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Biomedical subjects

R B Park

Publications and source records attributed to R B Park.

At least 19 recordsLinked to original sources
PubMed1987

Visual aberrations caused by optic components of posterior chamber intraocular lenses.

A 58-year-old airline pilot had cataract surgery with implantation of a posterior chamber intraocular lens with four positioning holes around the optic edge. During periods of maximum pupil dilation, such as at night, visual aberrations including glare, monocular diplopia, and haloes occurred and he was unable to work in his occupation. The symptoms were severe enough that lens exchange was required, and a posterior chamber lens with no positioning holes was successfully implanted. The symptoms immediately subsided postoperatively and his last known visual acuity was 20/15. This case, and the report of another patient with similar postoperative problems, illustrates that implantation of lens optics with a larger effective optical zone for posterior chamber lens implantation is desirable. This is particularly true now that younger, more active patients, many still engaged in occupations, are having lens implantations.

Cataract Extraction↗
PubMed1987

Anterior chamber lenses. Part I: Complications and pathology and a review of designs.

Clinicopathologic data to assist ophthalmologists in choosing a safe and efficacious anterior chamber intraocular lens (IOL) are rapidly becoming available. Two important factors that have led to an increased success rate with some anterior chamber IOL styles are (1) attention to lens design and (2) attention to modern manufacturing and lens finishing techniques. We now know much more about how to achieve appropriate lens flexibility, which decreases the need for perfect sizing. Increased attention has been given to the anterior-posterior vaulting characteristics of IOLs. This has reduced the incidence of various complications such as the intermittent touch syndrome and the uveal chafing syndrome. We recognize several design flaws in some lens styles. For example, there is now a considerable decrease in the number of small-diameter, round-looped anterior chamber IOLs being implanted, particularly those with a closed-loop configuration. Several problems have been and continue to be caused by some poorly manufactured anterior chamber lenses with sharp optic and haptic edges. Technology to assure smooth lens finishing and polishing is available and readily accessible to all manufacturers. Defective lenses should soon be a thing of the past.

Anterior Chamber↗
PubMed1987

Anterior chamber lenses. Part II: A laboratory study.

An analysis of 606 surgically removed anterior chamber intraocular lens (IOL) specimens revealed that 351 or 58% of these were small-diameter, round loop, closed-loop styles. Because of the extremely high percentage of IOLs with this design received in our laboratory and the correlation of clinical histories with our histopathologic findings, we have concluded that such IOLs do not provide the safety and efficacy achieved by other anterior chamber lens designs. The finely polished, one-piece, all-PMMA styles fared well in our study. Although these one-piece styles comprise well over 50% of the American market share of anterior chamber IOLs, they comprise only 14% of all anterior chamber IOLs accessioned in our laboratory, compared to 58% for closed-loop designs. We believe that implantation of anterior chamber lenses with small-diameter, round, closed loops is no longer warranted. Patients in whom these IOLs have already been implanted should be carefully followed. It is our opinion that the FDA should recall or closely monitor all IOLs of this design and that implantation of closed-loop lenses should be discontinued in the United States. Furthermore, we believe that an IOL deemed to be not medically sound or worthy of implantation in the United States should not be marketed or donated outside of this country.

Anterior Chamber↗
PubMed1976

Compositional characteristics of a chloroform/methanol soluble protein fraction from spinach chloroplast membranes.

Extraction of an aqueous suspension of spinach chloroplast lamellae with a chloroform/methanol mixture leads to solubilization of about 1/3 of the total membrane protein. Amino acid analysis of the chloroform/methanol-soluble protein shows that this fraction is largely enriched in the hydrophobic residues proline, leucine, alanine and phenylalanine and considerably depleted in polar amino acids, namely lysine and arginine. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the solubilized material reveals the presence of a variety of low molecular weight polypeptides (molecular weight less than or equal to 25 000), with more than 50% of the total fraction being contributed by a 25 000 dalton band. This band, which accounts for about 25% of the total chloroplast lamellar protein, has recently been identified as the main component of the light-harvesting chlorophyll-protein complex. The physiological role of most of the chloroform/methanol-soluble protein fraction is not known at present. From its chemical properties and apparent biological inertness, we propose that it plays mainly a structural role in situ, interacting with the lipid moiety of the chloroplast membrane. The material insoluble in the aqueous chloroform/methanol mixture is largely enriched in manganese, iron, cytochrome and water-soluble proteins, such as chloroplast coupling factor and ribulose diphosphate carboxylase.

Amino Acids↗
PubMed1975

Comparative studies on the polypeptide composition of chloroplast lamellae and lamellar fractions.

The polypeptide composition of spinach chloroplast membranes and membrane fractions has been examined by the technique of sodium dodecylsulfate-polyacrylamide gel electrophoresis. Chloroplasts were fragmented into grana (Photosystem II enriched) and stroma lamellae (Photosystem I in character) by the French press technique. The grana lamellae were further fractionated by the use of digitonin into two fractions, one enriched in Photosystem II and the other enriched in Photosystem I. These membranes are composed of at least 15 polypeptides two of which, with approximate weights of 39 and 50 kdaltons, are observed only in granal fractions. Quantitatively the primarily Photosystem II fractions are enriched in polypeptides in the 30-23 kdalton range whereas the Photosystem I (or Photosystem I-enriched) fractions are enriched in polypeptides in the 60-54 kdalton region. The experiments reported show that contamination by soluble proteins or other membranes is negligible. The results indicate that subtle differences in composition account for the large differences in structure and function within the chloroplast membrane system.

Chloroplasts↗