Functional connectivity correlates of attentional networks in insomnia disorder: A pilot study.

Insomnia disorder has been associated with poor executive functioning. Functional imaging studies of executive functioning in insomnia are scarce and inconclusive. Because the Attentional Network Test relies on well-defined cortical networks and sensitively distinguishes different aspects of executive function, it might reveal brain functional alterations in relatively small samples of patients. The current pilot study assessed functional connectivity during the Attentional Network Test performed using magnetic resonance imaging in 12 participants with insomnia and 13 self-defined good sleepers. ANCOVAs were used to evaluate group differences in performance and functional connectivity in the regions of interest representing the attentional networks (i.e. alerting, orienting and executive control) at p < 0.05, uncorrected. During the orienting part, participants with insomnia showed weaker connectivity of the precentral gyrus with the superior parietal lobe (false discovery rate-corrected), while they showed stronger connectivity between premotor and visual regions. Individual differences in connectivity between premotor and visual regions correlated inversely with reaction time. Reaction times suggested more efficient executive control in participants with insomnia compared with good sleepers. During the executive control part, participants with insomnia showed stronger connectivity of thalamic parts of the arousal circuit with the middle frontal and the occipital gyri. Conversely, connectivity between the inferior and superior frontal gyri was weaker. Participants with insomnia seem to recruit more cortical resources in visuo-motor regions to orient attention than good sleepers do, and seem to have enhanced executive control that relates to stronger connectivity of arousal-related thalamic areas. This latter result should be treated with caution and requires confirmation.

Sustained effects of prior red light on pupil diameter and vigilance during subsequent darkness.

Environmental light can exert potent effects on physiology and behaviour, including pupil size, vigilance and sleep. Previous work showed that these non-image forming effects can last long beyond discontinuation of short-wavelength light exposure. The possible functional effects after switching off long-wavelength light, however, have been insufficiently characterized. In a series of controlled experiments in healthy adult volunteers, we evaluated the effects of five minutes of intense red light on physiology and performance during subsequent darkness. As compared to prior darkness, prior red light induced a subsequent sustained pupil dilation. Prior red light also increased subsequent heart rate and heart rate variability when subjects were asked to perform a sustained vigilance task during the dark exposure. While these changes suggest an increase in the mental effort required for the task, it could not prevent a post-red slowing of response speed. The suggestion that exposure to intense red light affects vigilance during subsequent darkness, was confirmed in a controlled polysomnographic study that indeed showed a post-red facilitation of sleep onset. Our findings suggest the possibility of using red light as a nightcap.

Post-illumination pupil response after blue light: Reliability of optimized melanopsin-based phototransduction assessment.

Melanopsin-containing retinal ganglion cells have recently been shown highly relevant to the non-image forming effects of light, through their direct projections on brain circuits that regulate alertness, mood and circadian rhythms. A quantitative assessment of functionality of the melanopsin-signaling pathway could be highly relevant in order to mechanistically understand individual differences in the effects of light on these regulatory systems. We here propose and validate a reliable quantification of the melanopsin-dependent Post-Illumination Pupil Response (PIPR) after blue light, and evaluated its sensitivity to dark adaptation, time of day, body posture, and light exposure history. Pupil diameter of the left eye was continuously measured during a series of light exposures to the right eye, of which the pupil was dilated using tropicamide 0.5%. The light exposure paradigm consisted of the following five consecutive blocks of five minutes: baseline dark; monochromatic red light (peak wavelength: 630 nm, luminance: 375 cd/m(2)) to maximize the effect of subsequent blue light; dark; monochromatic blue light (peak wavelength: 470 nm, luminance: 375 cd/m(2)); and post-blue dark. PIPR was quantified as the difference between baseline dark pupil diameter and post-blue dark pupil diameter (PIPR-mm). In addition, a relative PIPR was calculated by dividing PIPR by baseline pupil diameter (PIPR-%). In total 54 PIPR assessments were obtained in 25 healthy young adults (10 males, mean age ± SD: 26.9 ± 4.0 yr). From repeated measurements on two consecutive days in 15 of the 25 participants (6 males, mean age ± SD: 27.8 ± 4.3 yrs) test-retest reliability of both PIPR outcome parameters was calculated. In the presence of considerable between-subject differences, both outcome parameters had very high test-retest reliability: Cronbach's α > 0.90 and Intraclass Correlation Coefficient > 0.85. In 12 of the 25 participants (6 males, mean age ± SD: 26.5 ± 3.6 yr) we examined the potential confounding effects of dark adaptation, time of the day (morning vs. afternoon), body posture (upright vs. supine position), and 24-h environmental light history on the PIPR assessment. Mixed effect regression models were used to analyze these possible confounders. A supine position caused larger PIPR-mm (ß = 0.29 mm, SE = 0.10, p = 0.01) and PIPR-% (ß = 4.34%, SE = 1.69, p = 0.02), which was due to an increase in baseline dark pupil diameter; this finding is of relevance for studies requiring a supine posture, as in functional Magnetic Resonance Imaging, constant routine protocols, and bed-ridden patients. There were no effects of dark adaptation, time of day, and light history. In conclusion, the presented method provides a reliable and robust assessment of the PIPR to allow for studies on individual differences in melanopsin-based phototransduction and effects of interventions.

