Both in medicine and optometry, clinical guidelines have become a relevant part of clinical practice decision making process. In our study, we aimed to refer to potential limitations related to specific undefined guidelines used in optometry that suggest near addition (add) values based on patient age. We measured near add binocularly at 40 cm distance with plus build up technique in 216 adults aged 35 to 80 years. Baseline subjective refraction, near visual acuity with and without add was analysed in a relation to age and the amount of near add. For further analysis, we randomly selected 30 patients and performed five different near add estimation techniques. Our results support that there is a positive, linear relationship of moderate strength between age and amount of near add (r = 0.73, P < 0.05). Relationship is positive and fairly strong (r = -0.78, P < 0.05) between near visual acuity without add and near add amount and moderate (r = -0.51, P < 0.05) between near visual acuity without add and patient age. Differences between plus build up technique is not statistically significant if compared with other clinical near add estimation techniques (P > 0.05). Guideline based technique (P < 0.01) provided 0.29 D higher near add while technique based on calculations from amplitude of accommodation (P < 0.01) provided 0.65 D lower near add. Based on our results, we highlight that usability of age expected near add in clinical environment is limited because of large individual differences.
Important optical parameter of the eye is intraocular light scattering. Straylight can reduce visual acuity, contrast
sensitivity. It is one of the main factors for glare, especially for drivers at night, when there is light source some distance
away from the fixation point. There are many factors, which can affect amount of light scattering in the eye. To assess
the effect of the color of the straylight source on retinal image quality at different light scattering levels, retinal straylight
was measured with and without light scattering occluder. Red, green and blue colors were choosed for straylight source.
Psychophysical and electrophysiological methods were used to evaluate light scattering effect on perception on different
color stimuli. Results show that straylight values are the greatest for blue color with and without light scattering
occluder. In measurements without light scattering occluder ratio of straylight values for red and green color are different
between subjects. Using light scattering occluder straylight values for green color are greater than for red color. Optical
and anatomical factors which can induce these spectral variations are discussed. Psychophysical and electrophysiological
methods showed the similar changes in results with straylight values when light scattering were increased.
In routine eye examination the visual acuity usually is determined using standard charts with black letters on a white
background, however contrast and colour are important characteristics of visual perception. The purpose of research was
to study the perception of isoluminant coloured stimuli in the cases of true and simulated amlyopia. We estimated
difference in visual acuity with isoluminant coloured stimuli comparing to that for high contrast black-white stimuli for
true amblyopia and simulated amblyopia. Tests were generated on computer screen. Visual acuity was detected using
different charts in two ways: standard achromatic stimuli (black symbols on a white background) and isoluminant
coloured stimuli (white symbols on a yellow background, grey symbols on blue, green or red background). Thus
isoluminant tests had colour contrast only but had no luminance contrast. Visual acuity evaluated with the standard
method and colour tests were studied for subjects with good visual acuity, if necessary using the best vision correction.
The same was performed for subjects with defocused eye and with true amblyopia. Defocus was realized with optical
lenses placed in front of the normal eye. The obtained results applying the isoluminant colour charts revealed worsening
of the visual acuity comparing with the visual acuity estimated with a standard high contrast method (black symbols on a
The paper reports on the development of the equipment for studies of the eye dominance and ocular stereoprevalence by
using black-and-white and color stereostimuli. The stereostimuli are separated either by color-filter goggles or phase
separating liquid-crystal-shutter goggles. The stability of the stereoprevalence is studied by artificial step-by-step
deterioration of the retinal image quality, particularly in the dominant eye. The stimuli are blurred using spatial Gaussian
filtering. The polymer-dispersed-liquid-crystal cell placed in front of the dominant eye induces a controllable light
scattering. The stimuli-blurring and light-scattering methods exhibit different influence on the eye ocular prevalence.
Blurring causes a smooth change of the prevalence towards the nonblurred stimuli eye. The influence of moderate
scattering depends heavily on stimuli color. At a sufficiently high scattering level the instable switching from the
prevalence of one eye to the prevalence of the other occurs.
Simulation of vision pathologies and adverse viewing conditions in laboratory conditions requires optical phantoms with different level of light scattering. Such obstacles are designed as passive or active elements applying several technologies. We used for studies two kinds of solid state smart materials with electrically controllable light scattering - electrooptic PLZT ceramics, polymer dispersed liquid crystals PDLC and obstacles with fixed light scattering - composite of polymer methylmethaacrilat PMM together with grinded glass microparticles. Report analyzes optical characteristics of such obstacles - attenuation, scattering, depolarization of different wavelength light at various scattering levels and changes of visual performance applying obstacles in vision science studies.
Following aspects related to human colour vision are included in experimental lessons for optometry students of University of Latvia. Characteristics of coloured stimuli (emitting and reflective), determination their coordinates in different colour spaces. Objective characteristics of transmitting of colour stimuli through the optical system of eye together with various types of appliances (lenses, prisms, Fresnel prisms). Psychophysical determination of mono- and polychromatic stimuli perception taking into account physiology of eye, retinal colour photoreceptor topography and spectral sensitivity, spatial and temporal characteristics of retinal receptive fields. Ergonomics of visual perception, influence of illumination and glare effects, testing of colour vision deficiencies.