.

The Association Between Corneal Biomechanical Properties and Progression of Visual Field Loss in Normal Tension Glaucoma

PURPOSE: To evaluate the association between corneal biomechanical properties and progression of visual field loss in normal tension glaucoma. METHODS: This study enrolled 73 eyes of 73 patients with normal tension glaucoma who were undergoing medical treatment, and classified them into progressing and nonprogressing groups by visual field trend analysis. The corneal biomechanical properties measured by the Ocular Response Analyzer (ORA; Reichert Instruments, Depew, NY, USA), central corneal thickness, and Goldmann applanation tonometry were comparatively analyzed between the 2 groups. RESULTS: Twenty-six eyes reached a progression endpoint. The prevalence of hypertension was higher in the progressing group (42.3%, progressing, 17.0%, nonprogressing; p = 0.03). Progressing eyes had lower corneal hysteresis (9.1 +/- 1.3 vs. 9.8 +/- 1.5 mm Hg, p = 0.03) and lower corneal resistance factor (9.5 +/- 1.5 vs. 10.4 +/- 1.4 mm Hg, p = 0.01) compared with nonprogressing eyes. Upon multivariate analysis, the presence of hypertension (odds ratio [OR] = 3.46, p = 0.03) and corneal hysteresis (CH) (OR = 0.66 per mm Hg lower, p = 0.02) remained statistically significant. CONCLUSIONS: The CH measurement with ORA was significantly associated with risk of visual field progression in normal tension glaucoma. Eyes with lower CH had a greater risk of progression of visual field loss than those with higher CH.

Factors Affecting the Ocular Response Analyzer Parameters in Normal Korean

PURPOSE: To identify the normal range of factors which can be measured with Ocular Response Analyzer (ORA, Reichert Inc., Depew, NY, USA) in normal Korean, and to analyze factors affecting ORA by measuring intraocular pressure (IOP) of noncontact tonometer (NCT) and central corneal thickness (CCT). METHODS: Three hundred and one normal Korean subjects who did not have specific ophthalmological diseases and surgeries in the past were recruited for this study. Corneal hysteresis (CH), corneal response factor (CRF), corneal-compensated IOP (IOPcc), and Goldmann correlated IOP (IOPg) were measured using ORA. In addition, IOP of NCT and CCT were measured and the results and factors analyzed. RESULTS: The mean CH measured among normal Korean subjects in this study was 10.70 mmHg. The mean CRF was 10.40 mmHg. CH and CRF were significantly higher in the juvenile group. IOPcc and IOPg as measures of IOP using the ORA had significant correlation with IOP of NCT. In particular, IOPcc appeared to be independent of CCT. CONCLUSIONS: CH and CRF were different according to age, indicating a difference in biomechanical properties of the cornea. In particular, IOPcc is more important as it is independent of corneal thickness and should be compensated in general measurements of IOP reflecting biomechanical properties.