Scanning slit delivery system

We describe the structure and function of a delivery system designed for use with an argon fluoride excimer laser for corneal surgery. The basic principle of the delivery system is to shape the laser beam with a slit mask to a defined configuration. The image of the slit is moved across the cornea in a mathematically defined pattern to ablate a given amount of tissue, creating a new anterior radius of curvature for the cornea. The location of the beam on the cornea is determined by a rotating dove prism and a translating spherical lens, each of which is controlled by computer-regulated servomotors. The system is versatile and can be used for laser myopic or hyperopic keratomileusis, for correction of astigmatism by surface ablation, for creation of radial or transverse linear cuts, for excision of corneal buttons, and for uniform lamellar corneal smoothing procedures. The delivery system is currently used in the laboratory for the ablation of nonhuman primate corneas.     

A simple saliency model predicts a number of motion popout phenomena

Visual search for a moving target among stationary distractors is more efficient than searching for a stationary target among moving distractors, and searching for a fast target among slow distractors is more efficient than vice versa. This indicates that the ease of search for a target with a particular motion is not determined simply by the difference between target and distractor velocities. We suggest a simple model for predicting ease of search for a unique motion, based upon a quantitative measure of target saliency. Essentially, search will be easier the more the target motion deviates from the general pattern of velocities in the scene. Our model predicts a number of well-known motion search phenomena, and suggests that one control for target saliency as well as target discriminability when drawing conclusions about visual system mechanisms from search experiments.     

The use of the femtosecond laser in penetrating keratoplasty

PURPOSE: To evaluate a new technique for penetrating keratoplasty (PK) with the use of a new software algorithm for a femtosecond laser that is designed to create penetrating cuts for PK in the treatment of a number of corneal diseases. DESIGN: Prospective, interventional case series. METHODS: All eyes were treated at the Ospedale Civile di Mestre, Umberto, Italy. Seven eyes of seven patients underwent surgery for PK using a 15-kHz femtosecond laser (IntraLase, Irvine, California, USA) and a new software specifically developed for corneal surgery. Of the seven patients, five were keratoconus patients and two had bullous keratopathy. New software was used to create penetrating cuts in a top hat or mushroom configuration. After surgery, all patients were evaluated with pachymetry, corneal topography, refraction, intraocular pressure measurement, and corneal optical coherence tomography (Visante; Carl Zeiss, Oberkochen, Germany). RESULTS: On postoperative day one, all seven eyes had nearly clear corneas with a good graft of the donor corneas to the patients' corneas. At three months, all eyes had clear corneas with good endothelial cell counts and quiet anterior chambers. Normal corneal thickness was achieved in each case. At the three-month visit, suture removal was performed in five eyes to adjust for astigmatism. CONCLUSIONS: Although this is a small number of eyes, early indications are that the use of the new IntraLase software for corneal surgery creates a more favorable environment for PK as a result of a better fit of the donor cornea and a quicker visual recovery for patients.     

Fluorescein angiography complication survey

This is a report on the results of a national survey designed to study the nature and frequency of moderate and severe complications of intravenous fluorescein angiography. In this survey, 2434 responding ophthalmologists reported on 221,781 fluorescein angiograms performed in the year 1984. Adverse reactions were classified as mild, moderate, severe, and death, depending on the duration of the effect, the necessity for medical intervention, the time required for its resolution, and the final outcome. The frequency rate for a moderate reaction was (1:63), for a severe reaction (1:1900), and for death (1:222,000). A review of previous studies on adverse reactions to the drug, a compilation of suggested methods for the amelioration and prevention of the complications, and a comparison of the responses of the general ophthalmic public to the members of The Macula Society are also reported.     

Additivity of red chromatic valence

The additivity of red chromatic valence was investigated by the hue cancellation method for 4 normal observers. Additivity held for wavelength combinations of 610-680 nm and 400-440 nm. When using 400-680 nm, additivity failure of enhancement type was found for two observers, reduction type failure for a third, and additivity, for a forth. The results suggest a nonlinear property of the red-green process for some observers and are discussed in terms of the contribution of B-cones to the process.     

