Artificial orbit for experimental surgery on the anterior segment.
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Anterior Eye Segment↗
Biomedical subjects
M T Mori
Publications and source records attributed to M T Mori.
Dynamic shifts in corneal topography after radial and transverse keratotomy.
PURPOSE: The authors aimed to quantitate the dynamic patterns of change in corneal topography after multistaged radial and transverse keratotomy using digitized video-keratography. METHODS: Single and paired radial and transverse keratotomies, with videokeratoscopy between each stage and at the end of the procedure, were performed on fresh animal cadaver eyes using an artificial orbit system. RESULTS: All incisions led to central flattening. A single radial keratotomy caused flattening adjacent to the incision, and steepening 180 degrees away. A paired radial keratotomy caused increased flattening in the meridian of the incisions, and less flattening 90 degrees away. A single transverse incision caused steepening adjacent to the incision and diffuse flattening elsewhere. A paired transverse incision caused flattening near the optical center along the meridian bisecting the incisions and steepening 90 degrees away. CONCLUSION: The authors have demonstrated that computerized videokeratography can be used successfully to systematically quantitate dioptric shifts in multiple hemimeridians and measurement zone diameters after refractive surgery.
Animals↗
Noninvasive visualization of the choriocapillaris and its dynamic filling.
PURPOSE: The choroidal microvasculature and its circulation are inadequately assessed by presently available techniques. Laser-targeted delivery was applied to generate local, repetitive angiograms of the choriocapillaris in primates. METHODS: Carboxyfluorescein was encapsulated in heat-sensitive liposomes and injected intravenously in monkeys. The liposome contents were then released locally in the choroid by application of a short heat pulse provided by an infrared laser. The bolus of dye spread rapidly downstream from the underlying arterioles into clusters of lobules. Video angiograms were generated with excitation illumination provided by an argon laser. RESULTS: Laser-targeted delivery choroidal angiography performed on three monkeys indicated that the fluorescence was emitted mainly from the choriocapillaris. Clusters of irregular shape with well-defined margins were observed. Adjacent arteries typically supplied separate clusters that fit together like a jigsaw puzzle. The dynamic filling and emptying patterns, recorded at video rate, revealed that macular lobules were filled by a central arteriole and drained by a venous annulus. The average dye transit time through a lobule (n = 10) was 118 +/- 26 msec (mean +/- SD), and the dye transit velocity was 2.53 +/- 0.55 mm/sec. CONCLUSIONS: This study clearly documents the segmental nature of the primate choroidal microvasculature. It also illustrates that choroidal angiography by laser-targeted dye delivery provides information useful for studying the response of the choriocapillaris to physiological and pathologic changes.
Animals↗
Enhanced visualization of vitreoretinal interface by laser biomicroscopy.
BACKGROUND: The use of slit-lamp biomicroscopy provides valuable information for the diagnosis and management of vitreoretinal disorders. However, intense backscatter from the fundus often precludes the visualization of fine structures in the vitreoretinal interface. METHODS: Laser biomicroscopy is a new method designed to improve the visualization of fine vitreoretinal structures at the macula. This method was applied to eyes suspected of traction maculopathies. With this method, the contrast and the lateral separation between the vitreal and retinal images are optimized while preserving information on the location of the slit on the fundus. RESULTS: The results indicated that fine structures in the vitreoretinal interface, which were difficult to observe with conventional slit-lamp biomicroscopy, could be clearly visualized. CONCLUSION: Laser biomicroscopy may be a useful tool in the diagnosis and management of diseases with vitreoretinal abnormalities.
Aged↗
Individual variability in the diurnal intraocular pressure curve.
BACKGROUND: Reduction of intraocular pressure (IOP) is a primary goal of most glaucoma treatments. However, because the IOP varies during the day, single measurements performed in an ophthalmologist's office do not necessarily provide information on the peak level and fluctuation of the IOP. METHODS: Home tonometry was performed to gain more information on the nature of the diurnal IOP curves and on their variability. One hundred seventy-six patients with open-angle glaucoma (OAG), 55 subjects with ocular hypertension (OHT), and 18 control individuals measured their IOP five times daily at home for 4 to 8 consecutive days using a self-tonometer. RESULTS: Well-defined diurnal IOP variations were observed in all three groups with a predominance of curves with morning or mid-day maxima. Erratic IOP curves without a diurnal rhythm were present in OHT (22%) and OAG (16%) patients but not in control subjects. Differences between the curves of the two eyes of an individual were frequent in OHT (33%) and OAG (36%) patients but not in control subjects (6%). Finally, the majority of OHT (72%) and OAG (66%) patients showed a difference in their diurnal curve patterns on repeat home tonometry performed months apart. CONCLUSION: The authors indicate that it is difficult to rely on one eye as a control for the other. They also indicate that changes in IOP observed in the office at different visits often may be due to a shift in the type of diurnal curve rather than to a true change in the mean IOP. Monitoring of the diurnal IOP may be necessary in some cases if the clinician relies, even partially, on the level of IOP when making a decision on patient management.