Iris color and visual functions.

BACKGROUND: The aim of this study was to evaluate if iris color is associated with differences in visual functions such as intraocular straylight (IOSL), contrast sensitivity (CS), or best-corrected visual acuity (BCVA). METHODS: In this retrospective cohort study, which is a subgroup analysis of a large prospective trial about visual impairments in European car drivers, we included 853 persons between 20 and 80 years of age and without a history of ocular surgery or any eye disease including cataract. Subjects participated in an ophthalmological examination, grading of lens opacity, and the measurement of visual functions such as IOSL, CS, and BCVA. Dependent on iris color, participants were divided into four groups: light-blue, blue-grey, green-hazel, and brown. RESULTS: Independent of age, IOSL was significantly (all p values < 0.0001, Fisher's LSD test) higher in participants with light-blue colored iris (1.14 log(IOSL) [95 % CI: 1.11-1.17]) compared to participants with blue-grey (1.07 log(IOSL) [95 % CI: 1.05-1.09]), green-hazel (1.06 log(IOSL) [95 % CI: 1.04-1.08]) or brown (1.06 log(IOSL) [95 % CI: 1.04-1.08]) iris color. CS was also lower in participants with light-blue pigmented irises (1.60 log(CS) [95 % CI: 1.58-1.62]) than in the other groups, but statistically significant (p = 0.013, Fisher's LSD test) only compared to brown iris color. For BCVA we could not found any difference between the four groups. CONCLUSIONS: We could show in this study that iris color has a significant impact on IOSL and to a lower degree on CS, but not on BCVA. Persons with light-blue iris color who showed significantly higher IOSL values therefore may experience disability glare in daily situations such as driving at night more often than others.

In-vitro recording of forward light-scatter by human lens capsules and different types of posterior capsule opacification.

The purpose of the present study was to elucidate the effect of posterior capsule opacification (PCO) on the straylight domain of visual function. PCO is heterogeneous with regard to morphology and severity; both aspects contribute to its functional effect. The isolated impact of capsule areas with specific morphology and severity on straylight was studied in-vitro by recording forward light-scatter. Forward light-scatter by four different capsule types, i.c. anterior capsule (AC), clear posterior capsule (PC), fibrotic and regeneratory PCO, was recorded at several visual angles with a goniometer, using different wavelengths. Angular (θ(a)) and wavelength dependencies (λ(b)) were studied by determining exponents a and b. Recorded straylight values of isolated capsule areas varied between 10× below to 10× above the value normal for the human eye, depending on the capsule's condition (clear to opacified). The angular dependence of light scattered by clear PCs was weaker, whereas in the other capsule types it was stronger than in the normal eye. On average, the wavelength dependence of light scattered by different capsule types was similar, but the variation was considerable. At the smallest visual angles, increased angular and decreased wavelength dependence was found, especially in fibrotic and regeneratory PCO. It was concluded that the range of straylight values found in-vitro in lens capsules properly corresponded to that found previously in in-vivo pseudophakics. Surprisingly, the wavelength dependence of PCO indicated that small-particle light-scattering is important in PCO. Refractile effects were more important at small visual angles, as indicated by the combined stronger angular and weaker wavelength dependence.

