Biomedical subjects
Publications and source records attributed to S M Archer.
Intravitreal injections of botulinum A toxin in two doses, 1.25 and 25 units, were performed in two rabbit eyes. The fellow eyes were injected with an equal volume of saline to serve as controls. The visual evoked potential was unchanged at one and two weeks post-injection when compared to pre-injection recordings in both botulinum and saline injected eyes.
We used electro-oculographic recordings of eye movement responses to a dynamic random-dot stereogram to assess stereopsis in normal infants and in infants with congenital esotropia. Normal infants showed an onset of stereopsis at about 4 months of age, consistent with previous reports. Four of nine infants with congenital esotropia demonstrated stereopsis when tested within two weeks of surgical alignment. No patient with congenital esotropia showed evidence of stereopsis when tested at a postoperative interval of more than two weeks.
Random-dot stereograms were found to be capable of producing fusional vergence amplitudes in the absence of monocular contours. These vergence amplitudes are not an artefact of monocular contours provided by the target borders or test instrument and are comparable in range to vergence amplitudes measured clinically with second degree fusion targets in an amblyoscope. We conclude that diplopia of monocularly recognisable contours is not necessary for producing fusional vergence amplitudes.
The effect was examined of ethanol extracts of normal sera (NS), cancer patients' sera (CPS), cirrhosis patients' sera (CirPS), and umbilical cord sera (UCS) on cortisol metabolism by lymphocytes (CML). All the ethanol extracts of these sera showed an inhibitory effect on CML. The most significant inhibition was obtained with CPS and CirPS followed by UCS. A significant inhibition of NS was obtained after doubling their equivalent volume.
The role of action potentials in the development of proper synaptic connections in the mammalian CNS was studied in the kitten retinogeniculate pathway. Our basic finding is that there is improper segregation of retinal inputs onto LGN cells after prolonged retinal action-potential blockade. Retinal ganglion cell firing was silenced from birth by repeated monocular injections of TTX. The resulting ganglion cell connections in the LGN were studied electrophysiologically after the action-potential blockade was ended. Most cells in the deprived LGN layers received excitatory input from both ON-center and OFF-center type ganglion cells, whereas LGN cells normally receive inputs only from ON-center or OFF-center ganglion cells, but not from both types. Improper segregation of ON and OFF inputs has never been reported after other types of visual deprivation that do not block ganglion cell activity. Control experiments showed that receptive fields in the nondeprived LGN layers were normal, that ganglion cell responses remained normal, and that there was no obvious ganglion cell loss. We also showed that individual LGN cells with ON and OFF excitatory inputs were not present in normal neonatal kittens. Two other types of improper input segregation in response to action-potential blockade were also found in the deprived LGN layers. (1) A greater than normal number of LGN cells received both X- and Y-type ganglion cell input. (2) Almost half of the cells at LGN layer borders were excited binocularly. Recovery of LGN normality was rapid and complete after blockade that lasted for only 3 weeks from birth, but little recovery was seen after about 11 weeks of blockade. The susceptibility to action-potential blockade decreased during the first 3 postnatal weeks. These findings may result from axon-terminal sprouting or from the failure of axon terminals to retract. The results are consistent with the idea that normally synchronous activity of neighboring ganglion cells of like center-type may be used in the refinement of retinogeniculate synaptic connections.
In an attempt to learn whether esotropia is present at birth or develops later in infancy, we observed 1,219 alert infants in a normal newborn nursery at a city hospital. Of these, 593 (48.6%) had orthotropic findings; 398 (32.7%) had exotropia, 40 (3.2%) had esotropia (intermittent in 17 with 14 varying between esotropia and exotropia and nine with a variable esotropia), and 188 (15.4%) were not sufficiently alert to permit classification. No infant displayed typical signs of congenital esotropia. We concluded that congenital-infantile esotropia is not connatal but rather develops in the first few weeks or months after birth.
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A class of arabinosyladenine (araA)-resistant mutants of baby hamster kidney (BHK 21/C13) cells exhibits multiple phenotypes: resistance to araA and deoxyadenosine, extreme sensitivity to adenosine (Ado) and varying degrees of deficiency in adenosine kinase (AK) activity. One of these Ados/araAr strains, ara-S10d, was isolated without mutagenesis and was shown to possess about 59% level of the wild-type AK activity. The AK from ara-S10d had an altered Km and pH optimum and was stimulated by K+ cations. A number of Ados to Ador revertants were isolated from ara-S10d, and in all of the 7 examined, the AK activity was reduced to a nondetectable level. The altered kinetic parameters of the AK enzyme in ara-S10d cells suggest a mutation of the AK gene that leads to the synthesis of an altered enzyme. The loss of AK activity in the Ador revertants suggests an association of the enhanced Ado sensitivity to the AK mutation.
