Studies on the feasibility of a subretinal visual prosthesis: data from Yucatan micropig and rabbit

BACKGROUND

To estimate the feasibility of the subretinal concept of a visual prosthesis, animal models and prototypes, each representing a certain aspect of the final prosthesis, were utilised to test for requirements for such a medical device: (1) the ability to elicit--by electrical stimulation--event-related central activity in the central visual system, and (2) the long-term biocompatibility and biostability of the implant within the subretinal space.

METHODS

(1) In rabbit and Yucatan minipig, cortical evoked potentials were recorded with chronically implanted epidural electrodes during stimulation with light flashes as well as during electrical stimulation in the subretinal space. Voltage pulses ranging from -3 V to +3 V were applied via an acutely implanted electrode array on a wired prototype. (2) For biocompatibility studies a silicon-based micro-photodiode array (MPDA) was used that closely resembled the design and composition of the final prosthesis. Fourteen months after implantation, angiography was performed and the histological findings of the retina in the immediate vicinity of the implant were evaluated.

RESULTS

(1) In both rabbit and minipig, subretinal electrical stimulation resulted in evoked cortical potentials that were comparable to visual evoked potentials. The lowest threshold levels for the subretinal stimulation were 0.6 V for rabbits and 2 V for minipigs. (2) Long-term stability of an implanted MPDA and its biocompatibility were proven for a postoperative period of 14 months.

CONCLUSIONS

Data from animal experiments with certain prototypes of the final prosthesis suggest the feasibility of the concept of a subretinal visual prosthesis: Both requirements were met: (1) the functioning of the subretinal stimulation and (2) the biocompatibility of the MPDA implant.

New substances for intraocular tamponades: perfluorocarbon liquids, hydrofluorocarbon liquids and hydrofluorocarbon-oligomers in vitreoretinal surgery

Perfluorocarbon liquids (PFCLs) and heavy fluorocarbon liquids (HFCLs) are being increasingly used as soft tools during vitreoretinal surgery. However, since long-term intraocular tolerance is still unsatisfactory, at present complete removal at the end of surgery is recommended. With the aim to improve long-term intraocular compatibility and to enlarge the spectrum of clinical applications, modified HFCLs have been developed. HFCL-oligomers with a higher viscosity represent the latest perspective. All three groups of fluorocarbon liquids will be compared with respect to their physical and chemical properties, experimental and clinical results, and prospects for clinical applications. Common features of PFCLs, HFCLs and HFCL-oligomers are biological inertness, specific gravity higher than water, immiscibility with water or blood, and a high gas binding capacity. In PFCLs such as decalin, octane, or phenanthrene. All carbon atoms of the carbon backbone are completely fluorinated. In experimental and clinical use, emulsification, vascular changes and structural alterations of the retina have been described. By only partial replacement of hydrogen atoms by fluorine, the specific gravity of HFCLs is reduced, whereas lipophilic properties increase. Thus HFCLs are potential solvents for intraocular silicone oil remnants. However. after long-term application, side-effects are similar to those observed with PFCLs. Substances of this group, such as F6H6, F6H8, 044, and 062 are used intraoperatively and are currently being investigated for clinical long-term application. With the aim to avoid emulsification and to improve intraocular tolerance, we have developed HFCL-oligomers consisting of 2-4 HFCL molecules with increased viscosity. The oligomers were tolerated well in rabbit eyes for up to 4 months. In contrast to PFCLs or monomers, they did not emulsify nor show vascular alterations. ERGs returned to normal after removal of the oligomer from the eye. Histology of the retina showed mild alterations.

CONCLUSION

according to physical properties, experimental intraocular compatibility and stability against emulsification, HFCL-oligomers are promising candidates for improved long-term tamponade of the lower retina. At present, indications for an application in human eyes have to be determined in clinical trials.

[Central retinal artery occlusion. Importance of selective intra-arterial fibrinolysis]

BACKGROUND

Conventional treatment of a central retinal artery occlusion usually has a poor prognosis but intra-arterial fibrinolysis (IF) of the ophthalmic artery is an invasive treatment option. The importance of IF was evaluated in 62 patients with central retinal artery occlusion and in addition the risk spectrum for this disease was considered.

MATERIAL AND METHODS

Data from charts of 62 patients were retrospectively analysed. Visual recovery after IF (n = 17) was compared to conventional treatment (e.g. decrease of IOP, improvement of rheological conditions, n = 45). Patients were excluded from IF if the occlusion was present for more than 8 h, if there was a history of bleeding and previous operations, or if they were older than 85 years. IF was performed using either urokinase (n = 7) or tPA (n = 10).

