Extraocular muscle changes after cryotherapy for retinopathy of prematurity and the development of strabismus in premature infants

To find out whether the cryotherapy for the treatment of the retinopathy of prematurity (ROP) causes structural changes of the extraocular muscle (EOM), and also whether the changes are related with the occurrence of strabismus. To examine the acute stage change, we conducted a transconjunctival cryotherapy around the superior rectus muscle of a rabbit and resected it 0, 3, 7, 14, and 28 days after the cryotherapy. In observing chronic changes, we first categorized patients who had an esotropia surgery into groups, one of which combined prematurity and cryotherapy and one group affected by prematurity but without having had cryotherapy. Then we compared the change of EOM with that of a fullterm infant group. In a rabbit, edema, acute inflammatory cells and a large amount of degenerated muscle fibers were observed immediately after the cryotherapy and on the 3rd day. On the 7th day, regenerated muscle fibers were observed and on the 14th day, the inflammatory cells decreased and the amount of regenerated muscle fiber increased. On the 28th day, abnormal findings were not observed any more and the muscle was found to be normal. When chronic changes of EOM in human on 1 1/2 to 8 1/2 years after cryotherapy, there were no abnormal findings observed in three groups. From the study, we can infer that cryotherapy can cause acute inflammation and necrosis of muscle fiber but such an acute change will improve and does not result in structural change in the long term. Therefore, the occurrence of strabismus in patients with ROP is considered to be attributable to reasons other than injury of EOM.

Effects of Platelet-derived Growth Factor and Laminin on Retinal Pigment Epithelial Cells

To investigate the effects of platelet-derived growth factor(PDGF)and laminin on the proliferation and morphological change of retinal pigment epithelial(RPE)cells, RPE cells(5 10(3))were cultured on either plastic or laminin-coated 24-well-plates for 6 days. One percent fetal calf serum and PDGF(0, 10, 20 ng/ml)were added in the culture media. Morphological change and the numbers of attached RPE cells were assessed at the end of the culture, using image analyzer and MTT assay. In image analysis, as the PDGF concentration were increased, area(A), perimeter(P), normalized perimeter(NP), diameter(D), minimum size(MinS), maximum size(MaxS), and eccentricity of binary object(EF)were increased while circle filling(Cfil)was decreased. Compared with the cells cultured on plastic, the cells on the laminin showed increase in all the parameters except EF. The proliferative effect on RPE cells were increased on both plastic and laminin as PDGF concentration were increased(P<0.05). These results suggest that proliferation and morphologic change of RPE cells might be influenced by PDGF and laminin.

The Relationship between the Mean Height of Contour of the Retinal Surface at the Temporal Disc Margin and the Reference Height in Analyzing Optic Disc using Heidelberg Retina Tomograph

The relationship between the amount of posterior displacement of the retinal surface at the temporal disc margin and the reference height(HRef)in analyzing optic disc using Heidelberg Retina Tomograph(HRT;Heidelberg Engineering, Heidelberg, Germany)was evaluated. The displacement was measured as mean height of contour(MHC)in the temporal 40degrees C segment(20degrees C superior and 20degrees C inferior to the horizontal midline)of optic disc. HRef is a value representing the location of the standard reference plane. The accordances of HRef and stereometric parameters between right and left disc were also evaluated. MHC in the temporal 40 degrees C and nasal 40 degrees C segment, HRef, and stereometric parameters of optic disc were measured with the HRT in 244 eyes of 122 subjects. HRef was 0.376+/-0.099 mm in the right disc and 0.385+/-0.090 mm in the left disc. There was good correlation between HRef and MHC in the temporal 40degrees C segment(r=0.97, p<0.01), but poor in the nasal 40 degrees C segment(r=0.29, p<0.01). The accordances of HRef and stereometric parameters increased as the difference of MHC in the temporal 40degrees C segment between right and left disc decreased. HRef was affected by the amount of posterior displacement of the retinal surface at the temporal disc margin, which occurs in instances such as a tilted disc. We should find the method to adjust stereometric parameters to the amount of disc tilt.

