Corneal epithelial thickness analysis of forme fruste keratoconus with optical coherence tomography

AIM:To explore the significance of corneal epithelial thickness analysis in diagnosing early keratoconus.METHODS:There were 26 clinical keratoconus,21 forme fruste keratoconus,40 high corneal astigmatism(ΔK)and 40 low ΔK eyes involved in the study.Fourierdomain optical coherence tomography was used to measure the corneal epithelial thickness of four groups.The morphological features of topographic map and the thickness of corneal epithelial thinnest point were analyzed.The distribution curve of corneal epithelial thickness at 45°,90°,and 135° axial directions that are through the pupil center was also analyzed.One-way ANOVA was performed to compare the data.RESULTS:The topographic map of forme fruste keratoconus corneal epithelial thickness was uniformity shape;crater shape existed only in clinical keratoconus group;and central island shape mainly existed in highΔK group.The thinnest point of corneal epithelial thickness of forme fruste keratoconus group was significantly lower than that of low ΔK group(P=0.022).The thickness of corneal epithelium in the forme fruste keratoconus at 90°was thinner than that in the low astigmatism group at -1,and -2 mm points(P_(-1mm)=0.015,P_(-2mm)=0.036).CONCLUSION:The analysis of the thinnest point in forme fruste keratoconus corneal epithelium appears earlier than corneal epithelial remodeling.The topographic map of corneal epithelium in high ΔK eyes appears in central island shape,and can be used for the differential diagnosis of early keratoconus.

Eye Rubbing as a Possible Cause of Clinical Progressive Keratoconus in a Forme Fruste Keratoconic Family

We report a case of a 21-year-old male patient who underwent corneal cross-linking (CXL) due to bilateral progressive keratoconus. Topographical screening of his family members was performed for the detection of possible familial keratoconus and showed abnormal topographical patterns resembling to Forme Fruste Keratoconus (FFK) in all the members of his family. The reported keratoconic patient that underwent CXL was the only individual of this family that referred eye rubbing in his personal ocular history;ocular and medical history of the other family members was clear. Eye rubbing could be a possible adjuvant risk factor that contributes to conversion of FFK to clinical progressive keratoconus.

Presence of Fleischer ring and prominent corneal nerves in keratoconus relatives and normal controls

AIMTo examine the occurrence of commonly known clinical signs of keratoconus (KC), i.e. Fleischer ring, prominent corneal nerves and thinning, among unaffected family members of KC patients and healthy control individuals.METHODSData of both eyes of 117 relatives of KC patients having no manifest disease based on videokeratography indices (KC relatives), and 142 controls were used for Pearson correlation and t-test statistics. Correlation of Fleischer ring, prominent corneal nerves and central pachymetry data were tested with each other and with videokeratography indices (KSI, KISA, 3 and 6 mm Fourier asymmetry, and I-S).RESULTSA moderate correlation was found between Fleischer ring and all examined topographical indices. Most important correlation was present with 6 mm Fourier asymmetry, and corneal pachymetry (r=0.272, P<0.001; r=-0.234, P=0.027, respectively). Similar correlations were found with prominent corneal nerves (r=0.234, P<0.001 for 6 mm Fourier asymmetry and r=-0.235, P=0.0265 for pachymetry). KC family members who exhibited Fleischer ring or prominent nerves had thinner and more asymmetric corneas than those without Fleischer ring or prominent corneal nerves (P<0.05 for pachymetry and topographic indices with t-test and Mann-Whitney rank sum test). Though rarely, Fleischer ring and prominent corneal nerves occurred among normal controls, indicating the existence of forme fruste cases in the normal population. Control subjects, who had corneal Fleischer ring or prominent nerves had corneas more similar to KC than other controls (t-test: increased KSI and KISA, P=0.048 and 0.012, respectively).CONCLUSIONIn KC family members and healthy individuals, Fleischer ring and prominent corneal nerves are associated with features of KC and may suggest a possibility of forme fruste KC. Searching for the possible presence of Fleischer ring or prominent nerves on the cornea may help in the decision whether or not to diagnose subclinical KC in a borderline case.

Comparisons of corneal biomechanical and tomographic parameters among thin normal cornea,forme fruste keratoconus,and mild keratoconus

Background:To compare the dynamic corneal response(DCR)and tomographic parameters of thin normal cornea(TNC)with thinnest corneal thickness(TCT)(≤500μm),forme fruste keratoconus(FFKC)and mild keratoconus(MKC)had their central corneal thickness(CCT)matched by Scheimpflug imaging(Pentacam)and corneal visualization Scheimpflug technology(Corvis ST).Methods:CCT were matched in 50 eyes with FFKC,50 eyes with MKC,and 53 TNC eyes with TCT≤500μm.The differences in DCR and tomographic parameters among the three groups were compared.The receiver operating characteristic(ROC)curve was used to analyze the diagnostic significance of these parameters.Back propagation(BP)neural network was used to establish the keratoconus diagnosis model.Results:Fifty CCT-matched FFKC eyes,50 MKC eyes and 50 TNC eyes were included.The age and biomechanically corrected intraocular pressure(bIOP)did not differ significantly among the three groups(all P>0.05).The index of height asymmetry(IHA)and height decentration(IHD)differed significantly among the three groups(all P<0.05).IHD also had sufficient strength(area under the ROC curves(AUC)>0.80)to differentiate FFKC and MKC from TNC eyes.Partial DCR parameters showed significant differences between the MKC and TNC groups,and the deflection amplitude of the first applanation(A1DA)showed a good potential to differentiate(AUC>0.70)FFKC and MKC from TNC eyes.Diagnosis model by BP neural network showed an accurate diagnostic efficiency of about 91%.Conclusions:The majority of the tomographic and DCR parameters differed among the three groups.The IHD and partial DCR parameters assessed by Corvis ST distinguished FFKC and MKC from TNC when controlled for CCT.