RESULTS

Out of 62 patients, 22 (35%) with central retinal artery occlusion underwent catheterisation. Stenosis of the carotid artery excluded IF in 5 out of these 22 cases, therefore only 17 patients were treated by IF. Of the patients, 40 (65%) were excluded from IF for various reasons: 47% (19/40) arrived later than 8 h after occlusion, 17% (7/40) did not consent to IF, 15% (6/40) had medical contraindications and 13% (5/40) were over 85 years of age. Two patients required no IF because of a cilioretinal anastomosis with moderate visual acuity and another patient showed spontaneous visual recovery during ophthalmic examination. Of the 17 patients treated with IF, 4 achieved an improvement of visual acuity by more than 2 lines, no change of visual acuity was observed in 12/17 patients and 1/17 lost more than 2 lines after treatment. Of the 45 conservatively treated patients, 16 achieved improvement by more than 2 lines and no change occurred in 29/45 patients. Three patients treated with IF suffered from a stroke during treatment. The main risk factor for central retinal artery occlusion was high blood pressure in 32% of all cases and nicotine abuse in 16%.

CONCLUSIONS

Many patients presented too late for IF. However, there was no statistical difference between patients with IF and conventional treatment with regards to the improvement of visual acuity. Additionally there is an increased risk of a stroke from IF, therefore a prospective study is necessary to evaluate the importance of IF. Stabilisation of high blood pressure may be the best prophylaxis for preventing a central retinal artery occlusion.

Subretinales Mikrophotodioden-Array als Ersatz für degenerierte Photorezeptoren?

A survey is given on the status of developments, concerning a subretinal electronic microphotodiode array that aims at replacing degenerated photoreceptors. Various prototypes have been developed, tested, and implanted in various experimental animals up to 18 months. The fact that electrical responses were recorded from the visual cortex of pigs after electrical stimulation by subretinal electrodes and the fact that responses are also recorded in-vitro in degenerated rat retinae, shows the feasibility of this approach. However, there are a number of open questions concerning the biocompatibility, the long-time stability, and the type of transmitted image to be solved before application in patients can be considered.

Exudative retinal detachment in macular hole surgery using platelet concentrates--a case report

INTRODUCTION

Retinal detachment after macular hole surgery is a rare complication, usually occurring because of small, peripheral holes. We present a patient with a high bullous exudative retinal detachment following pars plana vitrectomy.

CASE REPORT

A healthy 69-year-old patient presented with a macular hole stage III of the left eye. Corrected visual acuity was 20/200. Pars plana vitrectomy was performed without peeling of the internal limiting membrane or an epiretinal membrane, a few drops of platelet concentrate were instilled onto the hole, and the bulbus was filled subtotally with a non-expanding SF6/air mixture. On the 3rd postoperative day a small retinal detachment of the inferior half of the retina was noticed that increased over the next 3 days until it reached the inferior vascular arcade. During the following 3 days a spontaneous remission occurred with complete reattachment of the retina. Six weeks after operation the retina was completely reattached, the macular hole was closed, and the visual acuity was 20/200 with a slight cataract.

CONCLUSION

Retinal detachments after macular hole surgery are not always of rhegmatogenous nature but may also be exudative and related to an inflammatory reaction caused by adjuvants. When a retinal detachment occurs immediately after macular hole surgery without detectable holes it may be advisable to wait for some days before reoperation.

Epinephrine, but not dexamethasone, induces apoptosis in retinal pigment epithelium cells in vitro: possible implications on the pathogenesis of central serous chorioretinopathy

BACKGROUND

The pathogenesis of central serous chorioretinopathy is poorly understood. It is believed to be due to dysfunction of the retinal pigment epithelium and/or choroid and has been associated with elevated levels of epinephrine and administration of corticosteroids. Epinephrine and corticosteroids have previously been shown to induce apoptosis (programmed cell death) in various types of cells. The objective of this study was to investigate whether these agents can induce apoptosis in cultured retinal pigment epithelium cells. This may help elucidate the pathogenesis of central serous chorioretinopathy.

METHODS

Third-passage porcine retinal pigment epithelium cells were grown to confluence and incubated for 1-7 days in culture medium containing epinephrine (10(2)-10(9) pg/ml) or a corticosteroid, dexamethasone (4-4x10(4) ng/ml). The cultures were evaluated for apoptosis by phase-contrast microscopy and in situ terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling.

RESULTS

Epinephrine (7x10(7)-10(9) pg/ml) induced apoptosis in a dose- and time-dependent manner. Exposure to lower concentrations of epinephrine (10(2)-6x10(7) pg/ml) and all tested levels of dexamethasone did not result in apoptosis.

CONCLUSION

Retinal pigment epithelium cells may undergo apoptosis following exposure to elevated levels of epinephrine. These findings suggest a possible pathophysiologic mechanism for the development of central serous chorioretinopathy.

[Clinical results of intravitreal administration of tissue-type plasminogen activator (tPA) and gas for removal of subretinal hemorrhage in senile macular degeneration]

BACKGROUND

Subretinal hemorrhage in age related macular degeneration (AMD) usually causes acute visual loss and is associated with poor visual prognosis. In order to prevent retinal damage and to perform laser treatment of the underlying choroidal neovascularization (CNV) the subretinal hemorrhage has to be removed from the macular region. This could be achieved by intravitreal injection of tissue plasminogen activator (tPA) and gas.