Macular Blood Flows in Diabetic Patients

The authors investigated macular circulation in a group of 27 patients(54 eyes) with diabetes melitus to evaluate the change of macular blood flow according to the grade of retinopathy, the status of glucose control and the duration of diabetes. Blood volume, flow and velocity on macular area were measured by Heidelberg Retinal Flowmeter(HRF, Heidelberg Engineering). Paticents with moderate or severe diabetic retinopathy showed a significant increase in macular blood flow than patients with less degree of diabetic retinopathy(502.45+/-223.58 AU vs, 355.19+/-123.84 AU, p=0.003). Both blood volume and velocity were also significantly increased in the patients with more advanced diabetic retinopathy. Macular blood flow was increased in the patients with higher fasting blood glucose, although the statistical significance was in borderline(473.12+/-238.57 AU vs, 362.14+/-103.22 AU, p=0.066). These results show that macular blood flow increases in the diabetic patients with more advanced diabetic retinopathy, suggesting that the increase in the macular blood flow may play a role in the development of diabetic macular microangiopathy.

Surgical treatment of subretinal neovascular membrane

The visual results of laser photocoagulation for subfoveal choroidal neovascular membrane (CNVM) has not always been satisfactory. The surgical removal of the neovascular membrane may be another treatment option. To investigate the prognosis and risk factors of this surgery, we analyzed the results of surgical removal of subfoveal CNVM (23 eyes), subfoveal hemorrhage with CNVM (6 eyes), and subfoveal hemorrhage alone (6 eyes). The mean follow-up period was 17.7 months (range 2 to 47 months). The mean preoperative membrane size was 0.89 disc diameter and the mean postoperative retinal pigment epithelial (RPE) defect size was 1.33 disc diameter. Visual improvement was observed in 13 out of the 23 eyes (56.5%) with sufoveal CNVM, four out of the six eyes (66.6%) with subretinal hemorrhage and CNVM, and five out of the six eyes (83.3%) with subretinal hemorrhage only. The visual outcome of subfoveal CNVM surgery was related to the presence of a subfoveal RPE defect (p = 0.005) rather than to the size of the RPE defect. No recurrence of neovascular membrane was observed during the follow up period. In conclusion, surgical removal may be a good alternative treatment for subfoveal CNVM.

Clinical Manifestation of Asteroid Hyalosis

We investigated fifteen men and twenty one women, who were diagnosed to have asteroid hyalosis between June, 1997 and November, 1997 at Seoul National University Hospital. After obtaining their medical history a complete eye examination was performed. Specimen was examined by light microscope in one case. Funduscopic examination revealed bilateral involvement in 5 cases. Twenty six patients were diabetic and 12 were hypertensive. There was a significant association with diabetes. Light microscopic exam showed variable sized spherical structures with brown rim. Further decrease in visual acuity due to asteroid hyalosis was not observed in 35 cases in which follow-up exams were possible. In conclusion, asteroid hyalosis rarely caused visual loss and were likely to be monocular and to occur in old age.

Early Detection of Glaucoma with Retinal Nerve Fiber Layer Photograph

The purpose of this study was to evaluate the usefulness of retinal nerve fiber layer [RNFL] photography and Heidelberg Retina Tomograph [HRT, Heidelberg, Germany] in early detection of glaucoma. Among 2802 people who underwent routine health checkup at. Seoul National University Hospital from July I to Decernber 31, 1996, forty-nine persons were included whose IOP was above 21mmHg or cup/disc ratio was 0.5 or greater. RNFL photography, HRT and automated perimetry [Humphrey Field Analyzer, program C30-2] were performed. Twelve eyes were diagnosed as glaucoma and one sye as glaucoma suspect. Four eyes with glaucoma had RNFL defect with normal visual field and 7 eyes with glaucoma had both RNFL defect and glaucomatous visual field defect. Of 26 eyes suggested as glaucoma by FSM classification of HRT, only 8 eyes met the diagnostic cri-teria of glaucoma of this study. Among 21 eyes with decreased hump height in HRT only 7 eyes were diagnosed as glaucoma. RNFL photography increased the detection rate for glaucoma by 50% over that with visual field test. only. RNFL photography will be a valuable method for early detection of glaucorna while HRT may play a suppleinentary role.

Experimental Exudative Retinal Detachment in Albino Rats

To establish animal model of exudative retinal detachment in Sprague Dawley albino rats and to elucidate the possible role of retinal vein in the induction of exudative retinal detachments, rose bengal photosensitive dye was injected intravenously and argon laser was applied. In group A(10 eyes), laser was applied on intervascular retinal areas linearly. In group B (12 eyes), laser was applied on major retinal veins. In group C(4 eyes), laser was applied on major retinal arteris. In group D(3 eyes), laser was applied on major retinal veins without rose bengal dye and in group E(26 eyes), only the rose bengal dye was perfused. And in group F(3 eyes), normal eyes were fixed for negative controls. Exudative bullous retinal detachment occurred only in group B and these resutls were confirmed in histological examinations. In control groups (D and E), tissue injuries were not found. In conclusion, exudative retinal detachment could be induced by occlusion of retinal veins in albino rats and the abnormalities of retinal venous blood flow were required for the induction of exudative retinal detachment.

