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Biomedical subjects

A Negi

Publications and source records attributed to A Negi.

At least 73 records · Page 4Linked to original sources
PubMed1994

Vector analysis of corneal astigmatism after scleral buckling surgery.

We conducted a short-term prospective study of 125 eyes with retinal detachment to examine changes of corneal astigmatism about 2 weeks after scleral buckling surgery, using a vector method on 2-fold-angle rectangular coordinates. Segmental buckles of one to less than two quadrants produced significantly greater changes in astigmatism (1.65 +/- 0.97 dptr) than those of less than one quadrant (0.88 +/- 0.75 dptr) and those spanning two quadrants or more (1.09 +/- 0.38 dptr) (p = 0.0005, Kruskal-wallis test; n = 73). The amplitude of differential vectors after explant buckling surgery (1.33 +/- 0.89 dptr, n = 24) was significantly greater than after implant buckling surgery (0.65 +/- 0.45 dptr, n = 15) (p = 0.009, Mann-Whitney U-test) with buckles of one quadrant or less. Differential vectors tended to direct toward the buckles. There was no obvious directional tendency in the case of encircling procedures (n = 52).

Adolescent↗
PubMed1993

Surgical effects of trabeculotomy ab externo on adult eyes with primary open angle glaucoma and pseudoexfoliation syndrome.

OBJECTIVES: Retrospective and prospective studies examined the surgical effects in lowering intraocular pressure levels of trabeculotomy ab externo in adult eyes with either primary open angle glaucoma or pseudoexfoliation syndrome. We report the results of primary trabeculotomy as an intervention for glaucoma. PATIENTS: Included in the retrospective study were 357 eyes of 227 patients with primary open angle glaucoma and 82 eyes of 65 patients with pseudoexfoliation syndrome, each of which underwent trabeculotomy ab externo alone and none of which had a history of laser or surgical treatment for ocular disease. Included in the prospective study were 33 eyes of 22 patients with primary open angle glaucoma and 17 eyes of 15 patients (older than 40 years) with pseudoexfoliation syndrome. RESULTS: A life-table analysis for the retrospective study showed that the final success probability (mean +/- SE) at 5 years after surgery was 73.5% +/- 6.3% in eyes with pseudoexfoliation syndrome, which is significantly better than 58.0% +/- 3.1% in eyes with primary open angle glaucoma (P < .05). Also, the higher the preoperative intraocular pressure levels are, the less likely that the postoperative intraocular pressure levels will be brought under control (P < .01). Surgical outcome in the prospective study demonstrated success in 27 (79%) of 34 eyes after 3 years and in 16 (64%) of 25 eyes after 5 years, with medication. Complications included Descemet's membrane detachment (one eye), cyclodialysis (one eye), and decreased visual acuity due to progression of cataract (four eyes). CONCLUSION: The surgical results of trabeculotomy ab externo remain effective in controlling intraocular pressure levels for a long time in selected patients. It thus appears that trabeculotomy ab externo can be considered as an alternative choice of surgical treatment in some cases of glaucoma.

Adult↗
PubMed1993

Effects of hemicholinium-3, a photoreceptor and pigment epithelial toxin, on retinal adhesiveness and subretinal fluid absorption.

Retinal adhesiveness and subretinal fluid absorption was studied in Dutch rabbit eyes given intravitreal injections of hemicholinium-3 (HC-3) which causes loss of photoreceptor outer segments and retinal pigment epithelial (RPE) damage. After HC-3 administration, some areas of the fundus showed pigmentary changes and others appeared normal. Small, non-rhegmatogenous retinal detachments were made in both areas. Within 2-5 days after HC-3 injection, only in the areas of visible damage, subretinal fluid spread laterally to make very flat retinal detachments, and the fluid absorbed very quickly. At later intervals, absorption was slower than normal, presumably because of scarring and RPE metabolic damage. HC-3 provides an experimental technique for transiently weakening retinal adhesiveness in vivo but its use as a model must account for the effects of both outer segment and RPE damage.

Animals↗
PubMed1993

Axial length of eyes with rhegmatogenous retinal detachment.