Circadian Rhythm↗
Improved visualization of macular hole lesions with laser biomicroscopy.
We have developed instrumentation to improve the visualization of fine vitreoretinal structures at the macula during slit-lamp biomicroscopy. The instrument, mounted on a slit-lamp microscope, used a green helium-neon laser to deliver a narrow beam, 15 micron(s) in width and 2 mm in length. The intersection of the laser slit with the ocular structures was viewed at an angle, as in conventional slit-lamp biomicroscopy. The instrument was used to examine patients with idiopathic macular holes or cysts. The results indicated that the new illumination was superior due to the narrow width of the beam, the enhanced brightness, and the monochromacy in green, which reduced background scatter. These advantages allowed for visualization of fine retinal structures that are difficult to detect with conventional slit-lamp biomicroscopy. The findings in patients with idiopathic macular hole demonstrated that the operculum was located approximately 500 micron(s) anterior to the surrounding retina and moved minimally. This suggested that the operculum may be supported by partially detached posterior vitreous cortex, and that a macular hole is the result of tangential traction followed by axial traction caused by a contracted and detached cortical vitreous gel.
Aged↗
Feasibility of targeted drug delivery to selective areas of the retina.
A new method was developed to deliver locally a bolus dose of a drug to the retinal vasculature. The targeted delivery system was based on encapsulating the drug in heat-sensitive liposomes, which are injected intravenously and lysed in the retinal vessels by a heat pulse generated by a laser. To test if substances delivered in the vessels could also penetrate into the surrounding tissue, 6-carboxyfluorescein was encapsulated in liposomes and used as a marker for drug penetration. Moderate argon laser pulses were applied to the retinal vessels of Dutch pigmented rabbits to induce breakdown of the blood-retinal barrier (BRB). A suspension of liposomes at a dose of 2 ml/kg body weight, corresponding to a carboxyfluorescein dose of 12 mg/kg, was injected into the ear vein. The dye was released from the liposomes proximal to the damaged portion of the vessel. Fundus fluorescein angiograms were recorded with a video camera and digitized for subsequent image analysis. The penetration of carboxyfluorescein into the retinal tissue was evaluated by comparing the fluorescence intensity of the area around the damaged vessel with that of an adjacent control area. The dye penetration increased with the numbers of laser applications (P less than 0.001). The leakage was localized distally to the released site and was restricted to areas with a disrupted BRB. The mass of carboxyfluorescein that penetrated gradually spread with time. Both veins and arteries could be used for the targeted delivery. These results indicated that this delivery system, which is fully controllable by laser through the pupil, can deliver drugs inside the vasculature and into the retinal tissue wherever the BRB is disrupted.
Animals↗
Quantitative analysis of retinal hemodynamics using targeted dye delivery.
A new method designed to allow repeated mapping of retinal hemodynamics on a macro- and microcirculatory level was evaluated in the primate eye. The method, called "targeted dye delivery," consists of encapsulating a fluorescent dye in temperature-sensitive liposomes, injecting the liposomes systemically, and using a light pulse from an argon laser to release a bolus of dye in a targeted retinal vessel. The follow-up of the well-defined dye front thus generated allows calculation of the blood flow and capillary transit time. Evaluation of targeted dye delivery in a monkey indicated that centerline blood velocity and the vessel diameter can be measured with a reproducibility of 10% and 4%, respectively, in vessels that are 40 microns and larger. These measurements yielded flow values that had a reproducibility of 10% on the same day and 13% on different days. The normalization of flow rate by the vessel diameter was consistent with theoretic estimates and promises to be a circulation indicator independent of variations between individual and species. The transit time across capillary beds at different locations was found to be similar, thus indicating that the method could be used to evaluate the local viability of the microcirculation.
Animals↗
Visualization of the retinal microvasculature by targeted dye delivery.
