First Author: H.Matalia INDIA
Co Author(s): S. D A. Joshi M. Kumar S. Tejwani R. Shetty
Purpose:
Corneal biomechanics plays an important role in screening of refractive surgery patients and diagnosis of patients with potential risk of ectasia. Ocular Response Analyzer (ORA, Reichert) was the 1st instrument to evaluate corneal biomechanical properties in vivo. Newer Corneal Visualization with Scheimpflug Technology" (CorVis ST, Oculus Inc.), provides us real time imaging of the corneal deformation based on ultra-high speed Scheimpflug imaging, 4330 frame/sec. Though both the machines are based on similar principle of air puff applanation /distortion of the cornea, both the machine provide different variable, which are directly not comparable. Hence we decide to study the correlation between two different methods of studying corneal biomechanics in normal and keraconic eyes.
Setting:
Department of Cornea, Refractive Surgery & Ocular Surface, Narayana Nethralaya Super Speciality Eye Hospital & Post Graduate Insitute of Ophthalmology, Bangalore, India
Methods:
It was a prospective non-randomized observational case series. We studied normal eyes and eyes with keratoconic eyes using ORA and CorVis ST. Both the machines were studied for biomechanics; ORA: Corneal hysteresis (CH) & Corneal Resistant Factor (CRF) and CorVis ST: Deformation amplitude (Def amp). We also studied the intraocular pressure measurement on these two machines; ORA: Corneal compensated intraocular pressure (IOPcc) & Gold Standard calibrated intraocular pressure (IOPg). After confirming the normal distribution of data, using Pearmans correlation we tried to compare both these machines.
Results:
We studied 62 normal eyes and 25 eyes. In keratoconic eyes, for corneal biomechanics between CorVis ST (Def amp) and ORA (CH) there was very poor correlation r=0.01. Similarly between CorVis ST (Def amp) and ORA (CRF) there was poor correlation r=-0.12. However, between two variable of ORA (CH & CRF) there was an excellent correlation r=0.90 (p<0.0001) in keratoconic eyes. In normal eyes also there was no correlation between CorVis ST (Def amp) and ORA (CH): r=-0.11, CorVis ST (Def amp) and ORA (CRF): r=-0.29. Similar to keratoconic eyes, normal eyes too had excellent correlation between CH & CRF r=0.91 (p<0.0001). Regarding the intraocular pressure data, keratoconic eye did not show any correlation between CorVis ST IOP and ORA IOPcc (r=-0.03) and IOPg (r=0). Normal eyes showed poor correlation between CorVis ST IOP and ORA IOPcc (r=-0.25) and fair correlation between CorVis ST IOP and ORA IOPg (r=0.51).
Conclusions:
CorVis ST and ORA do not any show good correlation in terms of measurement of corneal biomechanics and intraocular pressure. Hence, these machines cannot be used interchangeably for various measurements of corneal biomechanics and intraocular pressure. Follow-up on the same machine is mandatory. FINANCIAL DISCLOSURE?: No
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