Influence of different types of astigmatism on visual acuity / Influencia de los diferentes tipos de astigmatismo en la agudeza visual

Purpose: To investigate the change in visual acuity (VA) produced by different types of astigmatism (on the basis of the refractive power and position of the principal meridians) on normal accommodating eyes. Methods: The lens induced method was employed to simulate a set of 28 astigmatic blur conditions on different healthy emmetropic eyes. Additionally, 24 values of spherical defocus were also simulated on the same eyes for comparison. VA was measured in each case and the results, expressed in logMAR units, were represented against of the modulus of the dioptric power vector (blur strength). Results: LogMAR VA varies in a linear fashion with increasing astigmatic blur, being the slope of the line dependent on the accommodative demand in each type of astigmatism. However, in each case, we found no statistically significant differences between the three axes investigated (0◦, 45◦, 90◦). Non-statistically significant differences were found either for the VA achieved with spherical myopic defocus (MD) and mixed astigmatism (MA). VA with simple hyperopic astigmatism (SHA) was higher than with simple myopic astigmatism (SMA), however, in this case non conclusive results were obtained in terms of statistical significance. The VA achieved with imposed compound hyperopic astigmatism (CHA) was highly influenced by the eye’s accommodative response. Conclusions: VA is correlated with the blur strength in a different way for each type of astigmatism, depending on the accommodative demand. VA is better when one of the focal lines lie on the retina irrespective of the axis orientation; accommodation favors this situation (AU)

Objetivo: Investigar el cambio en la agudeza visual (AV) producido por los diferentes tipos de astigmatismo (sobre la base del poder refractivo y la posición de los principales meridianos) en ojos con acomodación normal. Métodos: Se utilizó el método de desenfoque inducido con lentes para simular un conjunto de veintiocho situaciones de desenfoque astigmático en diferentes ojos emetrópicos sanos. Además, se simularon veinticuatro valores de defecto esférico en los mismos ojos, a fines comparativos. Se midió la AV en cada caso, representándose los resultados, expresados en unidades logMAR, frente a los módulos del vector de potencia dióptrica (desenfoque). Resultados: La escala LogMAR para AV varía de manera lineal, incrementando la distorsión astigmática, dependiendo la inclinación de la línea de la demanda acomodativa en cada tipo de astigmatismo. Sin embargo, en cada caso, no hallamos diferencias significativas entre los tres ejes analizados (0◦, 45◦, 90◦). No se hallaron diferencias estadísticamente significativas en cuanto a la AV lograda con el defecto miópico esférico (MD) y astigmatismo mixto (MA). La AV con astigmatismo hipermetrópico simple (SHA) fue más elevada que con astigmatismo miópico simple (SMA). Sin embargo, en este caso se obtuvieron resultados no concluyentes en términos de significancia estadística. La AV lograda con astigmatismo hipermetrópico compuesto (CHA) se vio altamente influenciada por la respuesta acomodativa del ojo. Conclusiones: La AV guarda relación con el desenfoque de modo diferente para cada tipo de astigmatismo, dependiendo de la demanda de acomodación. La AV es mejor cuando una de las líneas focales está en la retina con independencia de la orientación del eje; la acomodación favorece esta situación (AU)

Visual fatigue while watching 3D stimuli from different positions / Fatiga visual al observar estímulos en 3D desde diferentes posiciones

Purpose: When observers focus their stereoscopic visual system for a long time (e.g., watching a 3D movie) they may experience visual discomfort or asthenopia. We tested two types of models for predicting visual fatigue in a task in which subjects were instructed to discriminate between 3D characters. One model was based on viewing distance (focal distance, vergence distance) and another in visual direction (oculomotor imbalance). Method: A 3D test was designed to assess binocular visual fatigue while looking at 3D stimuli located in different visual directions and viewed from two distances from the screen. The observers were tested under three conditions: (a) normal vision; (b) wearing a lens (−2 diop.); (c) wearing a base-out prism (2▽) over each eye. Sensitivity and specificity were calculated (as Signal Detection Theory parameters: SDT). Results: An ANOVA and SDT analyses revealed that impaired visual performance were directly related to short distance and larger deviation in visual direction, particularly when the stimuli were located nearer and at more than 24◦ to the centre of the screen in dextroversion and beyond. Conclusion: This results support a mixed model, combining a model based on the visual angle (related to viewing distance) and another based on the oculomotor imbalance (related to visual direction). This mixed model could help to predict the distribution of seats in the cinema room ranging from those that produce greater visual comfort to those that produce more visual discomfort. Also could be a first step to pre-diagnosis of binocular vision disorders (AU)