间歇性外斜视眼位控制力评分综述

在间歇性外斜视患者的管理中,眼位控制力至关重要,它是评价手术时机的重要参考指标及监测和判断病情发展严重程度的必要指标之一。因此,眼位控制能力的量化成为间歇性外斜视评估中的重要环节。本文旨在对间歇性外斜视患者眼位控制力评估方法做一综述,帮助临床医生对间歇性外斜视患者制定合理的治疗方案。     

Innovations by ophthalmo-surgical instruments (author's transl)]

A demonstration is given of a cornea and sclera forceps for macro- and microsurgery, a sharp spatula for cyclodialysis, a modified blunt cone-shaped Bowman's probe, and a combined speculum forceps for perforating injuries.     

The placido wavefront sensor and preliminary measurement on a mechanical eye.

PURPOSE: The hardware and software of a novel wavefront sensor was developed (The sensor presented here is patent pending.). It has the same principal of the Hartmann-Shack (HS) and other sensors that are based on slope information for recovery of wavefront surface, but a different symmetry, and does not use individual microlenses. This polar symmetry might offer differences during practical measurements that may add value to current and well-established "gold standard" techniques. METHODS: The sensor consists of a set of concentric "half-donut" surfaces (longitudinally sectioned toroids) molded on an acrylic surface with a CCD located at the focal plane. When illuminated with a plane wavefront, it focuses a symmetric pattern of concentric discs on the CCD plane; for a distorted wavefront, a nonsymmetric disc pattern is formed (similar to images of a placido-based videokeratographer). From detection of shift in the radial direction, radial slopes are computed for a maximum of 2880 points, and the traditional least-squares procedure is used to fit these partial derivatives to a set of 15 conventional OSA-VSIA Zernike polynomials. Theoretical computations for several synthetic surfaces containing low-order aberration (LOA) and high-order aberration (HOA) were implemented for both the HS and the new sensor. RESULTS: Root mean square error (RMSE) in microns when theoretical data was taken as control, for HS sensor and new sensor, was 0.02 and 0.00003 for LOA (defocus, astigmatism) and 0.07 and 0.06 for HOA (coma, spherical, and higher terms), respectively. After this, practical preliminary measurements on a mechanical eye with a 5-mm pupil and 10 different defocus aberrations ranging from -5 D to 5 D, in steps of 1 D, were compared between sensors. RMSE for difference in measurements for HS and new sensor for sphere, cylinder, and axis, was 0.13 D, 0.07 D, and 11. Measurements were taken only on defocus aberrations. Qualitative images for astigmatism are shown. DISCUSSION: Although practical in vivo tests were not conducted in this first study, we also discuss certain possible alignment differences that may arise as a result of the different symmetry of the new sensor. To take any conclusive assumption regarding the accuracy and/or precision of this new sensor, when compared with other well-established sensors, statistically significant in vivo measurements will need to be conducted.     

Orientation discrimination for objects defined by relative motion and objects defined by luminance contrast

A bar-shaped area within a pattern of random dots was demarcated by moving the dots within the bar at a velocity equal and opposite to the velocity of dots outside the bar. Orientation discrimination for this motion-defined dotted bar was compared with orientation discrimination for a contrast-defined dotted bar that was created by switching off all dots outside the bar. Orientation discrimination was approximately as acute (approx. 0.5 deg) for a motion-defined bar as for a contrast-defined dotted bar, provided that dot contrast and speed were both high. Furthermore, this 0.5 deg discrimination compares with the most acute values reported for sharp-edged lines and sinewave gratings. For the motion-defined bar discrimination fell off rapidly when dot contrast was reduced, but remained acute for the contrast-defined bar for a further reduction of 0.6 log units. Thus, there was a 4:1 range of contrasts over which discrimination had collapsed for the motion-defined bar but remained acute for the contrast-defined bar. For the motion-defined bar discrimination also fell off rapidly at low dot speeds, but was almost unaffected by speed for the contrast-defined bar. These findings bear on the question whether orientation of motion-defined and contrast-defined bars are analyzed by the same or by different neural mechanisms, and pose a challenge for current theories of orientation discrimination.     

