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Biomedical subjects

M O Tso

Publications and source records attributed to M O Tso.

At least 91 records · Page 5Linked to original sources
PubMed1990

Effects of repeated photic exposures on the monkey macula.

The posterior pole of the eyes of rhesus monkeys was exposed to the light of an indirect ophthalmoscope. The tissue changes caused by repeated (three to five) photic injuries were compared with those produced by a single photic insult. The ophthalmoscopic and angiographic examinations showed a progressive involvement of the foveal area after multiple exposures to light. Histopathologic study showed that after one exposure the retinal pigment epithelium appeared focally atrophic. Plaques of proliferated retinal pigment epithelium could also be seen, and on the anterior surface of these plaques a layer of relatively cuboidal hypopigmented retinal pigment epithelial cells was present. With multiple exposures, focal areas of total absence of retinal pigment epithelium were seen in these eyes. The eyes that received only one exposure showed partially regenerated photoreceptor outer segments. After repeated photic exposures, the photoreceptor outer segments failed to regenerate even 6 to 8 months after the last exposure. In one eye exposed five times for 60 minutes, areas of total absence of photoreceptor cells could be seen, and the inner nuclear layer was directly apposed to Bruch's membrane. These experimental exposures to the light of an indirect ophthalmoscope were 60 to 120 minutes long and were not comparable to clinical exposures of the ophthalmoscope in patient examination. Our observation highlighted the cumulative effects of repeated light injury to the retinal pigment epithelial and photoreceptor cells and also showed the similarity between this animal model of photic maculopathy and the changes present in the eyes of human patients with atrophic agerlated macular degeneration.

Animals↗
PubMed1990

Respiratory epithelium in a cystic choristoma of the limbus.

A female newborn had a cystic, whitish gray mass at the inferotemporal limbus of the left eye. At age 3 weeks, the newborn underwent excision of the tumor, corneal patch grafting, and superior sector optical iridectomy. Histopathologic and electron microscopic examination of the excised tissue revealed a choristoma consisting of cysts lined with respiratory epithelium. To our knowledge, respiratory epithelium in a limbal choristoma has not been previously reported.

Choristoma↗
PubMed1990

Amelioration of retinal photic injury in albino rats by dimethylthiourea.

Light-induced formation of oxygen free radicals has been proposed as the underlying mechanism of photic retinal injury. We investigated the role of hydroxyl radical in retinal photic injury by treating dark-adapted albino rats with intraperitoneal dimethylthiourea 3 hours before exposure to intense fluorescent light. Dimethylthiourea is a specific antioxidant against hydroxyl radical. We demonstrated that dimethylthiourea penetrates well into retinal tissue and has a half-life of approximately 19 hours. Morephologic differences between the control and dimethylthiurea-treated rats were not remarkable 6 hours after light exposure, but they became significant 6 and 14 days after light exposure. Morphometric studies showed that there was significantly better preservation of photoreceptor nuclei in dimethylthiourea-treated rats 6 and 14 days after light exposure. Rhodopsin levels were significantly higher in the dimethylthiourea-treated rats 6 hours and 14 days after light exposure, while rhodopsin levels were comparable in the control and dimethylthiourea-treated rats 6 days after exposure. The differences in morphometry and rhodopsin levels between the control and dimethylthiourea-treated rats were statistically significant in relationship to dimethylthiourea treatment. The superior and temporal retinal quadrants appeared most vulnerable to photic injury in control rats 6 and 14 days after light exposure. These findings indicate that dimethylthiourea ameliorates retinal photic injury, and that hydroxyl radical plays an important role in mediating retinal photic injury.

Animals↗
PubMed1990

Macular dystrophy of the cornea. A systemic disorder of keratan sulfate metabolism.

The serum of most patients with type 1 macular corneal dystrophy (MCD), the most prevalent subtype, lacks detectable antigenic keratan sulfate (KS), and it has been postulated that such individuals may lack antigenic KS in their cartilage as well. To test this hypothesis, we studied the cornea, serum, and nasal cartilage from an MCD patient using light and electron microscopy, immunohistochemistry, and a quantitative enzyme-linked immunosorbent assay (ELISA) which uses a monoclonal antibody against a sulfated epitope on the KS chain to measure KS content. Histologically, corneal deposits seen were characteristic of MCD. No abnormal deposits were noted in the cartilage. The lack of immunoreactivity in corneal sections with antibodies against sulfated epitope on KS and the absence of this epitope in serum showed that the patient had type 1 MCD. The cartilage specimen showed no immunoreactivity in the chondrocytes or extracellular matrix. Quantitative analysis by ELISA demonstrated that the antigenic KS content of the cornea and cartilage was at least 800 times lower than that in normal controls. This provided direct evidence that the abnormality in the sulfation of keratan in type 1 MCD involves the cornea and cartilage.

