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In vitro corneal measurements for characterizing ophthalmic procedures

Grant number: 08/10389-4
Support type:Regular Research Grants
Duration: September 01, 2009 - February 29, 2012
Field of knowledge:Engineering - Biomedical Engineering - Medical Engineering
Principal Investigator:Liliane Ventura Schiabel
Grantee:Liliane Ventura Schiabel
Home Institution: Escola de Engenharia de São Carlos (EESC). Universidade de São Paulo (USP). São Carlos , SP, Brazil

Abstract

In order to develop Ophthalmic Technologies and study the properties of the ocular tissues, this work aims to develop a portable system for analyzing the UVA, UVB and visible wavelength transmission through the human cornea. As the photo-refractive surgery are becoming very popular currently [Bower KS, Weichel ED, Kim TJ; 2001] as well as the crosslinking technology for stagnating the keratoconus [Wollensak G, Spoerl E, Seiler, T.; 2003], it is imperative to pursue the preservation of the UV natural protection of the cornea as well as its transparency for the visible spectrum.Therefore we intend to develop a system for evaluating the average transmittance of the corneal tissue at 290nm-410nm, as required by the national and international standards [ANSI/ASQC Zl.4-1981, ANSI Z87.1; 2003].According to these standards, the maximum allowed transmission of ultraviolet radiation through the tissue is 2%, the accuracy of the system should be no greater than 0.3%Hence, several approaches will be performed:a.Evaluation of corneal tissue as it becomes thinner by the photo-refractive surgery. Recent studies has pointed out a reduced amount of UVA and UVB protection on rabbits corneal tissues after photo-refractive surgery [Walsh, J. E. et al; 2008];b.Evaluation of UVA and UVB protection in desepitelized corneal tissues and with wounded endothelium: this might be an supporting tool for eye banks for evaluating an additional aspect of the donor cornea;c.Evaluation of the safetiness of crosslinking procedure, which performs UV irradiation on the cornea, by spectroscopy methods in order to obtain information about the preservation of the corneal transparency; The portable UV measuring will be composed by an opto-electronic hardware, which consists of a UV emitting source (UVA and UVB), that will be detected by two sensors. One of the sensors is used for a reference signal. The digital processing and exhibiting of the report on a LCD display, as well as a management software, processing software, integration and control of the system will be implemented on the device.Therefore, for simulating the outcome of photo-refractive surgery, in order to evaluate the corneal tissues, several lamellas will be taken from the cornea with a microkeratometer. The procedure to be performed is: removing the cornea from the enucleated eye ball; measuring the corneal thickness with a pachymeter; measuring the transmission spectrum (290 - 800nm); measuring the corneal average transmission in the portable system (measuring the cornea in both systems, may assure the effectiveness of the portable system). This rotine will go on for the cornea after every removed lamella.For the crosslinking evaluation, the procedure will be irradiating the "in vitro" corneal tissue, using the regular clinical protocol, and obtaining the transmission or absorption spectrum of the corneal tissue previously and subsequently the irradiation. (AU)