Graft contraction: a comparison of acellular dermis versus hard palate mucosa in lower eyelid surgery

PURPOSE: To compare graft contraction rates of acellular dermis versus hard palate mucosa when used as free spacer grafts in lower eyelid surgery and to provide clinical outcome data. METHODS: A prospective, nonrandomized clinical trial involving the placement of 19 spacer grafts in the lower eyelids of 14 patients was performed. Indications for spacer graft placement included lower eyelid retraction and mildly contracted socket. Patients with lower eyelid retraction also underwent an endoscopic subperiosteal midface lift. For all procedures, the height of each graft was measured during and after surgery. The amount of contraction was measured for each graft, and a mean was calculated for each spacer material. The clinical success was evaluated for all procedures, based on improvement of the functional concern being addressed. RESULTS: The mean graft contraction rate was 57% for the acellular dermis and 16% for the hard palate mucosal grafts (P <0.005). Of the 7 procedures using acellular dermis for lower eyelid retraction, 6 were considered a success, and 1 was considered a partial success. Of the 6 procedures using hard palate for lower eyelid retraction, 5 were considered a success, and 1 was considered a failure unrelated to the graft. Of the 5 procedures with acellular dermis used for mildly contracted socket, 2 were considered a success, 2 were considered a partial success, and 1 was considered a failure because of graft contraction. The one case using hard palate for mildly contracted socket was considered a success. CONCLUSIONS: Acellular dermis contracts significantly more than hard palate mucosa when used as a lower eyelid spacer graft. Acellular dermis and hard palate mucosa were both associated with a high rate of clinical success in all categories except for patients with a mildly contracted socket who received acellular dermis; more than 60% of these patients (n=5) had only partial success or failure caused by graft contraction.     

Vitrectomy for diabetic eye disease. The prognostic value of pre-operative electroretinography and visual evoked cortical potentials

An investigation was carried out into the prognostic value of standard flash electroretinography (ERG) and visual-evoked cortical potentials (VECP) recorded for 87 diabetic eyes prior to vitrectomy. 95% of the eyes with a recordable ERG b-wave achieved a post-operative visual acuity (VA) of 0.05 or better (positive predictive value), but only 35% of the eyes with a good post-operative VA had a recordable b-wave (sensitivity). The corresponding values for the ERG a-wave were 67 and 72%, and for the VECP 77 and 69%, respectively. A non-recordable b-wave in the ERG was associated with a poor visual outcome (VA less than 0.05) in 45% of cases (negative predictive value), and 97% of the eyes with a poor visual outcome had a nonrecordable b-wave (specificity). The corresponding values for the ERG a-wave were 42 and 37%, and for the VECP 53 and 63%, respectively. Consequently, the odds ratio for an unfavourable visual outcome (VA less than 0.05) was greater for a non-recordable b-wave (15.7) than for a nonrecordable VECP (3.8) or a non-recordable a-wave (1.5). Recordability of the b-wave gave the best prediction for attached macula. Extensive photocoagulation diminished all ERG and VECP amplitudes. Vitreous opacities had no significant effect on the ERG or VECP.     

''Preferential looking'' for monocular and binocular acuity testing of infants.

