Lens Orientation Research Articles

An analysis of the factors influencing the residual refractive astigmatism after cataract surgery with toric intraocular lenses.

To investigate the influence of posterior corneal astigmatism, surgically-induced corneal astigmatism (SICA), intraocular lens (IOL) orientation, and effective lens position on the refractive outcome of toric IOLs. Five models were prospectively investigated. Keratometric astigmatism and an intended SICA of 0.2 diopters (D) were entered into model 1. Total corneal astigmatism, measured by a rotating Scheimpflug camera, was used instead of keratometric astigmatism in model 2. The mean postoperative SICA, the actual postoperative IOL orientation, and the influence of the effective lens position were added, respectively, into models 3, 4, and 5. Astigmatic data were vectorially described by meridional and torsional powers. A set of equations was developed to describe the error in refractive astigmatism (ERA) as the difference between the postoperative refractive astigmatism and the target refractive astigmatism. We enrolled 40 consecutive eyes. In model 1, ERA calculations revealed significant cylinder overcorrection in with-the-rule (WTR) eyes (meridional power = -0.59 ± 0.34 D, P < 0.0001) and undercorrection in against-the-rule (ATR) eyes (0.32 ± 0.42 D, P = 0.01). When total corneal astigmatism was used instead of keratometric astigmatism (model 2), the ERA meridional power decreased in WTR (-0.13 ± 0.42 D) and ATR (0.07 ± 0.59 D) eyes, both values being not statistically significant. Models 3 to 5 did not lead to significant improvement. Posterior corneal astigmatism exerts the highest influence on the ERA after toric IOL implantation. Basing calculations on total corneal astigmatism rather than keratometric astigmatism improves the prediction of the residual refractive astigmatism.

Astigmatism and soft torics–the challenge or is it?”

Astigmatism and soft torics–the challenge or is it?”

Contact lenses–what to expect in your pre- reg year

Contact lenses–what to expect in your pre- reg year

Normal and diseased personal eye modeling using age-appropriate lens parameters

Personalized eye modeling of normal and diseased eye conditions is attractive due to the recent availability of detailed ocular measurements in clinic environments and the promise of its medical and industrial applications. In the customized modeling, the optical properties of the crystalline lens including the gradient refractive index, the lens bio-geometry and orientation are typically assigned with average lens parameters from literature since typically they are not clinically available. Although, through the optical optimization by assigning lens parameters as variables, the clinical measured wavefront aberration can be achieved, the optimized lens biometry and orientation often end up at edges of the statistical distribution. Without an effective validation of these models today, the fidelity of the final lens (and therefore the model) remains questionable. To develop a more reliable customized model without detailed lens information, we incorporate age-appropriate lens parameters as the initial condition of optical optimization. A biconic lens optimization was first performed to provide a correct lens profile for accurate lower order aberration and then followed by the wavefront optimization. Clinical subjects were selected from all ages with both normal and diseased corneal and refractive conditions. 19 ammetropic eyes ( + 4D to −11D), and 16 keratoconus eyes (mild to moderate with cylinder 0.25 to 6D) were modeled. Age- and gender-corrected refractive index was evaluated. Final models attained the lens shapes comparable to the statistical distribution in their age.

Impact of intraocular lens haptic design and orientation on decentration and tilt

To assess the effect of intraocular lens (IOL) orientation (vertical versus horizontal) and haptic design (1-piece versus 3-piece) on centration and tilt using a Purkinje meter. Moorfields Eye Hospital NHS Foundation Trust, London, United Kingdom. Randomized pilot study with intrapatient comparison. In part 1 of this study, patients received plate-haptic IOLs (Akreos Adapt) in both eyes that were positioned vertically in 1 eye and horizontally in the other eye. In part 2, patients received a 1-piece IOL (Acrysof SA60AT) in 1 eye and a 3-piece IOL (Acrysof MA60AC) in the contralateral eye. Decentration and tilt were measured 1 month and 3 months postoperatively with a new Purkinje meter. In part 1 (n = 15), the mean decentration of plate-haptic IOLs was 0.4 mm ± 0.2 (SD) with vertical orientation and 0.4 ± 0.2 mm with horizontal orientation and the mean tilt, 1.5 ± 1.1 degrees and 2.9 ± 0.9 degrees, respectively. In part 2 (n = 15), the mean decentration was 0.4 ± 0.3 mm with 1-piece IOLs and 0.6 ± 0.8 mm with 3-piece IOLs and the mean tilt, 2.2 ± 7.2 degrees and 5.3 ± 2.4 degrees, respectively. Three-piece IOLs had a greater tendency toward more decentration than 1-piece IOLs, perhaps because of slight deformation of 1 or both haptics during implantation or inaccuracies in production when the haptics are manually placed into the optic. The IOL orientation for plate-haptic IOLs appeared to have no effect on IOL position. The Purkinje meter was useful in assessing the capsule bag performance of the IOLs. No author has a financial or proprietary interest in any material or method mentioned. Additional disclosures are found in the footnotes.