We conducted a prospective study of 226 eyes with nontraumatic rhegmatogenous retinal detachment; we examined patient characteristics as well as changes in axial length and corneal curvature induced by scleral buckling surgery. Eyes with a round hole in lattice degeneration were characterized by axial length that was longer than that of eyes with retinal tears with and without lattice degeneration. Sex and age also correlated significantly with axial length. Surgically induced changes in axial length depended upon the procedures performed, but the retinal detachment surgery primarily caused a change in the refractive status.

Adult↗
PubMed1992

The influence of argon laser panretinal photocoagulation on the rabbit ERG c-wave.

We observed the influence of panretinal photocoagulation on the ERG c-wave in rabbit eyes. DC-registered ERGs were recorded from rabbit eyes before and after photocoagulation, and compared with those of the fellow eyes. The rabbits were subdivided into 3 groups according to application numbers: 500, 1000, and 1500 spots. The ERG c-waves were found to have totally disappeared in all rabbits 3 days after panretinal photocoagulation, then reappeared with various intervals. In the 500 spot group, the c-wave reappeared after one week, and almost reached control levels in one and a half months. In the 1000 spot group, a 10 day delay was noted, and 90% of control levels were regained after 6 months. In the 1500 spot group, the c-wave didn't reappear until 2 weeks later, and regained 70% (of the control level) after 6 months. The recovery rates were related to the number of laser applications. These results indicate that the ultimate degree of recovery in c-wave amplitude and the time required for the reestablishment of retinal pigment epithelium function both depend on the size of the coagulated area.

Animals↗
PubMed1992

Lowering the calcium concentration in the subretinal space in vivo loosens retinal adhesion.

Retinal adhesiveness in vitro is reduced by lowering the external calcium (Ca2+) concentration. The effects of lowering subretinal Ca2+ concentration in living rabbit eyes was investigated by making experimental retinal detachments (blebs) filled with Ca(2+)-free disodium edetate solution. Unlike blebs made with Hanks' solution, these low-Ca2+ blebs enlarged progressively after they were formed, and they were surrounded by a wide whitish halo. This halo region had weak adhesion (shown by the rapid spread of fluorescein solution into the halo and by the measurement of local adhesiveness after enucleation). The retinal pigment epithelial microvilli in the halo appeared stretched toward the center of the blebs as if there had been retinal traction or movement. Measurements of retinal adhesiveness in vivo showed it to be decreased to about 30% of normal by use of this solution.

Adhesiveness↗
PubMed1991

Photothermal, cryogenic, and diathermic effects of retinal adhesive force in vivo.

Argon laser photocoagulation, cryoretinopexy, and diathermy of moderate intensity is applied to 140 rabbit eyes. Retinal adhesive force is measured from 1 day to 6 months following the treatment, using the authors' new in vivo method. A small retinal detachment is induced within the area surrounded by the burns. At the moment when the detachment starts to expand beyond the burns, subretinal pressure is measured using a resistance servo-nulling method. Retinal adhesive force is then calculated according to Laplace's law and compared with that of untreated eyes. Both photocoagulation and diathermy enhanced adhesiveness within 24 hours to 128% and 122%, respectively, of normal levels. Cryoretinopexy reduced the retinal adhesiveness during the first week, but afterwards generated as much adhesiveness as the other two methods. Beyond 6 months, under the conditions described here by the authors, the adhesive force was stronger after diathermy (279%) than after cryoretinopexy (214%) or laser photocoagulation (220%).

Animals↗
PubMed1991

Lamellar scleral resection enhances subretinal fluid absorption in eyes with choroidal congestion.

The effects of choroidal congestion and lamellar scleral resection on the absorption of subretinal fluid were studied in rabbit eyes. Small retinal detachments were induced and choroidal congestion was produced by ligating two vortex veins. Absorption time was prolonged in these eyes to roughly 138% of that in the control eyes. The choroidal congestion could be alleviated by partial thickness scleral resection, after which the absorption time was only 115% of that in untreated eyes. Our data suggest that lamellar scleral resection relieves elevated choroidal tissue pressure and helps to absorb the subretinal fluid.

Absorption↗
PubMed1991

A comparative study between hysterosalpingography and laparoscopy in case of infertility.

