Search PubMed⌕ Search

Biomedical subjects

R L Lindstrom

Publications and source records attributed to R L Lindstrom.

At least 109 records · Page 6Linked to original sources
PubMed1987

Soft intraocular lenses.

An in-depth review of the current status of soft intraocular lenses (IOLs) is presented. We have outlined the historical aspects of IOL development from polymethylmethacrylate material to newer soft polymers such as silicones and hydrogels. Chemical, physical, and biomaterial properties as well as the advantages and disadvantages of these materials and lenses are discussed. Clinical results from international investigators are presented, along with some thoughts about future trends in small incision cataract surgery and IOL substitutes.

Humans↗
PubMed1987

Neodymium:YAG laser interaction with Alcon IOGEL hydrogel intraocular lenses: an in vitro toxicity assay.

The objective of this study was to determine the potential toxicity generated by the interaction of the Nd:YAG laser and Alcon IOGEL intraocular hydrogel lens material. The IOGEL lens is composed of poly 2-hydroxyethylmethacrylate, containing 38% water, previously shown to be highly biocompatible in a wide range of tissue culture and implantation experiments. In this study, intraocular lenses (IOLs) immersed in serum-free cell culture medium were purposely exposed to exaggerated doses of laser energy to cause extensive damage. An IOLAB polymethylmethacrylate (PMMA) lens served as a control lens material. The resultant solutions were assayed for cytotoxicity in a bioassay system using fourth passage human corneal endothelial cells. No cytotoxicity was seen in the bioassay for the IOGEL hydrogel IOLs or the PMMA control IOL at any laser range/dosage tested over a 72-hour incubation period. Hydrogel lenses exhibited decreasing yellowing with decreasing energy levels, and no lens discoloration was apparent at the lowest level of irradiation, 5 mJ/50 laser bursts; the PMMA control lens exhibited moderate yellowing at 15 mJ/50 bursts. Lens marking was moderate for all IOGEL IOLs; the PMMA lens marking was severe at the power level tested.

Cataract Extraction↗
PubMed1987

Retinal detachment in axial myopia.

A retrospective review of the complications of extracapsular cataract extraction in 127 cases followed between August 1980 and February 1985 is presented. The incidence of retinal detachment in eyes with axial length greater than 25.00 mm was found to be 9.59%, while no detachments occurred in eyes less than 25.00 mm. All of the patients with detached lenses were male. Extracapsular cataract extraction, an intact capsule, and placement of a posterior chamber lens do not prevent retinal detachment. A male with an axial length greater than 25.00 mm is more predisposed to develop a retinal detachment following cataract extraction and should therefore be counseled regarding the symptoms of retinal detachment and followed with careful ophthalmoscopy.

Cataract Extraction↗
PubMed1987

Correction of hyperopia following radial keratotomy: quantification in human cadaver eyes.

Overcorrection is a significant complication following radial keratotomy (RK). This study using human cadaver eyes demonstrates that the use of interrupted sutures placed across radial incisions coincident with a 7-mm optical zone mark can induce a wide range of central corneal steepening and can therefore correct varying amounts of hyperopia following RK. A case presentation confirms the effectiveness of using interrupted sutures to steepen the cornea following RK, but it also shows that significant regression of the effect must be considered at the time of suture placement. Since placement of interrupted corneal sutures is a routine procedure, it is a very convenient technique for treating overcorrection following RK.

Adult↗
PubMed1986

Trapezoidal astigmatic keratotomy. Quantification in human cadaver eyes.

The mechanism by which surgical procedures correct astigmatism are incompletely understood and, therefore, the results are often unpredictable. In this study, a Terry keratometer was used to analyze the effect of each component part of a 3-, 4-, and 5-mm trapezoidal astigmatic keratotomy. Semiradial incisions along the horizontal meridian produced corneal flattening along the horizontal meridian twice that of the vertical meridian, therefore inducing positive cylinder astigmatism at 90 degrees. A single pair of tangential incisions placed 5 mm apart, when added to the semiradial incisions, accounted for 100%, 87%, and 78% of the maximal effect from the 3-, 4-, and 5-mm completed trapezoidal astigmatic keratotomies, respectively. This study suggests that maximal correction of astigmatism may be attained with a single set of tangential incisions placed 5 mm apart between two sets of semiradial incisions.

