Biomedical subjects
C J MacKay
Publications and source records attributed to C J MacKay.
S-cone function in patients with retinitis pigmentosa.
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The human S-cone electroretinogram and its variation among subjects with and without L and M-cone function.
PURPOSE: To examine the S-cone ERG in subjects with and without L and M-cone function. METHODS: Ganzfeld spectral flashes in the presence of strong Ganzfeld adapting fields are used to elicit S-cone ERGs. RESULTS: The S-cone ERG b-wave ranges from 0.2 to 4 mV in amplitude and 38-45 msec in implicit time. There is a progressive decrease in amplitude with age. The response is similar in subjects with or without L and M cone function. CONCLUSION: The S-cone ERG is detectable in subjects of all ages, but intersubject variability limits its diagnostic usefulness. The S-cone ERG is slightly later than but does not appear to be obviously influenced by the L and M-cone ERG.
Supernormal cone electroretinograms in central retinal vein occlusion.
In 12 successive cases of unilateral central retinal vein occlusion (CRVO), the strongly light-adapted cone electroretinogram (both a- and b-wave) was always slower and larger (supernormal) to long-wave stimuli compared with that of the unaffected eye. This supernormality became less as the level of light adaptation decreased; in the dark-adapted state, long-wave stimuli produced subnormal responses from the affected eye in all but two subjects. This supernormality was not caused by ineffectiveness of the adapting light related to a reduced cone quantal catch because it occurred in the dark. At any one state of adaptation, the supernormality increased with the wavelength of stimulation, paralleling the relative absorption ratio of long-middle wavelength-sensitive cones. This suggests that cones, especially long wavelength-sensitive cones, are less able to reduce their responsiveness to light with increasing levels of light adaptation in a retina affected by CRVO.
Retinitis pigmentosa misdiagnosed as complicated migraine.
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Electroretinographic responses of the short-wavelength-sensitive cones.
An electroretinographic response of the human short wavelength (S) cone system can be distinguished from that of the longer wavelength (L or M) cone system by using ganzfeld short-wavelength stimulation at relatively high levels of retinal adaptation. The S cone response has both an a- and b-wave component in its ERG, both of which are slower than those of the L or M cone response at the same level of retinal adaptation. Proof that this is the S cone response is obtained by action spectra and by examination of a sex-linked achromat who is known to have only S cone and rod vision. This approach allows the simultaneous and rapid assessment of both the S and the L or M cone systems in the human retina using conventional electroretinogram (ERG) equipment, ganzfeld blue flashes on a white background, and computer averaging.
Color vision defects in retinal disease.
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Light adaptation of the electroretinogram. Diminished in retinitis pigmentosa.
The cone electroretinogram has been examined at different levels of ganzfeld adaptation in normals and subjects with retinitis pigmentosa (RP). As light adaptation increases, the amplitude and time course (measured as b-wave implicit time) of the cone ERG decrease in both normal and RP subjects. The same level of light adaptation, however, decreases the amplitude and the implicit time more in normal than in RP subjects. The ineffectiveness of light for adapting the ERG of RP subjects is most easily explained by assuming that RP cones absorb less light than normal cones. By comparing these parameters between normal and RP subjects at different levels of light adaptation, it is possible to estimate this ineffectiveness of cone absorption in RP subjects. The results imply that RP cones can transduce and adapt but fail to absorb light as effectively as normal cones. The quantitative relationship between cone b-wave implicit time and retinal illumination provides a unique method for examining cone function as well for standardizing ganzfeld backgrounds in ERG laboratories.
Growth in amplitude of the human cone electroretinogram with light adaptation.
The human cone electroretinogram gradually increases in amplitude an average of 75% (range 23 to 157%) during light adaptation, over a period of approximately 20 min. This increase involves both the a- and b-wave components of this response, and both waves follow a similar time course, implying that the photoreceptors themselves are responsible for the effect. The phenomenon occurs with suprathreshold, but not with threshold, levels of stimulation, and the stronger the test light, the greater the effect. An increase in the intensity of the adapting light shortens the time course of the ERG response, measured as b-wave implicit time, but this occurs almost immediately, and the implicit time then remains constant during the slow increase in response amplitude. The stronger the background adapting light, the smaller is the ERG amplitude, but the percentage growth (or rate of recovery) is unchanged. This slow increase in amplitude is thought to reflect the redepolarization of the cones, after their initial hyperpolarization to an adapting field. It does not reflect the d.c. potential of the eye (the EOG). It is essential to control this phenomenon in any studies of the human cone ERG, in order to minimize variability.
