Efficient reactivation of latent herpes simplex virus type 1 infection by excimer laser keratectomy in the experimental rabbit ocular model.

PURPOSE: To investigate the role of excimer laser keratectomy as a trigger for the reactivation of latent HSV type 1 (HSV-1) in the New Zealand rabbit ocular model. There are conflicting reports in the current literature about reactivation of HSV-1 after excimer laser photoablation. METHODS: New Zealand rabbits were inoculated topically with HSV-1 McKrae or W strain in each eye, and culture-positive dendritic keratitis was documented on day 7. After the establishment of latency (21+ days), animals were divided into three groups: group I animals underwent excimer laser photoablation in each eye; group II animals received intrastromal injections of sterile water to act as positive controls (a standard method); and group III animals received no treatment and represented spontaneous shedders. All eyes were swabbed daily from days 1 through 10 and plated on A549 cells. Recovery of HSV-1 on days 1 through 10 postinduction was analyzed to compare the efficiency of the different methods of viral reactivation. RESULTS: Reactivation of latent HSV-1 after excimer treatment was observed in nine (45%) of 20 eyes and was equivalent to the rate of reactivation seen in the positive control animals (eight [44.4%] of 18 eyes) (P=.99). Both of these rates were significantly greater than those of the untreated animals (one [5.6%] of 18 eyes) (P=.018). CONCLUSION: Excimer laser keratectomy appears to be an efficient trigger for the reactivation of latent HSV-1 in the New Zealand rabbit ocular model.

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.

Effect of neodymium: YAG laser on sodium hyaluronate in vitro as a model for postcapsulotomy intraocular pressure change.

PURPOSE: To define one possible etiology for the rise in intraocular pressure (IOP) after neodymium: YAG (Nd:YAG) laser capsulotomy and provide information for the continued investigation of this process. SETTING: Laser Center, Eye and Ear Institute, Pittsburgh, Pennsylvania. METHODS: Samples of 1% sodium hyaluronate or balanced salt solution (BSS) (control) were placed in a closed system and exposed to varying amounts of Nd:YAG energy delivered by a Coherent YAG laser. This system was hydrostatically coupled to a pressure monitor, and changes in pressure were recorded as a function of time. RESULTS: Average pressure increase was 0.140 mm Hg/mJ of YAG energy in the sodium hyaluronate samples and 0.017 mm Hg/mJ in BSS (P < .01). The relationship between total energy delivered and maximum pressure recorded for both substances was nearly linear. Further analysis of treated sodium hyaluronate samples showed that Nd:YAG energy can produce structural alterations. CONCLUSIONS: Neodymium:YAG laser energy has a pronounced effect on sodium hyaluronate that exceeds the thermal effect seen with BSS when the pressure is monitored in a closed system. These structural changes might contribute to the IOP rise seen clinically.

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.

Polytetrafluoroethylene in experimental retinal detachment surgery.

Expanded polytetrafluoroethylene (PTFE) material was evaluated as an adjunctive material for retinal detachment surgery. A 4 mm sponge was wrapped in a 4 mm diameter tube of PTFE and sutured episclerally. Additionally, PTFE was rolled and sutured into an episcleral pocket as an implant material. Microscopic sectioning demonstrated a minimal inflammatory response and ingrowth of connective tissue into the PTFE. The intrascleral PTFE had also become successfully infiltrated with connective tissue, creating a thick, fibrovascular intrascleral implant. This material may prove useful in preventing extrusion of Silastic sponge exoplants, as a buckling element for intrascleral procedures, or as a covering for staphylomatous areas that require episcleral buckling.

A long-term implantable aqueous delivery system for the external rabbit eye.

An implantable system is described which continuously delivered an aqueous solution to the external surface of six rabbit eyes for 6 weeks. A polytetrafluoroethylene tube was implanted in the superior conjunctival fornix 4 weeks prior to the implantation of the Infusaid pump. The pump provides a fluid source which is easily refilled and requires no batteries or external power source.

A simple device to improve blinking.

A blink beeper was devised to remind patients with incomplete or infrequent blinking to blink completely and at normal intervals; the beeper worked by transmitting an audible tone every ten seconds through an earphone. In three postkeratoplasty patients, this simplistic approach not only resulted in a complete blink at regular intervals, but seemed to condition this response to continue when the blink beeper was taken away; this resulted in healing of large chronic epithelial defects. The blink beeper has also proved valuable in patients with either punctate epithelial erosions or those who wore hard contact lenses unsuccessfully because of infrequent or incomplete blinking.

Armrest support for the slit-lamp delivery argon laser system.

We designed a new armrest for use at the argon laser. The arm support can be used on either the right- or left-hand side of slit-lamp tables of varying thicknesses. The continuous screw adjustment allows for easy height adjustment of the arm support. The construction of the armrest facilitates the adjustment and manipulation of a fundus contact lens, which is so necessary to the successful performance of argon laser photocoagulation.