Biomedical subjects

Mark Wendt

Publications and source records attributed to Mark Wendt.

3 recordsLinked to original sources

PubMed2006

An improved method for the computation of ligand steric effects based on solid angles.

An improved algorithm has been designed to characterize ligand interactions in organometallic and coordination complexes in terms of the percentage of the metal coordination sphere shielded by a given ligand. The computations for ligand solid angles are performed numerically and employ introduced atomic radii that are larger than covalent but smaller than van der Waals radii. This approach enables facile evaluation of steric congestion in the metal coordination sphere, quantification of unfavorable interligand contacts, and in some cases prediction of the complex composition or ligand coordination on purely geometrical grounds.

Journal Article↗

PubMed2006

Accommodative changes in lens diameter in rhesus monkeys.

PURPOSE: Some debate surrounds the accommodative mechanism in primates, particularly whether the lens equatorial diameter increases or decreases during accommodation. This study has been undertaken to measure the relationship between changes in lens diameter and refraction during accommodation in rhesus monkeys. METHODS: Photorefraction was used to measure accommodation, and goniovideography was used to measure accommodative changes in lens diameter in the iridectomized eyes of two rhesus monkeys. Accommodation was stimulated through the full amplitude available to each eye by stimulation of the Edinger-Westphal nucleus of the brain. Dynamic measurement of refractive changes followed by dynamic measurements of changes in lens diameter for the same stimulus current amplitudes allow the relationship between refraction and lens diameter to be determined. RESULTS: Lens diameter decreased relatively linearly during accommodation by 0.055 mm/diopter (D), resulting in an overall decrease in lens diameter of approximately 7% of the unaccommodated lens diameter for approximately 12 D of accommodation. CONCLUSIONS: The rhesus monkey lens diameter decreases systematically with the refractive change during accommodation in accordance with the Helmholtz accommodative mechanism and in contrast to the accommodative mechanism originally proposed by Tscherning.

Accommodation, Ocular↗

PubMed2006

Accommodative lens refilling in rhesus monkeys.

PURPOSE: Accommodation can be restored to presbyopic human eyes by refilling the capsular bag with a soft polymer. This study was conducted to test whether accommodation, measurable as changes in optical refraction, can be restored with a newly developed refilling polymer in a rhesus monkey model. A specific intra- and postoperative treatment protocol was used to minimize postoperative inflammation and to delay capsular opacification. METHODS: Nine adolescent rhesus monkeys underwent refilling of the lens capsular bag with a polymer. In the first four monkeys (group A) the surgical procedure was followed by two weekly subconjunctival injections of corticosteroids. In a second group of five monkeys (group B) a treatment intended to delay the development of capsular opacification was applied during the surgery, and, in the postoperative period, eye drops and two subconjunctival injections of corticosteroids were applied. Accommodation was stimulated with carbachol iontophoresis or pilocarpine and was measured with a Hartinger refractometer at regular times during a follow-up period of 37 weeks in five monkeys. In one monkey, lens thickness changes were measured with A-scan ultrasound. RESULTS: In group A, refraction measurement was possible in one monkey. In the three other animals in group A, postoperative inflammation and capsular opacification prevented refraction measurements. In group B, the maximum accommodative amplitude of the surgically treated eyes was 6.3 D. In three monkeys the accommodative amplitude decreased to almost 0 D after 37 weeks. In the two other monkeys, the accommodative amplitude remained stable at +/-4 D during the follow-up period. In group B, capsular opacification developed in the postoperative period, but refraction measurements could still be performed during the whole follow-up period of 37 weeks. CONCLUSIONS: A certain level of accommodation can be restored after lens refilling in adolescent rhesus monkeys. During the follow-up period refraction measurements were possible in all five monkeys that underwent the treatment designed to prevent inflammation and capsular opacification.

Accommodation, Ocular↗