PATIENTS AND METHODS

In 8 consecutive patients, suffering from a massive macular hemorrhage (duration of visual problems: mean 9 days), tissue plasminogen activator (tPA) (40 micrograms in 400 microliters BSS) and SF6-gas (0.75 ml) was transsclerally injected into the vitreous cavity to achieve liquification and displacement of the hemorrhage.

RESULTS

In all patients liquification and displacement of the hemorrhage out of the macular region was achieved during follow up. During the first week after operation a significant increase of visual acuity was noticed in all patients, however ophthalmoscopically there was just little reduction of the hemorrhage in the foveolar area. After successful removal of the blood the choroidal neovascularization was treated successfully by laser coagulation in one patient. No laser treatment was performed in the other patients because of the subfoveal location of the neovascularisation or because of disciform scar. Visual acuity increased 4 lines after surgery. In one case the procedure was complicated by a persistent vitreous hemorrhage and vitrectomy had to be performed in another patient due to an endophthalmitis.

CONCLUSION

Intravitreal injection of tPA assisted gas displacement of subretinal hemorrhage due to AMD leads to a significant increase of visual acuity during the first week after operation. Although a nearly complete removal of the hemorrhage out of the macular area could be achieved, it was difficult to differentiate this from the spontaneous course. Laser photocoagulation could be performed in only few cases.

Listeria monocytogenes-induced endogenous endophthalmitis in an otherwise healthy

PURPOSE Listeria monocytogenes is a rare cause of endogenous endophthalmitis. To date 15 cases have been published in the literature. All eyes showed similar clinical features and profound visual loss mainly due to delayed diagnosis.

METHODS

An additional case of an otherwise healthy 73 year-old male, who was referred to our hospital because of acute iridocyclitis with secondary glaucoma, is reported. Within a few days the severity of the intraocular infection increased dramatically, resulting in the clinical picture of acute endophthalmitis. RESULTS In contrast to most published cases, early identification of the causative pathogen in the aqueous humor after anterior chamber puncture using polymerase chain reaction (PCR) and the initiation of a specific, systemic antibiotic medication, resulted in complete recovery of visual acuity.

CONCLUSIONS

PCR is very useful for the identification of the pathogen in intraocular infections. (Eur J Ophthalmol 1999; 9: 53-7).

Listeria monocytogenes-induced endogenous endophthalmitis in an otherwise healthy individual: rapid PCR-diagnosis as the basis for effective treatment

PURPOSE

Listeria monocytogenes is a rare cause of endogenous endophthalmitis. To date 15 cases have been published in the literature. All eyes showed similar clinical features and profound visual loss mainly due to delayed diagnosis.

METHODS

An additional case of an otherwise healthy 73 year-old male, who was referred to our hospital because of acute iridocyclitis with secondary glaucoma, is reported. Within a few days the severity of the intraocular infection increased dramatically, resulting in the clinical picture of acute endophthalmitis.

RESULTS

In contrast to most published cases, early identification of the causative pathogen in the aqueous humor after anterior chamber puncture using polymerase chain reaction (PCR) and the initiation of a specific, systemic antibiotic medication, resulted in-complete recovery of visual acuity.

CONCLUSIONS

PCR is very useful for the identification of the pathogen in intraocular infections.

[Surgical worm extraction in loa loa ophthalmia]

BACKGROUND

Loa Loa is a chronic parasitemic disease which is endemic in the tropical rain forests of Western Africa. Vector of this disease is a mangrove fly with the name Chrysops. Besides the eye worm and skin affections a systemic infection with microfilariae is common.

PATIENT

A West African tourist from Bangibe showed up at the university eye clinic. His complaints were a red eye and a mobile subconjunctival tumor (Fig. 1) that showed vermiform movements. The worm was transparent and 4-5 cm in length. After topical anaesthesia and the attempt to paralyze the worm (1) with Pilocarpine 2% it vanished. Two days later the patient showed up in the morning for the planned blood test. No worm was visible at that time but at noontime the blood test was carried out and at that time the worm was visible in the nasal conjunctiva. This time the worm was removed without delay under topical anaesthesia. The worm was fixed with a forceps through the conjunctiva which was opened for 0.5 cm. The worm was grasped with a second forceps and drawn out under massive vermiform movement. Systemic therapy was recommended with Hetrazan (Diethylcarbamazine) using Corticosteroides and Antihistamine to minimize allergic side effects by the therapy due to the systemic microfilariae blood load. Eosinophilia was 8%.

CONCLUSIONS

A subconjuctival Loa Loa worm can be removed under topical anaesthesia by fixing it with a forceps through the conjunctiva and opening it and grasping the worm with a second forceps. According to our experience the paralyzation with Pilocarpine cannot be realized. Careful systemic therapy avoiding reported allergic side effects with Hetrazan which is not available in Germany is necessary.

