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Biomedical subjects

Robert L Stamper

Publications and source records attributed to Robert L Stamper.

12 recordsLinked to original sources
PubMed2006

Intraocular pressure and ocular pulse amplitude comparisons in different types of glaucoma using dynamic contour tonometry.

PURPOSE: To compare the intraocular pressures (IOP) and ocular pulse amplitudes (OPA) in patients with different types of glaucoma, ocular hypertension (OHT), and normal controls (NC) using dynamic contour tonometry (DCT) and the goldmann applanation tonometry (GAT). METHODS: 906 eyes of 501 adult patients in the following five groups were included in this cross-sectional study: primary open angle glaucoma (POAG), normal tension glaucoma (NTG), Pseudoexfoliative Glaucoma (PXG), OHT, and NC. The following tests were performed simultaneously during a single visit: IOP using DCT and GAT; OPA using DCT and central corneal thickness (CCT) using ultrasound pachymetry. Mixed effects regression models were used to compare the DCT and GAT IOP measurements in the five groups; the effect of CCT on IOP and the relationship between OPA and IOP within each group. RESULTS: DCT consistently had higher IOP values than GAT in POAG, PXG, NTG, and controls (p < 0.001) but not in OHT (p = 0.84). DCT IOP did not change while GAT IOP showed a non-significant increase (p = 0.09) with increased corneal thickness in each group. OPA was found to be highest in OHT (3.61 mmHg) and lowest in the control group (2.86 mmHg) and significantly increased with IOP in all groups. CONCLUSIONS: DCT measures an IOP that is significantly higher than GAT IOP in glaucoma and control subjects but not in ocular hypertensives. Furthermore, the DCT may measure an IOP that is independent of the CCT, which may not be true for the GAT, which increases with the CCT. OPA was highest in OHT and may be affected by the IOP.

Blood Pressure↗
PubMed2006

Correlation between intraocular pressure, central corneal thickness, stage of glaucoma, and demographic patient data: prospective analysis of biophysical parameters in tertiary glaucoma practice populations.

PURPOSE: To determine the correlation of central corneal thickness (CCT) to Goldmann applanation tonometry (GAT) and dynamic contour tonometry (DCT, PASCAL), and to glaucoma stage as assessed by cup-to-disc ratio (CDR). DESIGN: Prospective, cross-sectional tricenter observation study. PATIENTS AND METHODS: From three glaucoma specialty practices a sample of 406 independent eyes was included. After ultrasound pachymetry, intraocular pressure was measured using PASCAL and Goldmann applanation tonometry and cup-to-disc ration was reassessed. Demographic data were included in the multivariate analysis. RESULTS: Mean corneal thickness was 540 microm. African Americans and normal-tension glaucoma patients showed the lowest values (518 microm and 522 microm, respectively). These values were significantly thinner than the central corneal thickness of Caucasians (549 microm) and ocular hypertensives (564 microm). Intraocular pressure assessed by Goldmann applanation tonometry shows a significant correlation with central corneal thickness (r = 0.068, P < 0.001), whereas PASCAL is not significantly associated with central corneal thickness (r < 0.001, P = 0.997). Increased IOP is significantly correlated with large ocular pulse amplitudes (r = 0.13, P < 0.001), which is predominantly seen in ocular hypertensives. A significant negative correlation was detected between cup-to-disc ratio and central corneal thickness (r = 0.102, P < 0.001). CONCLUSION: Glaucoma patients with thin central corneal thickness are more likely to be found at an advanced stage of the disease and among those with normal-tension glaucoma and black African ancestry. Underestimation of intraocular pressure by Goldmann applanation tonometry could be one causative factor.

Adolescent↗
PubMed2006

Dynamic contour tonometry: principle and use.

