Biomedical subjects

S S Oak

Publications and source records attributed to S S Oak.

15 recordsLinked to original sources

PubMed1999

Comparison of corneal endothelial image analysis by Konan SP8000 noncontact and Bio-Optics Bambi systems.

PURPOSE: Compare corneal endothelial image analysis by Konan SP8000 and Bio-Optics Bambi image-analysis systems. METHODS: Corneal endothelial images from 98 individuals (191 eyes), ranging in age from 4 to 87 years, with a normal slit-lamp examination and no history of ocular trauma, intraocular surgery, or intraocular inflammation were obtained by the Konan SP8000 noncontact specular microscope. One observer analyzed these images by using the Konan system and a second observer by using the Bio-Optics Bambi system. Three methods of analyses were used: a fixed-frame method to obtain cell density (for both Konan and Bio-Optics Bambi) and a "dot" (Konan) or "corners" (Bio-Optics Bambi) method to determine morphometric parameters. RESULTS: The cell density determined by the Konan fixed-frame method was significantly higher (157 cells/mm2) than the Bio-Optics Bambi fixed-frame method determination (p<0.0001). However, the difference in cell density, although still statistically significant, was smaller and reversed comparing the Konan fixed-frame method with both Konan dot and Bio-Optics Bambi comers method (-74 cells/mm2, p<0.0001; -55 cells/mm2, p<0.0001, respectively). Small but statistically significant morphometric analyses differences between Konan and Bio-Optics Bambi were seen: cell density, +19 cells/mm2 (p = 0.03); cell area, -3.0 microm2 (p = 0.008); and coefficient of variation, +1.0 (p = 0.003). There was no statistically significant difference between these two methods in the percentage of six-sided cells detected (p = 0.55). CONCLUSION: Cell densities measured by the Konan fixed-frame method were comparable with Konan and Bio-Optics Bambi's morphometric analysis, but not with the Bio-Optics Bambi fixed-frame method. The two morphometric analyses were comparable with minimal or no differences for the parameters that were studied. The Konan SP8000 endothelial image-analysis system may be useful for large-scale clinical trials determining cell loss; its noncontact system has many clinical benefits (including patient comfort, safety, ease of use, and short procedure time) and provides reliable cell-density calculations.

Adolescent↗

PubMed1995

Ocular blood flow velocity in age-related macular degeneration.

BACKGROUND: Changes in the structure of the ocular blood vessels associated with age-related macular degeneration (AMD) have been described in some detail, but comparatively little is known of the concomitant circulatory changes. The goal of this study is to evaluate changes in the ocular circulation that may be associated with AMD. METHODS: Ocular blood flow velocities and vessel pulsatilities were measured in volunteers with and without AMD using a color Doppler imaging unit. Spectral analyses were recorded from the ophthalmic artery, central retinal artery and vein, the temporal and nasal short posterior ciliary arteries, and the four vortex veins. RESULTS: Adjusting for age, pulsatility indices of all arteries were higher in subjects with AMD (central retinal artery [P = 0.02]; temporal and nasal short posterior ciliary arteries [P = 0.06 and 0.002, respectively]; and ophthalmic artery [P = 0.24]). End-diastolic blood flow velocity of the short posterior ciliary arteries tended to decrease in the presence of AMD. CONCLUSIONS: The combination of increased pulsatility and decreased velocity of the short posterior ciliary arteries, observed in the presence of AMD, are interpreted as evidence of increased vascular resistance. The clinical signs of AMD may be related to degradation of the metabolic transport function of the retinal pigment epithelium, resulting from impaired choroidal perfusion.

Aged↗

PubMed1992

Metabolic and morphologic changes in the corneal endothelium. The effects of potassium cyanide, iodoacetamide, and ouabain.