Impact of assay selection and study design on the outcome of cytotoxicity testing of medical devices: The case of multi-purpose vision care solutions

Medical device biocompatibility testing usually includes a cytotoxicity component. Assay selection and protocol design often depend on a specific testing standard rather than on the characteristics of the medical device. To better understand the impact of assay selection on study outcome of unstructured medical devices, we evaluated contact lens multi-purpose solutions (MPS) in the agar diffusion, direct contact and two elution cytotoxicity assays. To simulate the conditions of use, MPS were evaluated alone and in combination with contact lenses. All MPS passed the agar diffusion assay (n=3) and extracts prepared from contact lenses soaked in MPS passed the USP elution assay (n=3). Both the duration of contact and MPS concentration impacted the outcome of a modified elution assay. When tested at 25% strength for 48h, all MPS evaluated were non-cytotoxic (n>3). Test article movement and mechanical damage were significant issues with the direct contact assay. Movement was effectively controlled by manipulating contact lens orientation while using 0.8mL culture medium. All MPS passed the USP direct contact cytotoxicity test when evaluated using this optimized methodology (n=3). These data are consistent with MPS results in ocular irritation studies in rabbits (n=3).

Clinical Evaluation of Factors Affecting Soft Toric Lens Orientation

To evaluate the comparative orientation characteristics of currently available silicone hydrogel torics. The re-orientation characteristics of four toric lenses were assessed: three prism-ballasted (PB) designs, Purevision Toric (PVT), Air Optix Toric (AOT), Proclear Toric (PCT), and an "Accelerated Stabilization Design" (ASD) ACUVUE ADVANCE for Astigmatism (AAfA). In the first part of the study, the toric lenses were rotated, approximately 45 degrees in the infero-temporal direction and a video recording of lens reorientation was made from which blink-by-blink measurements of lens orientation were taken. In the second part of the study, subjects were positioned with their head orientated 90 degrees to the vertical and lens orientation photographed once it had settled. In Part 1, the speed of re-orientation from oblique mis location was similar for the four designs tested and ranged from 22°/min (PVT) to25°/min (AOT). Lenses showed more rotation during rather than between the blink (p<0.0001). Between blinks, AAfA and AOT showed significantly more rotation than PCT and PVT (p0.04). There were no significant differences between lenses for rotation during the blink. The PB lenses showed faster re-orientation further away from the zero position.AAfA showed no significant difference in rotation speed with varying orientation position. In Part 2, all the PB lenses rotated significantly more under the effect of gravity than the ASD lenses.The mean total rotation of the AAfA lenses,from their settled position, was 11.4° compared with 25.9° for PVT (p0.01), 18.4° with AOT (p0.02) and 37.4° with PCT (p0.0002) [corrected]. The mean total rotation of the AAfA lenses, from their settled position, was 11.2 degrees compared with 32.8 degrees for PVT (p < 0.001), 16.1 degrees with AOT and 33.1 degrees with PCT (p < 0.001). The four lens designs show similar re-orientation speeds. In the recumbent position, PB lenses rotate more from their normal settled position than ASD lenses.

Toric lens orientation and visual acuity in non-standard conditions

To evaluate and compare the effect of gravity and gaze direction on toric lens orientation and visual acuity (VA). This was a 14 subject, randomised, unmasked, non-dispensing study, relating to the effect of gaze direction and posture on toric lens orientation and VA. Four lens types were assessed: Acuvue Oasys for Astigmatism (AOfA), Purevision Toric (PVT), Air Optix for Astigmatism (AOT) and Proclear Toric (PCT). In the first part of the study, subjects were positioned on their side and once lenses had settled, VA was measured and photographs taken of the lens orientation position. In the second part, the subjects were positioned at a slit-lamp and video-recordings taken as they changed from the primary gaze position to the eight cardinal directions of gaze. In Part 1, all lenses rotated as a result of change in posture and head position. With subjects in a recumbent position mean rotation ranged from 11.0 degrees with AOfA to 29.1 degrees with PCT. The consequent mean reduction in VA ranged from 0.05logMAR for AOfA to 0.15logMAR for PVT and was significantly worse with PVT and PCT compared with AOfA (P<0.05). In Part 2, lenses tended to show inferior-nasal rotation on upgaze and inferior-nasal rotation on downgaze. The AOfA lenses showed less rotation on inferior-nasal version than each of the other designs (P<0.005). The AOT lenses showed significantly less rotation on superior-temporal version than PVT (P=0.01). Toric soft contact lens stability in extreme versions and postural positions can affect orientation and VA.

