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Mark S Humayun

Publications and source records attributed to Mark S Humayun.

At least 37 records · Page 2Linked to original sources
PubMed2004

Effects of indocyanine green injection on the retinal surface and into the subretinal space in rabbits.

PURPOSE: To evaluate the effects of indocyanine green (ICG) injection on the retinal surface and into the subretinal space of rabbit eyes. METHODS: Twenty-two Dutch-belted rabbits underwent two-port vitrectomy followed by injection of ICG (5 mg/mL) on the retinal surface and into the subretinal space. Balanced salt solution (BSS) was also injected subretinally. The locations where ICG was delivered (both epiretinal and subretinal) were exposed to light from an endoilluminator for 7 minutes. The animals were examined at 1, 7, and 14 days after surgery. The eyes were studied by fluorescein angiography as well as light and electron microscopy. RESULTS: No damage was observed after epiretinal ICG injection, but subretinal ICG injection resulted in damage to the outer nuclear layer, photoreceptor inner and outer segments, and retinal pigment epithelium. This damage was more severe with longer follow-up. Control experiments without ICG, in which balanced salt solution was injected into the subretinal space or light was delivered on the epiretinal surface, demonstrated only damage to the photoreceptor outer segments. CONCLUSION: Subretinal delivery of ICG (5 mg/mL) in rabbits induces retinal pigment epithelium, photoreceptor inner and outer segment, and outer nuclear layer damage. These mechanisms of damage may explain the retinal pigment epithelium changes that are sometimes seen after ICG-assisted internal limiting membrane peeling in humans.

Animals↗
PubMed2004

Virtual vitreoretinal surgical simulator as a training tool.

OBJECTIVE: To demonstrate the feasibility and potential applicability of a virtual reality simulator for vitreoretinal surgery as a training and/or assessment tool. METHODS: The subjects of this study included medical students, ophthalmologic residents, and trained vitreoretinal surgeons. There were three study groups. Group I comprised 22 subjects who performed a navigation task. The time to complete the task was recorded. The relationship between the completion time, experience, and stereopsis was evaluated. Group II included 6 subjects who consecutively performed the navigation task to evaluate their learning curve. Group III included 16 subjects who performed the membrane peeling task. The number of retinal contacts and the completion time were recorded. The relationship between experience and stereopsis with the number of contacts and the completion time were evaluated. RESULTS: The average completion time in Group I for students, residents, and trained surgeons was 121.6, 92.5, and 70.6 seconds. There was a significant difference between students and trained surgeons (P = 0.004). In Group II, there was a significant decrease in the completion time with training (P = 0.001). In Group III, the average completion time for students, residents, and trained surgeons was 197, 144, and 118.2 seconds; the respective number of retinal contacts was 14, 8, and 3. There was a significant difference between students and residents (P = 0.05) and between residents and trained surgeons (P = 0.003) for the average completion time in Group III. There was a significant difference between students and trained surgeons (P = 0.003) for the number of contacts per average time and between students and residents (P = 0.05). There was a significant inverse correlation between stereopsis vision score and completion time in Group I and number of contacts per average time (P = 0.0004 and P = 0.01, respectively). CONCLUSIONS: This study demonstrates potential applications of a vitreoretinal surgical simulator as a training and skills assessment tool for novice, inexperienced, and trained surgeons. A simulator can be used to teach specific techniques and train surgeons.

Adult↗
PubMed2003

Visual and electrical evoked response recorded from subdural electrodes implanted above the visual cortex in normal dogs under two methods of anesthesia.

