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Biomedical subjects

Barry A Weissman

Publications and source records attributed to Barry A Weissman.

14 recordsLinked to original sources
PubMed2006

Calculated tear oxygen tension under contact lenses offering resistance in series: piggyback and scleral lenses.

BACKGROUND: Models of oxygen delivery to the cornea with contact lens wear have considered the customary situation of one lens being worn on the cornea. However, two lenses, such as a rigid lens piggybacked on a soft lens, may be worn by patients with special ocular and visual needs. This paper extends existing single lens models to circumstances where two lenses offer resistance to oxygen in series. METHODS: Theoretical oxygen tensions are calculated for tear layers trapped beneath piggyback contact lens systems (and scleral lenses) and the anterior corneal surface with a simple single chamber corneal model using a personal computer software spreadsheet. RESULTS: Acceptable values are anticipated for contact lens materials of modern oxygen permeability values of approximately 60-100 Fatt Dk units under open eye conditions. CONCLUSIONS: The results of this spreadsheet model of oxygen supply to the anterior corneal surface offer a useful guide to clinicians concerned about providing their patients with physiologically acceptable piggyback lens systems.

Contact Lenses↗
PubMed2006

Baseline factors predictive of incident penetrating keratoplasty in keratoconus.

PURPOSE: To identify baseline demographic and clinical factors associated with undergoing penetrating keratoplasty (PK) in a prospective cohort of 1,065 keratoconus patients followed for eight years in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study. DESIGN: Multicenter, prospective, observational cohort study. METHODS: We report the rate of PK over eight years and baseline factors predictive of PK in 1,065 patients who, at the time of study enrollment, had not undergone PK in either eye. RESULTS: Eighty-two percent of patients completed the eight-year close-out visit. Twelve percent (126 of 1,065) had PK in one (9.3%) or both eyes (2.5%). Baseline factors associated with increased likelihood of PK included younger age, steeper keratometric values, worse visual acuity, corneal scarring, poorer contact lens comfort, and poorer vision-related quality of life. The percent of eyes undergoing PK was 15% for patients 40 years old and younger, 28% for eyes with a steep keratometric value greater than 52 diopters, 33% for visual acuity less than 20/40, and 24% for eyes with corneal scarring. CONCLUSIONS: The CLEK Study confirmed previous reports of the increased likelihood of PK associated with corneal scarring, steeper keratometry values, poorer visual acuity, and poorer contact lens comfort. The CLEK Study is among the first to report an increased risk of PK associated with younger age, worse vision-related quality of life, and flatter contact lens fits. Knowledge of these factors is beneficial to clinicians in patient education and may be useful in disease management.

Adolescent↗
PubMed2005

Bitoric gas-permeable contact lens application in pellucid marginal corneal degeneration.

PURPOSE: To evaluate the authors' experience fitting patients with pellucid marginal corneal degeneration (PMCD) with bitoric gas-permeable contact lenses. METHODS: The records of 11 patients with a confirmed diagnosis of PMCD were retrospectively reviewed. The numbers of diagnostic contact lenses at the first visit, office visits, and lenses ordered to complete the fitting; uncorrected, spectacle-corrected, and contact lens-corrected Snellen visual acuities; contact lens success or failure; and complications encountered were all assessed. These data were compared to historic data for patients with other corneal irregularities (keratoconus, penetrating keratoplasty, and refractive surgery). RESULTS: The mean number of diagnostic contact lenses used at the first visit was 1.09 +/- 0.302, and the number of lenses ordered to complete the fitting was 1.82 +/- 1.33. The number of visits during 4 months was 6.18 +/- 2.14. Uncorrected visual acuity (logMAR) was 0.957 +/- 0.398 (20/181 in Snellen); the best-corrected spectacle visual acuity (logMAR) was 0.231 +/- 0.309 (20/34 in Snellen); and the best contact lens-corrected visual acuity (logMAR) was 0.0424 +/- 0.06275 (20/22 in Snellen). Corrected vision in eyes with PMCD improved approximately two lines with bitoric gas-permeable contact lenses compared to that achieved with spectacles. Ten (91) of the patients met the criteria of contact lens success during the 4-month follow-up period. CONCLUSIONS: Bitoric gas-permeable contact lenses achieved a comfortable and visually successful fit in most eyes with PMCD. Patients with PMCD used the fewest contact lenses and had the fewest lens exchanges, but required more office visits than other groups of patients with various corneal irregularities.

