A Novel Method to Assess the Cornea Biomechanical Properties With Schiotz Tonometer

This study aims to use Schiotz tonometer to evaluate the corneal biomechanical properties. The administration of Schiotz tonometer is according to the routine protocol which is use to measure intra-ocular pressure. The results obtained from Schiotz tonometer will be compared with results obtained from ORA and/or Corvis.

Schiotz tonometer, since it firstly be developed more than 100 years ago by Hjalmar Schiotz, has been regarded as a classical method to evaluate intraocular pressure (IOP). In present study, we aims to measure the corneal biomechanical properties with schiotz tonometer and elucidate the clinical significance of this novel measurement. The corneal biomechanical property was calculated with subtracting the value displayed under loaded weight 5.5g from that under loaded weight 7.5g. We named the corneal biomechanical properties obtained with schiotz tonometer as Mulee factor, and the formulation is Mulee factor=value under loaded weight 7.5g (Value 7.5G)-value under loaded weight 5.5g (Value 5.5G).

People without keratoconus, history of ocular surgery, and other diseases mentioned in exclusion criteria. Normal people will receive treatment or measurement including: Schiotz tonometer measurement, UVA/riboflavin corneal crosslinking, Keratoplasty, Ocular morphology measurement,and routine ophthalmic examination.

Patients with keratoconus.Keratoconic patients will receive treatment or measurement including:Schiotz tonometer measurement, UVA/riboflavin corneal crosslinking,Ocular morphology measurement,and routine ophthalmic examination.

Patients received keratoplasty. Patients received keratoplasty will receive treatment or measurement including:Schiotz tonometer measurement,Keratoplasty, Ocular morphology measurement,and routine ophthalmic examination..

The corneal biomechanical properties will be measured using a Schiotz tonometer with routine manipulation protocol.This measurement will be used in normal people, keratoconic patients, patients received keratoplasty.

The UVA/riboflavin corneal crosslinking will be applied using a UV-X lamp (Peschke Meditrade GmbH, Switzerland) with routine manipulation protocol (3mW/cm2, 365nm, 30 minutes).This treatment will be used in keratoconic patients.

The keratoplasty mainly include femto-LASIK (Laser in situ keratomileusis), which will be applied using a Wavelight FS200 and Wavelight EX500 Excimer Laser (Alcon Inc. USA.).The keratoplasty will be applied in patients who would like to receive the surgery.

Cornea thickness will be measured with a pachymeter (Tomey SP-100 Pchymeter, Japan); cornea topography will be measured with Topolyzer Vario (Allegro, Wavelight GmBH, Germany); anterior chamber depth, white to white, and ocular axis length will be measured using a IOL master (Carl Zeiss Meditec, Germany). These measurements will be used in normal people, keratoconic patients, patients received keratoplasty.

Vision acuity will be measured with a decimal visual chart; IOP (Intra-ocular pressure) will be measured with a tonometer (Topcon CT-80, Topcon, Japan) , fundoscopy examination will be apllied with a direct ophthalmoscopy, slit lamp examination will be applied with a slit lamp. These examinations will be used in normal people, keratoconic patients, patients received keratoplasty.

Cornea biomechanical properties will be measured with a ocular response analyzer (Reichert, USA.) and/or a Corvis-ST (Oculus, Germany).These measurements will be used in normal people, keratoconic patients, patients received keratoplasty.

Mulee factor= Value displayed with Schiotz tonometer under 7.5g load-Value displayed with Schiotz tonometer under 5.5g load

Inclusion Criteria: People without the disease mentioned in exclusion criteria part. Exclusion Criteria: Patients with ocular diseases including keratitis, conjunctivitis, history of chronic eye/systemic diseases except myopia and keratoconus, history of ocular surgery except LASIK, pregnant or lactating females.