Dynamic light scattering in ophthalmology: results of in vitro and in vivo experiments

OBJECTIVE

To calibrate new dynamic light scattering (DLS) devices in defined solutions and post mortem porcine and human eyes. To examine all segments of the eye and to become familiar with the usage of the technique in living subjects. METHODS, DESIGN: Three new DLS devices for the usage in patients were developed. Mono-disperse solutions, poly-disperse solutions, gels, post mortem porcine and human eyes as well as healthy volunteers were studied. The detected signals were inverted into autocorrelation functions.

RESULTS

We constructed three DLS devices appropriate for in vitro as well as in vivo examinations. In mono disperse solution precise disintegration rates could be calculated. In poly-disperse solutions, in gel and in the vitreous the results did not correlate with movements of individual particles but we could calculate characteristics of the complete scattering system. In vivo measurements demonstrated that DLS can be used in all human eye segments.

DISCUSSION

DLS is a unique technique. With DLS the molecular composition of eye segments can be studied in living subjects. This can be used to understand the molecular basis of severe eye diseases. The presented data demonstrate that DLS delivers reproducible data from all eye segments.

CONCLUSIONS

It is possible to study the molecular structures of eye segments in living subjects. The developed devices were proved successfully in vitro as well as in vivo. Limitations are the low specificity of DLS and its sensitivity to background noise. Now clinical studies are necessary to demonstrate potential diagnostic benefits of DLS in specific eye diseases.

[A device for fluorescence diagnosis and photodynamic therapy of eye diseases, by using photosense]

By having a high photodynamic effectiveness and an ability of fluorescence, a Photosense photosensibilizer provides a way of combining photodynamic therapy (PDT) and monitoring its control within a session, which enhances the efficiency of treatment for the subretinal neovascular membrane. A slit lamp-based apparatus complex has been developed to employ the methods of fluorescence diagnosis (FD) and PDT, by applying this photosensitizer. The complex comprises an optical adapter that focusing laser radiation on the fundus of the eye in a range of 100-1000 microm, a video adapter that includes color and high-sensitive monochromic video cameras, as well as a personal computer and software that processes video information from the high-sensitive camera and displays the obtained images in real time. The original system of filters provides an image of the eye fundus in the fluorescent and usual color light at once during a FR procedure. The spatial resolution of the developed apparatus was tested on the test object specially devised for these purposes, which was 10 microm. The sensitivity of the complex is sufficient to record slightly fluorescent objects on the fundus of the eye.

The Role of Retinal Adaptation in Night Driving

PURPOSE

Driving is essentially a visuomotor task, and there is now compelling evidence that the disproportionate number of road accidents under night driving conditions is linked to changes in visual performance resulting from reduced lighting. The objective of this article is to establish the extent to which vision is either rod-or cone-dominated under night driving conditions.

METHODS

Visual thresholds are measured under lighting conditions that simulate urban lighting. Dark adaptation curves are obtained under three ambient lighting conditions ranging from low (0.1 cd/m) to high (5 cd/m) mesopic levels of retinal adaptation using circular discs of different sizes (1 degree, 2 degrees, 3 degrees, and 5 degrees) presented at retinal eccentricities of 0 degrees, 10 degrees, 20 degrees, 30 degrees, and 40 degrees.

RESULTS

The dark adaptation curves exhibit the classic inflection point between rod and cone activity for the lower levels of ambient illumination but a simple monophasic function for the high mesopic levels (>0.5 lux). Adaptation rates are four times faster for the higher compared with the lower illumination level and twice as fast for central compared with peripheral presentation.

CONCLUSIONS

The data suggest that vision is mediated by cone pathways at 5 lux and by rod pathways at 0.5/0.1 lux. This shift does not profoundly affect sensitivity, but because rod pathways are known to be slower than cone pathways, it will certainly affect observers' ability to respond to rapidly changing viewing conditions such as are encountered when driving at night.

Portable ophthalmic microscopes in the Philippines: an overview

BACKGROUND

Demonstrations were held all over the Philippines to teach local microscope operators basic maintenance skills and troubleshooting for their portable microscopes.

METHODS

Fifteen microscopes were examined and feedback was obtained from 16 microscope operators. The different parameters of the microscope were evaluated as follows: (i) user-friendliness, (ii) demand and availability of technical services and spare parts, (iii) portability and (iv) frequent problems encountered. Some suggestions for improvement are proposed.