Lightweight, wireless LED implant for chronic manipulation in vivo of spontaneous activity in neonatal mice.

BACKGROUND: Long-term manipulation of activity in the neonatal rodent brain can help us understand healthy development, but also involves a set of challenges unique to the neonatal animal. As pups are small, cannot be separated from their mother for long periods of time, and must be housed in a nest, many traditional techniques are unusable during the first two postnatal weeks. NEW METHOD: Here, we describe the use of magnetic resonance induction to allow wireless and chronic optogenetic manipulation of spontaneous activity in mouse pups during the second postnatal week. RESULTS: Pups were implanted with a lightweight receiver coupled to an LED and successfully returned to the homecage. A transmitter coil surrounding the homecage drove the implanted LED and was regulated by a microcontroller to allow flexible, precisely-timed and wireless control over neuronal manipulation. In vivo patch-clamp recordings verified that activation of the LED triggered bursts of action potentials in layer 2/3 neurons that expressed channelrhodopsin-2 in the visual cortex without directly affecting neighboring, non-expressing neurons. The implants are stable and functional for at least 10 days and do not have an impact on the weight gain of pups. Implanted pups' behavior is mildly affected only briefly after surgery, while maternal behavior of dams remains unaffected. COMPARISON WITH EXISTING METHOD(S): In contrast to most other methods for wireless optogenetic stimulation, the small size and low weight of the receiver allow complete implantation in animals that are as small as a newborn mouse. CONCLUSIONS: This method is ideal for investigating the function and development of cortical circuits in small and developing animals. Furthermore, our method is economical and easy to adapt to diverse experimental designs.

NINscope, a versatile miniscope for multi-region circuit investigations.

Miniaturized fluorescence microscopes (miniscopes) have been instrumental to monitor neural signals during unrestrained behavior and their open-source versions have made them affordable. Often, the footprint and weight of open-source miniscopes is sacrificed for added functionality. Here, we present NINscope: a light-weight miniscope with a small footprint that integrates a high-sensitivity image sensor, an inertial measurement unit and an LED driver for an external optogenetic probe. We use it to perform the first concurrent cellular resolution recordings from cerebellum and cerebral cortex in unrestrained mice, demonstrate its optogenetic stimulation capabilities to examine cerebello-cerebral or cortico-striatal connectivity, and replicate findings of action encoding in dorsal striatum. In combination with cross-platform acquisition and control software, our miniscope is a versatile addition to the expanding tool chest of open-source miniscopes that will increase access to multi-region circuit investigations during unrestrained behavior.

Straylight in the human eye: testing objectivity and optical character of the psychophysical measurement.

The point spread function or PSF of the human eye encompasses hugely different domains: a small-angle, high-intensity domain, called the 'PSF core', and a large-angle, low-intensity domain, usually referred to as 'straylight'. The first domain can be assessed by available double-pass or other optical techniques. For the second domain psychophysical techniques have been developed, in particular the Compensation Comparison or CC technique, recently made available for clinical application in the C-Quant instrument. We address the question of whether the psychophysical technique gives measures of straylight that are compatible with those made by optical methods. With a small adaptation the CC method can be used to assess straylight from physical light scattering samples, instead of straylight in the eye, using the same psychophysics, but without interference from the ocular straylight. The light scattered by each of seven light-scattering samples, encompassing the range of straylight values observed in human eyes, was measured by two optical methods and by the psychophysical technique. The results showed that the optical and psychophysical measurements for the seven samples were almost identical.