Ambulatory Care↗
PubMed2004

Anterior basement membrane corneal dystrophy and pseudo-unilateral lattice corneal dystrophy in a patient with recurrent corneal erosions.

PURPOSE: To report the utility of genetic testing in the diagnosis and management of patients with suspected corneal dystrophies. DESIGN: Case report. METHODS: A 58-year-old man with a history of recurrent corneal erosions was diagnosed with bilateral anterior basement membrane dystrophy and unilateral lattice corneal dystrophy. All 17 exons of the TGFBI gene were screened for mutations previously associated with lattice corneal dystrophy as well as novel coding region changes. RESULTS: No mutations were found in the 17 exons of the TGFBI gene. A nucleotide change in exon 6 (651C>G) did not result in a change in the encoded amino acid (Leu217Leu). CONCLUSIONS: In cases of suspected TGFBI corneal dystrophies, genetic testing is a useful tool to confirm the clinical diagnosis. In this case of suspected unilateral lattice corneal dystrophy, screening of the TGFBI gene ruled out the diagnosis, raising the possibility that the corneal changes were related to the coexistent anterior basement membrane dystrophy.

Basement Membrane↗
PubMed2004

Is contact lens "T" still important?

We studied oxygen supply to the contact lens covered cornea by means of a complex calculation method. We measured lens thicknesses, both centrally and at a 3mm peripheral location, of a range of optical powers of two different spherical silicone hydrogel contact lens designs (manufactured by Ciba Vision and Bausch & Lomb) and one "traditional" hydrogel. Using the measured values of lens thickness and the nominal oxygen permeabilities of these three plastics, we calculated the oxygen tension level in the tear layer posterior to the contact lens and anterior to the cornea and the oxygen flux through these contact lenses, under both open- and closed-eye conditions. We conclude that variable thicknesses of the silicone hydrogel contact lenses does not significantly affect the oxygen tension in the entrapped tear layer, given their high oxygen diffusion coefficients, under open-eye conditions, and probably only minimally under closed-eye conditions as well.

Journal Article↗
PubMed2004

Late-stage progressive corneal astigmatism after penetrating keratoplasty for keratoconus.

PURPOSE: Progressive corneal astigmatism occurring at least 10 years after penetrating keratoplasty for keratoconus is a late-phase complication of surgery. This report characterizes this condition in a series of patients from three corneal referral centers in the United States. METHODS: Charts were retrospectively reviewed which met the following criteria: penetrating keratoplasty performed for keratoconus at least 10 years ago, keratometry or simulated keratometry from topography as well as manifest refraction recorded at least 6 months after the last suture removal ("baseline"), and an increase in corneal astigmatism of at least three D over baseline recorded at least 5 years later. Patients who had any other corneal or intraocular surgery performed were excluded. RESULTS: Data from 15 patients (11 males and 4 females) who had penetrating keratoplasties performed by 8 different surgeons are included in this descriptive series. Postoperative follow-up averaged 17.27 years (range 11-24 years). The average donor button size was 7.83 mm (range 7.25-8.5 mm). Baseline corneal astigmatism was obtained an average of 5.2 years after penetrating keratoplasty (range 1.5-16 years) and was on average 3.57 +/- 1.8 D (10 with-the-rule [WTR], 3 against-the-rule [ATR], 2 oblique). Corneal astigmatism significantly increased to an average of 11.23 +/- 3.56 D (range 8.00-19.37 D, P < 0.0001) and most astigmatism was regular and WTR (9 WTR, 3 ATR, 3 oblique) 15.3 years (range 10-22 years) after surgery. Inferior steepening on topography was often noted, even those with oblique and ATR axes. CONCLUSIONS: High, late-stage, regular astigmatism after penetrating keratoplasty for keratoconus is described in a series of patients occurring at least 10 years after surgery. Possible mechanisms of this progressive astigmatism are recurrence of keratoconus in the graft, progressive corneal thinning of the host cornea, or progressive misalignment of the graft-host interface over time.

Astigmatism↗
PubMed2003

Bilateral corneal neovascularization and opacification associated with unmonitored contact lens wear.