Action potentials were silenced in one eye of neonatal kittens by repeated intraocular injections of tetrodotoxin for 5 to 8 weeks. After tetrodotoxin blockade was allowed to wear off, receptive field properties of individual relay cells in the lateral geniculate nucleus were examined. The many ON-OFF and binocular fields found in the layers that receive input from the treated eye suggest that these cells had extremely abnormal retino-geniculate synaptic connections. These effects were different in kind from those seen after deprivation rearing that does not silence action potentials. Lack of action potential activity was concluded to lead to abnormal development in the central nervous system.
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Ocular alignment was examined in a large population of normal infants to determine the prevalence of various motility findings at ages ranging from birth to 10 months. Exodeviations were frequently seen up to the age of 6 months. Esodeviations were occasionally seen in infants who did not go on to develop congenital esotropia, but not after 2 months of age. It is unclear whether precursors of pathologic strabismus, such as congenital esotropia, can be distinguished from these transient ocular deviations seen in normal infants. However, any strabismus persisting after the ages listed above should be considered abnormal and receive ophthalmologic evaluation.
The feasibility of a practical preferential looking technique, similar to Teller acuity cards, was investigated for the assessment of vernier acuity in preverbal infants. Forty-two infants ages 1 to 13 months were tested with cards having vernier offsets of 2 to 64 minutes of arc and spatial frequencies of 0.25 to 2.0 cycles per degree. All infants showed a robust preferential looking response to the largest vernier offsets. Vernier thresholds decreased with age from 64 minutes of arc at 1 month to 4 minutes of arc at 13 months. Smaller vernier offsets were more readily detectable when embedded in higher spatial frequency gratings. Vernier acuity can be assessed in preverbal infants using a preferential looking technique similar to that employed with the Teller acuity cards. Vernier acuity is known to be more sensitive to amblyopia than grating acuity; therefore, this technique may prove useful in the assessment of amblyopia.
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A retrospective study was performed on 18 consecutive patients with A-pattern esotropia and no apparent oblique muscle dysfunction, mechanical restriction, paresis, or previous muscle surgery. All patients underwent graded bilateral medial rectus recession for their esotropia with simultaneous vertical upshift to treat the A-pattern. The quantitative relationship between amount of upshift, amount of A-pattern correction, preoperative A-pattern, and preoperative esotropia was examined. We found that the amount of A-pattern correction was closely correlated with the size of the A-pattern preoperatively (r = 0.83), independent of amount of upshift. While the change in A-pattern did correlate with the amount of the upshift (r = 0.60), it was not a significant independent predictor of the surgical response. The amount of recession had little influence on the effectiveness of the procedure in correcting the vertical incomitance, and the transposition did not seem to affect the correction of the basic esotropia, adversely. We conclude that medial rectus recession with vertical upshift of the muscle insertions is an effective procedure for correcting the vertical incomitance in A-pattern esotropia, and that the amount of A-pattern correction achieved is determined primarily by the size of the preoperative A-pattern and not the amount of upshift.
We used an animal model of restrictive strabismus analogous to the fat adherence syndrome in humans to test the efficacy of topical intraoperative mitomycin-C (MMC) in preventing the development of restrictive scar tissue. A cicatricial adhesion was created between the inferior rectus muscle and the inferior orbital rim of each eye in eight rabbits, and passive forced ductions were quantitatively measured with a spring scale. Eight eyes were treated intraoperatively with topical MMC 0.5 mg/mL, the other eight with sterile water. Passive forced ductions were again measured 4 weeks postoperatively and representative orbits were exenterated for histopathologic examination. Significant restriction of motility was produced in six of the eight control eyes. Though prophylactic treatment with MMC may have been beneficial in some cases, on average, the restriction developing in these eyes did not significantly differ from that in the control eyes. In addition, longer exposure times to MMC led to marked orbital inflammation and severe restriction of ocular motility. Finally, histopathologic evaluation of the orbits of the MMC-treated eyes revealed marked fibrosis of perimuscular connective tissues. Although MMC may have a role in the management of fat adherence syndrome, further study is needed to establish safe and efficacious methods of delivery.