Objetivo: Cuando los observadores centran su sistema visual estereoscópico durante un tiempo prolongado (ej.: viendo una película en 3D), pueden experimentar molestias visuales o astenopia. Probamos dos tipos de modelos de predicción de la fatiga visual en un estudio, en el que se solicitaba a los sujetos que discriminaran entre caracteres en 3D. Un modelo se basaba en la visión lejana (distancia focal, distancia de vergencia), y el otro en la dirección visual (desequilibrio oculomotor). Método: Se diseñó una prueba en 3D para valorar la fatiga visual binocular mientras se observaban estímulos en 3D situados en diferentes direcciones visuales, y se veían a dos distancias de la pantalla. Se realizó la prueba a los observadores bajo tres situaciones: a) visión normal, b) utilizando una lente (-2 dioptrías); c) utilizando un prisma base externa (2▽) en cada ojo. Se calcularon la sensibilidad y especificidad (como parámetros de la Teoría de la Detección de Señales: TDS). Resultados: Los análisis ANOVA y TDS revelaron que el deterioro del desempeño visual guardaba una relación directa con la distancia corta y una mayor desviación de la dirección visual, en especial cuando los estímulos se situaban más cerca, y a más de 24◦ del centro de la pantalla en dextroversión y valores superiores. Conclusión: Estos resultados respaldan un modelo mixto, que combina un modelo basado en el ángulo visual (relacionado con la visión lejana) y otro basado en el desequilibrio oculomotor (relacionado con la dirección visual). Este modelo mixto podría ayudar a predecir la distribución de las butacas en las salas de cine, que oscila entre aquellas que producen un mayor confort visual y aquellas que producen más molestias visuales. También podría constituir un primer paso para el diagnóstico previo de los trastornos de la visión binocular (AU)

Effects of a myosin light chain kinase inhibitor on the optics and accommodation of the avian crystalline lens.

PURPOSE: While many studies investigate the cytoskeletal properties of the lens with respect to cataract development, examinations of how these molecular structures interact are few. Myosin light chain kinase (MLCK), actin, and myosin are present on the crystalline lenses of chickens. The purpose of this experiment was to determine whether contractile proteins found on the lens play a role in the optical functions of the lens at rest, and during accommodation. METHODS: Eyes of 6-day old white Leghorn chicks (Gallus gallus domesticus) were enucleated, with the ciliary nerve intact. One eye was treated with the MLCK inhibitor 1-(5-iodonaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine hydrochloride (ML-7) and the other eye with vehicle only. Three concentrations of ML-7 were used: 1 µM, 10 µM, and 100 µM. The back vertex focal lengths (BVFLs) were measured before, during, and after accommodation using an optical laser scanning monitor (Scantox™). To further confirm ML-7 activity, western blotting was performed to detect whether MLCK was inhibited. RESULTS: Western blots confirmed that MLCK was inhibited at all three ML-7 concentrations. Ten µM ML-7 treatments led to longer BVFLs at rest (p=0.0338), while 100 µM treatments led to opposite changes, resulting in shorter BVFLs (p=0.0220). While 1 µM treatments did not lead to significant optical changes (p=0.4416), BVFLs were similar in pattern to those of the 10 µM group. ML-7 had no effects on accommodative amplitudes (p=0.7848). CONCLUSIONS: Inhibition of MLCK by ML-7 led to differential changes in BVFLs that presumably affected lenticular integrity. No apparent effect on accommodative amplitudes was observed.

"Tonic" but not "Adie" pupils.

