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N Simha

Publications and source records attributed to N Simha.

7 recordsLinked to original sources
PubMed1991

Results of 87 cases of intraocular lens implantation at the front of the whole capsular bag.

To prevent or delay Elschnig pearl formation, we performed an unusual surgical technique on 87 patients: intraocular lens implantation at the front of the whole capsular bag. We tried to obtain tight adhesion between the anterior and posterior capsules so the lens epithelial cells could not proliferate and form Elschnig pearls. In fact, the patients exhibited no Elschnig pearls or Soemmering's ring, but developed large anterior capsular folds and a multilayer cell membrane between both capsules after two (three cases), six (19 cases), and 12 months (14 cases). This led to a decrease in visual acuity, and a Nd:YAG laser anterior and posterior capsulotomy was required in most cases (83%). Several months later, these eyes developed enormous Elschnig pearls emanating centrifugally from the laser opening, strongly suggesting that lens epithelial cells require aqueous humor for Elschnig pearl transformation. Since it is not yet possible to obtain perfect adhesion between anterior and posterior capsules, our results confirm the need to remove the anterior capsule after extracapsular cataract extraction.

Adult↗
PubMed1988

Effects of electrolytic lesions of the superior olivary complex and trapezoid body on brainstem auditory-evoked potentials in the guinea pig. I. Vertex-tragus recordings.

Brainstem auditory-evoked potentials (BAEP) were recorded between vertex and tragus in 22 guinea pigs, after destruction of the contralateral ear in order to produce monaural stimulation. Stimuli employed were 100 dB SPL clicks and tone bursts. Normative recordings showed five positive peaks, P1-P5 and four negative peaks, N1-N4. Electrolytic lesions were then made to the superior olivary complex (SOC) ipsilateral to the stimulation (6 animals), contralateral to the stimulation (8 animals), and trapezoid body (TB) (8 animals). In each group a statistical analysis of the results (amplitudes and latencies) was made (paired t test). After lesions to the ipsilateral SOC, there was an increase in the amplitude of P1 and a decrease in P3. After lesions to the contralateral SOC, there was a larger decrease in P3, which disappeared in 2 guinea pigs which had a large lesion involving many TB fibers. After TB lesions, there was a decrease in the P2-N2 composite wave, disappearance of P3, a decrease in P4, and an increase in the latency of P1 and P1-P2 and P2-P4 intervals. After ipsilateral SOC lesions, which certainly involved the uncrossed olivocochlear efferent tract, the increase in P1 suggested a disinhibition of the efferent fibers. The large decrease or the loss of P3 after TB lesions and SOC lesions involving many TB fibers suggested that P3 could be generated by the contralateral part of the TB fibers, in the vicinity of the contralateral SOC. These data are in agreement with the predominance of fiber tracts in the generation of BAEP.

Animals↗
PubMed1988

Effects of electrolytic lesions of the superior olivary complex and trapezoid body on brainstem auditory-evoked potentials in the guinea pig. II. Three-channel Lissajous' trajectory analysis.

Brainstem auditory-evoked potentials (BAEP) were studied both with vertex (positive) - tragus (negative) derivation and three-channel Lissajous' trajectory (3-CLT) planar analysis in guinea pigs (GP) after destruction of the ipsilateral superior olivary complex (SOC) (6 GP), contralateral SOC (8 GP) referred to the stimulation side, and trapezoid body (TB) in the sagittal line (8 GP). The size of the lesion was evaluated on histological examination. The right ear was locally destroyed with aminoside instillation. The left ear was stimulated with unfiltered clicks and tone bursts of different frequencies at 100 dB SPL. Three questions were the basis of this study: (i) What are the effects of brainstem lesions on 3-CLT? (ii) Is there a relationship between planar segments and underlying sources? (iii) What is the generator of planar segment C (P3) in GP? 3-CLT analysis was made on plane A (corresponding to P1 on a vertex-tragus channel), plane B (N1-P2) and plane C (P3.) Plane C disappeared after TB lesions and remained after ipsi- and contralateral SOC destructions. However, plane C disappeared after extensive lesions to the contralateral SOC affecting the TB. Planes A and B were always observed whatever the lesion, with sometimes a modification of their orientation. A localized brainstem lesion induced a local modification of the three-dimensional trajectory. These data are in agreement with the assumption that some planes of 3-CLT reflect the activity of underlying generators. However, the loop which contains the planar segment is a better indicator of the global electrical activity of the source. Plane C (P3) would have a contralateral source which is probably not the SOC but the afferent curved fibers of the TB close to the contralateral SOC.

Animals↗