The metabolic pathways of glycolysis and mitochondrial respiration in the corneal endothelial cell are the primary sources of the adenosine triphosphate (ATP) necessary to maintain endothelial structure and pump fluid to maintain the corneal stroma in its normally dehydrated and transparent state. The correlation between endothelial metabolism and morphology in rabbits was studied for 7 days after the application of three different agents: (1) iodoacetamide, used to inhibit ATP synthesis from both glycolysis and respiration; (2) potassium cyanide (KCN), used to inhibit ATP synthesis from respiration only; and (3) ouabain, used to inhibit fluid pumping but not ATP synthesis. After application of each of these three drugs to the corneal endothelium, changes in endothelial morphology were measured. The greatest change resulted from the use of iodoacetamide. Specular microscopic examination of the endothelium after the application of iodoacetamide showed progressive degradation of the integrity of the cellular structure; after 6 hr, there were no discernible cell borders. In those corneas treated with either KCN or ouabain, only minor changes in the endothelium were seen during the full 7 days of the investigation. Computer-assisted morphometric analysis showed an increase in the coefficient of variation of both cell area and perimeter in all cases. This increase was greater in the corneas treated with ouabain than those treated with either iodoacetamide or KCN. Redox fluorometry showed that the metabolic ratio (autofluorescence of reduced pyridine nucleotides divided by that of oxidized flavoproteins) decreased significantly in the iodoacetamide-treated corneas, increased significantly in the KCN group, and showed no significant change in the corneas in the ouabain group, all compared with a control group. The results showed that (1) when ATP produced by both glycolysis and respiration was inhibited by 0.1 mmol/l iodoacetamide, the endothelial cells could not survive, but (2) when ATP synthesis produced by respiration alone was inhibited by 1.0 mmol/l KCN, the cells could survive for at least 1 wk on the ATP produced by anaerobic glycolysis. Furthermore, the polymegathism seen after application of ouabain, a drug that is not believed to affect ATP synthesis but inhibits the endothelial pump function, is greater than that seen as a result of reduced pump function caused by inhibited respiration produced by 1.0 mmol/l KCN. Combining specular microscopy, computer-assisted morphometric analysis, redox fluorometry, and corneal pachymetry allowed correlations between corneal endothelial metabolism, pump function, and morphology to be studied.

Animals↗

PubMed1991

[Observation of cellular communication in the corneal endothelium using a small molecular weight fluorescent dye].

The metabolic and functional connection between corneal endothelial cells is thought to depend on the transfer of small molecules via gap junctions, as has been reported for other tissues. Cell-to-cell communication in the corneal endothelium was studied by monitoring the spread of fluorescence following the direct injection of Lucifer Yellow CH into single endothelial cells of the excised rabbit cornea. The image of the endothelial cells was observed during the injection and post-injection periods using specular microscopy and fluorescence microscopy. In the fresh cornea, the dye transferred readily from the injected endothelial cell to its neighbors. In damaged cells, dye transfer was slower or did not occur. After 5 hours of incubation in tissue culture medium 199, the specular microscopic image degraded, lowered cell membrane potential and decreased dye transfer rate were measured. This study showed that in normal corneal endothelial cells there were efficient cell communication channels between neighboring cells, and as the endothelium becomes less viable, cell communication is inhibited.

Animals↗

PubMed1989

Thermal cycling effects on the stored rabbit cornea.

Specular microscopy has proven itself a useful tool for evaluation of donor corneas. In many eye banks, corneas are stored at 4 degree C and warmed to room temperature for specular microscopic evaluation. On occasion it would be desirable to put the cornea back into storage provided there were no detrimental effects of the recooling and subsequent rewarming. The effects of repeated cooling and rewarming (thermal cycling) on the corneal endothelium were determined using rabbit corneas stored in M-K medium at 4 degree C. Some corneas were left in the refrigerator for a 7-day storage interval while others were removed daily, warmed to room temperature, evaluated morphologically and biochemically with the specular microscope and the redox fluorometer, respectively, and then placed back in the refrigerator. At the end of the 7-day storage period there were no statistically significant differences in either the biochemical signals or the specular appearance between thermally cycled corneas and corneas that were continuously stored at 4 degrees C for the same period of time. Repeated warming, specular microscopic observation, and cooling of the cornea appear not to be detrimental to the corneal endothelium.

