Handwriting with a preferred retinal locus for AMD with scotomas.

PURPOSE: Individuals with macular scotomas from age-related macular degeneration frequently have difficulty writing legibly. The purpose of this study was to investigate the causes of this difficulty by documenting the location of the retinal image of the pen used for writing in relation to the scotoma and fixational preferred retinal locus (fPRL). METHODS: Subjects with macular scotomas from age-related macular degeneration and visually normal age-matched controls wrote words while observing their hand, pen, and text in a scanning laser ophthalmoscope. Scanning laser ophthalmoscope video images were analyzed to find the retinal positions of the subject's scotoma, fixation area, and pen tip. RESULTS: Control subjects placed their fovea and scotoma subjects placed their fPRL on or very close to the pen tip for both cursive writing and printing. Scotoma subjects' written text sloped downward at a greater angle than controls'. Text angle was negatively correlated with fPRL eccentricity, visual acuity, and the amount the scotoma obscured the writing guides. When printing, control subjects placed their fovea precisely in the center of printing box guides, whereas scotoma subjects exhibited highly dispersed placement of the fPRL. CONCLUSIONS: The principal finding is that, because the retinal locations of the pen tip and the fPRL or fovea are coincident or very close, the fPRL and fovea are "monitoring" the pen tip and its location on the page. It is the PRL determined by asking subjects to fixate (i.e., the fPRL) that is used when handwriting, not a separate "handwriting" PRL. The poor handwriting performance of those with macular scotomas seems to be primarily caused by difficulty in placing letters in the appropriate location probably because of reduced visual acuity of the fPRL and scotoma obscuration of the area on which to write.

Preferred retinal locus--hand coordination in a maze-tracing task.

PURPOSE: Fine manual tasks require coordination of vision, eye movements, and motor control. Macular scotomas from age-related macular degeneration (AMD) may adversely affect this coordination. The purpose of this research was to find whether the preferred retina locus for fixation (fPRL) also guided the hand in performing fine manual tasks and how the fingers, fPRL, and scotomas interacted in task performance. METHODS: Subjects with bilateral macular scotomas from AMD and normally sighted controls traced an irregular "maze" line pattern with the index finger while viewing their hand and the maze in a scanning laser ophthalmoscope (SLO). Video images from the SLO showing the fingers and maze on the retina during the task were analyzed to produce retinal maps showing the scotoma and bivariate ellipses of fPRL and fingertip retinal positions. RESULTS: Fingertip retinal ellipses surrounded and were approximately centered on the fPRL ellipses. Fingertip retinal bivariate area was positively correlated with fPRL bivariate area and the percent time the fPRL was on the maze was correlated with visual acuity. Maze-tracing accuracy was positively correlated with saccade rate for scotoma subjects. CONCLUSIONS: Concentric overlap of fPRL and fingertip retinal ellipses indicates that it is the fPRL that guides the hand in the maze-tracing visuomotor task, just as the fovea guides the fingertip for visually normal subjects. It is likely that factors other than fPRL and scotoma characteristics contribute to poorer maze-tracing performance by scotoma subjects in comparison with controls.

Effect of bilateral macular scotomas from age-related macular degeneration on reach-to-grasp hand movement.

PURPOSE: Vision plays a critical role in reaching and grasping objects. Consequently, bilateral macular scotomas from age-related macular degeneration (AMD) may affect reach-to-grasp movements. The purpose of this work was to investigate changes in reach-to-grasp movement dynamics and to relate those changes to the characteristics of subjects' preferred retinal loci (PRL), scotomas, and visual acuities. METHODS: Three-dimensional positions of the index finger and thumb were recorded while subjects with bilateral scotomas and subjects with normal vision reached for and grasped blocks of three widths at two distances under binocular and monocular viewing conditions. Reach-dynamic parameters and the grip aperture (thumb-index finger distance) were calculated. Retinal locations and sizes of subjects' scotomas and PRLs were mapped with a scanning laser ophthalmoscope. RESULTS: Scotoma subjects' hand trajectories had longer movement durations, lower maximum velocities, and longer visual reaction times than those of control subjects. With monocular viewing, maximum grip aperture (MGA) increased as a function of block width at a significantly higher rate for scotoma subjects than for control subjects. MGA decreased with increasing PRL bivariate normal ellipse area, and visual reaction time increased with decreasing acuity of the eye tested. CONCLUSIONS: Compared with normally sighted subjects, subjects with bilateral macular scotomas from AMD have reach-to-grasp movements with longer trajectories, longer visual reaction times, lower velocities, and altered MGA-block width scaling. Visual reaction time and MGA are directly related to PRL characteristics. Deficits in reach-to-grasp movement caused by macular scotomas are greater in degree than those reported by others for real or artificial peripheral scotomas.