Distinctive tics suppression network in Gilles de la Tourette syndrome distinguished from suppression of natural urges using multimodal imaging.

BACKGROUND AND OBJECTIVES: Gilles de la Tourette syndrome (GTS) is a neuropsychiatric disorder characterized by tics. A hallmark of GTS is the ability to voluntarily suppress tics. Our aim was to distinguish the neural circuits involved in the voluntary suppression of ocular tics in GTS patients from blink suppression in healthy subjects. METHODS: Fifteen GTS patients and 22 healthy control subjects were included in a multimodal study using eye-tracker recordings during functional MRI (fMRI). The ability to suppress tics/blinks was compared both on subjective (self-rating) and objective (eye-tracker) performance. For fMRI analysis we used a novel designed performance-adapted block design analysis of tic/blink suppression and release based on eye-tracker monitoring. RESULTS: We found that the subjective self-reported ability to suppress tics or blinks showed no significant correlation with objective task performance. In GTS during successful suppression of tics, the dorsal anterior cingulate cortex and associated limbic areas showed increased activation. During successful suppression of eye blinks in healthy subjects, the right ventrolateral prefrontal cortex and supplementary and cingulate motor areas showed increased activation. CONCLUSIONS: These findings demonstrate that GTS patients use a characteristic limbic suppression strategy. In contrast, control subjects use the voluntary sensorimotor circuits and the classical 'stop' network to suppress natural urges. The employment of different neural suppression networks provides support for cognitive behavioral therapy in GTS.

Pupil size and retinal straylight in the normal eye.

PURPOSE: Glare problems originating from bright lights are generally experienced more strongly at night. The typical disability glare is known to result from retinal straylight. In this study, the effects of pupil diameter and, especially in the case of small pupils, of eye wall translucency on the amount of retinal straylight were investigated. METHODS: Straylight was measured as a function of pupil diameter ranging from 1.3 to >8 mm in five normal subjects by using a white-light, CRT-based system for scattering angles of 3.5 degrees , 7 degrees , and 14 degrees . In the study of red-free light, a yellow-LED based system was used with the same five subjects for scattering angles of 3.5 degrees , 10 degrees , and 28 degrees . Data were analyzed to assess effects of (1) inhomogeneity of light-scattering over the pupil plane, (2) translucency of the eye wall, and (3) effects of the periphery of the lens. To estimate the order of magnitude of pupil contraction in the typical glare situation, pupil reflexes resulting from the sudden appearance of headlight-equivalent bright lights were recorded in three subjects in a laboratory environment. RESULTS: For natural pupils (between 2 and 7 mm diameter), straylight weakly depends on pupil diameter (within 0.2 log units). For large scatter angles and small pupil diameters, eye wall translucency contributes significantly to straylight in a wavelength- and pigmentation-dependent manner. Pupil diameters decreased to photopic values under typical night-driving glare conditions. CONCLUSIONS: In normal eyes, straylight values measured with photopic pupils are by approximation also valid for mesopic and scotopic pupils, such as in night driving. Measurement of straylight under large angle and small pupil conditions can be used for quantitative assessment of eye wall translucency.

Straylight effects with aging and lens extraction.

PURPOSE: To assess possible gains and losses in straylight values among the population to consider straylight as added benefit of lens extraction. DESIGN: In this cross-sectional design, data from a multicenter study on visual function in automobile drivers were analyzed. METHODS: On both eyes of 2,422 subjects, visual acuity (logarithm of the minimum angle of resolution [logMAR] in steps of 0.02 log units), straylight on the retina (psychophysical compensation comparison method), and lens opacity (slit-lamp scoring using the Lens Opacities Classification System III [LOCS III] system) were determined. Three groups were defined: 220 pseudophakic eyes, 3,182 noncataractous eyes (average LOCS III score, <1.5), and 134 cataractous eyes (average LOCS III score, >3.0). RESULTS: Noncataractous straylight values increases strongly with age as: log(s) = constant + log(1 + (age / 65)(4)), doubling by the age of 65 years, and tripling by the age of 77 years. Population standard deviation around this age norm was approximately 0.10 log units. The cataract eyes (in this active driver group) had relatively mild straylight increase. In pseudophakia, straylight values may be very good, better even than in the noncataract group. Visual acuity and straylight were found to vary quite independently. CONCLUSIONS: Lens extraction holds promise not only to improve on the condition of the cataract eye, but also to improve on the age-normal eye. Lens extraction potentially reverses the strong age increase in straylight value, quite independently from visual acuity.