Although fluorescein angiography has proven to be an important tool in the diagnosis and management of retinal vascular diseases, it is subject to certain limitations, namely the presence of the choroidal background, which usually precludes a detailed examination of the retinal microvasculature. Moreover, the inability to repeat the bolus reduces the chance of obtaining high-quality photographs of early phases, and does not allow for a complete binocular examination or for testing the response to induced physiologic changes. We have developed a method of targeted dye delivery that consists of encapsulating the dye in lipid vesicles, injecting them intravenously, and causing them to release their contents locally when a short heat pulse is induced in a retinal artery by a laser. This method was applied in the rhesus monkey in order to visualize the retinal microvasculature. A well-defined bolus and absence of background fluorescence permitted both following of the dye front through the vasculature and clear imaging of the capillary network over the whole posterior pole. The bolus delivery could be repeated as many as 100 times in 45 min without significant loss of contrast. The comparison of these results with conventional fluorescein angiography illustrated the advantage of the new method. The examination of the safety of the delivery system indicates that there is no major obstacle to the eventual application to humans.
Animals↗
In vivo evaluation of a noninvasive method to measure the retinal thickness in primates.
To diagnose certain macular diseases earlier and monitor their therapy more sensitively, we are developing a noninvasive method to measure the retinal thickness. The new instrument, which is an extension of slit-lamp biomicroscopy, was used to obtain the data, which were analyzed with an algorithm to yield thickness measurements. The measurements performed in monkeys indicated that the retinal thickness can be visualized in a region extending from the optic disc to the fovea and that quantitative results can be obtained. The retinal thickness reproducibility was 6% for the same location on the same day, 15% for the same location on different days, and 12% for the same location in different eyes. The average retinal thickness in these areas was 335 microns, indicating that the reproducibility was between 20 and 50 microns. Measurements across the foveola illustrated that retinal thicknesses as low as 80 microns could be obtained.
Animals↗
Feasibility test of a new method to measure retinal thickness noninvasively.
There are many devastating ocular diseases that are directly related to an alteration of the retinal or nerve fiber layer thickness, such as glaucoma and macular edema. To diagnose these diseases earlier and to monitor their therapy more sensitively, an accurate measurement of the tissue thickness is needed. Since no clinical method is currently available, we developed and tested a new method capable of measuring noninvasively the retinal thickness. The separation between the images of the anterior and posterior intersections is quantitated by an optoelectronic system. The theoretical performance of the method has been calculated. Tests of the method in a model eye indicated that the measurements were basically diffraction limited, their reproductivity was +/- 9 microns, and their accuracy was 5.5 microns. Tests performed in vivo indicated that two intersections between the laser and the retina are present and correspond to the anterior and posterior surfaces of the retina. These intersections can be resolved and analyzed to yield quantitative data. These encouraging results indicate that this method is feasible and could yield sensitive measurements of the retinal thickness.
Calibration↗
An interactive model eye for use with ophthalmic instruments.
A model eye was found to be a practical and versatile simulator of conditions present in the application of different surgical and diagnostic ophthalmic instruments. It realistically simulated the thermal and acoustic effects of lasers on tissues and thus could be used for teaching and practicing laser therapeutics. The geometric optics were similar to those of the human eye, and realistic conditions of scatter and fluorescence could be created.
Fluorescein Angiography↗
Self-tonometry to manage patients with glaucoma and apparently controlled intraocular pressure.
We tested a self-tonometer than can be used by the patient alone to monitor intraocular pressure (IOP) in a normal environment. The instrument is safely and easily used after training. Normal subjects and patients with glaucoma who had an IOP of 22 mm Hg or less at three consecutive visits were referred for diurnal monitoring. After successful training, they received a self-tonometer and instructions to obtain five measurements daily between awakening and bedtime for three to six days. More than half the patients had one or more readings above 22 mm Hg. About half of the IOP peaks occurred at times outside of normal office hours. Interestingly, more elevated IOP readings were recorded in patients with suspected or documented progression of glaucomatous damage than in patients thought to be stable or in normal subjects. In eyes that have already sustained glaucomatous damage, the progression may be explained by the presence of previously undocumented IOP peaks. Valuable additional clinical information can be gained by diurnal IOP monitoring, and the self-tonometer is a practical tool for its measurement.
Circadian Rhythm↗
Application of a self-tonometer to home tonometry.
Although home tonometry has been advocated in the management and diagnosis of glaucoma, the lack of proper instrumentation has precluded its routine performance. We have developed a self-tonometer that can be used by the patient at home and at work and have evaluated the performance of the instrument under these conditions. The results show that reproducibility of self-tonometer measurements is +/- 1.4 mm Hg and is independent of the user. When the readings of the self-tonometer in a given individual were compared with those of the Goldmann tonometer, they varied by +/- 2.4 mm Hg. Patients who could be trained in the clinic performed well and safely on their own. An average of fewer than five attempts was necessary to obtain four readings at each time of day. Our preliminary findings obtained during home tonometry demonstrated some of the benefits of repeated diurnal curves.
Adult↗