In-vivo corneal biomechanical analysis of unilateral keratoconus

AIMTo evaluate and compare corneal biomechanical findings measured by ocular response analyzer, topographic and pachymetric findings in patients with unilateral keratoconus patients and healthy controls.METHODSThis is an observational, case-control study. Patients with keratoconus in one eye and forme fruste keratoconus in the fellow eye were compared with sex and age matched with controls healthy subjects. All subjects were evaluated with rotating scheimpflug imaging system. The receiver-operating-characteristic curves were analyzed to evaluate the sensitivity and specificity of the parameters.RESULTSTwenty-seven patients with keratoconus in one eye and forme fruste keratoconus in the fellow eye were compared with 40 eyes of 40 normal subjects. Corneal hysteresis (CH) was 8.0&#x000b1;1.7 mm Hg in keratoconus group, 8.3&#x000b1;1.6 mm Hg in forme fruste keratoconus group, and 9.8&#x000b1;1.6 mm Hg in control groups (P=0.54 between keratoconus and forme fruste keratoconus groups, P&#x0003c;0.01 between control group and other groups). Corneal resistance factor (CRF) was 7.1&#x000b1;2.2 mm Hg in keratoconus group, 7.8&#x000b1;1.2 mm Hg in forme fruste keratoconus group and 9.9&#x000b1;1.5 mm Hg in control group (P&#x0003c;0.001 between control group and other groups). Using receiver-operating-characteristic analysis, the area under curve values of the parameters to distinguish forme fruste keratoconus from control subjects were: CH (0.768), CRF (0.866). Best cut-off points were 9.3 mm Hg and 8.8 mm Hg for CH and CRF respectively.CONCLUSIONOcular response analyzer parameters (CH and CRF) are found to be significantly lower in forme fruste keratoconus patients compared to normal control subjects.

顿挫期圆锥角膜拟锥体参数与角膜动力学响应参数的关系

目的探索圆锥角膜拟锥体的中心位置和力学性质对角膜动力学响应参数的影响。方法基于90例顿挫期圆锥角膜(forme fruste keratoconus,FFKC)患者三维眼前节分析诊断系统给出的角膜形态数据,用锥体自动获取方法确定其拟锥体参数。依据所得拟锥体中心位置选取两组(水平组21例,下方组20例),分析组间角膜动力学响应(dynamics corneal response,DCR)参数的差异。基于健康眼球几何数据构建具有3种不同锥体位置的圆锥角膜有限元模型,改变锥体区域的力学参数,计算给出在空气脉冲作用下DCR参数的模拟结果,用于研究角膜锥体区域的位置和力学参数同DCR参数的关系。结果FFKC的拟锥体中心位置不同,在DCR参数中,最大压陷曲率半径(radius)、最大凹陷曲率(maximum inverse radius,MIR)和积分半径(integration radius,IR)存在统计学差异。当FFKC拟锥体中心位于角膜旁中心区域时,只有与拟锥体区域呈中心对称的区域的角膜厚度存在统计学差异。有限元模拟结果显示,锥体位于角膜正下方较位于水平侧的角膜顶点最大位移改变量大;当锥体位于角膜中心和正下方时,MIR变小,IR变大,且随着锥体区域力学参数的衰减,MIR和IR的变化量随之增大;当锥体区域位于水平侧时,MIR和IR的变化不大。结论FFKC拟锥体的中心位置和力学参数的衰减程度均对DCR参数(MIR和IR等)有显著影响。

联合Pentacam及Corvis ST诊断顿挫期圆锥角膜的研究

目的探索联合角膜形态学与生物力学特性诊断顿挫期圆锥角膜的其他组合方式,以发掘更多的潜在敏感参数。设计诊断试验。研究对象顿挫期圆锥角膜患者50例(50眼),同期欲行角膜屈光手术术前患者50例(50眼)。方法绘制受试者工作特征(receiver operating characteristic,ROC)曲线分析各纳入参数对顿挫期圆锥角膜的诊断效率并进行Delong检验。将ROC曲线下面积(the area under the ROC curve,AUC)>0.70的参数作为自变量,用前向逐步法建立Logistic回归模型对顿挫期圆锥角膜的诊断进行多因素分析。主要指标角膜最薄点厚度(TP)、角膜断层摄影和生物力学指数(TBI)及在体角膜弹性模量(E)。结果除Km F、Astig F、Kmax F、A1V、A2T、A2V、HCT、PD、bIOP外,其余参数的组间比较均存在统计学差异。在所纳入参数中,TP对顿挫期圆锥角膜的诊断效率最高(AUC=0.810)。对AUC>0.7的参数进行Logistic回归,结果显示TP和弹性模量E是顿挫期圆锥角膜确诊的独立危险因素:CP=e^(β)/(1+e^(β))(β=-0.063×TP-42.158×E+45.919)。ROC曲线分析显示,该模型预测值的AUC为0.916,可显著提高对于顿挫期圆锥角膜的诊断能力(CP与TP比较,Z=2.796,P=0.0052)。结论角膜最薄点厚度对顿挫期圆锥角膜的诊断效率与TBI无统计学差异;在圆锥角膜发病早期,虽然角膜中央3 mm区域内总平均曲率几乎无改变,但其下上方曲率差值呈现增大趋势;角膜弹性模量在顿挫期圆锥角膜诊断中的作用值得被关注,可作为补充参数用于疾病评估。