Search PubMed⌕ Search

Biomedical subjects

W J Stark

Publications and source records attributed to W J Stark.

At least 91 records · Page 5Linked to original sources
PubMed1990

Visual disabilities related to intraocular lens design.

Intraocular lens implantation after cataract extraction has become a common practice in the United States. However, unwanted optical images can correct an otherwise successful surgery into one that causes patient dissatisfaction. Refinements in manufacturing design and finishing have greatly improved the quality of present day intraocular lenses, but there is continued interest in simulating the optics of the human crystalline lens. We will discuss the optical requirements of intraocular lenses and how these are influenced by optic design and dimension, and spectral transmission characteristics.

Humans↗
PubMed1990

Low-dose ultraviolet-B irradiation of donor corneal endothelium and graft survival.

Donor rabbit corneal endothelium was pretreated with different doses of ultraviolet (UV-B) irradiation (302 nm) before grafting to test whether allograft survival could be favorably affected in comparison with untreated corneas grafted into the same recipients. Endothelial rejection was observed in 19 of 32 (59%) eyes that received no treatment compared with five of 32 (16%) eyes that received UV-B (P less than 0.001), and increasing doses of UV-B were associated with lower rejection rates (P less than 0.05). Although exposure of donor endothelium significantly reduced endothelial rejection at all doses tested, it resulted in primary graft failure in a substantial proportion of corneas treated at high doses. Class II (Ia) antigen staining of corneal tissue was present in conjunction with clinical evidence of rejection, and the magnitude of staining correlated with the histologic extent of inflammation. Scanning electron microscopy revealed various endothelial cell surface irregularities and membrane defects in high-dose UV-treated corneas. Endothelial cell cultures exposed in vitro to UV-B light showed a dose-dependent loss in cell viability. These data suggest that UV-B pretreatment of donor corneal endothelium prolongs graft survival but that toxic side effects must be carefully controlled.

Animals↗
PubMed1989

Posterior chamber intraocular lens implantation in the absence of capsular support.

To avoid the complications associated with anterior chamber intraocular lenses (IOLs), we have developed a technique for the implantation of a posterior chamber IOL in the absence of capsular support. The IOL is secured in the ciliary sulcus by suturing the haptics to the sclera at the ciliary sulcus inferiorly and to the sclera or iris superiorly. We have used this technique for secondary IOL implantation in 16 contact lens-intolerant patients with aphakia with a mean follow-up of 9 months (range, 5 to 20 months) and in eight eyes at the time of IOL removal. All eyes with secondary implants had equal or improved vision postoperatively; none developed persistent angiographic cystoid macular edema. In the 8 patients with IOL exchange, visual acuity improved in five eyes, remained the same in two, and decreased two lines in one. Suturing of an IOL in the ciliary sulcus has enabled us to use a posterior chamber IOL in eyes without a posterior capsule when secondary IOL implantation or IOL exchange is indicated. Secondary posterior chamber IOL implantation is recommended only when satisfactory vision cannot be achieved with glasses or contact lenses, and further follow-up is needed before this procedure can be widely recommended.

Aged↗
PubMed1989

Managing posterior pressure during pseudophakic keratoplasty.

Positive vitreous pressure during penetrating keratoplasty can be difficult to manage. Despite preventive measures, positive vitreous pressure may occur and appropriate intervention is necessary to prevent serious complications. We describe a technique that may be used intraoperatively to restore a formed anterior segment and to prevent vitreous loss when persistent positive vitreous pressure occurs, while attempting to implant a pseudophakos. A 27-gauge needle, passed across the anterior chamber from limbus to limbus, just anterior to the iris, will stabilize the pseudophakos, restore the anterior chamber depth, and allow donor-tissue suturing.

Cataract Extraction↗
PubMed1989

Protoporphyrin IX photosensitization of corneal endothelium.

Protoporphyrin IX, a naturally occurring precursor of hemoglobin found in serum and erythrocytes, is a photoactive compound that we have detected in aqueous aspirates of three patients with hyphemas (0.13, 0.33, and 0.67 microgram/dL). To determine whether corneal endothelial photosensitization could occur, rabbit corneas were exposed to physiologic concentrations of protoporphyrin and light (200 microEinsteins [microE]/m2 per second). Experimental corneas demonstrated endothelial swelling with loss of intercellular contact by scanning electron microscopy. Flux chamber experiments demonstrated an increase in the net endothelial inflow, indicating a loss of the endothelial barrier function. Control corneas had normal ultrastructural architecture and flux study results. These studies suggest that patients with long-standing hyphemas who may be exposed to long periods of light are possibly at risk for developing endothelial dysfunction and corneal blood staining. Patching of these patients' affected eyes may be prudent.

Animals↗
PubMed1989

Corneal healing following laser refractive keratectomy.

A 193-nm excimer laser system was used to ablate 4.5-mm optically contoured zones in the corneal stroma of rabbits to achieve optical flattening of 2, 4, 8, and 16 diopters. We studied the effect of edge profile and wound depth on reepithelialization and stromal remodeling using dichlorotriazinyl aminofluorescein, a vital dye that covalently binds to the stromal bed and delineates the boundaries of new collagen synthesis. All the corneas reepithelialized; no subsequent recurrent erosions occurred. All seven corneas that received an ablation of less than 50 microns were clear centrally at 8 weeks. At an ablation depth of approximately 100 microns, opacification and scarring were observed biomicroscopically and histopathologically in two specimens. No evidence of new collagen formation or epithelial hyperplasia was found in any of the seven corneas that remained clear. Stromal remodeling was observed in the two corneas that exhibited scarring.