Modulation depth threshold in the Compensation Comparison approach.

Recently, the "Compensation Comparison" method was introduced for measuring retinal straylight. In this article, basic aspects are described, in particular a generalization of the approach using the concept of "precompensation," and including flicker threshold as parameter in the psychophysical model. The model was experimentally verified in lab measurements with and without artificially increased straylight and was tested on the data from the multi-center GLARE study. The resulting flicker threshold estimates were analyzed to better understand their origin. An effect of flicker adaptation over distance was found. The new approach proved suitable to describe Compensation Comparison measurements including precompensation, and also for subjects with poor psychometric behavior.

Compensation comparison method for assessment of retinal straylight.

PURPOSE: Presently, no instrument or method exists that is generally accepted for routine clinical assessment of (functional) retinal straylight. Yet retinal straylight is the cause of major patient complaints, such as hindrance from glare and loss of contrast. It results from disturbances in the optical media that increase light-scattering over angles of 1 degrees to 90 degrees . Its assessment would help to decide whether to perform surgery for (early) cataract and would help in the evaluation of corneal or vitreal turbidity. METHODS: The psychophysical technique of the "direct compensation" method was adapted to make it suitable for routine clinical assessment. In the new approach, called "compensation comparison, " the central test field is subdivided into two half fields: one with and one without counterphase compensation light. The subject's task is a forced-choice comparison between the two half fields, to decide which half flickers more strongly. A theoretical form for the respective psychometric function was defined and experimentally verified in a laboratory experiment involving seven subjects, with and without artificially increased light scattering. The method was applied in a separate multicenter study. Its reliability was additionally tested with a commercial implement (C-Quant; Oculus Optikgeräte, Wetzlar-Dutenhofen, Germany). RESULTS: A repeated-measures SD of 0.07 log units was achieved, to be compared with differences in the young normal population of 0.4 log units and an increase with healthy aging by 0.5 log units at 80 years and by 1.0 or more log units with (early) cataract or corneal disturbances. Reliability was further found to be high when using the commercial version of the CONCLUSIONS: The compensation comparison method for measuring retinal straylight is suited for clinical use to diagnose patients with complaints caused by large angle light scattering in the eye such as early cataract.

Reliability of the compensation comparison method for measuring retinal stray light studied using Monte-Carlo simulations.

Recently the psychophysical compensation comparison method was developed for routine measurement of retinal stray light. The subject's responses to a series of two-alternative-forced-choice trials are analyzed using a maximum-likelihood (ML) approach assuming some fixed shape for the psychometric function (PF). This study evaluates the reliability of the method using Monte-Carlo simulations. Various sampling strategies were investigated, including the two-phase sampling strategy that is used in a commercially available instrument. Results are given for the effective dynamic range and measurement accuracy. The effect of a mismatch of the shape of the PF of an observer and the fixed shape used in the ML analysis was analyzed. Main outcomes are that the two-phase sampling scheme gives good precision (Standard deviation = 0.07 logarithmic units on average) for estimation of the stray light value. Bias is virtually zero. Furthermore, a reliability index was derived from the responses and found to be effective.

Reliability of the compensation comparison stray-light measurement method.