From the present study it can be concluded that both the procedures have their own importance and no one can substitute the other, in diagnosing all the diseases. HSG has been found to be more rewarding in cases of abnormalities of the lumen of uterus and fallopian tubes for their patency. On the other hand laparoscopy has been more rewarding for the abnormalities of the surface of uterus, fallopian tubes and ovaries. It is suggested that in all the cases of infertility both the procedures should be done and the HSG should be done first followed by laparoscopy.

Adolescent↗
PubMed1990

Effects of hemicholinium-3 on the pigmented rabbit retina and pigment epithelium.

Hemicholinium-3 effects on the albino rabbit neural retina have been described, but effects on the retinal pigment epithelium (RPE) have not been closely examined. We have studied retinal morphology and function in Dutch belted (pigmented) rabbits after single intravitreal injections of Hemicholinium-3 or saline. DC electroretinogram recordings show a decrease in a, b, and c-wave amplitudes, with the c-wave affected first. Experiments with sodium iodate show that the early decrease in the c-wave results from a loss of the RPE component of the c-wave, rather than the retinal Slow PIII component. After two days, ophthalmoscopic abnormalities of the fundus are severe in a large area with pigmentary changes. A sharp boundary appears between normally pigmented and depigmented fundus, indicative of a critical threshold for damage. The RPE contains clumped melanin. Pigmented cells are seen away from the basement membrane, an early histological observation temporally correlated with a loss of barrier function seen in fluorescein angiograms. After 10 days, apparent proliferation of non-pigmented RPE cells coincides with re-establishment of the barrier. Rod photoreceptor outer segments are lost 4-7 days after injection in the depigmented regions of the fundus, but outer segments are spared in normally pigmented fundus areas. This regional pattern is distinct from that seen in albino rabbit retina where outer segment loss is fairly uniform. We conclude that Hemicholinium-3 affects the RPE in pigmented rabbits in addition to known effects on retinal cholinergic neurons and photoreceptor disc synthesis.

Animals↗
PubMed1990

Measurement of retinal adhesive force in the in vivo rabbit eye.

A new method to evaluate the retinal adhesive force, which was defined as the force needed to achieve adhesive failure per unit length, in the in vivo rabbit eye was tested. A small dome-shaped retinal detachment (bleb) was made in the posterior pole by injecting balanced salt solution into the subretinal space. A separate measuring micropipette with a tip diameter of 5 microns was inserted into the subretinal space. The subretinal pressure was measured directly with the resistance servonulling method as the solution was injected repeatedly into the subretinal space. According to Laplace's law, the retinal adhesive force per unit length in normal Dutch rabbits was calculated to be (1.8 +/- 0.2) X 10(2) dyn/cm (n = 87). This value was about five times larger than that reported previously with in vitro peeling methods. The new method will resolve several problems encountered in the previous methods and will allow for the measurement of the retinal adhesive force more physiologically and precisely.

Adhesiveness↗
PubMed1990

[The effects of vortex vein ligation and partial scleral resection on the subretinal fluid resorption].

The effects of the choroidal congestion and lamellar scleral resection on the resorption of the subretinal fluid were studied. Small localized retinal detachments were made in pigmented rabbit eyes by injecting balanced salt solution into the subretinal space. In these control eyes, the subretinal fluid was gradually absorbed and the retina was reattached within 160 +/- 21 min. Choroidal congestion was obtained by ligating a couple of vortex veins. To avoid the effects of IOP on the subretinal fluid resorption, IOP was constantly maintained at 20 mmHg by manometry in all experimental eyes. In these eyes, the resorption time was prolonged about 45% compared with the control eyes. After releasing the choroidal congestion by partial thickness scleral resection, the prolonged resorption time was shortened about 19%, but was still 17% longer than that in the non-treated eyes. The present data suggest that the lamellar scleral resection releases the elevated choroidal tissue pressure and is helpful to evacuate the subretinal space.

Absorption↗
PubMed1989

Integrity of the blood-ocular barrier after intravitreal gas injection.