RESULTS

There was a general satisfaction among the operators with their microscopes; however, there was a lack of technical support services. Most microscopes were portable and the original casing was adequate for transport. Even though most microscopes were functioning, their quality could be improved with maintenance. The three most common problems identified were: mouldy/dirty lenses, expired mould pellets and poor alignment.

CONCLUSIONS

The portable operating ophthalmic microscope has an important role in the prevention of international blindness. The archaic attitude of sending microscopes to professional technicians for simple maintenance and repair should be abandoned. Instead demonstrations aimed at teaching these skills to local operators and surgeons should be held, in order to improve the technical support available. Different microscope operators can help provide microscope designers with feedback for future improvements. Similar demonstrations could be considered for other countries with a similar scarcity of technical support services.

Nouvelle méthode d’analyse de l’exploration visuelle

The term visual field corresponds to the angular field of view that is seen by the eyes when they are fixed on a point straight-ahead. In neurological patients--e.g. stroke, trauma, or tumour patients--visual field function can be restricted, depending on lesion site and size. In contrast, the term "functional visual field" describes the area of visual field responsiveness under more ordinary viewing conditions. The visual exploration, i.e. the capacity to explore and analyze our visual world, is dependent on the integrity of the visual system and the oculomotor system which has to move the fovea from one object of interest to the next. In this paper, we present a new method to assess the functional visual field, conceptualized as the area that a patient actively scans with eye movements to detect predefined targets placed on everyday scenes. This method allows us to compare three levels of visual field function: (a) the spatial distribution of successful search (hits, i.e. which targets did the patient find?), (b) the spatial distribution of fixations (i.e. where did the patient preferentially search for targets?), and (c) the retinotopic level (i.e. the visual field assessed by perimetry). By integrating these three levels, one can evaluate functional outcomes of visual field disorders. Of particular importance is the question of how a patient compensates for a visual field loss with appropriate eye movements. A further clinical application of this method is the comparison of pre- with post-treatment data. Patients with visual field disorders usually undergo specific exploration trainings, aimed at enhancing the number and amplitude of saccades towards the region of the visual field deficit. The first experiences and clinical application with this method are presented here.

Repeatability of autorefraction and axial length measurements after laser in situ keratomileusis

PURPOSE

To assess the repeatability and agreement of refractive error measurements and the repeatability of axial length (AL) measurements in patients after laser in situ keratomileusis (LASIK).

SETTING

The Ohio State University College of Optometry, Columbus, Ohio, USA.

METHODS

Subjective refraction, autorefraction measurements with the Grand Seiko and Humphrey autorefractors, and AL measurements with the IOLMaster were completed for 40 previously myopic LASIK patients under noncycloplegic and cycloplegic conditions on 2 separate occasions.

RESULTS

The mean difference between visits for axial length measurements was 0.008 mm +/- 0.04 (SD). The between visits repeatability for all refractive error measurements were <0.75 diopter (D). The mean difference between the subjective refraction and the Humphrey autorefractor for spherical equivalent was statistically significant under noncycloplegic conditions (-0.90 D, P<.0001) and cycloplegic conditions (-2.05 D, P<.0001). The mean difference between subjective refraction and Grand Seiko autorefraction measurements was not significant under noncycloplegic conditions (+0.05 D, 95% limits of agreement [LoA]=-0.99, 1.09; P=.52) conditions but was statistically significant, but not clinically relevant, under cycloplegic conditions (+0.17 D, 95% LoA=-0.73, 1.07; P=.03).

CONCLUSIONS

Refractive error measurements after LASIK using the Grand Seiko autorefractor are reliable and agree well with subjective refraction measurements.

Otto lowenstein, pioneer pupillographer

Otto Lowenstein, a pioneer in the study of pupil function, began his professional life as an academic neuropsychiatrist at the University of Bonn with an interest in experimental psychology. From his teacher Alexander Westphal, he developed a fascination with the pupil. He invented ingenious recording devices and took motion pictures of the pupils, graphing their movements. Forced to flee Nazi persecution in 1933, he took temporary refuge in Switzerland and eventually sacrificed a flourishing career in Europe to escape to New York. During the next 25 years, he collaborated with Irene Loewenfeld on experiments and publications related to the clinical use of pupillary signs and introduced pupillography to American neuro-ophthalmology.