Interindividual variability of central corneal thickness has been found to be a source of error for conventional Goldmann applanation tonometry. The dynamic contour tonometer represents a potentially new technology for non-invasive and direct intraocular pressure (IOP) measurement, and has been proposed to accurately measure the true IOP irrespective of the corneal thickness. It is based on the principle that when the tip of the device exactly matches the contour of the cornea, the pressure measured by a transducer placed on its tip is an accurate indicator of the true IOP. This device is also capable of measuring the ocular pulse amplitude, a variable that has controversial significance in the diagnosis and management of glaucoma. Even though this technique seems to be very promising, further studies are required to conclusively determine the effectiveness of the dynamic contour tonometer in patients having an abnormal or irregular corneal contour.

Equipment Design↗
PubMed2005

Clinical comparison of contour and applanation tonometry and their relationship to pachymetry.

OBJECTIVES: To compare intraocular pressure readings of recently introduced dynamic contour tonometry (DCT) with pneumatonometry (PTG) and Goldmann applanation tonometry (GAT) and to correlate central corneal thickness (CCT) with these readings. DESIGN: Prospective, cross-sectional observation and instrument validation study. We included 258 independent eyes with normal anterior segment examinations results, irrespective of glaucoma diagnosis or glaucoma suspect. After pachymetry, DCT, PTG, and GAT were performed in a randomized order. Intraocular pressures as measured by DCT, PTG, and GAT were compared with each other and with CCT. RESULTS: Eyes with thinner CCTs tended to yield lower intraocular pressure measurements by GAT. A significant correlation (Pearson product moment correlation, P<.001) between CCT and GAT was found with a regression of 0.25 mm Hg per 10 microm (R2 = 0.060). Variation of CCT had no significant effect on intraocular pressure measurements by PTG (P = .10; R2 = 0.01) and DCT (P = .80; R2<0.01). A piecewise regression model showed that GAT readings are not linearly correlated with CCT. Comparison of the slopes below and above 535 microm showed the highest significance (P<.001). CONCLUSIONS: Goldmann applanation tonometry readings are potentially influenced by CCT, whereas PTG and DCT seem to be less dependent on CCT. Correlation between CCT and GAT is not linear. A simple correction formula suggesting a linear relationship might not be correct.

Adolescent↗
PubMed2004

Accuracy of dynamic contour tonometry compared with applanation tonometry in human cadaver eyes of different hydration states.

BACKGROUND: In an experimental laboratory investigation we compared intraocular pressure (IOP) measurements obtained by dynamic contour tonometry (DCT), Goldmann applanation tonometry (GAT), and pneumatonometry (PTG) with intracameral manometry on human cadaver corneas of different hydration conditions. METHODS: Ten freshly enucleated eyes were de-epithelialized. Two tubes were placed in the anterior chamber in opposite directions and connected to a transducer and to a bottle system filled with balanced salt solution. The pressure in the eye was then adjusted between 5 mmHg and 58 mmHg by electronically altering the height of the bottle. Central corneal thickness (CCT) was registered and IOP measurements were obtained with DCT, GAT, and PTG at each manometric pressure reading. Immediately after the trial the same corneas were artificially dehydrated and the same measurement regimen was repeated. RESULTS: In the pressure range defined by the bottle height 10-50 cm, IOP values measured by DCT were 0.50 mmHg (95% CI=0.40-0.60) and 0.36 mmHg (95% CI=0.25-0.47) higher than manometric readings before and after dehydration, respectively. GAT showed consistently lower values than manometry, the difference being -3.48 mmHg (95% CI=-3.91 to -3.05) and -3.14 mmHg (95% CI=-3.39 to -2.89), respectively. Similar results were obtained with PGT, namely differences of -4.75 mmHg (95% CI=-5.21 to -4.29) and -3.98 mmHg (95% CI=-4.48 to -3.48) for the hydrated and the dehydrated corneal condition, respectively. Only DCT showed no significant change in accuracy between hydrated and dehydrated corneas. CONCLUSIONS: In this in vitro study DCT values for IOP were significantly closer to the manometric reference pressure than those obtained using GAT and PTG, independent of the state of corneal hydration.

Aged↗
PubMed2004

Dynamic contour tonometry: a comparative study on human cadaver eyes.

