A new method for assessment of changes in retinal blood flow.

This study validates the use of residence time distribution (RTD) functions in human subjects to assess changes in retinal flow by using the widely recognized model of flow changes due to oxygen breathing. Changes in retinal blood flow may provide important information for clinical decision-making in several populations, including those with diabetic retinopathy, sickle cell disease and retinitis pigmentosa. Normal volunteer subjects were studied before and after oxygen breathing. After i.v. injection, relative fluorescence was obtained using scanning laser ophthalmoscopy/image processing in all vessel branches (average, 17). For each experiment, 64 frames (2/s) were digitized and were normalized using the RTD method. Vessel diameters were measured using densitometry techniques on fundus photos, where the diameter data made it possible to weight each vessel according to relative cross-sectional area to obtain a true mean circulation time (MCT). MCT increased for the group of subjects when breathing oxygen compared to normal air (P = 0.001), representing a decrease in retinal blood flow. Average MCT increased 2.82 +/- 2.51 s for all subjects, with an increase of 2.93 +/- 2.26 s in repeat trials for one subject. The proposed method uses information from all retinal vessels and allows the assessment of overall, as well as selected, regional retinal flow. It is more comprehensive than previous methods analysing single vessel flow. This method will be potentially useful for assessing hemodynamic changes in the retina associated with a wide range of eye disease.

Temporal changes in posterior capsulotomy dimensions following neodymium:YAG laser discission.

We prospectively evaluated 20 eyes of 19 consecutive patients to determine the nature of temporal changes in posterior capsulotomy size, shape, and contour six weeks following neodymium:YAG laser posterior capsular disruption. Mean capsulotomy area increased by 32% (range 0 to 134%, P less than .05, Student t-test), although mean capsulotomy perimeter did not change appreciably. Capsular enlargement tended toward sphericity over time, with smoothing of edge contour from capsular tag retraction. Remodeling of opening size, shape, and contour was most likely to occur with preoperative evidence of capsular traction, and highly irregular capsulotomy borders immediately post-discission.

Corneal topography using rasterstereography.

Rasterstereography is a new method of determining the topography of the cornea. Unlike Placido disc types of systems it does not depend on the reflectivity of the corneal surface, and it can provide information about the entire corneal, limbal and interpalpebral conjunctival surfaces. Since a smooth reflective surface is not required, images can be obtained with epithelial irregularity or defects, sutures, or stromal ulceration. A grid of horizontal and vertical bars of light is projected onto the cornea, and the pattern of the grid on the ocular surface is determined by its topography. The image is obtained by a video camera, and digitized, stored, and analyzed by an image processor. A three dimensional image of the corneal surface, contour maps of corneal elevation, and corneal curvature can be displayed.

Corneal topography using computer analyzed rasterstereographic images.

This paper describes a new method for determining corneal surface detail utilizing a modified Zeiss photo slit lamp. This system projects a grid onto the cornea through a cobalt blue filter. The tear film is stained with fluorescein, causing the projected grid pattern to be visible on the corneal surface. A video image of the grid is then digitized by an image processor which calculates surface detail by evaluating the distortion of the grid lines. Information on curvature and surface detail is obtained across the full corneal surface, both the central optical axis and peripherally beyond the limbus.

Use of directly acquired digital fundus and fluorescein angiographic images in the diagnosis of retinal disease.

Direct on-line acquisition of digital fundus and fluorescein images is a useful alternative to conventional fundus photography. Immediately after acquisition, digital images may be electronically reassembled, manipulated, and displayed, avoiding the delays inherent in film development. Digital fundus images, conventional photographs, and fluorescein angiograms were obtained at the same sitting in 50 consecutive patients with retinal disease. Digital studies were displayed on a video monitor and diagnoses were made directly from the screen. The interpretations based on digital images alone were virtually identical to those made from photographs, although the resolution of digital images was not equal to that of the photographic images. Despite this disadvantage, the system proved extremely versatile, and for this reason, digital image acquisition was used to routinely document the retinal findings in the majority of the clinical patients.

Endothelial morphology in long-term keratoconus corneal transplants.

Endothelial morphology was studied in 55 long-term keratoconus grafts. Photographs were taken with a Zeiss non-contact endothelial lens and analyzed with a Zeiss MOP-3 digital analyzer. Donor ages were known in 39 cases. Statistical analysis was carried out correlating endothelial cell count with several parameters, including recipient age and cell form as expressed by the coefficient of variation. Cell counts varied from 502 to 1708 cells/mm2. No correlation between cell counts and donor age was found. Recipient age had an unexpected significance as a predictor of endothelial cell survival in that cell counts decreased as recipient age increased despite donor age. As the grafts aged, more cell pleomorphism was found as expressed by the coefficient of variation.