Étude de la dilatation pupillaire par l’insert ophtalmique Mydriasert®

PURPOSE

To evaluate the tolerance and efficiency of the Mydriasert(R) ophthalmic insert on pupil dilation.

METHOD

Two pharmaceutical forms of a combination of tropicamide and phenylephrine (HCl) were compared on both eyes of 80 patients. For each patient, one Mydriasert insert (Ioltech) was placed in the lower conjunctival sac of the eye. Dilation of the control eye was obtained using 0.5% tropicamide eye drops and 10% phenylephrine eye drops (Novartis Ophthalmics), which were instilled with three frequency regimens (5, 10 or 15 min). The pupil diameter was regularly measured until the maximal mydriasis had occurred.

RESULTS

Both subjective and objective tolerance of the insert was excellent. The size of the maximal mydriasis obtained when using the insert was significantly greater than that obtained when using the eye drops, regardless of the frequency of the instillation (p < 0.04). The difference in maximal pupil diameter ranged from +0.16 mm to +0.38 mm. Mydriasis kinetics was slower with the insert. The time necessary to obtain a maximal mydriasis was 47.3 min when the insert was used, whereas it was in the range of 31.4 to 38.5 minutes with the eye drops (p < 0.001). As far as pupil diameter is concerned, the superiority of the insert compared to the eye drops became observable only about 45 min after the insert had been placed in the eye. The relative efficacy of the insert compared to the eye drops did not correlate with patient features (p > or = 0.06).

CONCLUSION

Despite the small quantity of drug delivered by the insert, Mydriasert allows a much greater mydriasis compared to that usually obtained when the eye drops were used. However, a longer time lapse is necessary for this to occur.

Rapid quantification of adult and developing mouse spatial vision using a virtual optomotor system

PURPOSE

To develop a simple, rapid method of quantifying the spatial vision of mice.

METHODS

A rotating cylinder covered with a vertical sine wave grating was calculated and drawn in virtual three-dimensional (3-D) space on four computer monitors facing to form a square. C57BL/6 mice standing unrestrained on a platform in the center of the square tracked the grating with reflexive head and neck movements. The spatial frequency of the grating was clamped at the viewing position by repeatedly recentering the cylinder on the head. Acuity was quantified by increasing the spatial frequency of the grating until an optomotor response could not be elicited. Contrast sensitivity was measured at spatial frequencies between 0.03 and 0.35 cyc/deg.

RESULTS

Grating acuity was measurable on the day of eye opening (postnatal day [P]15: mean acuity, 0.031 cyc/deg) and reached a maximum (approximately 0.4 cyc/deg) by P24. A peak in the contrast sensitivity function emerged on P16 (4.7, or 21% contrast at 0.064 cyc/deg). The peak remained at 0.064 cyc/deg and climbed to a maximum sensitivity of 24.5, or 4% contrast, by P29. Acuity was obtained in each mouse in <10 minutes, and a detailed contrast sensitivity curve was generated in approximately 30 minutes.

CONCLUSIONS

The virtual optomotor system provides a simple and precise method for rapidly quantifying mouse vision. Behavioral measures of vision in mice are essential for interpreting the results of experiments designed to reveal the cellular and molecular mechanisms of vision and visual development and for evaluating potential treatments for visual diseases.

Comparison of various pupil dilatation methods for phacoemulsification in eyes with a small pupil secondary to pseudoexfoliation

PURPOSE

To compare 4 methods for intraoperative pupil dilatation in eyes with pseudoexfoliation syndrome and insufficient pupil size during phacoemulsification.

DESIGN

Prospective, randomized, comparative, interventional case series.

PARTICIPANTS

Forty eyes of 40 patients with pseudoexfoliation and maximally dilated pupil size smaller than 3.5 mm.

INTERVENTION

Mechanical pupil dilatation with iris-retractor hooks (group I), polymethyl methacrylate (PMMA) pupil dilator-ring (Morcher, Stuttgart, Germany) (group II), Beehler pupil dilator (group III), and bimanual stretching (group IV).

MAIN OUTCOME MEASURES

Performance (pupil size achieved), complications, and added surgical time.