PURPOSE: To report a case of severe bilateral deep stromal neovascularization and opacification associated with unmonitored contact lens wear. DESIGN: Observational case report. METHODS: A 46-year-old woman who had been using hydrogel contact lenses bought on the Internet without a prescription for 5 years was found to have dense, bilateral corneal opacities with deep stromal neovascularization. RESULTS: The patient's contact lenses were found to be tight-fitting. Medical history and serological studies were negative for infectious or rheumatologic causes of interstitial keratitis. CONCLUSIONS: The deep stromal neovascularization and the associated corneal opacification are most likely related to the unmonitored contact lens use and the lack of routine eye examinations. We believe it is critical that all contact lens wearers receive professional eye care on a regular basis regardless of where they obtain their contact lens supplies.

Contact Lenses, Extended-Wear↗
PubMed2003

Contact lens care in keratoconus.

PURPOSE: To quantify the complexity involved in fitting contact lenses on the eyes of patients with keratoconus. METHODS: The contact lens care of one randomly selected eye each of 38 keratoconus patients was retrospectively analyzed and compared to that of 38 gender and age matched controls. We evaluated the number of diagnostic contact lenses used to establish the initial contact lens order, number of ordered rigid gas permeable (RGP) contact lenses needed to complete the fit, number of office visits during the initial 4 months of care, best spectacle and RGP contact lenses corrected Log MAR visual acuities, complications encountered, and whether or not the patient was successful in contact lens wear. RESULTS: Keratoconic eyes statistically used more diagnostic lenses, more ordered lenses, and more office visits than did normal eyes. Visual acuities improved from an average of 20/40 with spectacles to an average of 20/20 by use of RGP contact lenses in keratoconic eyes. Visions were corrected to 20/20 with both spectacles and contact lenses in control eyes. Sixty nine percent (69%) of keratoconic eyes and 95% of controls were successful in contact lens wear. CONCLUSIONS: Contact lens care of keratoconic eyes is more challenging than care of normal eyes because of the need for more diagnostic and ordered contact lenses and the use of more professional time. Keratoconic eyes may suffer more complications than normals during contact lens care, but this does not affect the success rates, and such patients benefit from enhanced visual acuity with RGP contact lenses compared to that achieved with spectacles.

Journal Article↗
PubMed2003

Feasibility of contact lens fitting on keratoconus patients with INTACS inserts.

PURPOSE: To demonstrate the feasibility of contact lens fitting in keratoconus patients with INTACS inserts. METHODS: A chart review was conducted of all patients with bilateral keratoconus who were treated with INTACS inserts on one eye and who were subsequently referred for contact lens fitting in a university based contact lens practice between April 2000 and April 2002. The study was a retrospective, non-comparative case series. The uncorrected and best spectacle corrected visual acuity (BSCVA) after INTACS implantation surgery, postoperative best contact lens-corrected visual acuity (BCLVA), number of diagnostic contact lenses used, number of contact lenses ordered within a 4-month follow-up period, contact lens complications encountered, final base curves, final lens powers, and final wearing times were determined. RESULTS: Three keratoconic patients meeting the selection criteria were found through the chart review. Prior to surgery, all patients had uncorrected visual acuity (UCVA) of 2.0 logMAR (counting fingers). This improved to a mean of 0.81+/-0.25 logMAR (20/125-1) after surgery. Mean BSCVA also improved from 0.51+/-0.30 logMAR (20/60-2) to 0.30+/-0.16 logMAR (20/40). The mean postoperative best contact lens-corrected visual acuity was 0.02+/-0.10 logMAR (20/20-1). The number of diagnostic lenses ranged from 1 to 7. The numbers of contact lenses ordered during the 4-month follow up period ranged from 1 to 3. Two eyes were fitted with larger than usual lens designs made of rigid gas-permeable material and one eye was fitted with a toric soft lens. The final lens power ranged from +1.25 to -21.0D with a mean spherical equivalent of -7.46+/-11.89 D. Final wearing times ranged from 2.5 to 12.0h. CONCLUSION: Fitting contact lenses on keratoconus patients who have INTACS inserts is feasible and has a role in augmenting their vision.