The authors studied the effect of various intravitreal gases on the integrity of the blood-ocular barrier using a fluorophotometric technique. The gas (0.3 ml) was injected into the vitreous cavity of a pigment rabbit after paracentesis. Air and two long-acting gases, sulfur hexafluoride and perfluoropropane, were studied. The eyes that received only paracentesis served as controls. Fluorescein concentrations in the anterior chamber were determined by slit-lamp fluorophotometer 30 minutes following intravenous fluorescein administration. Fluorophotometry was repeated on days 1, 3, 7, and 14 after the gas injections. The eyes that received sulfur hexafluoride and perfluoropropane showed increased aqueous fluorescein concentrations in comparison with the control eyes and the air-injected eyes, although conventional slit-lamp biomicroscopic examination detected no anterior chamber inflammatory signs in these eyes. The aqueous fluorescein leakage decreased to the normal level after the intravitreal gas bubble was absorbed. These results suggest that intravitreal gas bubbles induce subclinical breakdown of the blood-aqueous barrier, which becomes re-established soon after the gas is absorbed.

Absorption↗
PubMed1989

Measurement of vitreous oxygen tension in human eyes.

The vitreous oxygen tension in the human vitreous body was measured using a polarographic oxygen electrode during vitreous surgery. To the best of the authors' knowledge, this is the first time these measurements have been taken in the human eye. The vitreous oxygen tensions in the anterior peripheral vitreous body, central vitreous body, and posterior vitreous body were 16.7 +/- 3.7 mmHg (mean +/- SD, n = 9), 15.9 +/- 2.8 mmHg and 19.9 +/- 4.8 mmHg, respectively. The preretinal oxygen tensions over the detached retina and detached macula were 30.0 +/- 4.8 mmHg (n = 5) and 15.3 +/- 2.1 mmHg (n = 3), respectively, with the latter significantly lower than the former (P less than 0.01). In one case, after inhalation of 100% oxygen the oxygen tension over the retinal scar resulting from cryoretinopexy in a previous retinal detachment surgery increased remarkably to 160 mmHg.

Diabetic Retinopathy↗
PubMed1989

Comparative study of vitreous oxygen tension in human and rabbit eyes.

For the first time, vitreous oxygen tension in the human vitreous body was measured using a polarographic oxygen electrode during vitreous surgery. The same method was used in a rabbit experimental model. In the human eye, the mean oxygen tensions of the anterior peripheral vitreous body, central vitreous body and posterior vitreous body were 16.7 +/- 3.7 mm Hg (mean +/- 1 SD), 15.9 +/- 2.8 mmHg and 19.9 +/- 4.8 mm Hg, respectively, while the preretinal oxygen tension of the detached retina was 30.0 +/- 4.8 mm Hg. In the rabbit eye, the mean oxygen tensions of the anterior peripheral vitreous body, central vitreous body and posterior vitreous body were 13.9 +/- 4.3 mm Hg, 16.0 +/- 3.5 mm Hg and 22.5 +/- 2.1 mm Hg, respectively. The preretinal oxygen tension of the attached retina in the rabbit eye was 39.5 +/- 3.4 mm Hg, while that of the detached retina decreased to 4.3 mm Hg. When comparing human with rabbit eyes, it appears that the vitreous oxygen tensions are similar, except over the detached retina, even though the ocular circulation differs. We believe that human retinal vasculature plays an important role in perfusing the detached retina with relatively high levels of oxygen.

Animals↗
PubMed1989

[A new method to evaluate retinal adhesive force in living rabbit eye].

A new method to evaluate the retinal adhesive force in rabbit eye in vivo is described. A small dome-shaped retinal detachment (bleb) was made in the posterior pole fundus of Dutch rabbit by injecting balanced salt solution into the subretinal space through a micropipette. The transmural pressure was directly measured with a micropressure measuring system, utilizing the resistance servo-nulling methods when the bleb started to extend again. According to Laplace's law, the retinal adhesive force of normal Dutch rabbits was calculated to be (1.8 +/- 0.2) x 10(2) dyn/cm (n = 84). This value was about 5 times larger than that previously obtained by peeling methods in vitro. Our newly developed method might resolve several problems encountered in the previous methods and allow for the measurement of the retinal adhesive force more physiologically and precisely.

Adhesiveness↗