Fractal analysis of eye movements during reading.

We present a new method for the analysis of reading eye movements based on the methods of nonlinear dynamics. In this preliminary study, the eye movements of normal and abnormal readers were analyzed for evidence of chaotic, nonlinear dynamical behavior. Both power spectral density analysis and fractal dimension determination showed evidence of nonlinearity as manifest in chaotic behavior. The computed fractal dimension of the system's presumed attractor seemed directly related to qualitative assessment of reading ability. Representative subjects did not differ in a similar analysis of pursuit movements. Although fractal analysis did not distinguish unconditionally between normal and abnormal reading in this preliminary study, it nevertheless offers a promising hitherto unused approach to the analysis of eye movements and the modeling of oculomotor behavior.

Detection of ophthalmoscopically occult maculopathy by focal electroretinography.

We performed focal electroretinography (FERG) in 10 patients with reduced vision of unknown cause. No patient gave a family history of uncorrectably reduced vision, and none had taken any drug known to damage the retina. Visual acuity claims ranged from 20/40 to finger counting. Color discrimination was reduced in all but one patient. Visual field sensitivity was reduced nonspecifically in five of the six patients who could perform perimetry reliably. Ophthalmoscopy showed no pertinent abnormality in four of 10 patients, mildly reduced foveal reflex in two of 10, arteriolar narrowing in two of 10, foveal pigment disturbance in one of 10, and preretinal gliosis in one of 10. Flash visual evoked potential (VEP) testing showed no abnormality in seven of 7 patients. The pattern VEP was reduced or delayed in five of 5 patients, only one of whom showed the expected amplitude loss with decreasing check size. Five patients completed full-field electroretinography, six patients completed fluorescein angiography, and none showed pertinent abnormality on either test. FERG was performed in both eyes of seven patients and in one eye of three others. Signals were non-recordable from four eyes, abnormal in nine, equivocal in three, and normal in one. The severity of FERG abnormality did not correlate with the severity of acuity loss. FERG abnormalities were found in fourteen of 17 eyes of 10 patients with vision loss out of proportion to clinical findings. In these patients only one of 5 pattern VEP tests, none of 5 full-field ERGs, and none of 7 fluorescein angiograms suggested correspondingly severe maculopathy. The FERG results in these cases mitigated suspicions of nonorganic vision loss and permitted speedier referral to retinal disease and low vision specialists.

MRI in Lhermitte-Duclos disease.

Lhermitte-Duclos disease (LDD) is a disorder sometimes referred to as a dysplastic gangliocytoma of the cerebellum. This is a focally indolent growth of the cerebellar cortex in which the folia enlarge due to a profusion of dysplastic cortical neurons and a thickening of the molecular layer. Loss of Purkinje cells and thinning of medullary white matter results. The enlarged folia lose their secondary foldings and asymmetrically expand the cerebellar hemisphere. These morphologic features produce a characteristic pattern on some CTs and all MRIs, affording an opportunity for a preoperative diagnosis. MRI of a pathologic specimen suggested that the abnormal T1 and T2 signals corresponded to the atrophic folial white matter, thickened granule cell layer, and outer molecular layer. Because of inherent Hounsfield artifact in posterior fossa with CT, MRI is the imaging modality of choice, with better visualized striated pattern. The uniqueness of these imaging features obviates the need for an obligatory biopsy for asymptomatic patients and either permits more definitive planning for surgical decompression or, in restricted lesions, guides more assuredly complete excision of the cerebellar mass.

Visual system electrodiagnosis in neurologic disease of childhood.

Electrodiagnostic examination of the visual system includes visual evoked potentials and electroretinography. These tests can be applied to all ages. Pitfalls in the clinical ophthalmologic examination of children, such as optic nerve pallor and pigmentary retinopathy, can be clarified by these tests. Investigation of neurodegenerative disease may be directed to the most likely defect by results of visual evoked potential testing and electroretinography. The child who is unable to meaningfully communicate sensory experience can be objectively evaluated by these studies. Familiarity with the applications and limitations of these tests will allow the examiner to choose the appropriate setting and time to apply each of them.

Conjugacy of spontaneous blinks in man: eyelid kinematics exhibit bilateral symmetry.

PURPOSE: To provide a quantitative description of the conjugacy of human eyelid movements during spontaneous blinks. METHODS: Eyelid movements occurring during spontaneous blinks were recorded bilaterally using a modification of the electromagnetic search coil technique. In off-line analyses, covariation of amplitude, peak velocity, and duration of blink down phases were determined for the two eyelids. Interocular differences in the timing of blink onset and offset, and time to peak velocity, also were evaluated. RESULTS: Human blink motor control systems act to link tightly the spatial and temporal characteristics of movements of the two eyelids. Data show that human spontaneous blinks are conjugate. Analysis of interocular covariation of blink amplitude, peak velocity, and duration yielded linear functions with high correlation coefficients. Interocular comparison of eyelid movement durations during blinks showed a particularly high correlation. There were negligible interocular differences in blink down-phase onset time, termination time, and time to peak velocity. A small percentage of blinks exhibited interocular differences in amplitude and peak velocity of > 20%; however, even in these cases, blink duration remained tightly linked. CONCLUSION: Spatial and temporal properties of eyelid movements occurring during spontaneous blinks are conjugate. These data support the hypothesis that a bilateral gating mechanism regulates blink duration. Elements downstream from the gate may differentially and unilaterally alter blink amplitude and peak velocity, but the duration of blinks remains time-locked for the two eyelids.

Ocular motor abnormalities from head trauma.

Head injuries cause the hospitalization of 200-300 persons per 100,000 population per year. Ophthalmologists provide diagnostic and therapeutic care to those trauma victims with damage to the globe, optic nerve, orbit, and ocular motor system. Eye movements can be affected by damage at any level of the central nervous system or peripheral motor unit. Comprehensive ocular motor assessment of the trauma patient can substantially contribute to the understanding of the patient's injury, recovery, and rehabilitation. This review examines all aspects of head and face trauma that can lead to ocular motility disturbances.

The electroretinogram in neurologic practice.

The ERG can be helpful to the neurologist who must evaluate patients with known or suspected retinal disease. The test is most useful in detecting (or excluding) outer retinal disease, especially in presymptomatic, very young, or mentally enfeebled patients. It can also help in interpreting the meaning of an abnormal VEP.