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Lutz Hesse

Publications and source records attributed to Lutz Hesse.

10 recordsLinked to original sources
PubMed2007

Intraocular fluid-air exchange reduces retinal ganglion cell activity.

AIM: To demonstrate the influence of intraocular fluid-air exchange on retinal ganglion cell activity. METHODS: In two cats lensectomy and vitrectomy were performed in a two-step approach 2 weeks prior to recording experiments. To measure retinal activity, up to two fiber microelectrodes were inserted via a scleral port. Precise micromanipulator positioning of the electrodes' tips onto the inner retinal surface were verified by ophthalmoscopy and simultaneous electrical recording. Neuronal activity of the retina was continuously recorded with or without visual stimulation. We maintained the intraocular pressure constant at 29 mm Hg. Fluid-air exchange and fluid refill were performed with an infusion tube integrated in the manipulator and slowly to avoid direct mechanical/stream-based damage of the retina. RESULTS: We found that fluid-air exchange leads to a rapid reduction of spontaneous as well as visually evoked retinal ganglion cell activity. The activity started to diminish within few minutes, and then it halved approximately every 3 min. Even 1 h after eye fluid refill, the retinal activity recovered only partially. CONCLUSION: Decrease in retinal activity after fluid-air exchange can be explained by mechanical stress-induced drying of the inner retinal surface and by potential changes of extracellular ion concentration. Since even moderate airstream-based fluid-air exchanges can lead to retinal damage, the surgeon should minimize the quantity of air passing open sclerotomy sites until a better understanding of the retinal effects of this essential technique in modern vitrectomy is available.

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PubMed2006

Visual resolution with retinal implants estimated from recordings in cat visual cortex.

We investigated cortical responses to electrical stimulation of the retina using epi- and sub-retinal electrodes of 20-100 microm diameter. Temporal and spatial resolutions were assessed by recordings from the visual cortex with arrays of microelectrodes and optical imaging. The estimated resolutions were approximately 40 ms and approximately 1 degrees of visual angle. This temporal resolution of 25 frames per second and spatial resolution of about 0.8 cm at about 1m and correspondingly 8 cm at 10 m distance seems sufficient for useful object recognition and visuo-motor behavior in many in- and out-door situations of daily life.

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PubMed2004

Subretinal implantation and testing of polyimide film electrodes in cats.

BACKGROUND: Progress in the field of microelectronics has led to the development of visual prostheses for the treatment of blinding diseases. One concept under investigation is an electronic subretinal prosthesis to replace the function of lost photoreceptors in degenerative diseases, such as retinitis pigmentosa. METHODS: In the subretinal prosthesis design concept, an array of stimulation electrodes is placed in the subretinal space. To test the feasibility of the concept and to determine basic stimulation parameters, wire-bound stimulation devices were used in acute trials for up to 12 h in three eyes in anaesthetised cats. These wire-bound stimulation elements were based on strips of polyimide film. The film strips were introduced through a sclerostomy into the vitreous cavity and via a retinotomy into the subretinal space during a modification of the standard three-port vitrectomy procedure. On entry through the retinotomy, the film was advanced mechanically to the desired position in the area centralis. Perfluorocarbon liquid (PFCL) was used to establish close contact between the electrode array and the outer retina. Stimulation was performed with computer-generated sequences of current waveforms in acute trials immediately after surgical implantation of the stimulation film. Cortical recordings in the primary visual cortex were performed with electrodes placed in locations corresponding to the retinal stimulus site. RESULTS: All three implantations were carried out successfully with the stimulation array implanted beneath the outer retina of the area centralis of the operated eye. The retina was attached over the stimulation array in all cases. No cortical responses were recorded in one of the stimulation sessions. The results from another session revealed clear intracortical responses to subretinal stimulation with polyimide films. Following single-site retina stimulation, the estimates of spatial cortical resolution and temporal resolution were approximately 1 mm and 20-50 ms, respectively. DISCUSSION: Our results indicate that focal subretinal stimulation evokes localised spatio-temporal distribution of cortical responses. These findings offer hope that coarse restoration of vision may be feasible by subretinal electrical stimulation.

Animals↗
PubMed2004

Double-blind, placebo-controlled trial of octreotide long-acting repeatable (LAR) in thyroid-associated ophthalmopathy.