Retinal image location of hand, fingers, and objects during manual tasks.

PURPOSE: A new method was developed using the scanning laser ophthalmoscope (SLO) to investigate the effects of central visual loss on eye-hand coordination in manual tasks. Using the SLO, the retinal positions of the hand, fingers, and objects are imaged and recorded while a subject performs a manual task. METHOD: A video camera images the subject's hand and objects to be manipulated in the SLO laser-beam raster, producing a video image of a subject's hand, fingers, and objects on the subject's retina while the objects are manipulated. A subject with bilateral central scotomas and an age-matched control subject with normal vision traced an ellipse with the index finger, tapped four disks in sequence, and carried out a pattern duplication task with pegs. Retinal positions of the fovea or preferred retinal locus (PRL), fingers, and objects were measured from digitized SLO images. RESULTS: In all tasks, the fovea or PRL was directed to an object or position before the fingers arrived. This lead time was much greater for the scotoma subject than the control subject ( approximately 1400 vs. approximately 400 ms, respectively). The scotoma subject was much less accurate in placing the PRL and fingers on objects and required substantially more time for task completion than the control subject. CONCLUSIONS: The coordination of foveal fixation and finger placement found with the SLO method was similar to that found by others using eyetracking techniques with visually normal subjects. The presence of a central scotoma and use of a PRL caused marked deterioration in the quality of this coordination. Unlike eyetracking methods, the SLO technique does not require calibration because the positions of the fingers and objects are directly observable on the retina. This method could be useful in studying eye-hand coordination of individuals with scotomas that affect foveal vision.

Collagen cross linking agents: design and development of a multifunctional cross linker.

A new cross linking reagent based on the first-generation polyamidoamine dendrimer (G.1 PAMAM) has been synthesized by reaction of the PAMAM with eight equivalents of p-nitrophenyl diazopyruvate. The resulting water-soluble octadiazopyruvoyl PAMAM (8G.1 DAP, 1.3) was shown to undergo Wolff rearrangements upon photolysis in methanol at lambda > 300 nm to yield the methyl esters of the ketenes formed from the loss of nitrogen. 8G.1 DAP also forms strong bonds with dehydrated collagen with glass as high as 36 N cm(-2). Collagen to collagen bonds with tensile strengths as high as 92 N cm(-2) were observed with fully dehydrated tissues. The bonding decreased rapidly with increasingly hydrated tissue possibly due to the increased distance between the collagen fibrils and the competition of H2O for the free ketene functions.

Retinal locus for scanning text.

A method of mapping the retinal location of text during reading is described in which text position is plotted cumulatively on scanning laser ophthalmoscope retinal images. Retinal locations that contain text most often are the brightest in the cumulative plot, and locations that contain text least often are the darkest. In this way, the retinal area that most often contains text is determined. Text maps were plotted for eight control subjects without vision loss and eight subjects with central scotomas from macular degeneration. Control subjects' text maps showed that the fovea contained text most often. Text maps of five of the subjects with scotomas showed that they used the same peripheral retinal area to scan text and fixate. Text maps of the other three subjects with scotomas showed that they used separate areas to scan text and fixate. Retinal text maps may help evaluate rehabilitative strategies for training individuals with central scotomas to use a particular retinal area to scan text.

