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Biomedical subjects

G Lafond

Publications and source records attributed to G Lafond.

At least 37 records · Page 2Linked to original sources
PubMed1985

Modification of the sublabial approach to midface, nasopharynx, and postnasal tumors.

The midline degloving approach to midfacial and nasosinal tumors is a procedure consisting of elevation of the midfacial soft tissue from a sublabial approach. A modification consisting of a composite flap laterally based on periosteum and soft tissue prevents flattening of the side of the nose. The method has distinct advantages over the transnasal, transpalatal, or lateral rhinotomy approach, giving wide exposure without external scars or disfigurement, and thus is suitable for benign as well as malignant lesions.

Face↗
PubMed1984

Lens opacities appearing during therapy with methoxsalen and long-wavelength ultraviolet radiation.

Therapy with methoxsalen and type A (long-wavelength) ultraviolet radiation (PUVA) has recently become a common method of treating psoriasis and other dermatologic conditions. This treatment could induce cataractous changes in the human lens through a reaction between the psoralen in the lens and either UVA or ambient light. In a 28-month-long prospective study of 78 patients treated with PUVA, small lens opacities appeared in 3 patients, aged 67, 48 and 32 years. The two younger patients had not worn their protective glasses for 24 hours after each treatment, as recommended. Therefore, although it cannot be concluded that PUVA therapy caused these opacities, eye protection during treatment and for 24 hours thereafter should be emphasized to the patients.

Adult↗
PubMed1983

Lesions simulating glomus tumors of the middle ear.

Several non-glomus middle ear masses may mimic glomus tumors. Clinical features alone may not be sufficient to differentiate these lesions. Radiography, particularly angiography is valuable in establishing the diagnosis in most cases. In some, however, diagnosis can only be made on tympanotomy. Four case reports are included in which the diagnosis turned out to be hemangioma, meningioma, high jugular bulb, and cholesterol granuloma. Careful assessment of the clinical, radiological, and operative findings is essential in order to avoid serious complications.

Cholesterol Esters↗
PubMed1983

Electroretinographic evaluation of diabetic retinopathy: sensitivity of amplitude and time of response.

Amplitude and delay of oscillatory potentials were studied in the electroretinograms (ERGs) of patients with diabetes to see which was the more sensitive for evaluating diabetic retinopathy. Loss of amplitude was more sensitive in identifying eyes with early stages of retinopathy, in which funduscopic evidence of retinopathy was still absent, whereas delay of response was more sensitive in grading eyes with later stages. With cases classified according to stage of retinopathy, loss of amplitude and delay of response, a theoretic curve of the electrophysiologic time-course of diabetic retinopathy was drawn. The curve showed that amplitude can distinguish normal from preretinopathic eyes, that with a loss of amplitude of less than 50% no retinopathy will be found ophthalmoscopically, and that with a delay of response greater than 8% the delay will correlate well with the stage of retinopathy.

Diabetic Retinopathy↗
PubMed1983

Effects of intensity of stimulation on signs of acute ischemia in the electroretinogram.

Acute retinal ischemia was induced in adult albino rabbits by clamping the retrobulbar blood vessels or raising the intraocular pressure. As the level of ischemia was increased, the b-wave amplitude and implicit time of response increased. However, the hyperresponsivity and delay of response were inversely related to the intensity of stimulation used, although at levels of ischemia above 70% there was a significant delay of response even with high-intensity stimulation. Thus, if early signs of acute ischemia are to be successfully monitored, low intensities of stimulation must be used.

Acute Disease↗
PubMed1983

Effects of dark adaptation on implicit time in the clinical electroretinogram.

Electroretinograms were recorded from 11 normal human subjects during dark adaptation, either in full dark adaptation or in the presence of light backgrounds of various intensities. Although the amplitude varied considerably depending on the state of dark adaptation, the timing of the response appeared to be much less influenced. For practical purposes, in the absence of a significant background the timing of the response can be considered constant for a given intensity of stimulation, whatever the state of adaptation.

Adult↗
PubMed1983

Hyper-response and delay in the electroretinogram in acute ischemia.

Acute ischemia was induced in 11 adult albino rabbits by clamping the retrobulbar blood vessels and in 5 others by raising the intraocular pressure. Total ischemia was achieved by raising the pressure in the hydraulic remote control system until total collapse of the retinal circulation was observed by indirect ophthalmoscopy and the response on the electroretinogram (ERG) disappeared. The level of ischemia was increased by 15% increments from 25% to 100%, and ERGs were recorded with a constant intensity of stimulation. The amplitude increased up to a peak at 55% ischemia, then decreased to extinction at 100% ischemia. The time of response increased to a maximum at 100% ischemia. The tentative conclusion is drawn that it is important to appreciate that ischemia, and not just degeneration, can cause a delay of the ERG response in humans.

