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F Schaeffel

Publications and source records attributed to F Schaeffel.

At least 19 recordsLinked to original sources
PubMed1997

Local changes in eye growth induced by imposed local refractive error despite active accommodation.

We have tested whether defocus imposed on local retinal areas can produce local changes in eye growth, even if accommodation is available to clear part of the imposed defocus. Hemi-field lenses were attached to little leather hoods that were worn by young chickens from day 11-15 post-hatching. The lens segments defocused either the nasal or the temporal visual field, or covered the full field. We found that negative lenses (-7.5 D) were incompletely compensated in all three cases but caused significant myopia in the defocused parts of the visual field (differences to fellow eyes with normal vision: nasal visual field -3.13 +/- 1.56 D, P < 0.001; temporal visual field -4.02 +/- 1.38 D, P < 0.001; full field -3.82 +/- 2.48 D, P = 0.01). Myopia was not enhanced if the lenses covered the entire visual field. Positive lenses (+6.9 D) caused larger changes in refraction than negative lenses and, again, there was no significant difference in the amount of induced hyperopia in the nasal or temporal retina, or in the amount of hyperopia with full-field lenses (difference to fellow eyes with normal vision: nasal visual field +6.2 +/- 2.69 D, P < 0.001; temporal visual field +5.95 +/- 2.22 D, full field +7.22 +/- 2.44 D, P < 0.001). To compare the shapes of the excised eyes after lens treatment, we wrote a fully automated image processing program that traced their outlines in digitized video images. We found that the shapes of the eyes treated with positive lenses did scarcely differ from their fellow eyes with normal vision, indicating that hyperopia over this 4 day period was caused mostly by choroidal thickening. Full field negative lenses produced significant axial eye elongation; the effects of locally imposed defocus on eye shape were less conspicuous and were significant only in some areas. That local compensation of defocus was possible for both negative and positive lenses, suggests that the retina can recognize the sign of defocus without accommodation cues. Even more striking is that the presence of accommodation is apparently ignored since the drift in the plane of focus during accommodation does not disturb the compensation process. We re-analyze previous experimental results that argue for different mechanisms for deprivation myopia and lens-induced refractive errors. We propose that lens-induced refractive errors are compensated by similar retinal mechanisms as the ones proposed by Bartmann and Schaeffel [(1994). Vision Research, 34, pp. 873-876] to explain deprivation myopia. The proposed mechanisms can integrate with long time constants over the spatial frequency content in the retinal image while the viewing distances change, and control both choroidal thickening and scleral growth. However, it turns out that the compensation of imposed myopia cannot be explained if only one constant viewing is available. Apparently, there is more than a retinal blur detector to guide refractive development.

Accommodation, Ocular↗
PubMed1997

Flicker parameters are different for suppression of myopia and hyperopia.

Axial eye growth rates in the chicken are controlled by local retinal image-processing circuits. These circuits quantify the loss of contrast for different spatial frequencies and promote axial eye growth rates in correlation with the amount of retinal image degradation ("deprivation myopia"). They also distinguish whether the plane of focus lies in front of or behind the retina. How the sign of defocus is detected still remains unclear. Cues from chromatic aberration are not important. In an attempt to isolate retinal circuits controlling the development of myopia or hyperopia, young chickens were raised in flickering light of different frequencies (12 and 6 Hz) and duty cycles (4-75%) produced by rotating chopper disks. The effects of flickering light on refractive errors and change in axial growth rates induced by translucent occluders or defocusing lenses were measured by infrared retinoscopy and A-scan ultrasound, respectively. Retinal electrical activity was evaluated by flicker ERG after matching flicker parameters and stimulation brightness at retinal surface. Changes in retinal and vitreal dopamine content caused by flicker in occluded and normal eyes were determined by HPLC-ECD. Strikingly, suppression of myopia occurred for similar flicker parameters, whether induced by translucent occluders ("deprivation") or negative lenses ("defocus"). The degree to which myopia was suppressed was correlated with the duration of flicker dark phase and with the ERG amplitude. In contrast, suppression of hyperopia did not correlate with these parameters. We conclude that two different retinal circuits with different temporal characteristics are involved in the processing of hyperopic defocus/deprivation and of myopic defocus, the first one dependent on flicker ERG amplitude. However, we did not find any correlation between the rate of dopamine release and the degree of inhibition of deprivation myopia in flickering light.

Animals↗
PubMed1997

Measurement of astigmatism by automated infrared photoretinoscopy.