A method is described for obtaining rapid and reliable estimates of acuity in infants, for both monocular and binocular viewing. The method depends on 'preferential looking', where the infant prefers to look at a striped pattern rather than a blank screen of matched mean luminance. A staircase procedure for testing is followed, with observations being recorded by a 'blind' observer (who does not know on which of the 2 screens the striped pattern is displayed). Monocular acuity estimates have been obtained for a group of infants 3 to 4 months old with normal refractions. Many of these infants show similar acuity values in the 2 eyes, with a few showing reliable differences between the eyes. To check reliability of the method a comparison of 2 independent interleaved staircase estimates of the same eye have been made. In general this check shows highly consistent estimates for a given eye of a given infant. Nearly all infants show slightly higher acuity estimates for binocular viewing than for monocular. The possible reasons for this difference are discussed. The clinical use of such a method is reported for a number of cases. The method has been found to be useful in a variety of clinical conditions where other available tests are not possible on young infants.     

Target crowding in foveal and peripheral stereoacuity

Disparity thresholds were obtained for a single point target when surrounded by a hexagonal array of comparison point targets. The experiment was carried out in two observers at the fovea and at retinal eccentricities of 3, 6, and 9 degrees. In each case the array diameter for best stereoacuity was determined. Care was taken that the data represented the optimum performance of the observer for the level of training in peripheral stereo tasks and also for the distance from the horopter. The results show a steady rise with eccentricity both for the stereothreshold and for the minimum target separations needed for uncrowded stereo performance. Both increase by a factor of about 10 between the fovea and the 9 degrees periphery, where a clear zone of at least 2 degrees diameter between test and comparison targets is needed for best stereoacuity.     

Vernier acuity with dot test objects.

Vernier thresholds were determined as a function of dot number, dot arrangement, and dot separation. The thresholds for a three-dot target with the middle dot movable were less than the thresholds for a two-dot target and for a three-dot target with the bottom dot movable. The thresholds for a two-dot target and for a three-dot target with the bottom dot movable were not reliably different. For both two- and three-dot targets, the thresholds increased as a linear function of interdot separation. The results are interpreted as supporting the hypothesis that vernier judgments with dot stimuli involve primarily a discrimination of orientation rather than of alignment. The results further suggest that information about orientation is not given directly but derived from position information.     

Digital photographic screening for diabetic retinopathy in the James Bay Cree

This study evaluates a single, 45-degree fundus image from a non-mydriatic camera for the triage of subjects at risk for diabetic retinopathy. A complete retinal assessment by a retina specialist was the main comparator for the camera. Inter-observer agreements were calculated for the reading of digital images with different grades of retinopathy. Two hundred eyes of 100 consecutive subjects were evaluated as part of the James Bay diabetic retinopathy screening project; 62% of subjects had no retinopathy, 12% had microaneurysms only, 24% had non-proliferative retinopathy, 5% had clinically significant macular edema (CSME), and 2% had proliferative disease (PDR). The Kappa statistic for two independent observers was 0.85 (p < 0.001) for the identification of retinopathy from the digital images. The sensitivity of the digital camera for the evaluation of any retinopathy was 84.4%, for CSME and/or PDR it was over 90%. The use of a single digital retinal image for the evaluation of diabetic retinopathy was performed with a high degree of inter-observer concordance and a high degree of sensitivity.     

Proton therapy of occult neovessels in age-related macular degeneration

INTRODUCTION: The interest of radiation therapy in the management of age-related macular degeneration inaccessible to photocoagulation is still controversial. Our purpose was to demonstrate the feasibility and the possible efficacy of a single dose delivered to the macular region using a 65-MeV proton beam. MATERIAL AND METHODS: A phase II trial was set up using the cyclotron in Nice, France. Fifty-eight patients were included after signing an informed consent. All patients presented with occult subfoveal choroidal neovascularization. A single dose of 9.1 Gy (i.e., 10 Gy cobalt equivalent) was delivered to the macular region. RESULTS: The results were analyzed 3, 6, 12 and, 18 months after proton therapy. At 3 months, the visual acuity was stable or enhanced for 86% of patients, at 6 months for 82.3%, at 12 months for 80%, and at 18 months for 61%. For 22 patients at follow-up at 18 months, the reasons for a decrease in visual acuity were a macular hemorrhage for 4 patients and a progression of the neovascular membrane for 3 patients. No secondary effects related to the treatment have been observed. Regarding the lesions visible on the angiographies (i.e., hemorrhage, exudates, subretinal detachment), we observed a stabilization or a decrease in two-thirds of the cases. CONCLUSION: Preliminary results of single-dose proton therapy are at least comparable to those obtained by other teams. A second study is in progress comparing 3 dose levels, looking for a dose-effect relationship. Furthermore, a randomized study comparing a single proton dose to a placebo will be necessary to assess the long-term value of proton treatment.     

