The Research Of Corneal Thickness And Intraocular Pressure Detector

The corneal thickness and the intraocular pressure (IOP) are both the significant parameters of ophthalmic diagnosis. To excimer laser surgery, the corneal thickness has been a determinant. And the higher intraocular pressure is an acknowledged symptom of glaucoma. It has been shown that there has a certain correlation between corneal thickness and IOP. Recent analysis reveals that a 10% difference in central corneal thickness (CCT) would result in a 3.4±0.9mmHg difference in IOP. Therefore, experts suggest it is necessary to measure CCT, when the high IOP is considered as an evidence of glaucoma.The paper reviews the development of the measurement of corneal thickness and IOP. A new method was designed to measure the corneal thickness with the pulse-echo of ultrasound, based on the comparing with several methods of ultrasonic thickness measurements. The corneal thickness is calculated from the time interval between the two echoes reflected on the front and rear interfaces of the cornea. This method is not only more accurate than optical pachometer, but also simpler in algorithm, no restriction to the detected surface and easier to implement. According to the principle of tonometer discussed by ELWIN MARG and R.STUART MACKAY, the pressure curves were obtained, which as a progressively greater force is applied to the probe to flatter a larger area of the cornea. The intraocular pressure was found out from the analysis of the curves.Based on AT89C52 single-chip, the system adopts CMOS integrated circuits and SMT elements. The software is programmed by C51 assembly language, which makes it efficient and fast. Both hardware and software are modular structure, so that it is convenient for both the function update and apparatus maintenance. We use differential circuit to increase radio-frequency, double-pulse counting to improve precision and some kinds of digital filters to enhance anti-interference proficiency.The equipment designed by this project can measure the corneal thickness and IOP simultaneously and has the properties: small volume, low power and high intellectualized.