Astigmatism↗
PubMed1986

Trapezoidal keratotomy. A vector analysis.

Twenty-three eyes in 23 patients ranging from 61 to 83 years of age underwent trapezoidal astigmatic (Ruiz) keratotomy. Preoperative regular astigmatism ranged from 3.13 to 13.00 diopters by keratometry. Fourteen of the eyes had high regular astigmatism following penetrating keratoplasty, eight following cataract extraction, and one eye had no history of surgery. Patient follow-up ranged from 1 to 15 months with a mean of five months. Trigonometric vector analysis of the keratometric readings demonstrated that the magnitude of surgically induced change in corneal curvature was inversely proportional to the size of the optical zone and ranged from 1.28 to 14.21 diopters. Frequently, due to the axis of surgically induced change, the magnitude of change in corneal curvature failed to be reflected by an equal magnitude of reduction in the residual corneal astigmatic error, and in many cases a residual error was created in a meridian differing significantly from that of the preoperative astigmatic error. There is no statistically significant difference in the slopes of the linear regression lines relating change in corneal curvature to optical zone size between this series and our previously reported cadaver study.

Aged↗
PubMed1986

Ultraviolet light absorption in intraocular lenses.

Implantation of ultraviolet (UV) light-absorbing intraocular lenses and the manufacturers developing these lenses has significantly increased over the past few years. In this paper, the need for filtration of UV light by intraocular lens implants is briefly examined and various new product development aspects of a UV-absorbing IOL are discussed. Two general approaches, additive and chemical bonding, to incorporating a UV-absorbing chromophore into polymethylmethacrylate lens material are described. Different UV-absorbing compounds that are being used in implants and the mechanism by which they absorb light and its dissipation is discussed. The extent of preclinical testing required to establish the biocompatibility, stability, and overall safety of new materials is summarized. Finally, a relative comparison of the extent of UV absorption by various commercially available UV intraocular lenses is presented.

Filtration↗
PubMed1986

Laser retinometry versus clinical estimation of media: a comparison of efficacy in predicting visual acuity in patients with lens opacities.

One hundred eyes with lens opacities requiring cataract extraction were examined preoperatively by laser interferometry. Sixty-eight of these eyes were also clinically evaluated by estimating media clarity with a direct ophthalmoscope. The predicted acuities obtained from these tests were compared to the actual postoperative Snellen acuity achieved. Both tests were found to be useful predictors; correlation coefficients for interferometry and media estimation were .91 and .88, respectively. Each test was less dependable in patients with the densest cataracts, with poorer correlation coefficients reflecting this; interferometry r = .49 and media estimation r = .19. These results confirm that both tests are useful predictors, but their strengths and weaknesses must be understood.

Adult↗
PubMed1986

Polysulfone corneal lenses.

Polysulfone is a thermoplastic compound first synthesized in 1965. A unique characteristic of polysulfone is its high refractive index (1.633), which allows very thin optical lenses to be manufactured. Over the last five years, D. Peter Choyce has surgically implanted over 40 polysulfone lenses into eyes of his patients. Analysis of his data indicates that polysulfone intraocular lenses are capable of correcting large refractive errors. Based on his work, a multicenter study was undertaken to evaluate the safety and efficacy of polysulfone as an intracorneal lens material in laboratory models. Four monkeys, eight baboons, and 24 cats were used as laboratory models; 5.0-mm to 6.0-mm diameter hyperopic (+28.5 diopter) and myopic (-17.0 and -25.5 diopter) lenses were surgically implanted within the corneal stroma in one eye of each of the laboratory models while a sham lamellar dissection was performed in the other eye. One hundred percent (4/4) of monkey eyes, 12.5% (1/8) of baboon eyes, and 70.0% (18/24) of cat eyes maintained clear media by ophthalmoscopic examination at follow-ups ranging from three to six months. Complications included both visually and nonvisually significant interface opacities, lens extrusion, anterior corneal necrosis, refractile particles, and epithelial thinning.

Animals↗
PubMed1986

Minnesota system corneal preservation.