Journal Article↗
PubMed2003

Phenotype of Pseudomonas aeruginosa isolates causing corneal infection between 1997 and 2000.

PURPOSE: To investigate the relationship between functional phenotype of and the associated human corneal infection. METHODS: This was an experimental pilot study of patients presenting with corneal infections at the Jules Stein Eye Institute with presumed infection during the period from 12/30/97 to 9/1/00. Thirteen patients were admitted to the study based on positive identification of the causative pathogen as and patient consent. Data were collected (including bacterial cultures, lens wear schedule and care, gender and age, completed history questionnaire, clinical photographs). Statistical analysis of possible correlations was performed. Phenotypes of were determined, and clinical factors associated with infection were explored. RESULTS: Both invasive and cytotoxic phenotypes of were isolated in equal proportion. Cytotoxic strains and invasive strains were found to be associated with patients younger than 50 years of age and older than 50 years of age, respectively. CONCLUSIONS: remains a significant pathogen in corneal infection, especially during contact lens wear. The age of the patient may influence the phenotype of causing infection. Since invasive and cytotoxic strains have different effects on corneal cells, treatment of the infection might require different approaches depending on this phenotype of the causative bacteria.

Adolescent↗
PubMed2002

Complexity of contact lens fitting after refractive surgery.

PURPOSE: To quantify and describe the complexity of contact lens correction on corneas altered by refractive surgery. DESIGN: A case-control study involving postrefractive surgery patients and controls from one multidisciplinary contact lens practice. METHODS: The contact lens care of one randomly selected eye of 30 postrefractive surgery patients (15 postincisional and 15 postlamellar refractive surgery cases) was retrospectively analyzed and compared with that of 30 age-and-gender matched nonrefractive surgery controls. We quantified the complexity by the number of diagnostic lenses used to establish the initial lens order, the number of ordered lenses required to complete the fit, and the number of office visits during the first 4 months of lens care. Final contact lens optical powers, corrected visual acuities, complications, and lens success/failure were also studied. The nonparametric Mann-Whitney U test was used for statistical analysis. RESULTS: Postrefractive surgery eyes utilized statistically more diagnostic lenses (P =.048), ordered lenses (P =.008), and office visits (P <.0001). There were no statistical differences in the number of office visits, number of diagnostic contact lenses used, and number of ordered contact lenses between the postincisional and postlamellar refractive surgery patients. Although final contact lens optical powers were not significantly different (P =.06) between the two groups, contact lens corrected LogMAR acuities were statistically worse (P =.013) in the postrefractive surgery eyes than in the control group. Contact lens failures occurred in four postrefractive surgery eyes, while no eyes in the control group failed to tolerate contact lenses. CONCLUSIONS: Corneas altered by either incisional or lamellar refractive surgery techniques are more challenging to fit with contact lenses than nonsurgically altered eyes, requiring more lenses and chair time, while resulting in slightly poorer contact lens corrected visions and more failures.

Adult↗
PubMed2002

Risk factors for contact lens associated microbial keratitis.

Although the risk of developing contact lens associated microbial keratitis is small, the potential consequences of this condition, such as vision loss, are serious. This paper presents an analysis of the risk factors that have been identified for contact lens induced microbial keratitis, which include extended wear, hypoxia, non-compliance, blepharitis, diabetes mellitus, epithelial trauma, steroid use, therapeutic lens use, tobacco use, and possibly travel to warm climates. By remaining mindful of these risk factors, practitioners can take action and offer advice to patients so as to optimize the safety of contact lens wear.

Journal Article↗
PubMed2002

Diagnosing glaucoma in pediatric aphakia.

BACKGROUND: Cataracts pose a serious threat to the visual system in infants and children, requiring prompt surgical intervention and rehabilitation to optimize visual development. Glaucoma is a serious complication following cataract surgery in infants and can lead to loss of vision. Early diagnosis of glaucoma, however, can be quite challenging in these patients. CASE REPORTS: Three cases are presented in which comeal edema was the initial presenting sign that led to the diagnosis of glaucoma during routine contact lens follow-up examinations for pediatric aphakia. CONCLUSION: The contact lens practitioner, during the course of management of aphakic infants and children, should always be suspicious of glaucoma as a complication of cataract surgery, and the presenting sign may be corneal edema.

Aphakia, Postcataract↗