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      • Record: found
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      Corneal hysteresis and corneal resistance factor in keratoectasia: findings using the Reichert ocular response analyzer.

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      Publication date:
      Journal: Ophthalmologica. Journal international d'ophtalmologie. International journal of ophthalmology. Zeitschrift für Augenheilkunde
      Keywords: Adult, Compliance, Cornea, physiology, ultrasonography, Corneal Diseases, diagnosis, physiopathology, Corneal Topography, Dilatation, Pathologic, Elasticity, Humans, Keratoconus, Prospective Studies

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          Abstract

          To examine corneal hysteresis (CH) and corneal resistance factor (CRF) in normal and ectatic corneas. CH and CRF were measured using the Reichert Ocular Response Analyzer in patients with clinically diagnosed keratoconus (KC), forme fruste KC (FFKC) and normal eyes. 21 eyes (13 patients) with clinically diagnosed KC and 30 eyes (18 patients) with FFKC were included in the study. Mean CH and CRF in FFKC did not differ from that in pachymetry-matched normal eyes. KC eyes had significantly lower CH and CRF than normal and FFKC eyes. A significant overlap in CH and CRF values among the 3 groups was evident. Our findings do not indicate a role for CH and CRF measurement as a single test to aid in the detection of early ectasia. It may be of use when used in conjunction with other parameters such as aberrometry. CH and CRF values may prove to be useful in monitoring ectasia progression. Copyright 2008 S. Karger AG, Basel.

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          Determining in vivo biomechanical properties of the cornea with an ocular response analyzer.

          David Luce (2005)
          To study the results of an ocular response analyzer (ORA) to determine the biomechanical properties of the cornea and their relationship to intraocular pressure (IOP). Reichert Inc., Depew, New York, USA. The ORA (Reichert) makes 2 essentially instantaneous applanation measurements that permit determination of corneal and IOP effects. Measurements of several populations indicate that corneal hysteresis, a biomechanical measure, varied over a dynamic range of 1.8 to 14.6 mm Hg and was only weakly correlated with corneal thickness (r(2)=0.12); this is related to the observation that some subjects with relatively thick corneas have less-than-average corneal hysteresis. Corneal hysteresis changes diurnally, presumably as a result of hydration changes. Keratoconus, Fuchs' dystrophy, and post-LASIK patients demonstrated low corneal hysteresis. The corneal hysteresis biomechanical measure may prove valuable for qualification and predictions of outcomes of refractive surgery and in other cases in which corneal biomechanics are important.
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            The use of the Reichert ocular response analyser to establish the relationship between ocular hysteresis, corneal resistance factor and central corneal thickness in normal eyes.

            P S Mantry, Mohammed Laiquzzaman, Ian Andrew Cunliffe … (2006)
            The aim of this study was to measure ocular hysteresis and corneal resistance factor (CRF), novel methods of analysing ocular rigidity/elasticity and to determine the relationship between central corneal thickness (CCT), hysteresis and CRF in normal subjects. Prospective, cross-sectional, clinical trial. The study included 207 normal eyes. Hysteresis and CRF were measured by the ocular response analyser. The CCT was measured using a hand held ultrasonic pachymeter. Ocular hysteresis and CRF in normal patients and their relationship with CCT. The mean hysteresis was 10.7+/-2.0 mmHg standard deviation (S.D.) (range 6.1-17.6 mmHg); the mean CRF was 10.3+/-2.0 (range 5.7-17.1 mmHg). The mean CCT was 545.0+/-36.4 microm (471-650 microm). The relationship between hysteresis and CCT; CRF and CCT; CRF and hysteresis were significant (p<0.0001). This study demonstrated that corneal hysteresis increased with increasing CCT, however, the correlation was moderate. It would appear that CCT, hysteresis and CRF may measure different biomechanical aspects of ocular rigidity and are likely to be useful additional measurement to CCT in the assessment of ocular rigidity when measuring intraocular pressure (IOP). This may be of particular importance when trying to correct IOP measurements for increased or decreased ocular rigidity.
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              Role of Orbscan II in screening keratoconus suspects before refractive corneal surgery.

              S. Rao (2002)
              To evaluate the relationship between videokeratographic keratoconus screening programs and Orbscan II topography. Prospective, observational case series and instrument validation study. Sixty consecutive eyes with suspicious videokeratography (TMS-1, Tomey Technology, Waltham, MA) were evaluated before undergoing laser in situ keratomileusis (LASIK) surgery. A control group of 50 consecutive eyes without suspicious features by videokeratography was also evaluated. Keratoconus screening programs, using the Rabinowitz and Klyce/Maeda methods and Orbscan II (Bausch & Lomb, Claremont, CA) topographies were performed on these patients. Specific parameters evaluated on the Orbscan II topographies were anterior elevation, posterior elevation, and thinnest pachymetry. Compared with a control group of patients without suspicious videokeratography, there was a statistically significant difference in the mean posterior elevation and mean anterior elevation in the groups with positive keratoconus testing with the Rabinowitz or Klyce/Maeda methods. For patients who met both the Rabinowitz and Klyce/Maeda criteria for keratoconus, the mean posterior elevation was 44 +/- 2.5 micro m compared with a posterior elevation of 21 +/- 0.6 micro m for the control group. There was no statistically significant difference in the mean thinnest pachymetry between the control group and all keratoconus suspect groups. Patients with positive keratoconus screening tests have higher anterior and posterior elevation on Orbscan II topography. When used in combination with videokeratography, the Orbscan II topography system may be helpful in identifying patients who are potentially at high risk for developing ectasia after LASIK.
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                Author and article information

                Journal
                PubMed ID:: 18628636
                DOI:: 10.1159/000145333

                ScienceOpen disciplines: Chemistry
                Keywords: Adult,Compliance,Cornea,physiology,ultrasonography,Corneal Diseases,diagnosis,physiopathology,Corneal Topography,Dilatation, Pathologic,Elasticity,Humans,Keratoconus,Prospective Studies
                Data availability:
                ScienceOpen disciplines: Chemistry
                Keywords: Adult, Compliance, Cornea, physiology, ultrasonography, Corneal Diseases, diagnosis, physiopathology, Corneal Topography, Dilatation, Pathologic, Elasticity, Humans, Keratoconus, Prospective Studies

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