Clinical Characteristics of Branch Retinal Vein Occlusion with Vitreous Hemorrhage

Forty three eyes with vitreous hemorrhage caused by branch retinal vein occlusion had been underwent pars plana vitrectomy and followed-up over 6 months. The eyes were classified into 4 groups according to intraoperative fundus findings-group 1; vitreous hemorrhage only, group 2; vitreous hemorrhage with fibrovascular proliferation, group 3; vitreous hemorrhage with traction retinal detachments, group 4; vitreous hemorrhage with rhegmatogenous retinal detachments. Analysis was focused on the clinical characteristics and postoperative outcome in each group. The durations of vitreous hemorrhage were longer significantly in group 2 and group 3. The vision improved postoperatively in 35 of 43 eyes(81.3%). The percentage of postoperative visual improvements was 100%(18 of 18 eyes) in group 1, 85.7%(12 of 14 eyes) in group 2, 66.6%(4 of 6 eyes) in group 3, and 20$(1 of 5 eyes) in group 4. The preoperative ultrasono-graphic findings of retinal status were accorded with intraoperative retinal findings in 74.4% of eyes.

Mechanism of Hypoxia-Induced Cytotoxicity in Cultured Rat Retinal Neurons

Retinal neurons are highly vulnerable to hypoxia/ischemia. Excitotoxicity and free radical injury have been proposed as the major mechanisms of ischemic retinal injury have been proposed as the major mechanisms of ischemic retinal neuronal death. In the present study, we examined these possibilities in retinal cultures. Exposure of these cultures to hypoxia for 48 hr induced selective death of neurons. Addition of an antioxidiant trolox markedly attenuated hypoxiainduced retinal neuronal death, whereas addition of glutamate antagonists, MK-801 or CNQX,did not. Morphologically, hypoxic neuronal death in cultures was accompanied by cell body swelling, a feature of necrosis, yet simultaneously exhibited some features of apoptosis such as TUNEL positivity and protection by cycloheximide. However, unlike in classical programmed cell death, adding buthionine sulfoximine, a potent inhibitor of glutathione synthesis, completely reversed the protective effect of cycloheximide. The results have demonstrated that free radical injury is the main mechanism of neuronal death in the present retinal culture, and suggest an intriguing possibility that free redical injury may become a prominent mechanism, when excitotoxic injury is masked.

Excitotoxic Cell Death in Cultured Retinal Neurons

We examined excitotoxicity, putatively a major mechanism of ischemic neuronal death, in primary rat retinal cultures. Retinal cultures were prepared from newborn rats (day 1 or 2). Exposure of these cultures (DIV8-10)to NMDA or kainate induced neuronal death. Furthermore, MK-801 or CNQX each partially attenuated glutamateinduced neuronal death, suggesting that both NMDA and kainate receptors mediate it. Thy-1(+) retinal ganglion neurons, like neurons as a whole, were equally injured by NMDA and by kainate. However, GABA(+) or calbindin (+) neurons of the inner nuclear layer were resistant to NMDA, but highly vulnerable to kainate. These neurons may have AMPA/kainate receptors that are highly permeable to Ca2+, as they take up cobalt with kainate stimulation. These results suggest that the AMPA/kainate receptor, rater than the NMDA receptor, may mediate this pattern of selective neurnonal death.

Antiangiogenic Effects of Retinoids on Corneal Neovascularization

We investigated the effect of topical application of retimids on the corneal neovascularization in the rat induced by chemical cauterization. The center of corneas of Wistar rats were Cauterized with a silver/potassium nitrate applicator for 5 seconds. And then they were treated topically with 0.1%, 0.2%, 0.5%, 2.0% all-trans retimids (retinol, retinoic acid, retinaldehyde) and dimethyl sulfoxide as a control four times a day. After appiications of eye drops for 5 days, each rat was kined and then perfused with a mixture of 11% gelatin 10% India ink-lactated Ringer's solution. Corneal flat preparation were made, and then the percent of the corneal area occupied by blood vessels were analized by computerized image analyzer. Percent vascularization of 0.1% and 0.2% retnoids were not significantly different from control group(p>0.05). Percent vascu1arization of 0.5% retinaldehyde and all 2.0% retnoids were significantly lower than the contml group(p>0.5). These naturally occurring retinoids were effective in antiarlgiogenesis of rat cornea at relatively high concentrations (>0.5%), when treated topicany, It will be necessary to further study on more potent antiangiogenic, at lower concentration, synthetic retimids for the treatment of angiogenic diseases.