Treatment of pigment epithelial detachments due to age-related macular degeneration with intra-ocular C3F8 injection

PURPOSE

To flatten pigment epithelial detachments (PED) due to age-related macular degeneration in an attempt to visualize the underlying choroidal neovascularization by fluorescein angiography (FA) and reveal a treatment target.

METHODS

Nine patients with PED received intravitreal gas injections via the pars plana and postured face down. Fluorescein angiograms were obtained before and after gas injection. In two patients, retinal scotopic sensitivity was also measured.

RESULTS

Eight patients demonstrated change in the shape and size of the PED following gas injection. Four patients showed a better delineation of underlying structures on FA. Three patients had focal laser treatment to the newly visible choroidal neovascular complex, but this was successful in only one patient with flattening of the PED.

CONCLUSION

Pigment epithelial detachments can be modified by intravitreal gas injection in some patients, but this treatment did not have a major impact on overall outcome or management.

Diagnosis of infectious endophthalmitis after cataract surgery by polymerase chain reaction

PURPOSE

To ascertain whether the use of the polymerase chain reaction (PCR) technique leads to more rapid diagnosis of infectious endophthalmitis after cataract surgery.

SETTING

University Eye Clinic Regensburg, Germany.

METHODS

The aqueous humor and vitreous of 16 eyes with infectious endophthalmitis (10 acute, 6 delayed) were evaluated by microscopy, diagnostic culture, and PCR to detect the infectious agent.

RESULTS

Microscopy of the vitreous was positive in 3 eyes and the culture media results were positive in 7 eyes, all with acute endophthalmitis. Significantly fewer positive results were obtained in the aqueous humor. Using PCR, an infectious agent was detected in the aqueous humor of all 16 eyes and in the vitreous of 14. The vitreous sample was negative in 2 eyes with delayed endophthalmitis.

CONCLUSIONS

Detection of the infectious agent was more successful using PCR than using conventional microbiological tests, especially in the diagnosis of delayed endophthalmitis where the pathogen was detected in the aqueous humor in all eyes.

The development of subretinal microphotodiodes for replacement of degenerated photoreceptors

There are presently several concepts to restore vision in blind or highly visually handicapped persons by implanting electronic devices into the eye in order to partially restore vision. Here, the approach to replace retinal photoreceptors by a subretinally implanted microphotodiode array (MPDA) is summarized. A survey is given on the present state of the development of MPDAs, the possibility of in vitro and in vivo tests as well as first results on biocompatibility and histology. Additionally, electrophysiological recordings in rabbits and rats are presented which have received such subretinal implants.

Severe ocular trauma managed with primary pars plana vitrectomy and silicone oil

PURPOSE

This study evaluated the outcome of severely injured eyes treated with early primary vitrectomy with silicone oil filling.

METHODS

A total of 435 eye injuries, which required surgical intervention, were reviewed retrospectively. In 13 eyes (3%) pars plana vitrectomy and silicone oil filling were performed as primary surgical repair. Silicone oil filling was restricted to cases with laceration of the retina larger than 4 disc diameters (nine eyes), primary retinal detachment larger than two quadrants (two eyes) and/or persistent intrasurgical hemorrhage (12 eyes). All patients underwent surgery within 24 hours.

RESULTS

After a mean follow-up period of 28.7 months (range, 9-70 months), 11 eyes achieved a visual acuity ranging from 20/25 to 20/200. Silicone oil was removed in 11 of 13 eyes after 5.8 +/- 4.6 months. Recurrent proliferative vitreoretinopathy developed in two eyes.

CONCLUSIONS

Silicone oil tamponade after early primary pars plana vitrectomy may be an alternative for primary repair after trauma, especially in severely injured eyes with retinal lacerations larger than 4 disc diameters, persistent intrasurgical bleeding, and/or primary retinal detachments.

[Treatment of recurrent corneal erosion using phototherapeutic keratectomy with the excimer laser]

BACKGROUND

Recurrent corneal erosion is a common corneal disease and may be a difficult disorder to treat with a number of patients suffering persistent symptoms despite conventional therapy.

PATIENTS AND METHODS

We present a series of 32 eyes who underwent Excimer-Laser phototherapeutic keratectomy (PTK) for recurrent corneal erosion. There were 11 eyes who were treated during an acute episode of recurrent erosion. All remaining patients were treated in a symptom-free interval. The affected area of epithelium was removed and a 25 pulse ablation was performed to Bowman's membrane.

RESULTS

In 30 eyes there was a marked improvement in symptoms postoperatively with no recurrences. However, 2 eyes experienced a recurrent episode 6 days and 2 weeks after PTK, respectively. Postoperative refraction and corneal topography was unaltered in all cases.

CONCLUSIONS

Excimer-Laser PTK appears to be a safe and promising procedure for recurrent corneal erosion in cases refractory to medical treatment.