Performance Modeling of a Thrust Vectoring Device for Hall Effect Thrusters

The ability to control the thrust vector direction on electric propulsion devices opens new possibilities for mission optimization. The addition of an external magnetic steering system and the nonsymmetric localized injection of propellant have been proposed to deviate the ion beam of a PPS®1350 Hall effect thruster. A two-dimensional hybrid model has been used to evaluate the preliminary design. Simulated results suggest the ion beam angular distributions may be varied in the range of 10 deg by changing the current in the external steering coils. However, a magnetic topography with field lines directly connected from the outer steering pole to the anode leads to a reduction of the Hall effect thruster performance. The erosion of the walls increases drastically as a function of the magnetic lens orientation (6 mm for 1000 h of thruster operation for high coil currents in the external coils). A localized axial injection of atoms has a positive effect on the steering angle of the ion beam (a few degrees), but exhibits additional erosion of approximately 10―15%. Qualitative comparisons with experimental results confirm the simulated trends.

An economical wireless cavity-nest viewer

Inspection of cavity nests and nest boxes is often required during studies of cavity-nesting birds, and fiberscopes and pole-mounted video cameras are sometimes used for such inspection. However, the cost of these systems may be prohibitive for some potential users. We describe a user-built, wireless cavity viewer that can be used to access cavities as high as 15 m and with entrance diameters as small as 2.5 cm. System components include a wireless camera, boom with near-infrared lighting system, hand-held television, and telescoping pole. The unit can be assembled in about one day with commonly available tools, and the total cost was about $850 (US). Our cavity-viewing system was used to monitor the nests of Western Bluebirds (Sialia mexicana) and proved to be reliable and effective. During two field seasons, we attempted to check the status of nests 928 times and were able to determine the nesting stage 901 times (97%). For those willing to assemble their own units, our cavity viewer permits safe, direct examination of cavity nests or open nests for investigators with limited budgets. SINOPSIS. Aparato inhalambrico de bajo costo para observar nidos en cavidades Para examinar nidos en cavidades y cajas de anidamiento, muchas veces es necesario usar instrumentos de fibra ´ optica y cde videos montadas en postes. Sin embargo, el costo de estos sistemas pudiera ser muy elevado para algunos investigadores potenciales. Describimos un aparato inhalque puede ser utilizado para examinar cavidades de hasta 15 m de altura y de 2.5 cm de dien su entrada. Entre los componentes del sistema encontramos una cinhalun sistema de iluminaci´ on infrarojo, un monitor de televisi´ on manual y un poste telescEl sistema puede ser montado en un dia (si hay las herramientas necesarias) y su costo es de $850 dolares. Nuestro sistema fue utilizado para monitorear nidos de Sialia mexicana yp rov´ o ser confiable y efectivo. Durante dos temporadas de campo intentamos determinar el estatus de nidos en 928 ocasiones y pudimos determiner la etapa en que se encontraban en 901 (97%) de estas. Para aquellos que est´ en en la disposicide ensamblar sus propias unidades de monitoreo, nuestro equipo es adecuado y se presta para estudios con presupuesto limitado y le permite al investigador hacer observaciones directas con seguridad.

X-ray refractive planar lenses in combination with planar X-ray waveguide

The optical system composed of an X-ray silicon planar refractive lens and an X-ray planar waveguide with air gap has been characterized with synchrotron radiation. The guiding structure consisted of two silicon plates, clamped by permanent magnets and divided by a spacer made of thin magnetic film. The system was studied in the energy range 8 - 17 keV on the Optics beamline BM05 at the ESRF (Grenoble). It was shown, that the number of resonant modes in the beam exiting from the waveguide could be controlled by planar lens orientation, so that minimal number of modes could be obtained. Refractive optics elements and X-ray planar waveguides are a good combination for synchrotron sources of last generation and free electron lasers.

Shear fracture pattern and microstructural evolution in transpressional fault zones from field and laboratory studies

Zones of transpressional shear deformation accommodate strike-slip and oblique-slip displacements. Field work in a transpressive shear zone, and transpressional analogue clay-box modelling, show that a P-oriented foliation and associated P-shears are preferentially developed over the more common R 1 Riedel-shears. The Carboneras fault system (CFS) in SE Spain is a left-lateral transpressional shear zone with an internal geometry characterized by first-order Y-oriented faults and widespread P-oriented second-order faults. The mesoscopic to microscopic gouge fabric reflects the regional architecture of the shear zone being dominated by a pervasive Poriented foliation and discrete Y- and P-shears. Friction experiments carried out to investigate the textural evolution of gouge fabrics showed four textural stages of fabric development, from foliation formation to extreme shear localization resulting in cross-gouge failure. Transpression clay-box models favoured the formation of secondary P-oriented shear fractures and P-oriented shear lenses. Further deformation caused differential shear lens rotation and shear lens orientations closer to the mean displacement direction. Our field studies and laboratory analogue experiments indicate that shear zones dominated by P-shears are diagnostic of a transpressional deformation regime.