Animals↗
PubMed1982

Electroretinographic evidence of miosis-induced peripheral ring scotoma.

The results of a previous series of experiments in rabbits suggested that under scotopic conditions miosis elevates the electroretinogram (ERG) threshold by casting a peripheral ring scotoma. In the present work similar experiments failed to show any change in the ERG under photopic conditions.

Animals↗
PubMed1980

Decreased ocular light penetration and electroretinographic response time.

The response time is an extremely important element of the clinical electroretinogram (ERG) with respect to the recording's clinical interpretation. It is related to the intensity of stimulation. A series of simple experiments was devised in which light penetration to the retina was impaired. We expected simple and straightforward results, with all situations resulting in a decreased effective intensity of stimulation. It seems, however, that different types of decreased ocular light penetration may have different effects on ERG sensitivity and response time. When light penetration to the retina is decreased by filters the peak time is normal at the threshold (50 microV) and the sensitivity is decreased. Miosis produces quite a different picture:both the peak time at the threshold and the sensitivity are decreased. The results with miosis are similar to those obtained with models of photoreceptor destruction. Vitreous hemorrhages seem to act, according to the amount and diffusion of blood, either as filters or by producing a focal loss of photoreceptor function.

Animals↗
PubMed1980

Electroretinographic alterations in retinal metallosis.

Electroretinographic responses can be modified by pathologic processes in two respects: response time and amplitude (or criterion threshold). Electrophysiologic syndromes can thus be defined. It is of clinical importance to recognize the effects of retinal metallosis on the electroretinographic response in cases of metallic intraocular foreign bodies: the sensitivity decreases while the response time remains normal for the intensity of stimulation. Iron appears to be more toxic than copper, but the secondary fibrosis induced by iron protects the retina more efficiently than that induced by copper.

Animals↗
PubMed1978

Timing of the electroretinogram response and dark adaptation.

The time response of the Electroretinogram (ERG) is an essential part of the examination. Peak time of response increases with dark adaptation and decreases with the intensity of stimulation. When working with constant amplitude during dark adaptation sensitivity increases but the intensity of stimulation decreases. It is essential to clarify the relationship of these two factors for valid interpretation of results. The present work suggests that the state of adaptation or retinal sensitivity affects amplitude, while peak time of the response is modified by the absolute value of the stimulating source whatever the state of adaptation. This observation has been done on rod responses and is valid as long as pigments remain unbleached and able to respond.

Animals↗
PubMed1978

ERG responses of rods and cones during dark adaptation.

We demonstrate the main electrophysiological events during dark adaptation. We correlate simultaneously the separate rod and cone responses, the ERC sensitivity curves, their timing and the biphasic dark adaptation curve.

Animals↗
PubMed1978

Intensity of stimulation and rod and cone response in clinical electroretinography.

We exposed adult Rhesus monkeys who were fully dark adapted to paired flashes of white light which increased in intensity by increments of 0.1 log. units. As intensity increased, the amplitudes of both the cone and rod systems increased while the implicit times decreased so that the responses overlapped. High intensities produce a complex waveform which prevents separation of the rod and cone components or timing of the peaks. On the other hand, low intensities separate the early and late receptor potentials (L.R.P.) of cones and rods well and make it easy to time normal and pathological variations.

Animals↗
PubMed1978

Breeding a pigmented strain of rats with tapetoretinal degeneration.

When Royal College of Surgeons (RCS) rats are bred with Wistar albinos the offspring are deeply pigmented and have normally functioning retinas. From this second generation, various breeding possibilities exist. In the course of successive cross-breedings one can obtain albinos, tan striped (RCS type) or pigmented animals, any one of which may be normal, carrier or affected. The skin pigmentation trait and that of retinal degeneration are independently inherited and follow autosomal recessive Mendelian laws. However normals for ERG studies vary with skin pigmentation. It is suggested that only one group should be chosen and preferably the pigmented variety.

Albinism↗
PubMed1978

Electroretinography in pigmented rats with tapeto-retinal degeneration.

We studied tapeto-retinal degeneration in the offspring of Royal College of Surgeons (RCS) and Wistar albino rats. Normal ERG values vary according to skin pigmentation: thresholds and implicit times are different. We believe the best experimental material is to be found in the affected pigmented offspring. Evolution of the degeneration over more than 9 months has been observed before extinction and the expressivity of the disease varies from one individual to another. This animal model closely resembles the ERG findings observed clinically in certain pigmentary degenerations of the retina.

Albinism↗