Excimer laser phototherapeutic keratectomy for recurrent erosions: a clinical study

BACKGROUND AND OBJECTIVE

Recurrent corneal erosion is a common corneal disease. It may be difficult to treat, with a number of patients suffering persistent symptoms despite having had conventional therapy. The aim of this study was to evaluate the usefulness of the excimer laser for the treatment of recurrent corneal erosions.

PATIENTS AND METHODS

The authors studied 31 eyes of 24 patients who underwent excimer laser phototherapeutic keratectomy (PTK) for recurrent corneal erosion. Three eyes were treated during an acute episode of recurrent erosion. The remaining eyes were treated during a symptom-free interval. The affected area of epithelium was removed and a 25 pulse ablation was performed to Bowman's membrane.

RESULTS

In 30 eyes there was a marked improvement in symptoms postoperatively, with no recurrences. However, 1 eye had one recurrent episode 2 weeks after PTK. Postoperatively, refraction and corneal topography were unaltered in all cases.

CONCLUSIONS

Excimer laser PTK appears to be a safe and promising procedure for cases of recurrent corneal erosion refractory to medical treatment.

[ProTon--a new portable tonometer. Initial experimental and clinical results]

To determine the accuracy of a new portable tonometer using the Mackay Marg principle (ProTon, Tomey) we measured three cadaver eyes in vitro and 196 eyes of 98 patients in vivo. The 325 manometric determined IOP values were compared to ProTon measurements in three enucleated, canulated human eyes. The correlation was r = 0.99. In a clinical study 196 eyes were measured with both the Goldmann and the ProTon tonometer. The results showed good correspondence with a correlation of r = 0.95. The statistical significance (paired t-test) was P < 0.001.

[Sensitivity to glare before and after Nd:YAG capsulotomy. Comparison between small and large capsulotomy]

AIM OF THE STUDY

The aim of this study was to determine whether capsulotomy size influences visual performance.

PATIENTS AND METHODS

Twenty eyes were included in this study and were divided into two groups: 10 eyes had small central capsulotomies without dilating the pupil, and 10 eyes had large capsulotomies through dilated pupils. We measured both, visual acuity and glare due to forward light scatter using a computer system.

RESULTS

Following treatment both groups had equally significant (< 0.001) improvements in visual acuity. However, a significant (p < 0.001) improvement of glare due to forward light scatter was only observed in the eyes with a large size capsulotomy.

CONCLUSIONS

Our study showed that measurements of forward light scatter are more sensitive than visual acuity testing in demonstrating loss of visual performance in patients with media opacities. It is recommended that pupils are dilated prior to Nd:YAG capsulotomy if forward light scatter from capsule remnants and the subsequent glare disability are to be minimised.

Expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) on proliferating vascular endothelial cells in diabetic epiretinal membranes

The present study demonstrated the expression of intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), the proliferating status of the neovascular endothelial cells, and the activation of vascular endothelial cells bearing the two cell adhesion molecules in diabetic epiretinal membranes by using double immunofluorescence and APAAP techniques. The results showed that ICAM-1 was detected in 36 out of 40 (90%) proliferative diabetic retinopathy epiretinal membranes, VCAM-1 was found in 32 out of 40 cases (80%); in 21 out of 26 (81%) vascularised membranes the endothelial cells of the new vessels in the membranes were still in a proliferative stage (positive for proliferating endothelial cell marker EN 7/44) and, further, in 20 out of 26 cases (77%) ICAM-1 was detected on the proliferating endothelial cells and VCAM-1 was found in 21 cases (81%). The expression of cell adhesion molecules, especially ICAM-1 and VCAM-1 in diabetic epiretinal membranes suggests that cell to cell interactions may play a significant role in the development of PDR membranes. In particular, the expression of ICAM-1 and VCAM-1 on proliferating endothelial cells indicates the activation of these cells, which is the first critical step for lymphocyte/endothelial cell interactions and the initiation of immune responses. The significance of proliferating status of the neovascularisation in the membranes may be related to the clinical course and prognosis of the disease.

Proliferation and activation of vascular endothelial cells in epiretinal membranes from patients with proliferative diabetic retinopathy. An immunohistochemistry and clinical study

In the present study, we investigated the status of proliferation and activation of vascular endothelial cells in epiretinal membranes from patients with proliferative diabetic retinopathy (PDR) by means of immunohistochemical techniques and compared the findings with the main clinical features of the patients. The results showed that of 21 vascularized membranes, 17 (81%) contained proliferating endothelial cells (positive for proliferating vascular endothelial cell marker EN 7/44) and 19 (90%) were positive for endothelial cell activation marker anti-VCAM-1; Furthermore, by using a double-staining technique we found that in 15 of the 17 cases (88%) the proliferating vascular endothelial cells were activated (expressing VCAM-1). Of the 18 type I diabetics, 15 (83%) contained activated proliferating endothelial cells, whereas in the 3 type II patients, only 1 membrane contained activated proliferating endothelial cells, Preoperatively, 18 patients had severe vitreous hemorrhage, among whom 15 (83%) contained proliferating endothelial cells, which were activated in 13 cases, and 16 patients had tractional retinal detachment, among whom 12 contained proliferating endothelial cells, which were activated in 11 cases. In all, 7 patients (33%) had vitreous rebleeding within 8 months postoperatively, whose membranes in 6 cases contained proliferating and activated endothelial cells. In contrast, of the 4 patients who were negative for EN 7/44, none had rebleeding, and of the 6 patients who were negative for EN 7/44 and anti-VCAM-1, only 1 had rebleeding.(ABSTRACT TRUNCATED AT 250 WORDS)