RESULTS

The mean pupil sizes achieved with the PMMA pupil-dilator ring, Beehler pupil dilator, and bimanual stretching were 5.9+/-0.6 mm, 5.5+/-0.8 mm, and 4.9+/-0.7 mm, respectively. A square-shaped pupil was achieved with iris-retractor hooks, and the mean size of the largest circle that can fit in this square was 5.6+/-0.6 mm. There were no statistically significant differences in the postdilatation pupil sizes between the 4 study groups (P>0.05). Apart from self-limited intraoperative hemorrhage from pupil margin, iris sphincter rupture was the only observed complication related to mechanical pupil dilatation. This occurred in 4 eyes in groups I and III, 3 eyes in group IV, and 1 eye in group II (P>0.05). The mean added surgical time for placement of iris-retractor hooks and for implantation of a PMMA pupil-dilator ring was 297+/-51 and 176+/-54 seconds, respectively. The additional time required for pupil dilatation with the Beehler pupil dilator and bimanual stretching was 65+/-8 and 55+/-10 seconds, respectively. The time needed for pupil dilatation in groups I and II is significantly longer than that in groups III and IV (P<0.001).

CONCLUSIONS

All 4 methods used in this study were effective procedures for the mechanical dilatation of small pupils secondary to pseudoexfoliation syndrome. Iris-retractor hooks and the PMMA pupil-dilator ring are the most time-consuming techniques but have the advantage of a stable pupil size throughout the surgery. The PMMA pupil-dilator ring causes the least iris trauma. The Beehler pupil dilator and bimanual stretching technique were the least time-consuming methods for mechanical pupil dilatation.

The cost-effectiveness of technology transfer using telemedicine

The high burden of disease in developing countries often makes it difficult for health systems in these countries to attain the same level of specialist skills as industrialized countries. Technology transfer is one way to improve specialist skills whilst at the same time reducing the burden of disease. This paper describes the use of teleophthalmology, a form of telemedicine, as a mode of technology transfer between the United Kingdom and South Africa. As the burden of eye disease in South Africa is high, the country cannot afford the level of ophthalmic specialization achieved in the UK. The paper estimates the cost-effectiveness of the technology transfer project in terms of a cost per Disability Adjusted Life Year (DALY) averted. We found the technology transfer project to be cost-effective in reducing the burden of eye disease, and that practitioners in South Africa also learned novel procedures that could help future patients and improve cost-effectiveness. Technology transfer using telemedicine is a cost-effective method that richer countries can employ to aid capacity building in the health care systems of poorer countries.

Plotting visual fields using contralateral fixation: a novel honeycomb device

A device that maintains steady fixation while plotting the visual field of an eye with a large central defect is presented. The device is composed of multiple adjacent pinhole tubes mounted on an eye shield and placed in front of the seeing fellow eye. The device constricts the visual field of the fixating nontested eye to preserve only the central 3 degrees, thus not interfering with the visual field of the tested eye. We tested 3 healthy volunteers with simulated visual field defects and more than 100 patients with unilateral loss of central vision. The use of this device allowed us to plot visual field defects with clear-cut borders while no meaningful results could be obtained without it. We found this device to be efficient, simple to use, and suitable for all varieties of perimetry.

A Comparison of Autorefractor Performance

PURPOSE

To compare the agreement between subjective refraction and autorefraction using two commercially available autorefractors.

METHODS

Prospective data were collected for 190 subjects using either the Nidek ARK-700A (Fremont, CA) or the Topcon KR-8000 (Paramus, NJ) and subjective refraction (masked to autorefraction). Refractions were compared in terms of spherical equivalent using Bland-Altman limits of agreement and astigmatic vector difference using median and 95th percentile.

RESULTS

The two groups were similar for age, gender, spherical equivalent, and astigmatic power. The differences in spherical equivalent between subjective and autorefraction were significantly different (mean +/- SD; Nidek, -0.03 +/- 0.36 D; Topcon, +0.11 +/- 0.34 D; analysis of variance, F = 7.84; p < 0.01). However, the 95% limits of agreement were similar: Nidek, -0.74 to +0.68 D; Topcon, -0.55 to +0.77 D. The median differences in astigmatic vector difference were also similar: Nidek, 0.27 D and Topcon, 0.25 D. However, the 95th percentile was 0.67 D for Nidek and 1.09 D for Topcon. There was a low frequency of large (>1.00 D) differences in spherical equivalent, 1.1% with each autorefractor. There were five cases with astigmatic vector difference >1 D, all with the Topcon KR-8000 (5.3%).

