Biomedical subjects

Alexander C Walsh

Publications and source records attributed to Alexander C Walsh.

4 recordsLinked to original sources

PubMed2007

Quantitative fluorescein angiographic analysis of choroidal neovascular membranes: validation and correlation with visual function.

PURPOSE: To compare computerized analysis with traditional grading methods in the analysis of fluorescein angiograms from patients with choroidal neovascularization (CNV) due to age-related macular degeneration (AMD) and to examine the clinical relevance of parameters generated by computerized analysis by testing their relationships with clinical measures of vision. METHODS: Custom quantitative fluorescein analysis (QFA) software was used to analyze 62 angiograms from patients with CNV for whom distance visual acuity (DVA) data were available. On applying QFA, we obtained three mathematical parameters for each lesion component: pixel area (PA), integrated intensity (II), and positive fluorescence (PF). Quotients (Q) were derived for the latter two parameters by correcting against background (b) or optic nerve (o) fluorescence (IIQ(b), IIQ degrees , PFQ(b), and PFQ degrees ). The new metrics were compared with traditional grading parameters of classic CNV and lesion area. The relationships of both sets of angiographic data with measures of vision were explored by regression analyses. RESULTS: Weighted kappa between QFA and traditional grading for lesion subtype assessment was high (kappa = 0.7). Regression analyses with PA, IIQ(b), IIQ degrees , PFQ(b), and PFQ degrees for each lesion descriptor (leakage, classic CNV, occult CNV, total lesion) as independent variables and DVA as the dependent variable showed that in every case PFQ(b) exhibited the most significant relationship with vision (adjusted r(2) = 0.26). Parameter estimates showed that for a change of 30 units on the PFQ(b) for classic CNV, a loss of 20 letters of DVA may be expected. No parameters from traditional grading methods showed statistically significant relationships with DVA. CONCLUSIONS: The markers of dynamic change in area and intensity of fluorescence exhibited stronger relationships with visual function than did area measurements alone.

Choroidal Neovascularization↗

PubMed2006

Automated detection of clinically significant macular edema by grid scanning optical coherence tomography.

OBJECTIVE: To compare the detection of clinically significant diabetic macular edema (DME) by an optical coherence tomography (OCT) grid scanning protocol and biomicroscopic examination. DESIGN: Retrospective case series. PARTICIPANTS: Outpatients at the Doheny Eye Institute. METHODS: The clinical and imaging records of a consecutive series of 71 eyes of 40 patients referred for DME who underwent OCT using the both the Macular Grid 5 (MG5) scanning protocol (to allow a more evenly distributed sampling of points in the macula) and the standard Fast Macular Thickness Map (FMTM) pattern were reviewed. An automated algorithm was developed to generate a retinal thickness map using the MG5 data, which was then compared with a normative database to identify presumed areas of retinal edema. Clinically significant macular edema (CSME) was also identified by clinical examination and stereoscopic fundus photographs for comparison with the results of the OCT protocols. MAIN OUTCOME MEASURES: Sensitivity and specificity of scanning protocols. RESULTS: Optical coherence tomograms were inspected visually, and automatically detected retinal boundaries were found to be correct in 69 of 71 MG5 scans and in 65 of 71 FMTM scans. Macular Grid 5 scanning was performed twice in each eye, and the repeatability (pooled standard deviation) of the total area of edema was 0.48 mm2 (coefficient of variation, 6.8%). Sensitivity and specificity of the MG5 for detection of CSME relative to the clinical examination were 89% and 86%, respectively, with kappa being 0.74. Macular Grid 5 and FMTM assessment of foveal CSME also showed good agreement, with kappa being 0.68. CONCLUSIONS: The analysis algorithm for the OCT MG5 grid scan seems to be accurate and repeatable. Automated detection of CSME by the MG5 analysis correlated well with the clinical grading and standard OCT analysis (FMTM). Macular Grid 5 provides more information regarding the perifoveal macula than FMTM and may be of value to clinicians in planning treatment and in future studies of macular edema.

Algorithms↗

PubMed2006

Errors in retinal thickness measurements obtained by optical coherence tomography.

OBJECTIVE: To report the frequency and severity of optical coherence tomography (OCT) retinal thickness measurement errors and to describe parameters that predict these errors. DESIGN: Observational case series. PARTICIPANTS: Two hundred consecutive patients undergoing OCT imaging. METHODS: One eye (primary) from each of 200 consecutive patients undergoing Stratus OCT imaging (Carl Zeiss Meditec, Dublin, CA) with radial lines or fast macular thickness-based acquisition protocols was selected for review by 2 graders. On each of the line scans, graders evaluated the position of the automated retinal boundary lines (inner retinal surface and retinal pigment epithelium band) used by the OCT machine for thickness calculations and graded the positioning on a 6-point subjective, categorical error scale to generate an error score. The presence of thickness errors was correlated with various parameters, including the analysis confidence assessment reported by the OCT software, disease diagnosis, retinal morphologic features, the foveal center thickness standard deviation (FCTSD), and the FCTSD-to-foveal center thickness (FCT) ratio. MAIN OUTCOME MEASURE: Average OCT retinal thickness error score. RESULTS: Errors of retinal boundary detection and thickness measurement were observed in 92% of eyes, but were severe in only 13.5% of eyes. The identification of an error or low analysis confidence by the OCT software was strongly associated with the severity of the retinal thickness errors. A higher FCTSD-to-FCT ratio and presence of subretinal fluid also were associated with more severe errors. Retinal cysts and a diagnosis of retinal vascular disease such as diabetic macular edema were less likely to be associated with significant errors. CONCLUSIONS: Retinal thickness measurement errors occur frequently with current OCT segmentation and analysis algorithms. Severe errors are more frequent in eyes with subretinal pathologic features, but generally are detected by the OCT software. A high FCTSD-to-FCT ratio (>0.1) also may alert the clinician to the possibility of thickness errors. Clinical studies, particularly those pertaining to subretinal diseases, should consider these errors when incorporating OCT imaging in the study design.

Diagnostic Errors↗

PubMed2005

Rapid recurrence of geographic atrophy after full macular translocation for nonexudative age-related macular degeneration.

OBJECTIVE: To report the recurrence of geographic atrophy (GA) in a patient with nonexudative age-related macular degeneration (AMD) after full macular translocation. DESIGN: Observational case report. METHODS: Review of the clinical, photographic, and angiographic records of a patient with GA who underwent full macular translocation. MAIN OUTCOME MEASURES: Progression of GA. RESULTS: A 73-year-old man with GA secondary to nonexudative AMD underwent a macular translocation with 360 peripheral retinectomy (MT 360) in his left eye. On postoperative month 4, fundus photography showed subtle alterations of the pigment underneath the translocated foveal region. On postoperative month 9, the visual acuity worsened to preoperative levels and there was frank retinal pigment epithelium atrophy involving the new macular region. CONCLUSIONS: The rapid recurrence and development of GA in the translocated fovea after MT 360 raise new questions regarding the pathogenesis of GA. They also raise concerns regarding the use of MT 360 in the management of nonexudative AMD.

Aged↗