BACKGROUND: There are basically two possibilities to measure cylindrical refractive errors by eccentric photorefraction. The first is to determine the size and the tilt of the light crescent in the subject's pupil. Sphere, cylinder, and axis can be obtained from two pictures with the knife edge at two different orientations by using equations derived by Wesemann et al. In natural eyes, the procedure has limitations because undetermined factors (not considered in the theory) affect size, shape, and intensity of the light crescent. A second possibility is to perform eccentric photorefraction separately in at least three different meridians. METHODS: We have tested the power of the second possibility. The three critical parameters (sphere, cylinder, and axis) were calculated from Euler's law, which describes curvatures (or refractions) at any given angle. The procedure relied only on empirical calibration and not on a theoretical treatment of the optics. Therefore, it was not necessary to identify all factors that determine the path of light. RESULTS: The procedure compared favorably with subjective refractive (first population: students, age 26-30 years, N = 7 (14 eyes); correlations: sphere, r = 0.983; cylinder, r = 0.867; axis, r = 0.935) and with a Canon R-1 Autorefractor (second population: children, age 4-14 years, N = 48 (96 eyes); correlations: sphere, r = 0.955; cylinder, r = 0.600; axis, r = 0.846). CONCLUSIONS: Because it is fast, the technique may be suitable for screening in children. The refractions in the different meridians are performed in real time (25 to 30 Hz) and a single reading (the average from 4-6 refractions in each of the 6 meridians) is obtained in 1-2 s. It constitutes a major improvement to commercially available videorefractors which use measurements only in two meridians in conjunction with the formula by Wesemann et al., although it is still not precise enough to permit spectacle prescription.

Adolescent↗
PubMed1996

Melatonin and deprivation myopia in chickens.

Chicken eyes elongate and become myopic if they are covered with translucent diffusors which degrade the retinal image ('deprivation myopia'). Since it has been shown that dopamine D2/D4 receptors (which mediate inhibition of melatonin synthesis) are also implicated in deprivation myopia, we have studied the role of melatonin in the visual control of eye growth. We have found that (1) diurnal melatonin rhythms and melatonin content in the retina are unchanged during deprivation myopia development despite the breakdown of both diurnal growth rhythms of the eye and diurnal rhythms in retinal dopamine metabolism, (2) diurnal melatonin rhythms and melatonin content in the retina remain unchanged after application of the neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) and presumably also after 6-hydroxydopamine (6-OHDA) application which both have a suppressive effect on deprivation myopia and (3) deprivation myopia was slightly reduced in both eyes after unilateral intravitreal injection of melatonin, despite that deprivation myopia is based on a mechanism intrinsic to the eye. We conclude that melatonin is not involved in the retinal signaling pathway translating visual experience to deprivation myopia.

5,7-Dihydroxytryptamine↗
PubMed1996

Timing of fiber arrival and dennervation of postsynaptic neurons is required for restoration of visual perception by regenerating axons.

Axotomized CNS neurons, whose regenerating axons are guided to their natural target areas in the brain with the aid of peripheral nerve grafts, are capable of establishing synaptic contacts with normal morphological and electrophysiological properties. The present study was undertaken to analyse the functional significance of the reestablished synaptic contacts made by these regenerated retinofugal neurons. Adult rats were trained in a T-maze to obtain a food reward with the aid of visual cues. One of their optic nerves was transected and the regenerating axons were guided into the optic tract with a peripheral nerve graft, in order to enable them to reinnervate the superior colliculus (SC) and thalamus. Postoperative testing of the animals showed a drastic improvement of visual perception. The protocol of dennervation of the SC (prior to, simultaneous or with a delay with respect to fiber arrival) determined the performance of the animals. Rats belonging to the first two groups performed almost as well as they did prior to the transplantation. The functional integrity of the retina was assessed by electroretinography (ERG) which revealed typical rod spectral sensitivity at 380 and 500 nm, but reduced responsiveness to illumination. In accordance, neuroanatomical assessment of the retinal ganglion cells revealed that about 15% of the axotomized neurons contributed to regeneration of axons. These findings show that a restricted population of retinofugal axons of capable of restoring higher visual functions such as light-discrimination-behaviour in the adult rat. Prerequisites for the restoration of visual perception are first the preservation of the intraretinal integrity, and second the temporal matching of fiber arrival and dennervation of postsynaptic neurons.

Animals↗
PubMed1996

A dose related response of 6-OHDA on chicken spectral sensitivity and oscillatory potentials of recording electroretinograms.

