Advanced research methods in visual psychophysics and optometry

Bruce Bridgman, who was the first to give a satisfactory explanation of the effect of saccade suppression, noted that the movements most frequently performed by humans are eye movements. Therefore, it is understandable that eye movements became the subject of researchers' interest as early as the end of the 19th century. We direct our gaze to objects or areas that are interesting for some reason. Thus, tracking eye movements is primarily, but not limited to, following the observer's "path of interest", answering questions about what the person is interested in or how the observation of an object or region located with the eyes is going.

The eye is a complex optical imaging system whose components  determine the first step of vision. Quantifying and measuring  the ocular quality, and how this affects the quality of the retinal  images, can allow us to better understand the visual process  and to improve diagnostics and correction methods. The optical  quality is lowered by aberrations (consequence of the shape of  the refracting surfaces), diffraction at the pupil, and scattering  (due to particles and nonuniformities localized in the transparent media of the eye). The  combined effect of these three factors is that light deviates from  the ideal trajectory and spreads over a deteriorated retinal image  that will limit the visual performance.

In order to understand the micro- and nanostructure of the corneal stroma, electron microscopy and X-ray diffraction were used as techniques allowing to obtain a resolution several orders of magnitude better than that offered by optical microscopy. These studies revealed that the basic building elements of the corneal stroma are collagen fibers, the diameter of which is approximately 30 nm and the average distance between them is approximately 55 nm. The fibers are gathered into strips called lamellae, about 1 µm thick and 100 to 150 µm wide. Operating the magnification required to visualize the described structures was obviously related to the limitation of the field of view to a very small area of the tested sample. Images of such small fragments of the cornea, on the order of few micrometers, did not allow for explaining how the fibrous structure of the cornea influences its biomechanical and optical properties and topography. Microscopic techniques were needed to fill the gap between magnification typical of electron microscopy and confocal laser scanning microscopy. Such techniques turned out to be techniques using non-linear optical phenomena: second harmonic generation and two-photon excited fluorescence. 

Confocal microscopes used in eye examination fill the gap between high-resolution OCT (visible individual photoreceptors, 
capillaries) and scanning electron microscopy (visible isolated biomolecules, e.g. rhodopsin). The lecture is devoted to 
single-photon laser scanning confocal microscopy.

One of the diagnostic tools at the disposal of the optometrist is the assessment of the patient's reading ability. This assessment
 is useful not only in making an initial diagnosis or monitoring vision therapy, but also in the selection of visual aids for patients 
with low vision. The reading speed achieved depends significantly on the method of presenting the text to the reader. Three 
basic methods are discussed in the lecture: drifting-text method, rapid serial visual presentation method (RSVP) and flashcard 
method.

The imperfect quality of the retinal image and its variability over time is the result of binocular, dynamic 
accumulations of optical aberrations, characteristic of a given patient, superimposed on classic sphero-cylindrical
 refractive errors. Advanced correction techniques should take into account all these factors, as far as possible, 
because they degrade the images formed at the back of the eye. In the current state of development of ophthalmic 
technologies, this can be achieved only in laboratory conditions thanks to adaptive optics, which allows the 
measurement and modeling of most of these factors in real time, in particular monochromatic aberrations of higher 
orders, including their dynamics (e.g. during accommodation) both mono- as well as binocularly.

Adaptive optics used in vision sciences is distinguished by a feature unseen in other applications. It is kind 
of bidirectional. On the one hand, it allows you to look deep into the eye and obtain images, also 
three-dimensional, of tissue structures of such good quality as if the optical elements of the eye involved in 
creating these images were almost completely free of monochromatic aberrations, and on the other hand, it allows 
you to propose a correction that as a result, it will give a retinal image of the surrounding world with sharpness
unattainable for the best-chosen sphero-cylindrical correction. It is estimated that thanks to this correction it 
will be possible to achieve visual acuity two rows below the zeroth row on the logMAR optotype tables. Hence, 
the term supervision was coined. It should not be confused with hyperacuity, which is, for example, vernier 
acuity. The lecture is devoted to the basics of adaptive optics and the imaging of eye tissue structures by 
instruments equipped with adaptive optics systems.

The academic bodies of physics departments approving the topics of diploma theses in optometry and evaluating 
the defense of these theses are quite liberal. They usually assume that the results of research work are results
in the field of physical sciences if they were obtained with the use of instruments created by engineering 
implementation of physical phenomena, especially if this implementation took place relatively recently, i.e. 
when the graduate student used modern research equipment. In view of the fact that the inventors of imaging 
technics as for example the nuclear magnetic resonance (MRI) and the X-ray computed tomography (X-ray CT) 
received the Nobel Prize in medicine, not physics, for their achievements, such a position of the university 
should be assessed as far-reaching pragmatism. In order to meet the above-described practice of including 
diploma theses in the discipline of "physical sciences", the author proposed including a 15-hour lecture 
"Advanced research methods in optometry and psychophysics of vision" in the program of second-cycle studies 
in the field of optometry at the University of Warsaw. The first lecture presents the classification of research
 appropriate for medical and paramedical sciences. The individual elements of this classification will be 
illustrated with examples. Advanced methods of field of view measurement will be discussed in more detail.