Sensitive methods are required to record electrical evoked potentials over the visual cortex to evaluate the efficacy and safety of a retinal prosthesis before it can be implanted on the retinal surface of patients afflicted by outer retinal diseases. This study was designed to examine subdural electrodes as a mean to evaluate cortical evoked potentials in response to light and electrical stimulation of the retina in three dogs under two methods of anesthesia-halothane and propofol. Results showed that subdural electrodes could be stabilized over the visual cortex for several (3-5) months, and that they were 6.95 times more sensitive than subdermal electrodes in recording cortical visual evoked potentials (VEPs) and 4.31 times more sensitive in recording cortical electrical evoked potentials under both methods of anesthesia. The waveforms' shape changed for each electrode in the subdural array during 6/6 (100%) and 20/38 (52%) multi-channel recording sessions under halothane and propofol, respectively. This change could point to a cortical retinotopic organization versus hierarchical organization of different cortical areas for a given retinal stimulus. In summary, subdural electrodes show promising results for recording visual and electrical evoked responses (EERs) and thus for evaluation of the retinal prosthesis.

Anesthesia↗
PubMed2003

Limited macular translocation for the management of subfoveal choroidal neovascularization after photodynamic therapy.

PURPOSE: To report our initial experience of limited macular translocation in patients with subfoveal choroidal neovascularization secondary to age-related macular degeneration following photodynamic therapy with verteporfin. DESIGN: Interventional case series. METHODS: Retrospective review of four eyes of four consecutive patients with subfoveal choroidal neovascularization secondary to age-related macular degeneration who underwent effective limited macular translocation following photodynamic therapy. The mean logarithm of minimal angle of resolution preoperative best-corrected visual acuity was 20/190 (range, 20/150 to 20/200), and in all eyes the visual acuity was 20/150 or worse. The major outcome measures were postoperative visual acuity and complications related to the surgery. RESULTS: The mean postoperative follow-up was 6.75 months (range, 6-8 months). Postoperative best-corrected visual acuity improved by 2 or more Snellen lines of visual acuity in three of four eyes (75%) and remained within 1 line in one of four eyes (25%). The mean postoperative best-corrected visual acuity was 20/100 (range, 20/40 to 20/150), and in two of the four eyes (50%) the visual acuity achieved was 20/100 or better. No complication was observed. CONCLUSIONS: Limited macular translocation may be a viable option in patients who have previously undergone photodynamic therapy.

Aged↗
PubMed2003

Characteristics of visual loss by scanning laser ophthalmoscope microperimetry in eyes with subfoveal choroidal neovascularization secondary to age-related macular degeneration.

PURPOSE: To evaluate the effects of subfoveal choroidal neovascularization secondary to age-related macular degeneration on functional parameters obtained by scanning laser ophthalmoscope microperimetry. DESIGN: Retrospective observational case series and cross-sectional study. METHODS: At the Doheny Retina Institute and Wilmer Eye Institute a consecutive series of 179 eyes of 175 patients with subfoveal choroidal neovascularization secondary to age-related macular degeneration was studied. The onset of visual symptoms, best-corrected visual acuity, fluorescein angiography, evaluation of fundus microperimetry and fixation pattern using the Rodenstock scanning laser ophthalmoscope were obtained for each patient. The main outcome measures were central retinal sensitivity and fixation pattern (fixation location and fixation stability) in eyes with subfoveal choroidal neovascularization and their relationship to the length of disease, type and characteristics of choroidal neovascularization, and visual acuity. RESULTS: Of 179 eyes, 135 (75%) had central fixation, 27 (15%) had poor central fixation, and 17 (9%) had predominantly eccentric fixation. Seventy-six eyes (42%) had stable fixation, 70 eyes (39%) had relatively unstable fixation, and 33 eyes (18%) had unstable fixation. In 50 eyes (28%) a dense central scotoma was noted. Eighty-nine of 100 eyes (89%) with length of symptoms of less than 3 months had predominantly central fixation and 58 (58%) had stable fixation; 14 of 34 eyes (41%) with length of symptoms of more than 6 months had predominantly central fixation, and 5 eyes (15%) had stable fixation. In 15 eyes of patients who elected not to receive treatment, successive scanning laser ophthalmoscope microperimetry were obtained over time (follow-up of 18 months after onset of symptoms). Three months or less after the onset of symptoms, 13 eyes (87.7%) had predominantly central fixation and 9 eyes (60%) had stable fixation. More than 3 months and 6 months or less after the onset of symptoms, 10 eyes (66.7%) had predominantly central fixation and 7 eyes (46.7%) had stable fixation. This trend was further demonstrated in eyes more than 6 months after the onset of symptoms. CONCLUSIONS: We conclude that the sequence of events leading to visual function deterioration appears to involve an initial mild decrease in central retinal sensitivity and visual acuity followed by progressive fixation instability and, ultimately, development of an absolute central scotoma with totally eccentric fixation. Increased length of disease is associated with worse fixation pattern and retinal sensitivity deterioration as assessed by scanning laser ophthalmoscope microperimetry. A better understanding of the characteristics of visual loss assessed by fixation pattern evaluation and microperimetry in age-related macular degeneration may help optimize timing, patient selection, and treatment options in eyes with this condition.