Aged↗
PubMed1990

Retinal injury induced by near-ultraviolet radiation in aphakic and pseudophakic monkey eyes. A preliminary report.

The effect of repeated exposures to low-intensity, near-ultraviolet (UV) radiation on the retinas of phakic, aphakic, and pseudophakic monkey eyes was studied. Ten eyes (4 aphakic eyes, 3 pseudophakic eyes, and 3 normal phakic eyes) of five rhesus monkeys were used. The near-UV radiation was generated by a high-pressure mercury vapor lamp with a total radiance of 14.43 mW/cm2/sr. Exposure regimens were 5 minutes a day for 10 days, 15 minutes a day for 5 days, or 60 minutes a day for 5 days. The retinas of aphakic and pseudophakic eyes were exposed to a daily dose of more than 0.97 J/cm2, or a total dose of more than 4.9 J/cm2 in 5 days at a retinal irradiance of more than 1.0 mW/cm2. Three of four aphakic eyes and one of three pseudophakic eyes showed clinical and pathologic retinal lesions after radiation. None of the three phakic eyes was damaged. The retinal lesions showed mild opalescent thickening ophthalmoscopically and retinal pigment epithelial staining by fluorescein angiography. Histopathologically, the retinal pigment epithelium was the site of primary injury by near-UV radiation.

Animals↗
PubMed1990

A comparative study of photic injury in four inbred strains of albino rats.

The effects of light damage were studied in four inbred strains of albino rats, Fischer (F344), Lewis (L), Wistar (W), and Buffalo (BUF). Thirty-five-day-old rats (3 from each strain) were kept in cyclic light for two weeks, after which they were exposed to constant fluorescent light (180-190 foot-candles, 490-580 nm) for 24 hours. The rats were sacrificed 6 days after exposure. Photic injury to the exposed eyes was evaluated morphometrically by measuring the mean outer nuclear layer (ONL) thickness and qualitatively by light microscopy. Statistical analysis of the quantitative data revealed that the Lewis and Buffalo strains were more severely affected than the Wistar and Fischer strains. The effects of injury were more severe in the superior and temporal quadrants. Taking both quantitative and qualitative assessment into consideration, it appeared that, among the strains studied, the rats from the Lewis strain were most sensitive to photic damage. These findings support previous findings of differential light sensitivity and further suggest that similar variability occurs among inbred strains with type 1 light damage.

Animals↗
PubMed1990

Effect of continuous versus multiple intermittent light exposures on rat retina.

The damaging effects of continuous light exposure to the albino rat retina have been well documented. However, the cumulative effects of multiple light exposures are not well defined. We therefore compared the retinal injury induced by a single 24 hour light exposure with that caused by three intermittent exposures of 8 hours each. Eight dark-adapted albino Lewis rats were exposed for 24 hours to green fluorescent light (490-580 nm) at an illuminance level of 175 foot-candles. A second group of 8 rats was exposed under similar conditions in three split doses of 8 hours each at intervals of 7 days between each exposure. Recovery was allowed in total darkness, and the animals were sacrificed 2 weeks following the last exposure. Retinal damage was assessed by morphometry and light and electron microscopy. Mild cumulative retinal injury, mostly in photoreceptor cells with relative sparing of the retinal pigment epithelium, was seen in the split dose group, while extensive damage involving photoreceptor cells and retinal pigment epithelium was noted in the group exposed continuously for 24 hours.

Animals↗
PubMed1990

An immunopathologic study of retinoblastoma protein.

We investigated the immunoreactivity of the retinoblastoma protein in eight retinoblastoma tumors of different stages of differentiation. All undifferentiated tumor cells failed to show immunoreactivity. In one patient, who had a family history of retinoblastoma and had been treated by radiation, the tumor had a large area of undifferentiated cells and small independent retinocytomas. The tumor cells in the retinocytoma and the cone cells in the adjacent retina, but not the undifferentiated tumor cells, showed positive staining with two anti-Rb antibodies. The immunoreactivity may be related to radiation or differentiation of retinoblastoma and cone cells.

Child, Preschool↗
PubMed1989

Cellular mechanisms of iris neovascularization secondary to retinal vein occlusion.

