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Biomedical subjects

P Macken

Publications and source records attributed to P Macken.

7 recordsLinked to original sources
PubMed1999

Agreement in assessing glaucomatous discs in a clinical teaching setting with stereoscopic disc photographs, planimetry, and laser scanning tomography.

PURPOSE: Agreement between three observers--two recently trained fellows and their supervisor--was measured using estimations of cup/disc ratio from stereoscopic optic nerve head photographs and planimetric measurements of cup/disc ratio. Agreement between the clinicians' planimetric measurements of cup/disc ratio and laser scanning tomographic measurements of cup/disc ratio also was assessed. METHODS: From 16 stereoscopic optic nerve head photographs of 16 subjects, the three observers performed clinical estimations of horizontal and vertical cup/disc ratios and planimetric measurements of cup/disc ratios. Interobserver agreement was measured using intraclass correlation coefficients (ICCs). Agreement between the planimetric cup/disc ratios and laser scanning tomographic cup/disc ratios obtained with the Heidelberg Retina Tomograph (HRT; Heidelberg Engineering, Heidelberg, Germany) also was measured using ICCs. The difference between the planimetric and HRT cup/disc ratios was calculated. RESULTS: The agreement between observers for clinical estimations from stereoscopic optic nerve head photographs (ICC = 0.74 horizontally and 0.83 vertically) was substantial. Agreement between the observers' planimetric measurements of cup/disc ratio was substantial (ICC = 0.79). Agreement between HRT cup/disc ratio and each observer's planimetric cup/disc ratio was moderate (ICC = 0.57-0.65), with large confidence intervals. The cup/disc ratio measured with HRT was an average of 0.07 to 0.11 larger than the planimetric cup/disc ratio. CONCLUSION: Substantial agreement between observers can be achieved when estimating cup/disc ratio with stereoscopic optic nerve head photographs and with planimetric measurements of cup/disc ratios, provided there is a standard protocol and sufficient training period. Good agreement is critical in a teaching institution to ensure accurate follow-up care of patients with glaucoma, especially if patients are examined by different clinicians. Laser scanning tomography is a more repeatable and objective method, which may provide further standardization of optic nerve head assessments. Future studies will determine the reference plane that optimizes agreement between the HRT findings and each clinician's estimations.

Confidence Intervals↗
PubMed1996

Glaucoma laser suture lysis.

AIM: Suture lysis is commonly performed after trabeculectomy to improve bleb function. It is often thought to be an innocuous procedure. This is the first large study to determine the safety of the procedure and compare results with a control group. METHODS: Two hundred successive trabeculectomies performed between January 1992 and October 1993 were analysed. RESULTS: Ninety nine eyes underwent trabeculectomy and suture lysis; 101 eyes underwent trabeculectomy and did not require postoperative suture lysis. The following complications were noted with suture lysis: flat chambers (13.1%), external aqueous leaks (9%), malignant glaucoma (2%), iris incarceration (2%), and large blebs (2%). All resolved with appropriate management. There was no significant difference in the final postoperative mean pressures between the lysis and the non-lysis groups. CONCLUSION: Suture lysis is not an innocuous procedure. However if managed appropriately, complications do not affect the intraocular pressure outcome.

Eye Injuries↗
PubMed1996

Accommodation and iridotomy in the pigment dispersion syndrome.

BACKGROUND AND OBJECTIVE: Iris concavity has been noted in pigment dispersion syndrome, and could have a role in producing iris-zonule contact. Iris concavity is most likely caused by a relative increase in anterior chamber pressure. The method by which this occurs remains speculative. The authors used ultrasound biomicroscopy to examine the role of accommodation in producing iris concavity and to document changes that occur following iridotomy. PATIENTS AND METHODS: Thirteen patients with clinically diagnosed pigmentary dispersion and pigmentary glaucoma underwent accommodation studies while being continuously imaged with ultrasound biomicroscopy. Anterior chamber depths were measured and iris configuration noted on distance and near fixation. These studies were repeated in 6 patients following laser iridotomy. RESULTS: All patients showed a decrease in anterior chamber depth with accommodation. Ten patients had a planar iris configuration on distance fixation and 3 concave. Eleven of 13 patients showed increased concavity of the iris on near fixation as compared with distance fixation. Following iridotomy in 6 patients, the iris showed a planar configuration that remained unchanged on near fixation. CONCLUSION: Accommodation increases iris concavity in some patients with pigment dispersion syndrome. The most likely explanation is an accommodation-induced relative increase in anterior chamber pressure secondary to anterior movement of the lens surface. Iridotomy prevents change in the iris profile with accommodation.

Accommodation, Ocular↗
PubMed1995

Ultrasound biomicroscopic imaging of the effects of YAG laser cycloablation in postmortem eyes and living patients.

PURPOSE: The authors performed a series of experiments designed to determine if early effects of YAG laser cycloablation could be detected by ultrasound biomicroscopy in postmortem eyes and living patients. They also designed an apparatus that allowed simultaneous ultrasound biomicroscopic imaging of YAG laser cycloablation. METHODS: Treated and untreated regions of postmortem eyes treated with YAG cycloablation were imaged and compared. Treatment was placed at varying distances from the limbus in postmortem eyes and the resulting effects imaged. Histologic examinations were performed after imaging. Six living patients had ultrasound biomicroscopy before and after YAG cycloablation. An apparatus combining contact YAG laser and ultrasound biomicroscopy was used in postmortem eyes. RESULTS: Early treatment effects imaged included ciliary epithelial disruption, ciliary epithelial separation, and bubble formation. Ultrasound biomicroscopic findings varied with the distance of treatment from the limbus and were maximal below the treatment site. Results of histologic examination showed close correlation to the ultrasound biomicroscopic images. Similar findings to those found in postmortem eyes were found in living patients after treatment. The apparatus combining contact YAG and ultrasound biomicroscopy allowed realtime imaging of effects of YAG laser cycloablation. CONCLUSIONS: The ability of ultrasound biomicroscopy to detect changes associated with cyclodestructive procedures potentially could provide us with a method of improving treatment precision and correlating treatment effect with clinical response.

Cadaver↗
PubMed1994

Ultrasound biomicroscopic features of pigmentary glaucoma.

We have developed a device capable of producing subsurface images in eyes at microscopic resolution. We call this method "ultrasound biomicroscopy." We examined 19 patients with pigmentary glaucoma or pigmentary dispersion syndrome using ultrasound biomicroscopy. Ten patients were found to have concave irides with small distances between the back of the iris and the zonule. In these patients iris-lens contact was greater than in patients without iris concavity and healthy patients. Nine patients did not show iris concavity or increased iris-lens contact. The finding of iris concavity and increased iris-lens contact is compatible with a theory of reverse pupil block producing intermittent iris-zonule touch, with a valve effect preventing posterior flow of aqueous. This theory was supported by the loss of concavity following iridotomy in three patients. The force that produces a reversal of the normal pressure gradient remains unclear, but recent evidence suggests that accommodation plays a major role. The patients who did not show iris concavity and increased iris-lens contact may have been examined at a time when these forces were not acting or had ceased to act.

Adult↗
PubMed1992

Superior sagittal sinus thrombosis--an unexpected cause of papilloedema.

Two patients with superior sagittal sinus thrombosis are reported. Papilloedema was an important diagnostic sign in both cases. Magnetic resonance imaging (MRI) provided the diagnosis in each case and proved to be the investigation of choice. Superior sagittal sinus thrombosis should be considered in the differential diagnosis of papilloedema as it is both potentially fatal and probably underdiagnosed.

Adult↗