Tonic pupils react poorly to light but constrict during viewing of a near stimulus. Adie's name is typically used in association with tonic pupils, but a review of Adie's articles reveals that he described the syndrome of tonic pupils and absent reflexes and not the pupillary abnormality per se. Therefore, it would be more appropriate to refer to a tonic pupil as simply a "tonic pupil" and leave Adie's name for the syndrome.

Mitochondrial "movement" and lens optics following oxidative stress from UV-B irradiation: cultured bovine lenses and human retinal pigment epithelial cells (ARPE-19) as examples.

Mitochondria provide energy generated by oxidative phosphorylation and at the same time play a central role in apoptosis and aging. As a byproduct of respiration, the electron transport chain is known to be the major intracellular site for the generation of reactive oxygen species (ROS). Exposure to solar and occupational ultraviolet (UV) radiation, and thus production of ROS and subsequent cell death, has been implicated in a large spectrum of skin and ocular pathologies, including cataract. Retinal pigment epithelial cell apoptosis generates photoreceptor dysfunction and ultimately visual impairment. The purpose of this article was to characterize in vitro changes following oxidative stress with UV-B radiation in (a) ocular lens optics and cellular function in terms of mitochondrial dynamics of bovine lens epithelium and superficial cortical fiber cells and (b) human retinal pigment epithelial (ARPE-19) cells. Cultured bovine lenses and confluent cultures of ARPE-19 cells were irradiated with broadband UV-B radiation at energy levels of 0.5 and 1.0 J/cm(2). Lens optical function (spherical aberration) was monitored daily up to 14 days using an automated laser scanning system that was developed at the University of Waterloo. This system consists of a single collimated scanning helium-neon laser source that projects a thin (0.05 mm) laser beam onto a plain mirror mounted at 45 degrees on a carriage assembly. This mirror reflects the laser beam directly up through the scanner table surface and through the lens under examination. A digital camera captures the actual position and slope of the laser beam at each step. When all steps have been made, the captured data for each step position is used to calculate the back vertex distance for each position and the difference in that measurement between beams. To investigate mitochondrial movement, the mitochondria-specific fluorescent dye Rhodamine 123 was used. Time series were acquired with a Zeiss 510 (configuration Meta 18) confocal laser scanning microscope equipped with an inverted Axiovert 200 M microscope and 40-x water-immersion C-Apochromat objective (NA 1.2). The optical analysis showed energy level-dependent increases in back vertex distance variability (loss of sharp focus) from 0.39 +/- 0.04 mm (control, n = 11) to 1.63 +/- 0.33 mm (1.0 J/cm(2), n = 10) and 0.63 +/- 0.13 mm (0.5 J/cm(2), n = 9). Confocal laser scanning microscopy analysis of both bovine lenses and ARPE-19 cells showed that following treatment at 0.5 J/cm(2) the mitochondria stopped moving immediately whereas at 1.0 J/cm(2) not only did the mitochondria stop moving, but fragmentation and swelling was seen. Untreated control tissue exhibited up to 15 microm/min of movement of the mitochondria. This could represent normal morphological change, presumably allowing energy transmission across the cell from regions of low to regions of high ATP demand. Lack of mitochondrial movement, fragmentation, and swelling of mitochondria may represent early morphological changes following oxidative stress that may lead to activation of caspase-mediated apoptotic pathways.

Treatment of presbyopia with conductive keratoplasty: six-month results of the 1-year United States FDA clinical trial.

PURPOSE: To provide 6-month results of a 1-year clinical trial evaluating conductive keratoplasty (CK) for the treatment of presbyopic symptoms in emmetropic and hyperopic eyes. METHODS: A total of 143 patients with presbyopic symptoms were enrolled in this 1-year United States FDA clinical trial and treated to improve near vision in 1 eye (unilateral treatment). In addition, 33 fellow eyes were treated to improve distance vision (bilateral treatment). For near vision correction, the target refraction was up to -2.0 D in the nondominant eye, and for distance vision correction, 0.0 D. Enrolled patients had a preoperative spherical equivalent of plano to +2.00 D, no more than 0.75 D of refractive astigmatism, and were 40 years of age or older. No retreatments were performed. RESULTS: Of the eyes treated for near, 77% had uncorrected near vision of J3 or better at 6 months postoperatively. A total of 85% of all patients had binocular distance UCVA of 20/25 or better along with J3 or better near, a combination that represents functional acuity for a presbyope. Sixty-six percent of eyes treated for near had a manifest refractive spherical equivalent (MRSE) within +/- 0.50 D of intended at 6 months. In 89% of eyes, the MRSE changed 0.05 D or less between 3 and 6 months postoperatively. After month 1, the incidence of variables associated with safety was 1% or lower. Seventy-six percent were very satisfied or satisfied with their procedure. CONCLUSIONS: CK appears to be very safe and effective in producing functional visual acuity in presbyopic eyes up to 6 months following the procedure. Patient satisfaction with the procedure is similar to that of monovision LASIK.