Retinal degeneration with nanophthalmos, cystic macular degeneration, and angle closure glaucoma. A new recessive syndrome.
Seven related patients had a progressive pigmentary retinal degeneration, characterized by nyctalopia, visual field restriction, and cystic macular degeneration in younger patients and a macula of nonspecific atrophic appearance in older patients. In addition, each patient had high hyperopia (+9.50 to +16.00) and nanophthalmos (axial lengths, less than 20 mm), with diffuse choroidal thickening on ultrasound. Younger patients had slitlike anterior chamber angles; older patients developed progressive synechial angle closure and eventual glaucoma. Chromosomes were normal. On electroretinographic testing, younger patients had absent rod signals, with normal cone wave form and near-normal b-wave amplitudes but markedly delayed cone b-wave implicit times; older patients had severely diminished or extinguished electroretinograms. This family appears to represent a newly recognized autosomal-recessive syndrome.
Metastatic patterns of retinoblastoma.
Of 23 cases of metastatic retinoblastoma treated between 1922 and 1979, seven had metastases limited to the cranial vault and 13 had cranial metastases plus distant metastases. Globe pathology showed invasion of the optic nerve and/or the choroid in all but two patients, but was not predictive of the metastatic pattern. Initial signs of metastases were neurologic impairment and an orbital or body mass; first symptoms were anorexia or weight loss, vomiting, and headache. Most cases occurred by 3 years of age. Death occurred within 5.8 months on the average, despite therapy. Useful tests for determining the extent of disease were bone marrow aspiration, lumbar puncture, skull films, EEG, and brain scan. Computed tomographic scans of the head, bone scans, bone marrow aspiration, automated blood chemistry analysis, and lumbar puncture with immediate ethyl alcohol processing should prove to be useful to detect metastatic disease.
Cone dystrophy, nyctalopia, and supernormal rod responses. A new retinal degeneration.
An unusual retinal degeneration considered to be inherited as an autosomal recessive trait occurred in two of four children in a Hispanic family. The abnormality causes a progressive and generalized loss of cone vision, including decreased acuity, decreased color vision, central scotomas to small test objects, photo-phobia, and a profound diminution of the cone-mediated electroretinographic (ERG) pattern. A loss of the foveal reflex and an increased granularity of the macula is seen funduscopically. In addition, there is a most unusual alteration of the rod system detectable in the rod-mediated ERG pattern. This rod response is supernormal in amplitude (greater than 1,000 microV, extrapolated), delayed in time course, and insensitive to dim stimuli, ie, the function relating response to light intensity has been drastically altered. The insensitivity to dim stimuli is accompanied by a mild nyctalopia. Some of these abnormalities could be caused by a defect in the retinal enzyme, cyclic nucleotide phosphodiesterase.
The effects of toluene and alcohol on psychomotor performance.
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Sicca complex and cholangiostatic jaundice in two members of a family probably caused by thiabendazole.
An entire family (father, mother, and three daughters) were given thiabendazole because one of the children had acquired pinworm infestation. The mother and one daughter (non-infected) developed a sicca complex (keratoconjunctivitis sicca and xerostomia) accompanied by cholangiostatic jaundice. Sjögren's syndrome is an autoimmune disease and presents many immune mechanism aberrancies. An association between autoimmune liver disease and sicca complex has been reported. Labeled mitochondrial antibodies bound to the parotid duct have been noted in patients with autoimmune cholangiostatic jaundice and such antibodies may be similar to the antibody against salivary duct found in Sjögren's syndrome. It is suggested that in these two patients, thiabendazole may have acted as a hapten and by binding to the body protein induced the production of autoantibodies which may have acted against the biliary epithelium, the salivary duct epithelium, and the lacrimal gland ducts.
Sicca complex and cholestatic jaundice in two members of a family caused by thiabendazole.
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