Several uncontrolled studies suggest octreotide is beneficial in thyroid-associated ophthalmopathy (TAO); however, the natural tendency of TAO to improve mandates randomized, controlled trials. We report results of a double-blind, placebo-controlled trial of octreotide long-acting repeatable (LAR). Fifty euthyroid patients (11 males, 39 females; age 22-74 yr, median 50 yr) with active TAO [clinical activity score (CAS) > or =3, NOSPECS (no signs or symptoms; only signs, no symptoms; signs only; proptosis; eye muscle involvement; corneal involvement; sight visual acuity reduction) 2a-5a] of median duration 0.9 yr received either 30 mg LAR or placebo every 4 wk for 16 wk; both groups then received 30 mg LAR for wk 16-32 and were followed up without treatment for a further 24 wk. Objective assessments included all individual parameters of TAO, CAS, and derived scores for soft tissue inflammation (STI) and ophthalmopathy index (OI). During wk 0-16 there was significant reduction in STI, subjective diplopia, and CAS in LAR-treated patients; STI and CAS were also reduced with placebo. The OI reduced by -1.12 in LAR (P = 0.0017) vs. -0.23 in placebo (P = 0.33), giving a barely significant treatment effect by Wilcoxon (P = 0.043), but analysis of covariance failed to confirm this (P = 0.16). During wk 16-32 there was no significant change in OI in either group. The overall results (wk 0-32) showed reduction in STI and CAS in both groups. In this double-blind, placebo-controlled trial, no significant therapeutic effect of octreotide LAR was seen in patients with moderately severe TAO. The improvements in both treated and placebo groups emphasize that the results of open studies must be viewed with caution.

Adult↗
PubMed2003

Towards the cortical representation of form and motion stimuli generated by a retina implant.

BACKGROUND: A retina implant for restoring basic visual perception in patients who are blind due to photoreceptor loss should not only evoke focal phosphenes at high resolution, but should also generate cortical representations of form and motion. We are currently exploring these potential capabilities in anaesthetised cats. METHODS: Fibre electrodes were inserted through a small scleral incision onto the retinal surface for stimulation. For the recording of cortical population activities we placed up to 16 fibre electrodes in areas 17 and/or 18. Retinal and cortical electrodes were adjusted to corresponding sites, i.e., overlapping receptive fields. Electrical stimuli were charge-balanced impulses (200 micros, 10-100 microA). Basic form stimuli were generated by the selective and synchronous activation of some of the seven retinal stimulation electrodes. Movement stimuli were generated by spatio-temporal shifting of form stimuli. From multiple microelectrode recordings we computed stimulus-related spatio-temporal cortical activation profiles. We used these profiles to estimate the relations between stimulation distance and spatial resolution (form) and between stimulus velocity and spatio-temporal resolution (movement). Influences by the retino-cortical pathway were assessed by comparing cortical activations evoked by true form or motion stimuli with synthetic responses composed by superpositioning of responses to appropriate subsets of form and motion stimuli. In addition, we compared cortical responses to form and motion stimuli by a receptive-field-based backprojection of cortical activities. RESULTS: We confirmed our previous finding that electrical retina stimulation may yield a spatial resolution of 1-5 degrees visual angle and a temporal resolution of about 20 ms. We found that the spatio-temporal cortical activation profiles are commonly related to retinal form and motion stimuli. Cortical activity analyses showed that for two-point form stimuli the neuronal interaction depends on the stimulation electrodes' distance and that local cortical group activities can exhibit some tuning to the directions or the velocities of moving electrical bars'. Projections of cortical activations to visual space were consistent with electrical form and motion stimulation of the retina. CONCLUSIONS: Our data indicate that retinal stimulation with electrical form and motion stimuli can lead to spatio-temporally related cortical activations. However, the selective activation of single cortical neurones with specific visual tuning properties by electrical retina stimulation and the potential adaptation of the visual system to long-term stimulation with retina implants should be addressed in future work.

Animals↗
PubMed2002

Activation zones in cat visual cortex evoked by electrical retina stimulation.

BACKGROUND: A retina implant for restoring simple basic visual perception in patients who are blind due to photoreceptor loss requires optimisation of stimulation parameters for obtaining high spatio-temporal resolution. We developed effective low-power epi-retinal stimulation and intracortical recording in semichronically prepared cats. METHODS: Individually driveable fibre electrodes were inserted through a small scleral incision and positioned at the area centralis. Polyimide-platinum film electrodes were inserted via a corneal incision and fixed by instillation of perfluorocarbon liquid on the internal limiting membrane. For electrical stimulation we used short charge-balanced current impulses of 100-400 micro s duration and amplitudes ranging from 1 to 100 micro A. During stimulation we recorded multiple single-cell and population activities from areas 17 and 18. Recordings were stored digitally. Stimulus-response relations including response strength, cortical activation zones, information transmission, and electrical receptive fields were analysed off-line. RESULTS: We found low-threshold activations with fibre electrodes and polyimide-platinum film electrodes in close mechanical contact to the retina. Retinal stimulation with bipolar charge-balanced impulses resulted in cortical activation zones corresponding to 1-5 degrees visual angle at paracentral locations dependent on the eccentricity of the retinal stimulation point. Retino-cortical transinformation analysis revealed 20-30 bits/s per electrode, corresponding to 10-15 four-level pictures/s. Electrical receptive fields had sizes of 1-3 degrees visual angle. CONCLUSIONS: Coarse visuomotor coordination and navigation seems possible with retina implants.