[Trials in ab-interno sclerostomy with a pulsed dye laser using a scleral dye: reactive black 5]

Several reports have described the successful performance of ab interno sclerostomies using a pulsed dye laser (666 nm) a goniolens and methylene blue as a scleral dye. However, the laser energy was found to have a bleaching effect on the methylene blue; therefore, methylene blue was replaced by reactive black-5 (RB-5), which seemed to be a more stable dye. To assess laser parameters using RB-5 we compared the number of pulses needed to perforate excised human sclera at different pulse durations (4-8 microseconds), energy levels (50, 100, 130-150, 200, 300 mJ) and delivery angles (20 degrees, 30 degrees, 45 degrees, 90 degrees). Fewer pulses were needed at a shorter pulse duration and higher energy levels. Above 200 mJ, 8 pulses for perforation could not be reduced; however, the width of the fistula increased. With a decrease in the delivery angle, the number of pulses for perforation increased non-proportionally above the calculated increase of the length of the fistula. At an angle of 20 degrees no perforation could be achieved even if 200 pulses of the maximal energy of 200 mJ were applied. This indicates that eyes with flat anterior chambers cannot be successfully treated.

[Problems with silicon oil removal. A study of 63 consecutive cases]

Silicone oil is used in the treatment of complex retinal detachments, but late complications have been reported by many authors. Silicone oil removal (SOR) is therefore performed in order to reduce these complications. SOR was investigated in 63 consecutive cases. All these eyes had had a totally attached retina for at least 3 months before SOR was performed, there were no signs of traction or reproliferation, and the minimum vision was 4/200. The duration of silicone oil tamponade was less than 6 months in 13 eyes, 6-12 months in 18 and more than 1 year in 32 eyes. In post-traumatic and diabetic cases it was possible to remove silicone oil after 8 to 10 months and in PVR cases after 14 months. Redetachment of the retina was the most frequent complication of SOR, appearing in 18/63 eyes; 16 of them were refilled. In 9 eyes, the visual acuity present before silicone oil removal was reestablished. The redetachment rate was similar in PVR, diabetes and trauma cases and had no correlation with the duration of silicone oil tamponade. Increased intraocular pressure was observed in 13 eyes before SOR but it returned to normal levels afterwards in 8 cases without further surgery. The results of our study show that even if the indication is established very carefully, SOR results in a relatively high rate of complications, such as redetachment of the retina. Therefore every case undergoing this procedure must be evaluated in detail.

[Quantification of indocyanine-green enhancement of diode laser photocoagulation]

The enhancement by indocyanine-green (ICG) of diode laser photocoagulation was quantified. Since ICG concentration in blood increases and decreases rapidly after a single injection, it is difficult to quantify the exact enhancing effect of ICG. A steady-state plasma concentration (about 30 micrograms/ml) of ICG was achieved by injection of 2.5 mg/kg of ICG followed by continuous injection of 0.45 micrograms/kg/min of ICG. The threshold energy values to obtain grayish white retinal burn or choriocapillary occlusion were evaluated at this steady concentration of ICG, and compared with the values in the absence of ICG. The use of ICG decreased the energy values 7% for retinal burn and 8% for choriocapillary occlusion. Although the total dosage of ICG during the continuous injection was high, the enhancement of retinal burn and choriocapillary occlusion was small.

Surgical removal of massive subretinal hemorrhage associated with age-related macular degeneration

The authors report on 11 patients with age-related macular degeneration associated with massive subretinal hemorrhage, who were treated with surgical removal of the hemorrhage and associated fibrosis. Preoperative visual acuity ranged from 20/400 to hand motions. Postoperative visual acuity ranged from 20/200 to light perception with a minimum of 3 months of follow-up. Complications included partial or total retinal detachment in four patients (36%) and cataract in four patients (36%). Four of 11 patients showed some improvement in vision (36%). All four of these patients had surgery within 1 week of the onset of severe visual loss. Although surgical removal of large subretinal hemorrhages is technically feasible, visual recovery is limited, even in uncomplicated cases, by macular degenerative changes.

[Does silicone oil improve the prognosis of severe proliferative diabetic retinopathy?]