Ice lens formation at a silt–sand interface

A major experiment simulating ground freezing around a buried chilled pipeline in a controlled-environment facility provided an opportunity to examine the form and orientation of ice lenses associated with a vertical interface between silt and sand. The heave of the silt decreased towards the interface and ice lenses in the silt were found to dip at an increasing angle in the same direction. Consideration of the thermal regime suggests that the direction of heat flow influences the orientation of the lenses. The interface was irregular and ice lenses at the lower part of the interface were closely aligned to it, indicating that changes in soil texture also influence ice lens orientation. Deformation of ice lenses appears to have occurred in the silt near to the interface. The arrangement of the lenses can be explained by the different thermal properties and thermodynamic behaviour of the two materials and by the mechanical "anchorage" of the sand in which there is no ice lens formation. Cycles of freezing and thawing modify soil structure and produce cumulative residual deformations which are modified by a soil interface. Key words : frost heave, ice lenses, frozen soil, vertical silt–sand interface, chilled pipeline, differential heave.

Clinical performance of a daily disposable contact lens: a 3-month prospective study

Thirty-one myopic patients, 20 of whom were experienced contact lens wearers, were fitted with 1-Day Acuvue lenses, −253(±0.18) dioptres (D) on average, at initial dispensing. These lenses are inserted in the morning and disposed of every night. After an initial examination, the patients were followed up after 1 week and 12 weeks of lens wear. Visual acuity was 1.25(±0.02) on average, at the 12-week follow-up, significantly ( P <0.005) better with the 1-Day Acuvue lenses than with the patients' previous lenses. Subjectively reported symptoms decreased significantly ( P <0.02) after the patients' previous lenses were replaced with the 1-Day Acuvue lenses (20 patients); dryness/burning decreased from 35% to 5% ( P <0.001). Slit-lamp findings also decreased significantly ( P<0.001), injection from 23% to 0% and tarsal abnormalities from 20% to 0% (20 patients). There were no true complications. All 20 experienced lens wearers had deposit problems before the study, but these disappeared with the 1-Day lenses. When the experienced wearers compared their former lenses with their new 1 -Day Acuvue lenses, the latter were judged significantly ( P <0.01–0.001) better regarding comfort and vision, equal regarding determination of lens orientation and worse ( P <0.01) regarding lens handling. Overall satisfaction — a general assessment — favoured the 1-Day lenses at a highly significant ( P <0.001) level, however. Thus, the 1-Day Acuvue concept appears very attractive with regard to complication rate as well as performance.

The spherical aberration of aphakic eyes corrected with intra‐ocular lenses

The spherical aberration of eyes corrected with intra-ocular lenses is investigated using a model eye with realistic levels of corneal asphericity. The results indicate that the aberration is intermediate between that of paraxial schematic eyes and real eyes. By using standard optical aberration theory, it is shown that for a plano-convex lens with the curved surface facing the cornea, the aberration is similar to that of normal phakic eyes and therefore probably too low to be of any clinical significance. However, for other lens orientations or designs, the level of aberration is usually higher and may lead to a refractive error varying with pupil size and a loss of acuity with large pupil diameters.

Directional acoustic microscopy for observation of elastic anisotropy

A directional acoustic microscope is described that has enhanced contrast for elastically anisotropic materials. Directional detection of surface acoustic waves by the acoustic lens is demonstrated on (100) and (111) silicon crystals. The grains of a polycrystalline silicon sample have contrast which varies as a function of lens orientation. Symmetry of contrast variations and measurement of surface wave phase velocity may provide a new way to determine the orientation of microscopic grains.

A comparison of three methods of measurement of toric soft lens orientation.

A group of five subjects were fitted with truncated toric soft lenses varying in minus cylinder power from 1 to 4 D in 1 D steps at axes of 90 and 180. After 15 min of lens wear, the location of the lens was measured by three techniques: the projected slitlamp photographic technique, measurement with a protractor graticule in the slitlamp eyepiece, and alignment of the slitlamp beam with markings on the lens. Analysis of the data by a four-level analysis of variance and a t-test showed no significant difference between the three methods of measuring the toric soft lens orientation.

LENS DEVELOPMENT: FIBER ELONGATION AND LENS ORIENTATION.

When the lens of the 5-day chick embryo is surgically reversed so that its epithelium faces the neural retina the elongation of those lens cells which have already differentiated is arrested and the epithelial cells differentiate into a new set of lens fibers. This internal reorganization, together with a reversal in polarity at the lens equator, results in a complete reversal of the polarity of the-entire lens.