The clinical and laboratory results with a modified Minnesota system of organ culture corneal preservation are presented. A refinement of our preservation technique using a closed system, as well as the addition of chondroitin sulphate to the medium is presented. Laboratory results show preservation of corneal endothelial integrity for at least 21 days with maintenance of normal corneal thickness. In addition, a 10-day quarantine system reduces the risk of donor contamination and secondary endophthalmitis. Preliminary results of the 34 degrees C and 4 degrees C closed Minnesota corneal preservation system using chondroitin sulphate show that it is safe and efficacious and allows intermediate to long-term maintenance of sterile thin tissue prior to corneal transplantation.

Animals↗
PubMed1985

Endothelial cell survival on transplanted human corneas preserved by organ culture with 1.35% chondroitin sulfate.

We transplanted 30 donor corneas preserved at 34 C for 15 to 33 days in culture medium containing 1.35% chondroitin sulfate and compared them with 30 corneas transplanted during the same period, but preserved only in McCarey-Kaufman medium at 4 C for one to 81 hours. Two months after keratoplasty there was no statistically significant difference in central endothelial cell loss between the organ-cultured grafts and those preserved in McCarey-Kaufman medium (9% vs 7% cell loss, respectively). The study detected with 90% power a difference in cell loss of approximately 10% or more. On the first postoperative day, the organ-cultured grafts were thicker than those grafts preserved in McCarey-Kaufman medium, and the thickest corneas were those cultured for the longest times. The corneal thickness was similar in the two groups after three weeks. These results demonstrated that donor corneal endothelial cells preserved for up to one month at 34 C in 1.35% chondroitin sulfate appear to survive and function after keratoplasty as well as those preserved at 4 C for one to three days in McCarey-Kaufman medium.

Adult↗
PubMed1985

Efficacy of laser interferometry in predicting visual result of YAG laser posterior capsulotomy.

One hundred fifteen patients with cloudy posterior capsules that required capsulotomies were evaluated by laser interferometry. The predicted acuity was within one line of postoperative acuity in 44 patients (38.3%) and within two lines in 73 patients (63.5%). The correlation coefficient between the predicted and actual post-capsulotomy acuities was 0.38. However, the predicted retinal visual acuity was compared to postoperative Snellen visual acuity and found to differ by an average of three lines. A large number of false negative results reduced the clinical usefulness of the test.

Adolescent↗
PubMed1985

Effect of incision size and Terry keratometer usage on postoperative astigmatism.

The efficacy of the Terry quantitative surgical keratometer in minimizing early postoperative astigmatism was evaluated in a retrospective study. Intraoperative use of the Terry keratometer reduced the keratometric corneal astigmatism in the early postoperative period for the 6.5-mm chord length phacoemulsification-lens implant incision as well as for the 10.0-mm to 11.0-mm chord length planned extracapsular cataract extraction-lens implant incision. In addition, the 6.5-mm chord length incision yielded a significant reduction in early postoperative astigmatism when compared to the 10.0-mm to 11.0-mm chord length incision. Furthermore, there was a reduction in the number of patients who required suture cutting in the keratometer group. The Terry quantitative surgical keratometer is a useful tool for reducing early postoperative surgical astigmatism and decreases the number of patients who require suture cutting.

Astigmatism↗
PubMed1985

Neodymium:YAG laser interaction with intraocular lenses: an in vitro toxicity assay.

Use of the Nd:YAG laser is an effective technique to open an opacified posterior lens capsule. However, in the presence of a posterior chamber intraocular lens (IOL), precise focusing of the laser on the capsule is required to avoid pitting the lens optic. The question has been raised whether toxic products may result from laser damage to the IOL. We addressed this issue in the present study by exposing primary human corneal endothelial cell and human corneal organ cultures to solutions produced by purposefully hitting IOLs immersed in cell growth medium with a Nd:YAG laser. The lenses studied were lathe-cut polymethylmethacrylate (PMMA), injection-molded non-UV PMMA, injection-molded UV PMMA, and cast-molded UV PMMA. Samples of each material were irradiated in a holder containing 1 ml of cell culture medium using the following conditions: 5, 10, and 50 laser bursts at 10 millijoules (mJ), and 50 laser bursts at 5 mJ. The solutions were applied to the endothelial cell cultures (all materials) and to the corneal organ cultures (injection-molded non-UV lenses only). There was no toxicity in either assay for any of the materials studied.

Cells, Cultured↗