OBJECTIVE: To compare intraocular pressure measurements obtained by recently introduced dynamic contour tonometry (DCT), Goldmann applanation tonometry (GAT), pneumatonometry (PTG), and intracameral manometry in human cadaver eyes. METHODS: Sixteen freshly enucleated human cadaver eyes were deepithelialized and dehydrated with dextran. A tube was placed in the anterior chamber and connected to a transducer and to a bottle system filled with balanced salt solution. The pressure in the eye was then altered between 5 mm Hg and 58 mm Hg. Intraocular pressure measurements were obtained with DCT, GAT, and PTG at each manometric pressure reading. RESULTS: On average, DCT values measured 0.58 +/- 0.70 mm Hg higher than real intracameral pressure. The GAT and PGT showed consistently lower values, -4.01 +/- 1.76 mm Hg and -5.09 +/- 2.61 mm Hg, respectively. At all bottle heights, DCT values were significantly closer to the reference pressure than GAT and PTG (P<.001). CONCLUSIONS: Measurement with DCT provides IOP values significantly closer to true manometric levels than either GAT or PTG. Further studies are warranted to determine its reliability in patients and the effect of corneal thickness.

Aged↗
PubMed2004

Central corneal thickness of Caucasians, Chinese, Hispanics, Filipinos, African Americans, and Japanese in a glaucoma clinic.

OBJECTIVE: To characterize the central corneal thickness (CCT) of Asian (Chinese, Japanese, and Filipino), Caucasian, Hispanic, and African American patients in a multiethnic glaucoma practice. DESIGN: Retrospective study (chart review). PARTICIPANTS: Glaucomatous (n = 600) and nonglaucomatous (n = 201) eyes of 801 patients examined in a San Francisco glaucoma clinic from June 2002 to April 2004 who met inclusion criteria were included in the study. The 6 racial (ethnic) groups represented in the study were Caucasian (n = 186, 23.2%), Chinese (n = 157, 19.6%), Japanese (n = 121, 15.1%), Hispanic (n = 116, 14.5%), Filipino (n = 114, 14.2%), and African American (n = 107, 13.4%). METHODS: Central corneal thickness was measured by means of ultrasound pachymetry in Asian (Chinese, Japanese, and Filipino), Caucasian, Hispanic, and African American participants with glaucomatous and normal eyes. The relationship between CCT and race was investigated using multivariate regression analyses, controlling for confounders. One eye of each of 801 participants was included for analysis. MAIN OUTCOME MEASURES: Correlation of mean CCT with race, glaucoma diagnosis, age, spherical equivalent, gender, and history of ocular surgery. RESULTS: The mean CCT of all participants was 542.9 mum. Central corneal thicknesses of Chinese (555.6 microm), Caucasian (550.4 microm), Filipino (550.6 microm), and Hispanic (548.1 microm) participants did not significantly differ. The CCT of Japanese participants (531.7 microm) was significantly less than that of Caucasians, Chinese, Filipinos, and Hispanics (all, P< or =0.001) and greater than that of African Americans (P = 0.03). African Americans had a CCT (521.0.0 microm) less than that of all races (P< or =0.05). Glaucoma suspects and patients with normal tension glaucoma (NTG), primary open-angle glaucoma (POAG), pseudoexfoliation glaucoma (PEX), and chronic angle-closure glaucoma (CACG) had corneas significantly thinner than those of normal participants (P< or =0.004), whereas ocular hypertensives had significantly thicker corneas (P<0.0001). Among all participants, decreasing values of CCT were significantly related to older age (P<0.01). Less negative or more positive refractive errors, gender, and history of ocular surgery were not associated with changes in CCT (P = 0.38, P = 0.50, and P = 0.97, respectively). CONCLUSIONS: Studies examining individual Asian subpopulations in isolation suggest that differences in CCT may exist among different Asian groups. The results of this study indicate that CCT does, in fact, vary among Asian subpopulations; Japanese have thinner corneas than Chinese and Filipinos. Caucasians, Chinese, Hispanics, and Filipinos have comparable CCT measurements, whereas the corneas of African Americans are significantly thinner. Additionally, older individuals; glaucoma suspects; and participants with NTG, POAG, PEX, and CACG have thinner corneas. Ocular hypertensives, however, have thicker corneas.