OBJECTIVE: To further study the contribution of dopamine system to the local growth controlling mechanisms, a dose related response of 6-hydroxydopamine (6-OHDA) was studied by recording electroretinograms (ERGs). METHODS: The spectral sensitivity of the b-waves and spectral efficiency function of oscillatory potentials (OPs) including OP1, OP2 and OP3 in 4 different doses group were measured. The effect of ascorbate that must be contained in solution of 6-OHDA was first tested with the spectral sensitivity of the b-waves and a correlation between response of the OPs and age, as well as a difference in both own eyes was analyzed for determining an intra-subject and inter-subject variance. RESULTS: An enhanced response was found in OP1, OP2 with doses of 175 micrograms and OP3 with dose of 150 micrograms, and the effect of OPs was mainly in wavelength from 620 nm to 480 nm. No significant increase was found in the spectral sensitivity of the b-waves. The dose 200 micrograms seemed to be toxic to the retina estimated by both spectral sensitivity of the b-waves and spectral efficiency function of the OPs. CONCLUSIONS: The dose 175 micrograms and 150 micrograms of 6-OHDA yielded an effect on the chicken retina.

Adrenergic Agents↗
PubMed1995

A negatively powered lens in the chameleon.

Chameleons are arboral lizards that spot their prey visually and catch it by highly precise shots with their long sticky tongue. They scan their environment by large-amplitude independent saccadic eye movements; once an insect is detected, the head axis is aligned towards the target ('head tracking', both eyes come forward to fixate the insect and, in a phase called 'initial protrusion', the sticky tongue is loaded with tension by a special hyoid apparatus and subsequently shot out of the mouth with great precision. Lenses placed in front of the eyes produce predictable errors in distance estimation, suggesting that chameleons rely on accommodation cues when measuring the distance to their prey, but focusing has never been measured directly. Using a new technique to measure accommodation, we now show that accommodation is precise enough to serve as the major distance cue. Because accurate focusing requires large retinal images, we have tested image magnification and find that it is higher than in any other vertebrate eye scaled to the same size. This is a result of a unique optical design: unlike other vertebrate eyes, the crystalline lens of the chameleon has negative refractive power. Although there is a trend among vertebrates to increase corneal power and to decrease lens power with higher visual acuity, only in the chameleon eye has this tendency led to a reversal of the sign of the power of the lens.

Accommodation, Ocular↗
PubMed1995

Studies on the role of the retinal dopamine/melatonin system in experimental refractive errors in chickens.

We have found that development of both deprivation-induced and lens-induced refractive errors in chickens implicates changes of the diurnal growth rhythms in the eye (Fig. 1). Because the major diurnal oscillator in the eye is expressed by the retinal dopamine/melatonin system, effects of drugs were studied that change retinal dopamine and/or serotonin levels. Vehicle-injected and drug-injected eyes treated with either translucent occluders or lenses were compared to focus on visual growth mechanisms. Retinal biogenic amine levels were measured at the end of each experiment by HPLC with electrochemical detection. For reserpine (which was most extensively studied) electroretinograms were recorded to test retinal function [Fig. 3 (C)] and catecholaminergic and serotonergic retinal neurons were observed by immunohistochemical labelling [Fig. 3(D)]. Deprivation myopia was readily altered by a single intravitreal injection of drugs that affected retinal dopamine or serotonin levels; reserpine which depleted both serotonin and dopamine stores blocked deprivation myopia very efficiently [Fig. 3(A)], whereas 5,7-dihydroxy-tryptamine (5,7-DHT), sulpiride, melatonin and Sch23390 could enhance deprivation myopia (Table 1, Fig. 5). In contrast to other procedures that were previously employed to block deprivation myopia (6-OHDA injections or continuous light) and which had no significant effect on lens-induced refractive errors, reserpine also affected lens-induced changes in eye growth. At lower doses, the effect was selective for negative lenses (Fig. 4). We found that the individual retinal dopamine levels were very variable among individuals but were correlated in both eyes of an animal; a similar variability was previously found with regard to deprivation myopia. To test a hypothesis raised by Li, Schaeffel, Kohler and Zrenner [(1992) Visual Neuroscience, 9, 483-492] that individual dopamine levels might determine the susceptibility to deprivation myopia, refractive errors were correlated with dopamine levels in occluded and untreated eyes of monocularly deprived chickens (Fig. 6). The hypothesis was rejected. Although it has been previously found that the static retinal tissue levels of dopamine are not altered by lens treatment, subtle changes in the ratio of DOPAC to dopamine were detected in the present study. The result indicates that retinal dopamine might be implicated also in lens-induced growth changes. Surprisingly, the changes were in the opposite direction for deprivation and negative lenses although both produce myopia. Currently, there is evidence that deprivation-induced and lens-induced refractive errors in chicks are produced by different mechanisms. However, findings (1), (3) and (5) suggest that there may also be common features. Although it has not yet been resolved how both mechanisms merge to produce the appropriate axial eye growth rates, we propose a scheme (Fig. 7).