The compensation comparison (CC) method is a psychophysical technique to measure retinal stray light. It uses a two alternative forced choice (2AFC) measurement paradigm. The 25 binary (0 and 1) responses resulting from the 2AFC test are analyzed using maximum likelihood estimates. The likelihood function is used to give two quantities: the most likely stray-light level of the eye under investigation, and the accuracy of this estimate [called expected standard deviation (ESD)]. The CC method is used in 2422 subjects of the GLARE study. Each eye is tested twice to allow analysis of measurement repeatability. Furthermore, the large amount of responses is used to evaluate the shape of the psychometric function, for which a mathematical model is used. The shape of the psychometric function found by averaging the 0 and 1 responses fit well to the model function. Data sorted according to ESD show differences in the shape of the psychometric function between good and bad observers. These different shapes for the psychometric function are used to reanalyze the data, but the stray-light results remain virtually identical. ESD proves to be an efficient tool to detect unreliable measurements. In clinical practice, ESD may be used to decide whether to repeat a measurement.

Simulating the straylight effects of cataracts.

PURPOSE: To study the additional straylight falling on the retina (retinal straylight) caused by cataract and find commercially available filters to simulate the cataract straylight effects. SETTING: Research laboratory. METHODS: The retinal straylight addition of cataract was derived from straylight parameter data in the literature. The scattering characteristics of cataract-simulating filters were measured using a scatterometer. RESULTS: The straylight addition due to cataract follows a power law as a function of angle with power of -2.12 and straylight parameter log values of up to 1.6 for relatively mild cataract cases. Of the commercial filters that were tested, the Tiffen Black Pro Mist (BPM) filters resembled the straylight characteristics of cataracts fairly well. The filters had a limited effect on visual acuity and contrast sensitivity, which was also found for early cataracts. The BPM 2 followed a power law as a function of angle with power of approximately -2.21 and straylight log values of 1.12. CONCLUSIONS: The BPM 2 filter is a good early-cataract-simulating filter. Stacking such filters is a good way to increase the cataract density. A drawback is that the BPM 2 filter has a transmission of 66% so stacking filters reduces the overall transmission significantly.

Individual Differences in Sleep Timing Relate to Melanopsin-Based Phototransduction in Healthy Adolescents and Young Adults.

STUDY OBJECTIVES: Individual differences in sleep timing have been widely recognized and are of particular relevance in adolescents and young adults who often show mild to severely delayed sleep. The biological mechanisms underlying the between-subject variance remain to be determined. Recent human genetics studies showed an association between sleep timing and melanopsin gene variation, but support for functional effects on downstream pathways and behavior was not demonstrated before. We therefore investigated the association between the autonomic (i.e., pupil diameter) and behavioral (i.e., sleep timing) readouts of two different downstream brain areas, both affected by the same melanopsin-dependent retinal phototransduction: the olivary pretectal nucleus (OPN) and the suprachiasmatic nucleus (SCN). METHODS: Our study population included 71 healthy individuals within an age range with known vulnerability to a delayed sleep phase (16.8-35.7 y, 37 males, 34 females). Pupillometry was performed to estimate functionality of the intrinsic melanopsin-signaling circuitry based on the OPN-mediated post-illumination pupil response (PIPR) to blue light. Sleep timing was quantified by estimating the SCN-mediated mid-sleep timing in three different ways in parallel: using a chronotype questionnaire, a sleep diary, and actigraphy. RESULTS: All three measures consistently showed that those individuals with a later mid-sleep timing had a more pronounced PIPR (0.03 < P < 0.05), indicating a stronger blue-light responsiveness of the intrinsic melanopsin-based phototransduction circuitry. CONCLUSIONS: Trait-like individual differences in the melanopsin phototransduction circuitry contribute to individual differences in sleep timing. Blue light-sensitive young individuals are more prone to delayed sleep.

Individual Differences in the Post-Illumination Pupil Response to Blue Light: Assessment without Mydriatics.