We developed an animal model that allows the early phases of iris neovascularization to be studied in detail. Three major retinal branch veins were occluded with the argon laser in five eyes of cynomolgus monkeys, after which the eyes were enucleated at various time intervals. We observed three phases of the neovascular process in the iris. The early phase was characterized by vessel dilation and intense uptake of tritiated thymidine in the vascular endothelial cells. In the intermediate phase, prominent new vessels, ectropion uveae, peripheral anterior synechiae, and elevated intraocular pressure developed. Also noted were a decrease in tritiated thymidine uptake of the endothelial cells, a remarkable increase in stromal cell tritiated thymidine activity, and the formation of a neovascular membrane in association with the anterior migration of stromal cells. The late phase was marked by a further reduction of tritiated thymidine uptake and regression of the neovascular membrane.

Animals↗
PubMed1989

Transscleral iontophoresis of dexamethasone.

Transscleral iontophoresis has been suggested to be a potentially useful noninvasive technique in intravitreal introduction of ionizable drugs, such as cefazolin sodium, ticarcillin disodium, and gentamicin sulfate. To investigate the usefulness of this technique in the administration of corticosteroids, we performed transscleral iontophoresis of dexamethasone sodium phosphate (300 mg/mL, 20 mmol/L edetic acid [EDTA]) into rabbits at a current of 1.6 mA for 25 minutes. Eyes were enucleated at different time intervals and frozen in liquid nitrogen. The frozen vitreous bodies and adherent sensory retina were collected and sonicated, and dexamethasone levels were measured using high-pressure liquid chromatography. In addition, to study the facilitation of drug transport by cryotherapy, a second group of rabbits were given a single application of cryotherapy (-78 degrees C, 45 seconds) 3, 7, and 14 days before iontophoresis in the same region. Without cryotherapy, the initial level of dexamethasone in the vitreous body-sensory retina after iontophoresis was 139.3 +/- 51.5 mg/L (mean +/- SE) (n = 6) with a half-life of less than 2 hours. In the cryotreated group, the levels of dexamethasone immediately after iontophoresis 3, 7, and 14 days after cryotherapy were 61.5 +/- 31.7 (n = 6), 88.4 +/- 55.1 (n = 6), and 112.2 +/- 32.5 (n = 6) mg/L, respectively, indicating that levels were lower compared with the group without cryotherapy. Our results suggest that a high dose of dexamethasone can be delivered by using this noninvasive technique and that cryotherapy before iontophoresis does not increase drug levels in the vitreous body.

Animals↗
PubMed1989

Histopathologic study of autosomal dominant vitreoretinochoroidopathy. Peripheral annular pigmentary dystrophy of the retina.

Autosomal dominant vitreoretinochoroidopathy (ADVIRC), a recently described disease, is clinically characterized by a slowly progressive or stationary circumferential peripheral pigmentary retinopathy with fibrillar condensation of the vitreous. Histopathologic study of an 88-year-old patient with this disease showed disorganization of the peripheral retina with focally atrophic retinal pigment epithelium (RPE). Altered pigment epithelial cells surrounded retinal blood vessels and lined the internal limiting membrane. At the equator, a remarkable and possibly unique multifocal loss of photoreceptor cells was seen. An extensive preretinal membrane, consisting of condensed vitreous with cellular debris and layers of Müller cells, was demonstrated by electron microscopic examination and immunohistochemistry. Histologically, this entity has some similarities to and some differences from retinitis pigmentosa. The clinical features are distinctive.

Aged↗
PubMed1989

Sympathetic ophthalmia following neodymium:YAG cyclotherapy.

Neodymium:YAG cyclotherapy has been demonstrated to lower intraocular pressure dramatically in patients with uncontrolled glaucoma, with potentially fewer side-effects than cyclocryotherapy. We report the clinical course and histopathological features of a case of sympathetic ophthalmia occurring soon after YAG cyclotherapy.

Adult↗
PubMed1988

Sporothrix schenckii endophthalmitis in a patient with human immunodeficiency virus infection.

A 30-year-old homosexual man with a positive serologic test for human immunodeficiency virus and a history of successfully treated disseminated cutaneous sporotrichosis developed a granulomatous uveitis that worsened with topical and subconjunctival steroid therapy. Culture of the aqueous aspirate yielded Sporothrix schenckii. The patient was treated with intravenous amphotericin B and intravitreal amphotericin B, kanamycin sulfate, and amikacin sulfate. Subsequent aqueous and vitreous cultures were negative, but the intraocular inflammatory process progressed and ultimately led to enucleation of the eye. Histopathologic examination revealed granulomatous inflammation of the anterior uvea and scattered S schenckii in the anterior and posterior chambers. Electron microscopy demonstrated that most of the organisms had disorganized protoplasm. Although treatment failed to ameliorate the progressive intraocular inflammatory process, the negative cultures and the electron microscopic observations suggest that the treatment was reasonably effective in killing S schenckii within the eye. To our knowledge, this is the first case report of S schenckii endophthalmitis in a patient with human immunodeficiency virus infection.

