Biomedical subjects

A Neetens

Publications and source records attributed to A Neetens.

At least 19 recordsLinked to original sources

PubMed1992

Foveal flicker-fusion frequencies: a simple, new apparatus (4F).

While spatial resolution may be easily assessed with contrast-sensitivity frequency (CSF) data, determination of foveal flicker-fusion frequency (4F) is a simple method of providing the ophthalmic practitioner with accurate information about temporal resolution. The authors describe a simple apparatus that controls luminance, light intensity, light intervals, stimulus size, homogeneity of background illumination, and binocular gaze, especially when using two wavelengths, allowing an increased number of applications with reliable and comparable results. It may prove to be a useful tool for screening, clinical and subclinical assessment, and for evaluating visual acuity, also during follow-up.

Adolescent↗

PubMed1992

[Optic neuritis in non-Hodgkin's lymphoma].

Optic neuropathy during non-Hodgkin lymphoma is a late central nervous system complication of unfavourable prognosis. It appears especially with involvement of the bone marrow. A normal cerebrospinal fluid, lack of any beneficial effect of the chemo-corticotherapy and absence of papilledema suggest paraneoplastic, or iatrogenic (radio and (or) chemotherapeutic) neuropathy with conclusive histopathological proof only at autopsy. More frequently, cerebrospinal fluid containing malignant cells, papilledema and a beneficial effect of the chemocortico-therapy suggests malignant infiltration of the optic nerve as occurs in our case. Optic neuropathy during non-Hodgkin lymphoma may exceptionally precede the systemic disease by several years. Early oculomotor involvement suggests meningeal malignant infiltration as found in meningeal carcinomatosis.

Evoked Potentials, Visual↗

PubMed1992

Recent pathogenic concepts of primary open angle glaucoma and soft glaucoma (POAG).

Loss of mainly field in POAG is due to Schnabel's cavernous atrophy of the axons at their scleral passage, built up by aligned stacks of glial collagen (IV and I) tissue plates, which contain capillaries. Organisation, size and structural surroundings encircle isolated or grouped axons not evenly distributed. The stereotype pattern of fieldloss linked to a characteristic optic nerve lesion suggests POAG be considered a N.O. disease as raised IOP may be only one of the risk factors. Are cavernous atrophy (loss of field) and the trabecular spaces narrowing (rise of IOP) both the result of the same pathogenic mechanism acting on the collagen fiber (IV and I) of the scleral coat, resp. lamina cribrosa (posterior segment) and trabecular meshwork (anterior segment)? If so, IOP-rise only worsens the condition as will do a hemodynamic energy crisis at the level of the axons. Interactive dominance at any of both levels may explain unexpected discrepancies between IOP and fieldloss. Considering "to treat or not to treat" accurate field loss predictability testing, urgent research topic, are discussed.

Anterior Chamber↗

PubMed1991

Photon correlation spectroscopy of light scattered by eye lenses in in vivo conditions.

The application of photon correlation spectroscopy on mammalian eye lenses in vivo is revisited. It is shown that the use of a short wavelength laser type and a logarithmic correlator improves the signal-to-noise ratio to such an extent that shorter measurement times are possible without impairing the information content of the correlation function. Experimental correlation functions obtained in vivo on a rabbit eye lens, are analyzed with several techniques. The histogram approach is most successful for the determination of the distribution function of relaxation processes in the correlation function and proposes four different populations of components in the lens. This result is comparable to that from in vitro measurements on highly concentrated solutions of alpha-crystallins and of fiber cell cytoplasm, the former proteins being the main scattering components both in vivo and in vitro in the eye lens system. Our results indicate that the application of photon correlation spectroscopy on eye lenses in vivo offers new perspectives to use this technique as a fast, noninvasive tool to study relaxation phenomena in normal and cataractous lenses. The sensitivity of the method allows it to be used as an important analytical technique in the study of prevention and treatment of cataract.

Absorptiometry, Photon↗

PubMed1991

[Macular neuroretinopathy].

The isolated presumably inflammatory involvement mostly acute and unilateral of the photoreceptor layer of the retina, in the macular region, has been described as clinical entity: macular neuroretinopathy. Three cases are presented. Its evolution, ophthalmoscopic appearance (cuneiform tear drop), negative angiofluorography, normal electroophthalmography, differentiates neuroretinopathy from cystoid edema (CME), retinoschisis, acute macular multifocal placoid pigmentepitheliopathy, pigmentepitheliitis, and "Multiple evanescent white dot syndrome" (MEWDS). Visual acuity is mildly decreased but its recovery is poor even after a long period of time. Secondarily the pigmentepithelium may be involved. MEWDS is characterised by a primary fruste involvement of the pigmentepithelial layer simultaneously with a secondary involvement of the choriocapillaris, and possibly photoreceptor layer.

Adult↗

PubMed1979

Pattern and flash visual evoked responses in multiple sclerosis.

In multiple sclerosis (MS), increase of delay may be important, but the earlier change is the behavior of the wave shape; amplitude is always lower even in MS patients without visual subjective symptomatology, provided not only flash but also pattern stimulation is performed. Normal amplitude with pattern stimulation does not necessarily mean normal with flash. Combining both stimulation methods, we obtained lowering of amplitude and change of wave shape in 100% of cases while latency was increased in only 77% of cases. Sectorial ischemic neuropathy, and open angle glaucoma patients show the same findings, which emphasizes that the method is not specific for demyelinating diseases, nor selective for papillomacular bundle involvement, but that VER, considering only its first components, reflects axonal damage somewhere in the visual pathway. Flash and pattern VER might be even more pathognomonic in MS than oligoclonal gammaglobulin fractionation on agar, positive in 75% of cases. It is suggested that subclinical MS cases should be submitted to full electro-ophthalmographic investigation.

Form Perception↗

PubMed1979

The superior oblique: a challenging extraocular muscle.

Isolated paralysis of one or both superior oblique muscles in a consecutive series of 43 patients was found to occur most often by indirect injury to the skull. The etiology in the group of spontaneous cases was mostly vascular. With rare exceptions the latter recovered spontaneously. Those with traumatic palsy may be due to "contrecoup" trauma at the decussation of the nerves or by decompensation of the cerebral fusional mechanism, with dissociation of the images of the two eyes and subsequent vertical deviation. The traumatic cases never recover spontaneously and recession or myectomy of the ipsilateral inferior oblique with or without recession of the contralateral inferior rectus is recommended but only in cases of more than 8 diopters squint, and in cases which do not adapt themselves by minor head-tilting.

Adult↗

PubMed1979

Pattern and flash evoked responses in disseminated and selective optic pathway damage.

In multiple sclerosis (MS), an increase in delay in visual evoked responses (VER) may be important, but an earlier change is the behaviour of the wave-shape; amplitude is always lower even in MS patients without subjective visual symptoms, provided not only flash but also pattern stimulation is used. Normal amplitude with pattern stimulation does not necessarily mean normal amplitude with flash stimulation. Combining both stimulation methods, we found lowering of amplitude and change of wave-shape in 100 per cent of cases while latency was increased in only 77 per cent. Flash and pattern VER might be even more pathognomonic in MS than oligoclonal gammaglobulin fractionation on agar, which is positive in 75 per cent of cases. We recommend that subclinical cases of MS should be submitted to full electro-oculographic investigation. Patients with sectoral ischaemic neuropathy and open angle glaucoma (OAG) show the same findings; this emphasizes that the method is not specific for demyelinating diseases, nor selective for papillo-macular bundle involvement, but that VER, considering only its first components, reflects axonal damage somewhere in the visual pathway.

Evoked Potentials↗

PubMed1979