Aged↗
PubMed2003

Visual perception in a blind subject with a chronic microelectronic retinal prosthesis.

A retinal prosthesis was permanently implanted in the eye of a completely blind test subject. This report details the results from the first 10 weeks of testing with the implant subject. The implanted device included an extraocular case to hold electronics, an intraocular electrode array (platinum disks, 4 x 4 arrangement) designed to interface with the retina, and a cable to connect the electronics case to the electrode array. The subject was able to see perceptions of light (spots) on all 16 electrodes of the array. In addition, the subject was able to use a camera to detect the presence or absence of ambient light, to detect motion, and to recognize simple shapes.

Aged↗
PubMed2003

Visually guided performance of simple tasks using simulated prosthetic vision.

Loss of photoreceptor cells is one of the major causes of blindness. Several groups are exploring the functional replacement of photoreceptors by a retinal prosthesis. The goal of this study was to simulate the vision levels that recipients of retinal prostheses with 4 x 4, 6 x 10, and 16 x 16 electrode arrays may experience, and to test the functionality of this vision. A PC video camera captured images that were converted in real time into dots ("pixels"). The PC monitor and a head-mounted display worn by test subjects displayed the pixelized images. To assess performance of normally sighted individuals with each array, we designed a set of tasks including: four-choice orientation discrimination of a Sloan letter E, object recognition and discrimination, a cutting task, a pouring task, symbol recognition, and two reading tasks. In the letter E task, subjects were found to have visual acuities of 20/1,810, 20/1,330, and 20/420 with the 4 x 4, 6 x 10, and 16 x 16 arrays, respectively. Most subjects were able to read fonts as small as 36 point with the 16 x 16 array, corresponding with a visual acuity of 20/600 in our system. The test subjects partially overcame the visual limitation of the system by scanning the video camera over the letters allowing spatial and temporal integration of visual information. In all categories, subjects performed best with the 16 x 16 array and least well with the 4 x 4 array. Even with the lowest resolution array, however, some subjects could recognize simple objects and symbols.

Adult↗
PubMed2003

Angiographic characteristics in patients undergoing macular translocation for subfoveal choroidal neovascularization secondary to age-related macular degeneration.

PURPOSE: To review in a standardized fashion pre- and postoperative fluorescein angiographic characteristics in patients undergoing limited macular translocation (LMT) with scleral imbrication to treat subfoveal choroidal neovascularization (SFCNV) secondary to age-related macular degeneration (AMD). The current study was undertaken to assess any potential effects of the translocation procedure on altering the angiographic characteristics of SFCNV before laser photocoagulation. METHODS: A consecutive series of patients undergoing LMT for AMD was identified retrospectively. The pre- and postoperative fluorescein angiograms were reviewed in a masked fashion. Angiographic characteristics evaluated included pre- and postoperative lesion components, stability of lesion, and the amount of retinal translocation obtained. RESULTS: Eighty-eight patients (90 eyes) had angiograms of adequate quality to permit evaluation. Time between the preoperative and the prelaser angiogram ranged from 2 to 84 days (median 7.5 days). Neovascular complexes remained unchanged or decreased in size in 79% of patients. There was no statistically significant difference in lesion size between the pre- and postoperative periods (P = 0.34). Retinal movement ranged from 160 microm to 3,320 microm (median 960 microm), with 61% of cases undergoing effective translocation (i.e., the fovea was moved away from the neovascular complex). None of the lesion components or demographic factors evaluated affected the amount of translocation obtained. Larger lesions were more likely to remain subfoveal following translocation (P = 0.004). CONCLUSION: The size and lesion characteristics appear relatively stable following translocation. Amount of retinal movement is not associated with angiographic lesion characteristics. Only size was associated with achievement of desired translocation in the final model, with large lesions being less likely to achieve desired translocation. In our study group, the amount of retinal translocation was variable with 61% of cases undergoing effective translocation.

