The measurement of the optical and morphological properties of the human crystalline lens is very demanding due to its position inside the eye. In this work are presented preliminary results of a pilot study developed to compute the crystalline lens curvature and thickness from images obtained with a slit-scanning system. The system was applied to 2 different eyes and the first results are promising
This study aimed to investigate if the compensation effect that exists between cornea and the internal optics of the eye changes with a computer near vision task. Nineteen emmetropic students of University of Minho (19 eyes) with a mean age of 22.7 years old (range from 19 to 25 years old) performed a computer reading task (with an accommodative demand of 2.50 D) for 30 minutes. Ocular and corneal aberrations were measured immediately before and after the task using the Visionix VX 120 (VisionixLuneau,Chartes,France) equipment. The results were evaluated for a 5 mm pupil diameter. The compensation factor was computed from the RMS values of the low order aberrations (LOA) 3rd order to 6th order aberrations, coma, spherical aberrations (SA) and high order aberrations (HOA). Results showed a decrease in the compensation factor for LOA, third order aberration and coma but others suffer no changes. It seems that there was an interaction between corneal and internal aberrations during the computer near vision. The visual system seems to adapt to compensate the changes provoked by the task, leading to a diminution of total ocular aberrations, allowing a reduction of ocular optical quality with the task less intensified.
The lighting systems that is used in our daily tasks are an important factor in our vision quality. These systems must be suitable to the visual needs required by these type of tasks. The aim of this work is to evaluate the influence of coloured lighting on ocular accommodation and quantify its response with the lighting used. Twenty subjects, with ages ranged from 18 to 26 years old, participated in the study. All subjects had 20/20 corrected visual acuity or better, normal colour vision and no history of ocular disease or surgery. The amplitude of accommodation was measured and compared under normal lighting conditions (assuming white LED light) and under coloured LED lighting tuned at peak wavelengths of 515 nm and 635 nm. Improvements over the reference light source on the parameters that were analysed will be identified and assumed as better lighting conditions (>0.05). It was found a general decrease on the amplitude of accommodation when measured under coloured lighting and compared against the normal lighting. The most statistically significant decrease was found for the red light with a difference of 1.45D (p=0,05). Special care was taken to ensure same viewing and illuminance on all test conditions. These results seem to suggest that there is an impact of the colour of the lighting in use in the availability of the amplitude of accommodation.
The main goal of this study was to investigate the effect of performing a near task on eye's optical quality.
Wavefront aberrations data of 35 young emmetropic eyes were measured with the L80 Wave+: (1) ocular aberrations were measured with the wavefront sensor, (2) corneal wavefront aberrations were computed from the Placido disk system's data and (3) the internal wavefront component of the eye were determined as the difference between ocular and corneal wavefront aberrations. The measurements were performed before and after a reading task was completed. Several corneal and internal aberration terms changed in opposite directions with the reading task, most of them changing its sign relative to the pre-task condition. The opposite sign between the cornea and the internal optics produced a partial balance that leaved the eye with less aberrations than the individual components. Furthermore, the optical quality of the eye and the retinal image quality changes with a reading task.
Overall optical quality of the eye and its components reduced with the near task, as a consequence of the increase in wavefront aberrations after the reading. The reading task induced a myopic shift of 0.18 D in the distance M value of the emmetropic subjects.
The main goal of this study was to investigate the effect of accommodation on eye's optical quality. Wavefront aberrations data of 35 young emmetropic eyes were measured with the L80 Wave+: (1) ocular aberrations were measured with the wavefront sensor, while the subjects fixated at far and near (40 cm), (2) corneal wavefront aberrations were computed from the Placido disk system's data for distance vision conditions and (3) the internal wavefront component of the eye were determined as the difference between ocular and corneal wavefront aberrations. Ocular wavefront aberrations pattern changed with accommodation, particularly due to changes in the primary spherical aberrations towards negative values. Furthermore, the optical quality of the eye and the retinal image quality changes during near vision.
The aim of this work was to find out if differences exist in accommodative and convergence response for different
computer monitors' and a printed text. It was also tried to relate the horizontal heterophoria value and accommodative
response with the symptoms associated with computer use.