Bonding corneal tissue: applications of photoactivated diazopyruvoyl cross-linking agent.

Photoactivated bis-diazopyruvamide-N,N'-bis(3-diazopyruvoyl)-2,2'-(ethylenedioxy)bis-(ethylamine), (DPD)-was previously shown to bond materials containing type I collagen. However, tensile strength of bonded collagenous tissue ( approximately 78% water) was low compared with that of dehydrated collagenous gelatin ( approximately 14% water). Here we investigated the role of water in corneal tissue bond strength and in bonding corneal tissue to glass. Bonding corneal tissue to glass may be of value in surgically anchoring keratoprostheses to corneas to alleviate problems with extrusion. Bovine corneal samples were lyophilized for various times resulting in tissue hydrations of zero (no water content) to approximately 3.7 (normal water content). The lyophilized corneal tissue was bonded to solid gelatin sheets, to other corneal samples and to glass using 0.3M DPD in chloroform. Control runs used chloroform only. Samples were irradiated with 100 or 200 J of 320-500 nm light. Strong bonds formed with all three materials when corneal tissue hydration was 1. No bonding occurred with chloroform alone. Formation of strong bonds only occurs with hydration levels

Retinal location of the preferred retinal locus relative to the fovea in scanning laser ophthalmoscope images.

PURPOSE: It is difficult to determine the position of a preferred retinal locus (PRL) relative to the fovea in scanning laser ophthalmoscope (SLO) images as a result of disease-related retinal morphologic changes that obscure the fovea. To overcome this problem, we developed a method for determining retinal foveal position based on normal fixation position relative to the optic disk. The normal foveal position measurements can then be used to estimate the distance between a PRL and the fovea. METHODS: Using the SLO, foveal position was determined for 50 normal subjects by measuring the retinal locus of fixation relative to the optic disk in undistorted SLO images. The resulting normal foveal fixation area is described by a bivariate normal ellipse that can be plotted on any undistorted SLO image. Measurement reliability was assessed by repeated measurements. The PRL relative to the normal foveal fixation area was determined for 24 subjects with macular degeneration and bilateral central scotomas. RESULTS: The normal foveal fixation area based on all 50 subjects is described by a p = 0.9 bivariate ellipse whose centroid is located 12.6 degrees temporal to the temporal optic disk edge and 1.4 degrees inferior to a horizontal line bisecting the disk. PRL area is shown to increase with distance from the foveal fixation ellipse centroid. The shape of the PRL, characterized by the ratio of PRL ellipse major to minor axis, was found to depend on whether the PRL was vertically or horizontally aligned with the foveal fixation centroid. CONCLUSIONS: PRL position relative to the fovea can be reliably estimated by plotting the normal foveal fixation bivariate ellipse on undistorted SLO images of retinas in which the fovea is obscured as a result of the disease process.

An inexpensive, automated instrument for laser irradiation of cultured cells.

OBJECTIVE: Laser irradiation of cultured cells is a valuable technique for elucidating the mechanisms of low-level laser therapy, but is often tedious because of the need to manually change the position of the laser beam. Consequently, we developed a computer-based system that automatically moves a cell culture plate over a laser beam and times the exposure. BACKGROUND DATA: There are presently no commercial devices available for automated laser irradiation of cultured cells. Many investigators thus manually aim and time laser exposure, a time-consuming task that is prone to errors. MATERIALS AND METHODS: We used outdated, surplus computer components to construct a system for automated laser exposure of cultured cells. This design strategy makes the system quite inexpensive. RESULTS: Construction and operation of the system is described and an example of its use is presented. Alternate means of accomplishing automated laser irradiation are also presented. CONCLUSION: Inexpensive and relatively simple devices can be constructed for automated laser irradiation of cultured cells. These devices can eliminate the tedium and errors of manual laser exposure.

Distortion and size calibration of the scanning laser ophthalmoscope (SLO) laser-beam raster.