We report on a series of 135 consecutive cases of pars plana vitrectomy for proliferative diabetic retinopathy (average period of observation was 13 months). BSS was used in 69 eyes and silicone oil was used in 66 eyes as a vitreous substitute, the indications for silicone oil in these cases were the presence of several retinotomies or retinectomies as well as sharply increased risk for rebleeding. Postoperatively and after a minimum follow up of 6 months (55 eyes) the two groups with BSS or silicone oil achieved comparable functional results despite the different anatomical preoperative situation. Thus 18 out of 23 eyes of the silicone oil group, originally with detached macula and visual acuity of HM or FC, achieved a visual outcome of greater than = 0.02, showing the best postoperative result. In the BSS-group, with attached macula prior to the operation and same visual acuity, this result is attained by 27 out of 35 eyes. We interpret these figures as meaning, that silicone oil in proliferative diabetic retinopathy reduces some of the problems connected with more advanced retinal changes like retinal detachment and rebleeding thereby allowing a visual outcome which corresponds to the macular condition.

Intravitreal silicone oil injection: complications and treatment of 415 consecutive patients

Silicone oil injection in conjunction with pars plana vitrectomy was carried out by five surgeons in 415 consecutive patients using the same surgical equipment, the same surgical techniques and the same highly purified silicone oil (viscosity, 5000 mPa.s). Indications for silicone oil injection after vitrectomy included advanced stages of proliferative vitreoretinopathy following rhegmatogenous retinal detachment (49%), severe proliferative diabetic retinopathy (38%), and proliferative vitreoretinopathy following retinal detachment due to ocular trauma (13%). Postoperative complications were noted in a 6- to 30-month follow-up period. Cataractous changes of varying degree were seen in all phakic eyes. Silicone oil entered the anterior chamber in 6% of all phakic and pseudophakic eyes. Subretinal silicone oil was noted in 4%. Other complications associated with the use of intravitreal silicone oil included biomicroscopically visible silicone oil emulsification (0.7%), keratopathy (5.5%), glaucoma (6%), closure of the inferior iridectomy (6%), and reproliferation of epiretinal and subretinal fibrous membranes (40%). We anticipate that the physico-chemical characteristics of the highly purified silicone oil (viscosity, 5000 mPa.s) and the routine performance of an inferior iridectomy in all aphakic eyes had a positive impact on the low incidence of silicone-oil-related complications such as emulsification, keratopathy and secondary glaucoma.

Nd:YAG laser photodisruption of hemorrhagic detachment of the internal limiting membrane

We used a Q-switched Nd:YAG laser to create an opening in the internal limiting membrane in three eyes with hemorrhagic detachment of the internal limiting membrane. In all instances, after membranotomy blood was rapidly cleared from the preretinal space resulting in prompt improvement in visual acuity. No retinal injury was observed. Nd:YAG laser photodisruption may be useful in the treatment of some cases of subinternal limiting hemorrhages.

Analysis of intraocularly applied silicone oils of various origins

Complications during the intraocular use of silicone oil can be caused by two factors: first, mechanical interaction with the surrounding tissue and, second, the physiochemical properties of the oil itself. The properties of 14 oils of various origins in clinical use were investigated: 12 of the 14 oils contained various amounts of low-molecular-weight components (cyclosiloxanes and molecules with a molecular weight of less than 2,400), which are able to diffuse into the surrounding tissue and may incite toxic or inflammatory reactions. Some of the samples had a ten-fold lower volume resistivity than others, an indicator of the presence of ionic impurities, such as catalyst remnants, which may also be responsible for adverse reactions.

Silicone oil with high specific gravity for intraocular use

Silicone oil with a higher specific gravity than that of intraocular fluid or polydimethylsiloxane may have special indications in vitreoretinal surgery. Trifluorsiloxane is such a substance, and therefore its biological compatibility was investigated in rabbit eyes. It was found that this substance was clinically well tolerated within the observation time of up to 6 months, even if there was some neovascularisation from the inferior limbus. Histologically both an inflammatory response and tissue impregnation were more pronounced than with normal polydimethylsiloxane.

[Clinical relevance of a dosage device for laser photocoagulation]

Fundus reflectometry constitutes a procedure with which dosage can be precisely regulated during the coagulation process. During retinal coagulation, for example, it is possible with this method to administer coagulations of uniform intensity regardless of variations in either the quality of the fundus image or the absorption of the pigmented structures. This can be useful for coagulation procedures which have to be confined for the most part to the pigment epithelium, as for example in the treatment of central serous retinopathy or in panretinal photocoagulation, where the functional therapeutic principle is still not clearly understood. Another area of application for reflectometric laser coagulation will be laser trabeculoplasty, in which barely detectable lesions have to be placed in the trabecular meshwork.

Theoretical investigations of laser thermal retinal injury

A thermal damage model including heat conduction for retinal lesions is described to explain thermal threshold damage and compare it to experimental values in the regime of 1 ms to 300 ms. With the aid of these model calculations unspecific thermal damage (denaturation of proteins) could be separated from thermally induced damage to the photoreceptors. Furthermore, the thermal model allows an extrapolation to hazards to the fundus from intense light irradiation that have not been investigated experimentally.