[Experimental study of magnetic field influence on transitory instability of display image]. / Eksperimental'noe issledovanie vliianiia vneshnego magnitnogo polia na vremennuiu nestabil'nost' izobrazheniia displeia.

The article presents results of experimental study that determined threshold level of external magnetic field causing no flashing effect and spectral distribution of image instability, if general and local influence of magnetic field on display.

Accommodative function of eyes in persons exposed to ionizing radiation.

Results of a comparative study of accommodative capability of eyes in individuals exposed to various doses of ionizing radiation and in a control group are presented. The mean values for ranges of accommodation in the control group were consonant with previous data. However, the range of accommodation was found to be reduced in exposed patients from younger age groups. It has been established that the ranges of accommodation depended, besides the age, on the absorbed dose of ionizing radiation: the greater the dose absorbed, the lesser the range of accommodation in the same age group. The effect of ionizing radiation seems to be additive to that of age.

[Laser puncture in the combined treatment of a weak degree of myopia in schoolchildren]. / Lazeropunktura v kompleksnom lechenii miopii slaboi stepeni u detei shkol'nogo vozrasta.

To increase effectiveness of treatment, the influence of laser puncture on some functional indices of myopic eyes has been studied. Comparative analysis of results after laser puncture used as an independent method in 45 children (85 eyes)--group I, and in a complex accommodation-convergence system, of the eye in 66 children (130 eyes)--group II, has shown that laser puncture has a positive influence on visual acuity and accommodation-convergence system. As compared with group I, in group II normalization of functional indices (reserves of accommodation, convergence and divergence) begins earlier and stability of the results obtained is higher.

Complications of argon laser retinal buckling performed in myopic subjects presenting rhegmatogenous degenerations.

Twenty-two eyes of twenty-two patients suffering from retinal peripheral degenerations underwent preventive equatorial buckling with argon laser photocoagulation. The fellow eye was used as control. We evaluated the effects of laser photocoagulation on corneal sensitivity, on accommodation, on pupillary diameter and light reflex. In the postoperative period, up to the 3rd month, results were significant with respect to the control eye. The mechanisms to which the onset of these undesired alterations is due are discussed.

Effects on choroidal nerves after panretinal xenon arc and argon laser photocoagulation.

The effect on range of accommodation, size of pupil and corneal sensitivity of panretinal photocoagulations was investigated in 30 diabetic patients. Treatments with the xenon arc or the argon laser produced significant changes in the 3 parameters one month after photocoagulation, but only when retrobulbar anaesthesia was used. After 6 months the range of accommodation and the size of the pupil were almost normalized. The corneal sensitivity remained significantly reduced.

Internal ophthalmoplegia after argon laser panretinal photocoagulation.

Internal ophthalmoplegia was found in eight eyes of four patients with juvenile-onset diabetes. All eight eyes had received argon laser panretinal photocoagulation (PRP) for proliferative diabetic retinopathy. Internal ophthalmoplegia was not found in any of the 14 eyes of seven patients with juvenile diabetes who had not had photocoagulation treatment. This group included one patient in whom internal ophthalmoplegia was present after treatment. Laser injury to the short ciliary nerves, as they course anteriorly on the inner surface of the sclera, is the probable cause of internal ophthalmoplegia in these patients. To my knowledge, this complication has not been reported previously, but it appears to be a common side effect of PRP.