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Biomedical engineering

Sharp sight

Sensor does a more detailed diagnosis of visual imperfections

Surgeries to correct problems of vision, such as astigmatism, short-sightedness and far-sightedness, are a humdrum practice in Brazilian ophthalmologic clinics. These surgeries are done today with the help of personalized measures of the each of the patient’s eyes, based on information gathered in the preoperative examinations using devices called wavefront sensors, which analyzes the light that hits the eyeball. At the moment, all the devices of this kind used in Brazil are imported. But in a short time this may change, because Eyetec Ophthalmic Equipment, a company from São Carlos (SP), is getting ready to contend for this market with a new apparatus, also based on wavefront technology, but with a sensor that uses a different principle from the others.

“Instead of several small square, symmetrical lenses, one next to the other, a circular lens was created, with a continuous focus that indicates the deformation of the eye, point by point”, says ophthalmologist Paulo Schor, head of the Ocular Bioengineering Sector of the Federal University of São Paulo (Unifesp). “The mapping done by the new sensor, at each point of the eye, makes it possible to make more detailed diagnoses, which increases precision and flexibility in the surgeries.”

Schor and another ophthalmologist, Wallace Chamon, took the proposal for developing the equipment to Professor Jarbas Caiado de Castro Neto, of the Optics Group of the Physics Institute of the University of São Paulo (USP), and one of the partners in Eyetec. The company received from FAPESP under the Small Business Innovation Research Program (PIPE), in a project that has Castro Neto as its coordinator. The new apparatus has been patented in Brazil and abroad, and has been given, informally, the name of Castro sensor, in homage to the professor from USP responsible for the innovative technological solution.

Stars and galaxies
The wavefront was used initially, and for a long time, in astronomy, to analyze and correct the distortions of the light of stars and galaxies, allowing them to be seen with an excellent quality, even thousands of light-years away. In 1994, the possibility was glimpsed of the wavefront technology being used in ophthalmology as well. In that year, a group of researchers from the University of Heidelberg, in Germany, published a first work that dealt with the use of optic sensors to measure eye deformities. It was the kickoff for ophthalmologic instruments based on this technology to begin to be developed by Europeans and Americans.

The commercially available wavefront sensors are made up of hundreds of small lenses, called lenticles, similar to the eye of an insect. A microcamera behind the lenticles produces spaced out dots, distributed regularly. The regularity determines whether the image that reaches the retina and, consequently, forms vision, is normal or not, because for an eye without any problems, it is possible to identify the regular distribution of the dots. But in eyes with defects of irregularities, it is not possible to identify this regularity. Calculations and graphs made by software indicate the exact shape of the wavefront that leaves the eye, and this makes it possible to take the measurements of astigmatism, short-sightedness and far-sightedness, and also of more subtle irregularities. “We set off from the principle that irregularities of the eye have a circular symmetry”, says Castro. That is why several circular lenses were created, to map the problems point by point. When light is cast on the back of the eye during the examination, it accompanies the symmetry and catches all the nuances, indicating the exact place where the irregularity is to be found. “Technological innovation means the capacity to map eye defects at each spot, with high precision and simplicity”, says Schor.

Ideal vision
Before the wavefront technique is used in refractive surgeries, so called because they change the degree, or refraction, of the patient’s eye, the only possibility used to be to correct problems such as short-sightedness, astigmatism and far-sightedness by changing the ocular curvature outwards or inwards. “Today, the form of the cornea is changed to improve the quality and quantity of vision”, Castro says.

The wavefront analyzer defines and corrects the patient’s degree in a much more precise way than the traditional apparatuses used to take the measurements for the prescriptions for glasses measured in multiples of 0.25 degrees. As the optical sensor captures and quantifies the deformities that the images of the objects suffer when being observed by each point of the eye, the correction carried out by surgery may improve night vision in some patients, because the pupils dilate in the dark, and the irregularities existing in the peripheral vision become more evident in this period. Carried out in the preoperative stage, the examination reproduces a three-dimensional map of the optical irregularities that is transferred to the laser at the moment of the surgery.  As a result of the use of the wavefront sensor, the images are now captured on the retina with better resolution and clarity, without irregularities or subtle aberrations, which were neither detected nor corrected before. And many patients, after refractive surgery, can have a quality of sight better than from conventional surgery.

The advances achieved with the national wavefront equipment, which maps the irregularities at each point of the eye, the fruit of a partnership between researchers from Unifesp and USP, are not the only result of the joint work of the two research groups. The first was the development of an apparatus to measure the curvature of the cornea, launched by Eyetec in 1998, for use in surgeries for short-sightedness. “In those days, the only similar equipment was imported, which was very expensive by Brazilian standards”, says Schor. The topographer sold about 400 units in the domestic market. “If imported, each topographer would cost the country about US$ 20 thousand. So the hard currency savings were roughly US$ 8 million”, reckons Castro. The work that resulted in the apparatus was also one of the bases for the Ocular Bioengineering Sector to establish itself at Unifesp, six years ago, created to develop multidisciplinary technology. With the new sensor, now at the preclinical test stage, the partners also expect good results, since, besides the innovation, for the product not being associated with any specific kind of laser, like the other apparatuses currently in use, it can be sold for diagnoses and used in ophthalmological offices and clinics.

The Project
Development of equipment for determining ocular aberrations using wavefront measurement (nº 00/06810-4); Modality Small Business Innovation Research Program (PIPE); Coordinator Jarbas Caiado de Castro Neto – Eyetec; Investment R$ 325,750.00 and US$ 12,250.00 (FAPESP)