Chemical studies of intraocular lenses after experimental generation of lesions by a short-pulsed Nd-YAG laser

It is theoretically possible that lesions generated by a Q-switched Nd-YAG laser could lead to chemical changes in polymethylmethacrylate (PMMA) intraocular lenses. These changes could be of clinical relevance. Therefore, we measured the residual monomer content of intraocular lenses before and after generation of lesions by means of a short-pulsed Nd-YAG laser. Despite the explosive destruction of the lens surface caused by this type of laser, there is no measurable release of monomer in the sense of a depolymerization of the PMMA material, even when over 100 lesions are generated. The lesions generated on intraocular PMMA lenses with the Nd-YAG laser are predominantly of a mechanical nature and include the chipping away of small particles from the intraocular lens.

Vitreous morphology after carbon dioxide laser irradiation

The immediate vitreous changes produced by a continuous-wave carbon-dioxide laser beam in freshly enucleated bovine and pig eyes were studied by gross examination with a dissecting microscope, and histopathologically by light microscopy and transmission electron microscopy. The lesions produced by the laser beam on the vitreous in an air tissue interface technique were remarkable for their ring-shaped vitreous condensations. The diameter and density of these condensations increased with irradiance. With the same irradiation parameters the lesions at the anterior hyaloid membranes showed greater size and density than those in the central area of the vitreous. These vitreous condensations were demonstrated to consist of heat-denatured collagen fibrils. For light microscopic evaluation of the vitreous a modified method of tissue processing according to Szent Györgi has proven optimal in reducing vitreous shrinkage from dehydration. This method of fixation and tissue processing appeared to be useful in evaluating lesions of the vitreous and their relationship to their surroundings.

Experimental studies of laser thermal retinal injury

In damage tests conducted on rabbit and monkey eyes, the threshold values for retinal damage resulting from different laser radiation were determined. The reproduction of the "worst-case" situation was ensured by the test apparatus. All physical parameters, such as power/energy, exposure time, and retinal spot, were carefully controlled. Probit analysis showed a very precise determination of the threshold values based on ophthalmoscopical visibility. The attempt of a simple physical interpretation of the thresholds leads to contradictions in major points, so a detailed calculation of damage functions and thermal model calculations are necessary.

[Possibilities for ocular vessel coagulation (author's transl)]

Present-day possibilities of influencing pathological ocular vessels using an argon laser are presented. A distinction is made here between indirect methods such as area coagulation and direct methods with which specific vessels are treated. Whereas clinical tests involving vessel coagulation with pigmented epithelium absorption have already been carried out more or less successfully, selective vessel coagulation with hemoglobin absorption is still largely at the experimental stage. Our own experiments on animals have shown, however, that with the selection of a suitable coagulation technique and the use of suitable exposure parameters, vessel occlusion can be induced with the argon laser. To achieve this, shortening of the exposure times is particularly necessary.

Minimal spot size on the retina formed by the optical system of the eye

A knowledge of the quality of the ocular optical system is of primary importance in light- and laser-photocoagulation of the fundus. A study was therefore undertaken to determine the minimal spot size of a Helium-Neon laser focused on the retina of rabbits: freshly enucleated eyes were carefully mounted in a specially designed eye holder. A small hole was then trepanized through the sclera and neural retina in the macular region. A minimal spot was produced on the retina and the spot size was measured by scanning the intensity distribution of an enlarged image. It was shown that a diffraction limited spot size can be obtained under certain circumstances. The light scattering out of the focus, however, is about fify percent.

Q-switched ruby laser induced damage of the adult rabbit lens capsule

The technique of Q-switched ruby laser induced mechanical destruction of the lens capsule was used to study the reactions of the adult rabbit lens. The defect produced in the anterior lens capsule was larger than the 40-60 micrometer focus, which was due to rolled-up edges of the capsule. Long-term observations revealed some decrease in size of developing localized opacification and a healing of the defect by outgrowing lens epithelium with the formation of a new capsule. The rupture of the posterior capsule led to a slowly progressive opacification with little intraocular macrophage reaction.

[Diathermy procedures, light and laser coagulation, cryocoagulation. Experimental and clinical considerations]

The clinical and experimental results from the methods of coagulation currently in use are presented. The advantages and disadvantages of trans-scleral methods (diathermy and cryopexy) and trans-ocular methods (Xenon arc and argon laser) are discussed. Experiments on absorption, the mode of action of intense light, the optimal time and method of application, the necessary intensity and the extent of the coagulated area are communicated. Of the trans-scleral methods, cryopexy is to be prefered. The trans-ocular methods have the advantage of a more exact localisation and dosage. Either route can often be chosen in any particular case, though at present no overriding advantage has been shown for either.