The world through the eyes of a model
An experimental model, developed by scientists from VNIIEF in Sarov and their colleagues, ophthalmologists from ‘Mikrokhirugiya Glaza’ [Optical Microsurgery] means that it is possible, quite literally, to see the world with someone else’s eyes. Financial support was given to the researchers for the creation of a model of the human eye by the International Science and Technology Center.
‘The actual initiators of the project were the Moscow-based developers of new artificial crystalline lens models and microsurgeons,’ explains project manager and lead scientist of the VNIIEF Institute of Laser Physics Research Leonid Zykov. ‘The fact is that when treating cataracts they, just as all world specialists, use such an approach widely. A patient’s clouded lens now hinders rather than facilitates sight, is replaced by an artificial crystalline lens, a so-called intraocular lens made of plastic.
‘In addition to the fact that the most suitable crystalline lens has to be selected precisely for the given patient, and they come in all forms and materials and optical parameters, a further problem then arises. After the operation the crystalline lens can shift slightly in the patient’s eye, simply from the reaction of the organism to the implanted body. The doctors themselves have no way of learning how this is reflected on the patient’s sight, on the picture a person sees; they have to rely on the feelings and statements of the patients themselves, a most subjective material to have to work with.
‘And so the surgeons came to us with what at first seemed to be a task from the realms of the fantastic; make a model, meaning an installation, that would allow the crystalline lens developers and doctors to see with their own eyes an object as it would be seen by their patient. This was to make it possible to change artificial crystalline lenses, shift them in a way that they could be shifted in the human eye and determine how the image that falls on the retina changes, all for further analysis. Only in this instance the job would be done by computer and not the human mind. And this is the model of the eye, at least its experimental sample, that we have succeeded in creating. Initially, of course, once we had developed a mathematical model.’
The experimental model almost completely reproduces the optical system of the human eye: the cornea, front chamber, lens, hyaline body and retina. The experiments and calculations have shown that such a device is completely effective in reproducing the optics of the eye. The lens being tested, the artificial crystalline lens, is placed in a special holder into a bath filled with distilled water. The holder can be moved- shifted from side to side, turned and moved forwards and backwards.
The front wall of the bath is a convex retina, just as in the real eye, made of polymethylmetacrylate, generally better known to us as Plexiglas, only of very good quality. In terms of its optical properties it is very similar to a real cornea. In the opposite wall is a wall of the same polymer as the cornea. All components of the model correspond with the average statistical human eye in size and distance between them. With one exception. The thickness of the bath is less than the distance from the cornea to the image, formed by the model. In other words, in a real eye the image appears on the retina, while in the model it is as if suspended in the air ‘behind the back’ of the bath. But at the ‘correct’ distance, 24mm as in the average physiological human eye.
Using a special optical objective it is increased by almost six times and it then hits the CCD-matrix of a video camera. Owing to the limited size of this matrix, the size of the image is not great – just 1.1mm x 0.83mm. As a result the digitized image of the object, as seen by the model, can be viewed on a computer screen and further, which is especially important, it can be characterized qualitatively.
The scientists propose that the quality of the image, obtained with one or other crystalline lens, however it may be located, be verified using the same tables that are usually used by ophthalmologists. Just like before a patient in the optician’s room, letters of varying size and thickness, grids and groups of vertical lines such as on a barcode, all drawn on paper, are held before the model. And one can discern in qualitative terms on the computer screen how the model ‘sees’ them.
‘As well as the experimental model, we have also developed a rated model of the eye, more precise than its first version,’ continues Zykov. This model also reproduces the optical system of the eye and makes it possible to see a rated picture of the image displayed on its retina. We rate the picture using a special program. It enables the setting of optical and geometric parameters of elements of the eye in wide limits and facilitates the obtaining of a picture of the image on the screen of a personal computer. In particular, the program foresees the possibility of shifts of the crystalline lens along and across the optical axis and possible incidence. This program has a convenient and clear user interface with depiction of the optical system of the eye and dialog boxes.’
Andrew Vakhliaev | alfa