Adult↗
PubMed2003

Visual acuity and its measurement.

Despite its critical importance to our daily life, the most common measurement of visual function, visual acuity, is a relatively crude and narrow one testing only a small portion of the broad range of visual functions. Visual acuity is the measurement of the ability to discriminate two stimuli separated in space at high contrast relative to the background. Clinically, this is measured by asking the subject to discriminate letters of known visual angle. The visual acuity is represented as the reciprocal of the minimal angle of resolution (the smallest letters resolved) at a given distance and at high contrast. Other measurements of visual acuity also exist, including Vernier acuity. Newer charts, such as the ETDRS chart, use letters of equal recognition difficulty and use the log of the minimal angle of resolution; these charts have significant advantages over the old Snellen-type charts. This article reviews visual measurements in children and in patients with low vision, and it reviews factors affecting visual acuity, such as pupil size, refractive error, media opacities, and pharmacologic agents.

Eye Diseases↗
PubMed2002

Enzymatic sclerostomy: pilot human study.

OBJECTIVE: To evaluate the feasibility and safety of enzymatic sclerostomy as a new modality to lower intraocular pressure in patients with open-angle glaucoma. METHODS: This single-center, prospective, noncomparative, interventional case series included 15 blind symptomatic eyes of 15 patients with primary open-angle glaucoma. Enzymatic sclerostomy was performed with the patient under topical or peribulbar anesthesia. A specially designed polymethylmethacrylate enzyme applicator filled with a mean +/- SD of 123 +/- 13 microg of collagenase was introduced through a 5-mm peritomy, and affixed to the limbus by means of cyanoacrylate tissue glue. After 22 to 24 hours, the applicators were removed and the patients were followed up for 1 year. Intraocular pressure changes from baseline and complications related to the procedure were the main outcome measures. RESULTS: Controlled thinning of the treated sclera associated with aqueous percolation and shallow filtration bleb was seen in all eyes in the immediate postoperative period. The mean +/- SD intraocular pressure decreased from 43.5 +/- 9.8 mm Hg (while the patients were receiving a mean +/- SD of 1.75 +/- 0.75 antiglaucoma medications) preoperatively to 24.8 +/- 10.6 mm Hg (a 43.0% decrease from baseline with no antiglaucoma medication) on the first postoperative day and to 34.8 +/- 10.5 mm Hg (a 20.0% decrease from baseline with no antiglaucoma medication) at the end of 1 year. Ophthalmic adverse effects were limited to the treated area and included immediate postoperative transient conjunctival reaction ranging from mild chemosis to conjunctival maceration. Immediate full-thickness perforation developed in 1 eye; the patient was treated and excluded from data analysis. Two eyes developed symptoms related to increase in intraocular pressure after 9 months; the patients were treated and excluded from further data analysis. No systemic complications were noted. CONCLUSIONS: Enzymatic sclerostomy demonstrated immediate and sustained intraocular pressure reduction and provided symptomatic relief in blind eyes with primary open-angle glaucoma. The procedure, however, needs further technical refinement.

Aged↗
PubMedDate not supplied

Primary drug treatment for glaucoma: beta-blockers versus other medications.

This set of Viewpoints articles examines the merits of beta-blockers versus other medications as the primary drug treatment for glaucoma. Ophthalmologists must balance issues such as efficacy, compliance, cost, and side effects when deciding on the appropriate medication to prescribe. Dr. Stamper stresses the advantages of tailoring the choice of medication to the needs of the individual patient. Drs. Wigginton and Higginbotham review the benefits of beta-blockers and present some of the disadvantages of the non-beta-blocker class of medications.

Adrenergic alpha-Agonists↗