PURPOSE: The Rodenstock scanning laser ophthalmoscope (SLO) is useful for mapping retinal function and for developing and evaluating visual rehabilitation methods. It is essential to know the visual angle subtended by stimuli in the SLO laser-beam raster and to accurately measure angular distances between objects in the final SLO image. To accomplish this, the angular extent of the SLO laser-beam raster must be calibrated. METHODS: We developed a simple method and apparatus for calibrating the raster and used it for repeated calibrations during a 3-month period. RESULTS: The laser-beam raster is quite stable in shape and size, but it is trapezoidally distorted in the vertical direction. Consequently, SLO images are distorted. CONCLUSIONS: Trapezoidal distortion of the SLO laser-beam raster can cause stimulus size to change as much as 10% from the top to the bottom of the raster. Measurements of fixed horizontal retinal landmark distances in SLO images can also vary as much as 10%. We developed a straightforward mathematical method for correcting distortion in SLO image measurements.

A photoactivated diazopyruvoyl cross-linking agent for bonding tissue containing type-I collagen.

On the basis of the earlier examples of diazopyruvoyl (DAP) groups reported by Lawton for covalent binding and cross-linking of proteins and oligopeptides and our recent demonstration that a coumaryl diazopyruvamide was used to label Type-I collagen, we have extended our investigations to the synthesis and cross-linking capabilities of a bis-DAP polyethylene glycol to cross-link Type-I collagen. The new photoactivated cross-linking agent, N,N'-bis(3-diazopyruvoyl)-2,2'-(ethylenedioxy)bis(ethylamine) (DPD, 2), has been designed and synthesized specifically to "weld" collagenous tissues by cross-linking Type-I collagen. A working model for the photochemical welding studies of collagenous tissues was developed using gelatin strips (gel strips) composed of denatured Type-I collagen. Gel strips are transparent to near-UV and visible light, uniform in thickness, and have reproducible composition. Furthermore, the availability of nucleophilic amine sites in gel strips was demonstrated by reaction with o-phthalaldehyde, producing a fluorescent derivative of the protein. Gel strips were coated with a solution of DPD in chloroform 7 irradiated at 320-390 nm, and the resulting bonded gel strips were tested for the strength of the weld. The welds were generally brittle and had average tensile strengths that exceeded 100 N/cm2. Welds were not formed in the absence of light or DPD. Scanning electron microscopy studies revealed a pockmarked surface from severed welds. Welds of rabbit Achilles tendon were also obtained using the tethered diazopyruvamide. These welds were much weaker, having an average tensile strength of 11.95 N/cm2 for DPD-2,2'-ethylenedioxy(bis)ethylamine comonomers in the cross-linking reaction. In both studies the welds obtained by this method were significantly stronger than the controls.

Photoactivated coumaryl-diazopyruvate fluorescent label for amine functional groups of tissues containing type-I collagen.

The design, synthesis and application of a new fluorescent-labeling reagent for collagen has been developed as a prerequisite for the design of a photoactivated collagen-crosslinking compound for surgical wound closure. The amine groups in collagen are the targets of a rational design for a new fluorophore because natural collagen crosslinks are formed between primary (1(o)) amine groups of lysine and hydroxylysine. The availability of 1(o) amines for crosslinking in native collagenous tissues was evaluated by reacting tendon and corneal samples with o-phthalaldehyde and dansyl chloride, fluorophores commonly used for the detection of 1(o) and 2(o) amines. The resulting fluorescent collagen fibrils indicated the presence of amines in native tissue. Subsequently, a photoactivated fluorescent label for 1(o) and 2(o) amines, coumaryl gamma-amino-butyric acid diazopyruvate (CGDP), was designed and synthesized. CGDP was first used to photolabel poly-L-lysine, forming a fluorescent, covalent bond to the 1(o) amine. CGDP was then photoreacted with corneal and tendon tissue samples to produce CGDP fluorescent-labeled samples that were statistically significantly more fluorescent than were the controls. These experiments support the postulate that 1(o) or 2(o) (or both) amines in native collagenous tissues are available to serve as targets for photoactivated collagen crosslinkers for wound closure.