Lower thresholds of motion for gratings as a function of eccentricity and contrast

We investigated the lower threshold for motion (LTM) of gratings as a function of position in the visual field, spatial frequency and contrast and we compared motion thresholds for sine wave and square wave luminance profiles. For contrasts below 0.05 the lower threshold for motion was raised; the increase in threshold being dependent upon spatial frequency. At contrast levels above 0.05, LTM was found to be a constant velocity at any given spatial location but increased with eccentricity of view. Raised thresholds for motion at eccentric locations could be compensated by increasing the size of eccentric gratings in proportion to M-1, where M is the cortical magnification factor, a procedure which standardises the cortical representation at differing eccentricities. Thus LTM could be expressed as a constant cortical velocity for grating contrasts above 0.05 at all stimulus locations investigated. We interpret our data as support for a ratio model of velocity coding.     

Occlusion contact lenses (author's transl)]

A reliable inconspicuous occlusion therapy is achieved by fitting different, specially manufactured contact lenses. Based on a study of a number of cases, the author discusses the indications for a occlusion contact lens. These lenses provide a means for treating amblyopia in schoolchildren and adults, as well as for eliminating diplopia, photophobia and metamorphopsia.     

Visual evoked potentials for reversals of red-green gratings with different chromatic contrasts: asymmetries with respect to isoluminance

Human visual evoked potentials (VEPs) were recorded for abrupt 6.25-Hz reversals of 2 c/deg square-wave gratings combining red-green contrast with different levels of luminance contrast. Response characteristics-- amplitudes and peak latencies as a function of luminance contrast--were compared for four different pairs of red-green colors and an isochromatic yellow grating. For each of the red-green color pairs, the plots of VEP amplitudes and latencies were nonsymmetrical with respect to isoluminance. The amplitude dropped to a minimum within a region of rapid phase change, at a different contrast for each color pair but always at a luminance contrast for which the greener color had the higher luminance. When the contrast-response curve for each of the four red-green pairs was modeled by a simple |CL - CM| opponency of L- and M-cone contrast using a fixed CL/CM weighting ratio of about two, there was a close correspondence between the contrast giving a null in the modeled response and that giving a minimum in the VEP amplitude. So for the stimulus parameters applied here, the reversal VEP appeared to be dominated by L/M-opponent response contributions for which the signed CL/CM-cone weighting ratio was close to a value of minus two rather than to a value of minus one, which is characteristic of the psychophysical red-green detection mechanism and representative of CL/CM weighting ratios for precortical cells in the parvocellular pathway.     

Intraocular lens power calculations for multifocal intraocular lenses.

We performed calculations for anterior and posterior chamber intraocular lenses, determining the necessary power for emmetropia and 3 diopters of myopia for various axial lengths and corneal powers. Our results demonstrate that to achieve an effective add of 3.00 diopters at the spectacle plane (reading distance of 33 cm), the fabricated add (labeled add) on an intraocular lens must vary from 3.3 diopters for an anterior chamber lens in a patient with a flat cornea, to 5.1 diopters for a posterior chamber lens in a patient with a steep cornea. For most patients, targeting for an effective add of 3 diopters is appropriate, but factors such as availability of fabricated adds from the manufacturer and unusual patient requirements for near vision, may alter this target. We reviewed alternatives with monofocal lenses, such as monovision and compound myopic astigmatism.