Acquired Immunodeficiency Syndrome↗
PubMed1988

Heterogeneity in macular corneal dystrophy.

Macular corneal dystrophy is an autosomal recessive disorder in which abnormal deposits in the corneal stroma have been identified. We examined the corneal buttons of 12 patients, who had clinical features of macular dystrophy, by histochemical staining, transmission electron microscopy, and immunohistochemical techniques. All corneas exhibited positive staining with Muller Mowry's colloidal iron. Using monoclonal antibodies 1/20/5-D-4, J-10, J-19, and J-36 that recognize specific sites on the sulfated keratan sulfate molecule, we stained corneal sections by an avidin-biotin-peroxidase complex method and identified two groups of macular corneal dystrophy. One group consisting of four corneas reacted positively with all four antibodies, and the other group consisting of eight corneas did not react with any of the antibodies used. These results confirmed those recently presented by Yang et al that there may be subgroups of macular dystrophy that can be identified by immunohistochemical methods. Also, serum levels of sulfated keratan sulfate were determined in seven patients. One patient who displayed a normal level of serum keratan sulfate had positive corneal immunoreactivity. Of the six patients who lacked serum keratan sulfate, four showed negative and two had positive corneal immunostaining, suggesting at least three subgroups in the disease. An attempt was made to correlate the clinical features, histochemical-staining characteristics, and ultrastructural morphology with the immunoreactivity to keratan sulfate antibodies, but no correlations could be made.

Adult↗
PubMed1988

Monkey trabecular meshwork cells in culture: growth, morphologic, and biochemical characteristics.

We established tissue cultures of trabecular meshwork cells from cynomolgus monkey eyes. The cultures were initiated within 4 h of enucleation on Falcon Primaria flasks. Using medium containing 10% fetal bovine serum and 5% calf serum, trabecular meshwork cells could be grown for up to eight passages without additional growth factors. The growth pattern and cell morphology were distinct from those seen in fibroblastic or endothelial cultures derived from neighboring tissues. Ultrastructurally, our cells showed the characteristics of trabecular meshwork cells, exhibiting prominent basement membranes, intercellular junctions, pinocytotic vesicles, microvillous projections, and branched cell extensions. These cells were grown mostly as monolayers. However, they also appeared to form multi-layered arrays in densely confluent areas when plated at a high density. The extracellular matrix material was surrounded by cells and cell processes, simulating in vivo trabecular beam formation. Radiolabeling experiments demonstrated that our trabecular meshwork cells had the capacity to produce collagen. These results indicated that our cultured cells retain many in vivo characteristics and may be used for various biologic studies of trabecular meshwork.

Animals↗
PubMed1988

Nanophthalmic sclera. Fibronectin studies.

The authors performed fibronectin studies on scleral specimens derived from a patient with nanophthalmos. Immunohistochemical staining with antifibronectin was conducted using both formaldehyde-fixed, paraffin-embedded tissue sections and unfixed tissue-cultured scleral cells. In each case, the nanophthalmic samples exhibited fibronectin staining stronger than that obtained from normal human subjects. Results from an enzyme-linked immunosorbent assay (ELISA) confirmed the histologic findings that, in tissue culture, the patient's scleral cells contained and secreted a higher amount of fibronectin than did the normal control cells. The elevated fibronectin level may be related to the development of nanophthalmos.

Adult↗
PubMed1988

Factors associated with age-related macular degeneration. An analysis of data from the first National Health and Nutrition Examination Survey.

Data from the first National Health and Nutrition Examination Survey collected between 1971 and 1972 were used to determine what factors are associated with the prevalence of age-related macular degeneration. The study was limited to those who were at least 45 years old at the time of the ophthalmology examination. Stratified analysis, adjusting for age, showed that education, systolic blood pressure, past history of hypertension, cerebrovascular disease, and refractive error were all associated with macular degeneration. With the exception of education, these factors remained statistically significant when simultaneously entered into a logistic regression model. The frequency of consumption of fruits and vegetables rich in vitamins A and C suggested a negative association with the prevalence of macular degeneration after stratified adjustment for age. In a logistic regression analysis, adjusting for demographic and medical factors, the inverse association of vitamin C with age-related macular degeneration was no longer present. The frequency of consumption of fruits and vegetables rich in vitamin A remained negatively correlated with age-related macular degeneration even after adjustment for demographic and medical factors.

Age Factors↗