Animals↗

PubMed1988

Corneal endothelial changes following minor trauma.

The healing processes that occur when corneal endothelial cells are subjected to only mild trauma are not known. To study these processes we have developed a system that enables only a few endothelial cells to be traumatized or destroyed under continuous specular microscopic observation in vitro. Experiments in which a small group of cells were traumatized by gentle wounding with a microglass tip produced an immediate and distinct dark area having the same size as the tip. Using this method we have produced and observed two types of wound by controlling the force of wounding. The first type of wound, produced by a gentle touch, recovered within 1 hr. The second type of wound, produced by moderate touch, took about 24 hr to recover completely from the trauma. In the second type of wound, we observed migration, elongation, coalescence and mitosis during the healing process. Histological examination revealed that in the first type of wound, the cells remained intact with no apparent damage seen by vital staining and light microscopy. For the second type of wound, the cells were completely missing although there was no apparent damage to Descemet's membrane.

Animals↗

PubMed1987

Morphometric analysis of corneal endothelium following radial keratotomy.

We performed morphometric analysis of the central corneal endothelium on 24 eyes of 19 patients who had had anterior radial keratotomy. The endothelium was analyzed for a variety of parameters, including cell area, perimeter, side lengths, cell shape, and number of sides. Mean, standard deviation, and coefficient of variation were calculated for each parameter. The mean cell density decreased from 2,835 to 2,677 cells/mm2, mean cell perimeter increased from 71.4 micron to 74.3 micron, and mean side length increased from 11.8 micron to 12.3 micron following surgery. The changes in these three parameters were statistically significant (P less than 0.05). The coefficient of variation of cell area (polymegathism) changed from 0.319 to 0.307, the hexagonality changed from 62.5% to 59.6%, and the cell shape changed from 0.872 to 0.867. The changes in these parameters were not statistically different before and after surgery. The group of patients that had no reported microperforations showed only a small decrease of cell density (1.6%), while the group of patients that had microperforations showed a large decrease of cell density (14.3%). The cell perimeter and side lengths showed a similar pattern. The group of corneas with the optical zone diameter less than 3.5 mm showed a decrease in mean cell density from 2,994 to 2,725 cells/mm2, and the cell shape changed from 0.874 to 0.866 following surgery. The changes in these parameters were statistically significant (P less than 0.05) before and after surgery. Among all factors associated with radial keratotomy, microperforation and a small diameter of central optical zone appear to be the two greatest risk factors.

Adult↗

PubMed1984

Coalescence of endothelial cells in the traumatized cornea. III. Correlation between specular and scanning electron microscopy.

Sequential specular microscopy has shown that coalescence of endothelial cells occurs after thawing in cryopreserved rabbit corneas. Scanning electron microscopy of corneas studied in vitro by specular microscopy showed the same large, fused endothelial cells. As observed in the electron micrographs, these cells showed no evidence of the cell borders that had disappeared during the specular microscopic examination. These data support the reliability of our specular microscopic observations and provide additional evidence for the occurrence of fusion or coalescence of corneal endothelial cells.

Animals↗

PubMed1984

Evidence for mitosis in the adult corneal endothelium.

Intracellular structures probably representative of mitotic figures were seen by specular microscopy in the endothelium of a corneal graft following a rejection reaction. Serial measurements over an eight month period initially showed grossly enlarged cells and apparent mitotic figures. Subsequently, clusters of cells smaller than any cells previously seen were observed. Measurements of endothelial cell area over this period demonstrated a highly significant (P less than 0.0001) decrease in cell area, or increase in cell density, with time. These observations indicate that at least under some circumstances mitosis occurs in the endothelium of the adult human cornea.

Cataract Extraction↗

PubMed1983

Specular microscopy of corneal epithelium.