5,7-Dihydroxytryptamine↗
PubMed1995

Myopia.

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Accommodation, Ocular↗
PubMed1994

A simple mechanism for emmetropization without cues from accommodation or colour.

We propose and test the simple hypothesis that a chicken eye can emmetropize without cues derived from accommodation or colour just by maximizing retinal image contrast. Using different translucent occluders with known modulation transfer functions we found that deprivation myopia is correlated with the amount of image degradation. Equipped with a long-term integrator, a mechanism minimizing image degradation by changing the axial eye growth rate would therefore be sufficient to place the plane of focus of the eye at the average viewing distance.

Accommodation, Ocular↗
PubMed1994

6-Hydroxy dopamine does not affect lens-induced refractive errors but suppresses deprivation myopia.

Degradation of the retinal image by translucent occluders during postnatal development induces axial myopia in chickens, tree shrews and monkeys. Local visual deprivation produces myopia even in local regions of the eye and neither accommodation nor intact connection between the eye and the brain are necessary. Therefore, it is an important question whether a similar local-retinal pathway translating visual information into growth or stretch signals to the underlying sclera is acting to emmetropize the growing eye. It is not known until now whether occluder deprivation triggers similar eye growth (or scleral stretch) mechanisms that are also responsible for visual guidance of normal refractive development. We here report that, in chickens, 6-hydroxy dopamine suppresses deprivation-induced myopia but has no effect on the magnitude of changes in axial eye elongation that are induced by spectacle lenses. The result suggests that, in chickens with normal accommodation, two pharmacologically different feedback loops may be responsible for deprivation myopia and lens-induced refractive errors.

Animals↗
PubMed1994

Lower-field myopia and astigmatism in amphibians and chickens.

In some afoveate vertebrates refractive state appears to vary over the eye to match the average viewing distances of different areas of the visual field. However, precise measurements are difficult to obtain even in anesthetized animals, because standard methods of refraction are not designed for off-axis measurements and because the presence of astigmatism may fog the results. Therefore we developed a new automated objective technique, automated infrared photoretinoscopy, and measured off-axis refractions in alert chickens and amphibians. We found, in agreement with previous studies, that chickens (Gallus domesticus) are myopic and also have some astigmatism in the lower visual field. Lower-field myopia was, however, variable. It did not match the distance to the ground precisely, but it declined with age (as increased head height would predict). With-the-rule astigmatism was noticed in early posthatching development; it was striking even along the optic axis. The astigmatism lessened with age, as it does in human infants. Frogs (Rana pipiens and Rana temporaria) displayed pronounced myopic astigmatism that was confined to the lower visual field. Salamanders (Salamandra salamandra) and toads (Bufo bufo) showed less variation in refractive state across the visual field, although toads also were myopic in the lower visual field.

Animals↗
PubMed1994

Chick eyes under cycloplegia compensate for spectacle lenses despite six-hydroxy dopamine treatment.

PURPOSE: To test whether eye growth changes produced by spectacle lens wear are mediated by changes in ciliary muscle tonus in chicks. METHODS: Because there is evidence that deprivation myopia is based on a local-retinal mechanism in the eye that probably remains functional after cycloplegia as well as after ciliary ganglion or Edinger-Westphal lesions, none of these treatments provides insight into whether accommodation tonus is also important in the control of axial eye growth. Because 6-hydroxy dopamine (6-OHDA) suppresses deprivation myopia, to isolate growth changes mediated by accommodation the authors injected 6-OHDA and paralyzed accommodation in addition (by corneal application of vecuroniumbromide). To quantify the state of cycloplegia, the abnormal pecking responses of cyclopleged chickens were studied. RESULTS: The authors found that cycloplegia could be maintained for 3 hours daily by corneal application of vecuroniumbromide. To ensure that visual exposure was restricted to the time period of cycloplegia, chickens were transferred to a 3-hour light/21-hour dark cycle. Control experiments showed that emmetropization was still functional under the changed light cycle. Strikingly, even with suppressed local-retinal growth control mechanisms (as indicated by the lack of deprivation myopia in a 6-OHDA injected group of chickens with occluders) and paralysis of accommodation, the eyes compensated for the defocus imposed by spectacles by changing their axial growth rates to be similar to those of eyes with functional accommodation. CONCLUSIONS: The findings show that the ciliary muscle and the activity of the iris sphincter muscle are not involved in emmetropization in chicks. If accommodation mediates the growth effects with lenses, it must happen via another pathway. Based on previous results, the authors propose that either the choroidal nerves from the ciliary ganglion to the choroid are important or that another yet unknown pathway from the Edinger Westphal nucleus to the eye transmits the necessary information.