Melanopsin-containing retinal ganglion cells play an important role in the non-image forming effects of light, through their direct projections on brain circuits involved in circadian rhythms, mood and alertness. Individual differences in the functionality of the melanopsin-signaling circuitry can be reliably quantified using the maximum post-illumination pupil response (PIPR) after blue light. Previous protocols for acquiring PIPR relied on the use of mydriatics to dilate the light-exposed eye. However, pharmacological pupil dilation is uncomfortable for the participants and requires ophthalmological expertise. Hence, we here investigated whether an individual's maximum PIPR can be validly obtained in a protocol that does not use mydriatics but rather increases the intensity of the light stimulus. In 18 participants (5 males, mean age ± SD: 34.6 ± 13.6 years) we evaluated the PIPR after exposure to intensified blue light (550 µW/cm²) provided to an undilated dynamic pupil. The test-retest reliability of the primary PIPR outcome parameter was very high, both between day-to-day assessments (Intraclass Correlation Coefficient (ICC) = 0.85), as well as between winter and summer assessments (ICC = 0.83). Compared to the PIPR obtained with the use of mydriatics and 160 µW/cm² blue light exposure, the method with intensified light without mydriatics showed almost zero bias according to Bland-Altman plots and had moderate to strong reliability (ICC = 0.67). In conclusion, for PIPR assessments, increasing the light intensity is a feasible and reliable alternative to pupil dilation to relieve the participant's burden and to allow for performance outside the ophthalmological clinic.

The ciliary corona: physical model and simulation of the fine needles radiating from point light sources.

PURPOSE: Most people see, around bright lights against dark backgrounds, a radiating pattern of numerous fine, slightly colored needles of light-the so called ciliary corona. The purpose of this study was to try to explain this phenomenon. METHODS: Recently, it has been shown that light-scattering in the eye, measured psychophysically and on human donor lenses, can be explained assuming the presence of specific distributions of small particles in the eye. Light entering the eye is diffracted by these particles. Each such particle causes a circular diffraction pattern on the retina of tens of degrees, much like the well-known Airy pattern. The optics of combining many such diffraction patterns was modeled and the resultant pattern simulated graphically. The simulations were compared with observations on the ciliary corona, as seen by the natural eye. RESULTS: The diffraction discs originating from all the particles coherently superimposed on the retina. Because of phase differences this resulted in breaking the Airy-like discs into a fine spotted pattern when monochromatic light was used. For white (polychromatic) light, the spots line up to form the very fine-line pattern seen in the ciliary corona. Details such as the width and color of the needles follow from the theoretical treatment and were demonstrated by simulations. CONCLUSIONS: The details of the ciliary corona can be understood on the basis of polychromatic light-scattering by the particles predicted to be present in human eye lenses on the basis of light-scattering studies of donor lenses.

Biometry of phakic intraocular lens using Scheimpflug photography.

PURPOSE: To examine lateral and axial positioning of phakic intraocular lenses (IOLs) with iris fixation in the anterior chamber and to examine short-term stability of the IOL position. SETTING: The Netherlands Opthalmic Research Institute, Amsterdam, the Netherlands. METHODS: Thirty patients participated in the study. Thirty-one eyes were implanted with the 204 type myopia IOL, 14 eyes with the 206 myopia IOL, and 8 eyes with the 203 hyperopia IOL. Scheimpflug slitlamp photographs were made through the optical axis along 4 meridians of the eyes. Ray tracing was used to obtain the lateral and axial position of the IOLs. RESULTS: Centration of the IOL with respect to the pupil's center and the tilt angle of the IOL with respect to the optical axis of the eye were measured. Standard deviation of decentration was 0.21 mm vertically and 0.16 mm horizontally. Standard deviation of tilt was 1.30 degrees vertically and 0.90 degrees horizontally. Tilt and decentration are proportional to each other. Vaulting, the distance between the crystalline lens and the IOL, was constant over a period of 24 months, ranging from 0.2 to 0.8 mm, depending primarily on the radius of curvature of the crystalline lens. A geometric model for this dependence was formulated. CONCLUSION: Phakic IOLs with iris fixation can be positioned in the eye with submillimeter precision. Axial position of iris-fixated phakic IOLs over time is excellent. Axial position and vaulting can be predicted when the radius of curvature of the crystalline lens is known. The IOL behaves as if mounted slightly above a sphere-the anterior surface of the crystalline lens.