Two independents experiments were carried out in this study. The first experiment was measuring the accommodative
response on 89 subjects using the Grand Seiko WAM-5500 (Grand Seiko Co., Ltd., Japan). The accommodative
response was measured using three computer monitors: a 17-inch cathode ray tube (CRT), two liquid crystal displays
LCDs, one 17-inch (LCD17) and one 15 inches (LCD15) and a printed text. The text displayed was always the same for
all the subjects and tests. A second experiment aimed to measure the value of habitual horizontal heterophoria on 80
subjects using the Von Graefe technique. The measurements were obtained using the same target presented on two
different computer monitors, one 19-inch cathode ray tube (CRT) and other 19 inches liquid crystal displays (LCD) and
printed on paper. A small survey about the incidence and prevalence of symptoms was performed similarly in both
experiments.
In the first experiment, the accommodation response was higher in the CRT and LCD's than for paper. There were not
found significantly different response for both LCD monitors'. The second experiment showed that, the heterophoria
values were similar for all the stimuli. On average, participants presented a small exophoria. In both experiments,
asthenopia was the symptom that presented higher incidence.
There are different accommodative responses when reading on paper or on computer monitors. This difference is more
significant for CRT monitors. On the other hand, there was no difference in the values of convergence for the computer
monitors' and paper. The symptoms associated with the use of computers are not related with the increase in
accommodation and with the horizontal heterophoria values.
Nowadays, cataract extraction with IOL implantation aims not only to restore the crystalline lens' transparency, but also
to improve patients' retinal image quality. The refractive outcome and visual quality in pseudophakic eyes is mainly
determined by the combination of corneal and internal optics resulting from the implanted IOLs. The optical function of
the IOLs depends on its position in the eye. The IOL distance to the corneal apex determines the optical power needed
for optical correction.
In this paper it is described the usage of a slit-scanning imaging system to determine IOL positioning. Through the
projection of the light from a slit onto the eye, this tomography system allows to acquire multiple sections of the anterior
eye segment, at different meridians. The developed system's software corrects geometric and optical distortion of the
images and provides 3-dimentional models of the eye's structures from the 2-dimensional sections. With this noninvasive
technique, cross-sectional images of an eye with an aphakic IOL were obtained in order to reconstruct its 3-
dimensional model of the lens and assess its position in the anterior segment camera.
The introduction to our school’ students of the wonders of light and optics and its understanding can and should be made as extensively as possible. As soon as at kindergarten level! A hands-on approach leading the students to observe experiment and discover themselves in a critical committed and active way the different aspects of light and optics should be employed at all school levels and must be the main driving pedagogical practice of all learning process of science and technology. In this communication we present a series of experiments and support material designed in this hands-on perspective to be used to introduce the study of optics to kindergarten and early basic school students. A critical evaluation of the first results of the application of these material with students aged 4 to 10 years will be presented.
In this work the authors present an optical corneal tomographer that uses two Scheimpflug cameras attached to an
innovative illumination system that allows a rotary scanning of the entire cornea. The measurements are made from
corneal optical sections obtained by illumination with a collimated beam expanded in a fan by a small cylindrical lens.
This lens is provided with motor driven rotation in order to perform automated rotary scan of the whole cornea. The
authors expect to achieve a scanning speed that will allow producing complete tomography maps without consideration
of eye movements. Two Scheimpflug cameras are used to capture the images of the optical sections.
With this system it is possible to obtain 3-D representation of the corneal thickness as well as corneal topography. Maps
of the corneal thickness and elevation maps are shown. As Scheimpflug cameras are used, it is expected to obtained data
from the lens too.
Contact lens' fitting evaluation is of critical importance in the contact lens' prescription process. For the correction of eye's refraction problems the use of contact lens' is very appealing to the user. However its prescription is far more demanding than the one of eye glasses. The fitting of a contact lens to a particular cornea must be carefully assessed in order to reduce possible user's physical miscomfort or even medical situations.The traditional way of easily checking the fitting of a contact lens is to perform a fluorescein test. The simple visual evaluation of the 'smoothness' of the color/brightness distribution of the fluorescence at the contact lens' location gives the optometrist an idea of the fitting's quality. We suggested the automation of the process simply by the substitution of the optometrist's eye by a CCD camera, and the use of appropriated simple image processing techniques. The setup and the digitalization and processing routines will be described in this communication. The processed images may then be directly analyzed by the optometrist in a faster, easier and more efficient way. However, it is also possible to perform an automated fitting evaluation by working out the information given by the image's intensity histograms for the green and blue RGB' channels.
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