Accommodation, Ocular↗
PubMed1993

Diurnal growth rhythms in the chicken eye: relation to myopia development and retinal dopamine levels.

1. If the eyes of young chickens are deprived of clear vision by translucent occluders, they develop considerable amounts of axial myopia within days. At the same time, the day time retinal dopamine levels drop by about 30%. Because the retinal dopamine levels of normally sighted chicks also differ diurnally and are low at night, we expected that the rate of axial eye growth might also differ during this time. 2. Unexpectedly, eyes grew in length only during the day (about 0.13 mm/day) and even shrank during the night (about -0.04 mm/night, average net growth +0.09 mm in 24 h). 3. If the eyes were occluded, they grew both during the day and also at night (average net growth: +0.16 mm in 24 h). Therefore, development of deprivation myopia was a result of the lack of growth inhibition at night rather than of excessive growth during the day when the actual deprivation occurred. 4. Suppression of dopaminergic retinal pathways by intravitreal injections of the neurotoxin 6-hydroxy-dopamine (6-OHDA) also suppressed development of deprivation myopia and it restored the growth inhibition at night. With normal visual experience, the drug had no effect on axial eye growth and refractive state. 5. Diurnal growth rhythms of the eyes disappeared under continuous light.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

[Age dependence of pupillary near reflex].

BACKGROUND: This study was performed to gain age correlated normal values for the pupillary near reflex. METHODS: Accommodation and pupillary near reaction were measured by means of simultaneous infrared video retinoscopy and pupillography in 64 healthy volunteers aged between 5 and 55 years. Measurements were done at a reduced, near mesopic, light condition with accommodation to 10, 14, 20 and 33 cm. RESULTS: The pupillary near response varied highly with age: persons younger than 20 years of age showed a significantly smaller pupillary near response as compared to those older than 20 years. In most of the children younger than 10 years the pupil near response was very small (less than 10% constriction) at accommodation distances longer than 10 cm. There was a significant difference between the age groups younger and older than 20 but no statistically significant differences within these age groups. CONCLUSION: A change of the pupillary near reaction takes place around the age of 20. We conclude that this change does not only reflect the aging of the cristalline lens but is due to an age related change of the supranuclear control.

Accommodation, Ocular↗
PubMed1993

Inter-individual variability in the dynamics of natural accommodation in humans: relation to age and refractive errors.

1. To study the relationship between accommodation under natural viewing conditions, age and refractive errors, we have measured time courses of accommodation in thirty-nine human subjects aged 5-49 years using a newly developed technique. The technique is based on infrared photoretinoscopy and involves fully automated on-line image processing of digitized video images of the eyes with a sampling rate of 5.3 Hz. 2. The distance between the subject and the video camera was about 1.3 m. Head movements of the subject required little restriction because the eyes were automatically tracked in the video image by the computer program. All subjects were tested under binocular viewing conditions. 3. Both refraction of the right eye and pupil diameter were measured with a precision of 0.2-0.4 dioptres (D) and 0.1 mm, respectively, and were plotted on-line. The data were subsequently automatically analysed. 4. Automated infrared photoretinoscopy proved to be very convenient and easy to handle in both children and adults. 5. The maximal speed of accommodation for a target at a distance of 5 D declined in the subjects with age (from up to 21.7 D s-1 for accommodation and 32.7 D s-1 for subsequent accommodation to a distant target ('near to far accommodation') in children down to 2-18 D s-1 in adults). There was a striking inter-individual variability in the maximum possible speed of accommodation and near to far accommodation. 6. Speed of accommodation and of near to far accommodation was correlated for each subject. However, in most of the subjects, the process of near to far accommodation was faster than accommodation (P < 0.005, if averaged over all subjects). This correlation was independent of age. 7. The accommodation-induced pupillary constriction (pupillary near response) was absent in children for a 4 D target; even at 10 D, there was no reliable pupillary response. The pupillary near response increased to about 1.6 mm D-1 of accommodation at the age of 47. Since a pupillary near response could still be elicited in presbyopic subjects unable to accommodate, the ratio of pupillary constriction per dioptre of accommodation approached infinity. 8. The magnitude of the pupillary near response was highly variable even among subjects of the same age but was typical for each subject. There was a correlation (P < 0.01) to refractive error: corrected myopes had weaker pupillary near responses than emmetropes or hyperopes.(ABSTRACT TRUNCATED AT 400 WORDS)

Accommodation, Ocular↗