Antiangiogenic Effects of Retinoids on Corneal Neovascularization

We investigated the effect of topical application of retimids on the corneal neovascularization in the rat induced by chemical cauterization. The center of corneas of Wistar rats were Cauterized with a silver/potassium nitrate applicator for 5 seconds. And then they were treated topically with 0.1%, 0.2%, 0.5%, 2.0% all-trans retimids (retinol, retinoic acid, retinaldehyde) and dimethyl sulfoxide as a control four times a day. After appiications of eye drops for 5 days, each rat was kined and then perfused with a mixture of 11% gelatin 10% India ink-lactated Ringer's solution. Corneal flat preparation were made, and then the percent of the corneal area occupied by blood vessels were analized by computerized image analyzer. Percent vascularization of 0.1% and 0.2% retnoids were not significantly different from control group(p>0.05). Percent vascu1arization of 0.5% retinaldehyde and all 2.0% retnoids were significantly lower than the contml group(p>0.5). These naturally occurring retinoids were effective in antiarlgiogenesis of rat cornea at relatively high concentrations (>0.5%), when treated topicany, It will be necessary to further study on more potent antiangiogenic, at lower concentration, synthetic retimids for the treatment of angiogenic diseases.

Induction of vitreolysis and vitreous detachment with hyaluronidase and perfluoropropane gas

To simulate the posterior vitreous detachment (PVD) in the rabbit, 1 IU hyaluronidase and/or 0.2 ml of perfluoropropane gas was intravitreally injected. Ophthalmoscopic, light microscopic examination prepared by cryotechnique, electron microscopic examination, and electroretinogram were done on the 3rd and 28th postoperative days. As a result, the eyes undergone simultaneous intravitreal injection of 1 IU hyaluronidase and 0.2 ml perfluoropropane gas showed membranous structure split from the internal limiting membrane of the superior retina in 3 days after injection. The eyes also demonstrated membranous structure separated from the superior retina after 28 days, simulating vitreous detachment. On the contrary, neither agent alone induced vitreous detachment. No toxic retinal changes associated with simultaneous intravitreal injection of 1 IU hyaluronidase and 0.2 ml perfluoropropane gas were observed. Therefore, with a future support by histologic examination other than cryotechnique and by immunohistochemical analysis, the simultaneous intravitreal injection of perfluoropropane gas and hyaluronidase would be a promising method to induce vitreous detachment in non-vitrectomized eye.

Retinal circulation times in branch retinal vein occlusion

To investigate the retinal hemodynamics in branch retinal vein occlusion (BRVO), we measured retinal circulation times using scanning laser ophthalmoscope (SLO) and studied their relationships with clinical findings. Arm-retina time (ART) and arteriovenous passage time (AVP) were measured in 30 eyes of 30 patients. Mean ART was 13.07 seconds. ART showed no difference in relation to sex and systemic diseases, but increased with age. Mean AVPs were 3.00 sec. and 3.39 sec. in superotemporal and inferotemporal BRVO, respectively. AVPs were delayed significantly in occluded branch of retinal veins. AVP was delayed three-fold when the area of capillary nonperfusion was over 6 disc area, but showed no difference according to the duration of disease or macular edema. These results suggest that SLO may be a useful tool for studying retinal hemodynamics in BRVO.

Study on Retinal Circulation by Scanning Laser Ophthalmoscope I. Evaluation of Retinal Circulation Times in Non-proliferative Diabetic Retinopathy

The scanning laser ophthalmoscope was used to measure arm-retinal time(ART) and arteriovenous passage time(AVP) in 27 non-proliferative diabetic retinopathic eyes(NPDR eyes) and 22 normal controls. The ART in NPDR eyes(12.10 +/- 4.21 sec) was similar to that in normal eyes(12.79 +/- 3.59 sec). The AVPs measured from each quadrant were significantly longer in all quadrants in the NPDR eyes (2.41 +/- 0.85 sec in superior temporal quadrant (ST), 2.29 +/- 0.63 sec in inferior temporal one(IT) , 2.41+/-0.88 see in superior nasal one (SN), and 2.30 +/- 0.72 sec in inferior nasal one(IN)) than in normal eyes(1.73 +/- 0.61 sec in ST, 1.81 +/- 0.75 sec in IT, 1.83 +/- 0.58 sec in SN, and 1.83 +/- 0.58 sec in IN). This results suggest that retinal blood flow and its velocity are reduced in NPDR.