Specular microscopy was used to study the morphologic appearance of normal and regenerating rabbit corneal epithelium before and after corneal abrasion or heptanol application. Specular photomicrographs of the denuded area and healing epithelium were taken for two to three weeks as the epithelium regenerated, as well as prior to trauma. During the healing process the cells appeared much larger than normal and had an abnormal morphologic appearance. In addition, specular photomicrographs of the corneal epithelium in topically anesthetized human subjects were obtained. These results indicate that this method is suitable for diagnostic observation and clinical research in human subjects, as well animal experimentation.

Alcohols↗

PubMed1983

Coalescence of endothelial cells in the traumatized cornea. II. Clinical observations.

In the rabbit, cells coalesce to repair a damaged corneal endothelial layer. Clinical specular microscopy showed that this phenomenon also occurs in human beings. The resulting endothelial cells are large, irregularly shaped, and multinucleated. They are quite different in their specular microscopic appearance from corneal endothelial cells seemingly undergoing mitosis, which was observed in a successful penetrating keratoplasty and which represents another apparent mode of repair. Additional evidence for coalescence of endothelial cells is derived from evaluation of histograms of cell size v age that have been published previously.

Adult↗

PubMed1983

Coalescence of endothelial cells in the traumatized cornea. I. Experimental observations in cryopreserved tissue.

After thawing, cryopreserved rabbit corneas were stained with trypan blue and cellular damage was evaluated with the specular microscope using indirect illumination. Thereafter, the cornea was maintained at 35 degrees C, and specular microscopy, performed from the endothelial side, was used to observe the same area of endothelium for several hours. Dead endothelial cells interfered with specular reflection and appeared as dark areas devoid of cellular definition. Viable cells, presumably damaged by freeze-thaw injury, began to effect repair within one hour after thawing and coalesced to form a single larger cell. Our photographic evidence suggests that coalescence of injured corneal endothelial cells represents an important step in the early repair process, resulting in a reduction of the total number of cells but enabling damaged cells to survive.

Animals↗

PubMed1983

Clinical examination of the crystalline lens by retrocorneal specular microscopy.

Normal crystalline lenses and a variety of primary and secondary cataracts were photographed with a contact clinical specular microscope having a new W10X long working distance objective. In the normal lens, the anterior and posterior cell pattern and the lens fiber pattern could be seen. In patients with developing cataracts, a variety of abnormal structures was observed; in some cases the detailed morphologic structure of the light scattering objects could be appreciated. In pseudophakic patients, precipitates, leukocytes, and debris were observed on the surface of IOL implants. The methods described enable cellular and morphologic changes occurring with time in the lens and capsule to be studied. The results obtained show the potential usefulness of specular microscopy for evaluation and documentation of retrocorneal pathologic structures at high magnification.

Adult↗

PubMed1981

Endothelial mosaic in Fuchs' dystrophy. A qualitative evaluation with the specular microscope.

The progressive morphological changes of cornea guttata in Fuchs' endothelial dystrophy have been characterized by clinical specular photomicroscopy. Five specific stages in the development of excrescences can be discerned using this in vivo technique. Several stages can be observed in the same cornea at a given time, although in most cases the majority of guttate changes seemed to have progressed to the same stage of development. All five stages of cornea guttata discerned in this study can occur in a cornea clinically free of edema. Two types of cornea guttata can be identified in vivo. One has a smooth, regular posterior surface, whereas the posterior contour of the second is irregular.

Cornea↗

PubMed1981

Corneal edema secondary to vitreocorneal contact.

Aphakic eyes, some with edematous corneas, and others with corneas free of edema, but all with formed vitreous humor in contact with the corneal endothelium, were studied. Removal of vitreous humor from the anterior chamber by closed vitrectomy resulted in substantial improvement in the state of corneal hydration and, in some cases, in the elimination of clinically notable corneal edema. Specular microscopy showed endothelial abnormalities in the edematous corneas that were not present in corneas with vitreous contact that remained free of edema. However, those endothelial changes seen in edematous corneas before vitrectomy seemed to persist after vitrectomy and corneal deturgescence. Thus, elimination of vitreous contact may result in clinical reversal of corneal edema despite a prolonged period of vitreous contact and in the face of seemingly irreversible endothelial changes.

Aged↗