CONCLUSIONS

Both autorefractors show excellent agreement with subjective refraction. Despite a statistically significant difference in mean spherical equivalent (0.14 D), near identical limits of agreement (0.10 D difference) suggest clinical equivalence. Conversely, for astigmatism, despite similar median scores, major outliers were more likely with the Topcon, reflected in a 0.42 D larger 95th percentile, which suggests a small advantage for the Nidek for avoiding large astigmatic errors.

Caring for academic ophthalmology in Croatia

Like any other area of academic medicine in Croatia, academic ophthalmology has always been limited by or has depended on the factors outside the profession itself: during the communist regime, it was mostly political and ideological correctness of academic ophthalmologists, and today during the social and economic transition, it is the lack of finances, planning, and sophisticated technology. The four university eye clinics, which are the pillars of academic ophthalmology in Croatia, provide health care to most difficult cases, educate students, residents, and specialists, and do research. On the other hand, they lack equipment, room, and financial recognition. This ever growing imbalance between requirements imposed on academic ophthalmology today and its possibilities make it less and less attractive, especially in comparison with private practice. The possible solution lies in increasing the independence of ophthalmology from pharmaceutical industry and politics, especially in research and financial aspects.

[Research-and-production enterprise "Neuron": equipment for ophthalmology]

The paper is dedicated to a small enterprise functioning in the field of medical engineering, i.e. the "Neuron" research-and-production Co. (Ufa), which has been designing and assembling the therapeutic outfit for ophthalmology.

LADARWave Wavefront Measurement in Normal Eyes

PURPOSE

We evaluated the correlation of Alcon LADARWave wavefront measurements with clinical refraction and corneal topography.

METHODS

In a retrospective, non-comparative case series, 60 eyes (30 patients) of healthy individuals evaluated by preoperative examination for refractive surgery were enrolled (manifest sphere, -11.00 to +4.50 D; manifest cylinder, 0 to -4.75 D; 45 eyes were myopic, 12 eyes were hyperopic, and 3 had mixed astigmatism). Correlation of manifest refraction, cycloplegic refraction, and topographic data with wavefront refraction and higher order aberration was assessed. Match percentage given by the wavefront was analyzed. This number represents how much of the wavefront refraction is due to sphere and cylinder (high percentage match) or is influenced by higher order aberration (low percentage match), in which case aberrometer refraction will not be close to phoropter refraction. Pearson's correlation coefficient was assessed for two continuous variables, adjusting for repeated measurements.

RESULTS

The median match percentage was 91%. Mean values for all higher order aberration components in a 7.0-mm pupil were: coma = 0.35 +/- 0.29 microm, spherical aberrations = 0.36 +/- 0.31 microm, and other terms of higher order aberrations = 0.31 +/- 0.14 microm. Wavefront sphere, cylinder, and axis terms were highly correlated to manifest and cycloplegic measurements. The high match subgroup had a higher correlation coefficient than the low match subgroup for refraction. Topographic cylinder and axis were not strongly correlated to wavefront refraction, but manifest axis was significantly correlated to topographic axis.

CONCLUSION

In 60 normal eyes, the Alcon LADARWave wavefront measurement was highly correlated with refraction, but less well with corneal topography.

[A review of the medical equipment displayed at the "Health care-2003" exhibition]

Medical equipment displayed at the "Healthcare-2003" exhibition, that was most representative in the recent years, is surveyed in the paper including the most novel medical devices and apparatuses as well as X-Ray, radiological, intensive-care and neonatal equipment. Besides, outfit for diagnostics, ophthalmology and dentistry, laboratory medical equipment, medical instruments, technological medical equipment and portable medical devices were demonstrated at the exhibition. Therefore, considering the diversity of medical equipment displayed, any medical facility in Russia would be able to choose the devices it needs.

Sealed-capsule irrigation device

We present a sealed-capsule irrigation technique and a disposable instrument that facilitate selective targeting of lens epithelial cells after phacoemulsification.