Animals↗
PubMed1989

Contact lenses for visual rehabilitation after corneal laceration repair.

A contact lens fitting was tried after corneal laceration repair in 26 eyes. The mean patient age was 25 years; 22 eyes were aphakic and there were 23 males. Many patients had been referred for penetrating keratoplasty. Intact sutures in 13 eyes did not hinder contact lens fitting which was performed within 6 months in 12 cases. A contact lens was fit and successfully worn in 21 eyes (81%) and was fit in the remaining five patients, but not worn because of suboptimal vision (4 eyes) or an unsatisfactory fit (1 eye). Success rates were higher for small, peripheral lesions and in younger patients. Visual acuity was at least 20/30 in 12 patients and follow-up averaged 10.1 months. A contact lens can usually be fit after corneal lacerations, despite aphakia, with good visual results, thereby avoiding penetrating keratoplasty and intraocular lens implantation.

Adolescent↗
PubMed1989

Idiopathic presenile cataract formation and galactosaemia.

Five hundred patients undergoing cataract surgery were prospectively examined, and 46 Caucasian patients were found to have strictly idiopathic cataracts severe enough to warrant surgery on or before age 55. In a masked fashion we determined the activity of galactokinase (GK) and galactose-1-phosphate uridyl transferase (GPUT) in these patients as well as on 53 age matched controls. With respect to GK no cataract patient had an enzyme level of less than 2 standard deviations below the control mean. However, 3 of 45 (6.7%) patients in the cataract group had a GPUT level less than 2 standard deviations below the mean for controls, and were presumably heterozygotes for this enzyme. In comparison with the expected population rate of 0.8% this is highly significant (p = 0.006). Abnormalities in galactose pathway enzymes may therefore predispose to development of presenile cataracts. In affected people there is a possibility of treating these patients clinically by dietary restriction of dairy products or by using aldose reductase inhibitors to prevent or reverse cataract formation.

Adult↗
PubMed1989

Dextran efflux from McCarey-Kaufman-stored corneas as measured by nuclear magnetic resonance.

Dextran, a high molecular weight polymer of glucose, is used as an osmotic agent in McCarey-Kaufman (MK) (corneal storage) medium. It has been proposed that Dextran may cause deleterious effects on living cells either by high molecular weight toxicity or by the induction of an immunological reaction against transplanted tissues. Prolonged retention of Dextran in transplanted corneas, therefore, may produce deleterious side effects. The efflux of Dextran from MK-stored human corneas was monitored by transferring corneas to 2 ml of fresh Krebs Ringer bicarbonate solution (BSS) containing 5.5 mM 1-13C-labeled glucose at approximately 1 h intervals for 1-24 h. Chemical shifts of 98.7, 74.5, 72.5, 71.2, 70.6, and 66.5 ppm were found for the naturally abundant 13C NMR spectrum of 40,000 molecular weight Dextran. Peak heights for the 70.6 ppm Dextran chemical shift were measured and plotted against total wash time to determine the slope for Dextran efflux from each cornea. The results of this study suggest that all of the Dextran absorbed into human corneas stored for up to 2 weeks in MK medium is eluted in about 19 h and that the rate of Dextran efflux is unaffected by donor age, time of storage in MK, or corneal viability.

Adult↗
PubMed1989

Posterior chamber intraocular lens implantation in the absence of posterior capsular support.

Because of the high incidence and great variety of complications associated with anterior chamber intraocular lenses, we have developed a technique for the implantation of a posterior chamber intraocular lens in the absence of posterior capsular support. The posterior chamber IOL is placed in the ciliary sulcus by suturing the superior haptic to the iris and the inferior haptic to the sclera at the ciliary sulcus. We have used this technique successfully in both complicated extracapsular surgery and secondary intraocular lens implantation.

Follow-Up Studies↗
PubMed1989

Complications of cataract extraction with intraocular lens implantation.

Due to continued improvement in lens design, lens manufacturing, and surgical technique, the incidence of complications of cataract surgery with intraocular lens (IOL) implantation have decreased in recent years. Complications may be categorized into operative and postoperative, both early and late onset. Operative complications include posterior capsule rupture with or without vitreous loss, loss of all or part of the lens nucleus, iris damage, and stripping of Descemet's membrane. Early postoperative complications include pupillary block, hyphema, elevation of the intraocular pressure associated with the use of viscoelastic substances, persistent uveitis with or without hypopyon, and endophthalmitis. Late postoperative complications include IOL malposition, secondary glaucoma, cystoid macular edema, retinal detachment, and pseudophakic bullous keratopathy.

Cataract Extraction↗
PubMed1989

Lamellar keratectomy and repeat epikeratoplasty following failed epikeratoplasty. A clinicopathologic report.

Although epikeratoplasty (epikeratophakia) for aphakia in children has achieved a high degree of success, there remains a significant incidence of complications, some of which may result in removal of the lenticule. We report a 2-year-old child in whom epikeratoplasty was followed by an acute suppurative keratitis, necessitating removal of the epikeratoplasty lenticule. The recipient bed remained scarred following removal of the lenticule with anterior stomal fibrosis, which precluded good vision. We were able to avoid a penetrating keratoplasty by performing a superficial lamellar keratoplasty with a repeat epikeratoplasty that has remained clear.

Child, Preschool↗