Animals↗
PubMed2002

Tissue plasminogen activator plus gas injection in patients with subretinal hemorrhage caused by age-related macular degeneration: predictive variables for visual outcome.

PURPOSE: To assess factors predicting final visual outcome after displacement of subretinal hemorrhage (SRH) by intravitreally injected tissue plasminogen activator (TPA) and gas in patients suffering from age-related macular degeneration (ARMD). METHODS: We evaluated retrospectively the records of 67 patients (32 men, 35 women, mean age 77.2 years) suffering from SRH caused by ARMD who underwent TPA and gas injection between April 1996 and October 2000. Visual acuity (VA; preoperative, 1 week and 3 months postoperative) was analyzed with respect to duration and dimension of bleeding (diameter and thickness) and patient's age. RESULTS: Mean preoperative VA was 0.063, compared with 0.1 at 3 months after injection. Twenty-nine of 47 patients (76%) had an increase in VA 1 week after treatment but 14 of these eyes worsened slightly during follow-up. Visual outcome 3 months after therapy was negatively correlated to thickness ( P<0.05) and diameter ( P<0.001) of the SRH. In a statistical model of a multiple regression analysis, postoperative VA and the shift of VA could be predicted by preoperative VA and diameter of SRH. Patient's age, duration and thickness of SRH had no prognostic value for postoperative visual outcome. CONCLUSION: After SRH caused by ARMD, the best visual outcome after TPA + gas injection can be expected in patients with preoperative VA of less than 0.1 caused by a small SRH. In the presence of large SRH (diameter >5 mm) an increase in VA after therapy is unlikely.

Aged↗
PubMedDate not supplied

Retino-cortical information transmission achievable with a retina implant.

Blind subjects with photoreceptor degeneration perceive phosphenes when their intact retinal ganglion cells are stimulated electrically. Is this approach suitable for transmitting enough information to the visual cortex for partially restoring vision? We stimulated the retina of anesthetized cats electrically and visually while recording the responses in the visual cortex. Transmission of retino-cortical information T was quantified by information theory. T was 20-160 bit/s (per stimulation and recording site) with random electrical or visual impulse stimulation at rates between 20 and 40 s-1. While increasing spatial density of independent electrical stimulation channels T did not saturate with 7 electrodes/mm2 retina. With seven electrodes up to 500 bit/s was transmitted to 15 cortical recording sites. Electrical stimulation basically employs temporal stimulus patterns. They are intimately linked with intensity/contrast information coded by the spike density of retinal ganglion cells. From the cortical information spread we estimated the spatial resolution as 0.5mm cortex corresponding to 0.5-1.0 degrees visual angle. If the human cortex can receive and decode the information transmitted by a retina implant, our quantitative results measured in cats suggest that visuo-motor coordination and object recognition in many in- and out-door situations will be possible.

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PubMedDate not supplied

[The predictive value of a classification for proliferative diabetic vitreoretinopathy].

BACKGROUND: Kroll's classification of proliferative diabetic vitreoretinopathy (PDVR) defines stage A (vitreoretinal proliferations without retinal detachment), stage B (partially detached retina not involving the macula), stage C (partially detached macula) and stage D (completely detached macula). The purpose of this study was to analyse the prognostic value of Kroll's classification in respect of the postoperative results of vitreoretinal surgery based on our group of patients. PATIENTS AND METHODS: The charts of 563 patients who underwent vitrectomy because of PDVR between 1990 and 1997 were examined retrospectively. Postoperative visual acuity, possible risk factors, frequencies of silicone oil tamponade and revitrectomies were related to the preoperative staging of PDVR. The influence of possible predictive factors on the postoperative visual outcome were evaluated using multivariate logistic regression analysis. RESULTS: After vitreoretinal surgery mean postoperative visual acuity was significantly better in stage A compared to stage C (p < 0.01) or D (p < 0.0001). In 179 out of 563 eyes (31.7 %) revitrectomy (including silicone oil removal) was required and in 51 eyes (9.1 %) more than one revitrectomy was performed. Silicone oil tamponade was used in 22 out of 253 eyes (8.7 %) classified as stage A, in 27 out of 201 eyes (13.4 %) of stage B, in 17 out of 78 eyes (21.8 %) of stage C and in 10 of 31 eyes (32.3 %) of stage D. Postoperative increase of visual acuity of more than 3 lines was significantly less frequent in stage B (p < 0.014), C (p < 0.039) and D (p < 0.001) compared to stage A. CONCLUSION: Kroll's classification for PDVR has a high prognostic value for the postoperative visual outcome and level of surgical risk management. Thus patients with good prognosis can be identified easily, facilitating the decision for surgery.

Adult↗