With age, the crystalline lenses tend to become less transparent, diffusing light and degrading the retinal image. The advanced stages of this situation are a condition called cataracts; the lens is nearly opaque leading to a low quality of vision. This loss of transparency mainly occurs with age, although there are some other causes, as traumatism or some previous eye diseases. Although there are no studies showing prevention factors, it is widely accepted that diminishing UV exposure may delay cataract development. A cataracts lens causes glare, halos, vision impairments and, in the most extreme case, blindness. The standard, and successful, treatment consists in the surgical replacement of the cataractous lens with an artificial implant, called intraocular lens (IOL) that restores the eye’s ability to form clear images on the retina. Phacoemulsification is a technique that breaks the cataracts lens by ultrasound and then those small fragments are suctioned by a small incision. An IOL is then inserted in the capsular bag. Cataract surgery is almost painless and ambulatory and nowadays the most common eye surgery. The Organization for Economic Co-operation and Development (OEDC) reported in 2010 a ratio of 756 surgeries per 100000 persons in Europe on average, what means approximately 4 million cataracts procedures. The World Health Organization informs that age related cataract is responsible for 48% of world blindness, which represents about 18 million people. This seems paradoxical considering the relatively simple surgery required. In addition, it should be considered that even in the developed world a quite significant fraction of cataract patients had the surgery at advanced stages of the process (what is called a “mature” cataract). This means many years of a low quality of vision.
Controlling light in scattering media
More than 40 years ago, there were the first attempts to test vision in a cataract eye. That was perhaps the first antecedents to this project. In an older eye, it is common that cataract appear in combination with other eye conditions, in particular different types of retinal diseases. It is then very important to known in advance the contribution of each problem, but typically a dense cataract impedes to evaluate the retinal damages. This is critical since the potential benefit of the cataract surgery cannot be fully predicted. Daniel Green proposed a clever way to evaluate vision through cataracts using an interferometric method. In his technique for measuring the visual acuity of cataract patients the light from a laser was used to form interference patterns of variable fineness on the patient’s retina. The fineness of the interference pattern that the patient can detect gives an indication of the potential for improved vision. Comparison of this estimate of the potential with the patient’s vision after cataract extraction shows that this test can indicate the condition of the fovea behind a cataract. The approach was limited only to projected gratings and depended on the presence of clear areas in the lens allowing the beam to reach the retina. Inspired with this pioneering work, a more general solution would be however required.
While the control and correction of the optical aberrations is now nearly routine and implemented in many laboratories and even in commercial instruments, the possible correction of scattering is still in its infancy. Imaging of focusing light through turbulent media is one of the frontiers of photonics technology. There have been several attempts to achieve this important goal by using different approaches.
Refractive index inhomogeneities cause light to be strongly scattered in many materials of technological and biomedical relevance. When light enters a thin scattering medium, one can observe a beam of refracted light that is exponentially extinguished as it progresses deeper into the medium. In a non-absorbing medium, the energy in the beam is not lost, but is instead converted into a diffuse scattered light that impedes imaging and focusing of light in many applications such as art preservation, biomedical imaging, laser therapy or photonic crystal fabrication. Holography showed that light scattering by time independent media does not lead to an irretrievable loss of information, which is scrambled into disordered interference patterns. The ability to manipulate interference in multiply scattered light has recently given rise to new focusing and imaging techniques in which focusing of light is possible even in scattering media. Several techniques have also been proposed for imaging through scattering media.
OBJECTIVES of SEECat
The main objective of thisproject is to develop techniques to correct for the degradation induced by scattered light in the human eye. This presents quite significant challenges, but if achieved, even partially, would render immediate benefits, especially in cataract patients. There are now conditions that would allow us to explore, with a reasonable risk-opportunity factor, this possibility.
Our objective is to develop new techniques based in the spatial manipulation of the light incoming the eye and in methods to measure scatter to remove partially the scattered light contribution.
Beyond the scientific objective of controlling light scattering in the eye, there are important practical objectives of the project.
a) To obtain good quality images of the retina in cataract patients by imaging through the scattered media. This would allow evaluating and treating possible retinal diseases in those patients.
b) To develop a new concept of optoelectronic goggles that would permit to improve vision in patients with cataracts. This will offer a temporary relieve to patients until surgery is performed or in a permanent basis on those cases where for some reasons cataract surgery cannot be performed.
c) To devise methods to be applied in normal subjects with normal or slightly elevated amount of intraocular scatter. This would provide improved vision with reduced glare of interest in some specific visual tasks.