The effects of ascorbic acid on free radical injury in cultured retinal pigment epithelial cells

This study was conducted to investigate the effect of ascorbic acid on oxidative injury of cultured porcine retinal pigment epithelial (RPE) cells induced by t-butylhydroperoxide. The porcine RPE cells were cultured in Dulbecco's modified Eagle's medium and the culture medium was replaced with one containing 0.01 mM to 5 mM ascorbic acid and/or 0.2 mM t-butylhydroperoxide. After 2 hours incubation, the test medium was replaced with the control medium. The number of cells was counted with a Coulter counter after a 2-day incubation period. The medium was pretreated with 900 U/ml and the previous procedure was repeated to eliminate the toxic effects of hydrogen peroxide induced by ascorbic acid. Not only t-butylhydroperoxide (p 0.05). The cytotoxicity of t-butylhydroperoxide decreased when 1 mM and 5 mM of ascorbic acid was added to the culture media with catalase pretreatment (p = 0.0277). These results indicate that ascorbic acid was toxic to RPE cells in our culture model but this cytotoxicity was not detected in the presence of catalase. With catalase pretreatment, ascorbic acid in relatively high concentration provided protection against oxidative injury of t-butylhydroperoxide.

Effects of mitomycin C on delayed adjustment in experimental strabismus surgery

In adjustable strabismus surgery, a satisfactory final result would be achieved with delayed adjustment. However, the postoperative adhesions following strabismus surgery make delayed adjustment impossible. We evaluated the efficacy of mitomycin C in reducing the severity of postoperative adhesions following strabismus surgery and in delaying the time adjustment after surgery. Experimental rabbits underwent a hang-back recession procedure in the superior rectus muscle. A topical application of mitomycin C was made between the conjunctiva and the sclera for 5 minutes during the operation. We then studied the possible time of delayed adjustment and estimated the minimal forces required for the adjustment. The topical application of 0.1 mg/ml mitomycin C between the conjunctiva and sclera allowed for a 2-week delayed adjustment after surgery, and 0.2 mg/ml mitomycin C prevented the adhesions between these tissues and the muscle 5 weeks after surgery. These results suggest that topical mitomycin C may enhance the success rate of strabismus surgery with delayed adjustment and reduce postoperative adhesions.

The Absorption of Intraocular Gas and Its Relationship with IOP

We performed the intravitreal injection of air and pure perfluoropropane(C3F8) gas in the pigmented rabbits and observed the changes of gas levels by the ultrasonography. We also observed the changes of the intra-ocular gas levels by the ultrasonography and measured the intraocular pressures(IOPs) in 9 patients who had undergone vitrectomy and fluid-gas exchange with 20% sulfur hexafluoride(SF6) and 14% perfluoropropane(C3F8) gases. In the pigmented rabbits, the air was not expanded and completely absorbed within 2 days, and the C3F8 gas was expanded maximally at 3 to 7 days and completely absorbed after 3 weeks. Among nine human eyes treated with vitrectomy and fluid-gas exchange, the intraocular pressures were elevated above 25mmHg at 1 day after operation in 2 eyes, which were controlled with medical therapy. The lOPs were significantly correlated with the amount of the intraocular gases(r=0.3476, p<0.05). The assessment of intraocular gas level by ultrasonography seems to be easier and more objective method than others previously reported.

The Effect of Laser Treatment on Branch Retinal Vein Occlusion

We did clinical analysis of 72 patients with branched retinal vein occlusion, who were diagnosed by indirect opthalmoscope and fluorescein angiography and treated with laser photocoagulatlon from Jan, 198l to May, l990. The results were as follows; 1. Final visual acuity has a Significant statistical correlation with macular edema in terma of 'quadrant area' 2. We were unable to demonstrate any statistical correlation between final visual acuity and the following factors: degree of nonperfusion, neovascularization type of laser photocoagulatlon, duration of symptoms before laser photocoagulation.