Adult↗
PubMed2003

Advances in the development of visual prostheses.

Visual prostheses are based on neuronal electrical stimulation at different locations along the visual pathway (ie, cortical, optic nerve, epiretinal, subretinal). In terms of retinal prostheses, advances in microtechnology have allowed for the development of sophisticated, high-density integrated circuit devices that may be implanted either in the subretinal or epiretinal space. Analogous to the cochlear implants for some forms of deafness, these devices could restore useful vision by converting visual information into patterns of electrical stimulation that would excite the remaining spared inner retinal neurons in patients with diseases such as retinitis pigmentosa and age-related macular degeneration. The different types of implants and recent results are discussed, but special emphasis is given to retinal implants.

Electric Stimulation↗
PubMed2003

Facial recognition using simulated prosthetic pixelized vision.

PURPOSE: To evaluate a model of simulated pixelized prosthetic vision using noncontiguous circular phosphenes, to test the effects of phosphene and grid parameters on facial recognition. METHODS: A video headset was used to view a reference set of four faces, followed by a partially averted image of one of those faces viewed through a square pixelizing grid that contained 10x10 to 32x32 dots separated by gaps. The grid size, dot size, gap width, dot dropout rate, and gray-scale resolution were varied separately about a standard test condition, for a total of 16 conditions. All tests were first performed at 99% contrast and then repeated at 12.5% contrast. RESULTS: Discrimination speed and performance were influenced by all stimulus parameters. The subjects achieved highly significant facial recognition accuracy for all high-contrast tests except for grids with 70% random dot dropout and two gray levels. In low-contrast tests, significant facial recognition accuracy was achieved for all but the most adverse grid parameters: total grid area less than 17% of the target image, 70% dropout, four or fewer gray levels, and a gap of 40.5 arcmin. For difficult test conditions, a pronounced learning effect was noticed during high-contrast trials, and a more subtle practice effect on timing was evident during subsequent low-contrast trials. CONCLUSIONS: These findings suggest that reliable face recognition with crude pixelized grids can be learned and may be possible, even with a crude visual prosthesis.

Adult↗
PubMed2003

The value of preoperative tests in the selection of blind patients for a permanent microelectronic implant.

PURPOSE: To determine the best candidates (ie, those requiring lowest current levels delivered to the retina to elicit visual perceptions) for long-term implantation of a microelectronic retinal implant through a series of preoperative visual, psychophysical, and electrophysiological tests. METHODS: This study protocol was granted an investigational device exemption by the Food and Drug Administration and was approved by the institutional review board at the University of Southern California. After informed consent was obtained, all subjects underwent the following preoperative tests: dark-adapted bright flash and 30-Hz flicker electroretinograms, electrical evoked responses (EERs) using a Burian-Allen corneal electrode to stimulate the globe, and psychophysical tests to evaluate the light and electrically elicited visual perceptions. Intraocular stimulation (IOS) of the retina was performed by an array of electrodes positioned on the internal limiting lamina. RESULTS: Lower vision correlated with less sensitive psychophysical responses (P<.0001). Lower vision and less sensitive psychophysical tests correlated with higher EER values for stimulus pulse widths of 2 ms (P<.0008) and 4 ms (P<.0002). Lower IOS currents correlated with more sensitive psychophysical responses (P<.02) and lower EER values at 4 ms (P<.04). CONCLUSIONS: Preoperative testing, especially psychophysical and electrophysiological tests to assess light and electrically driven visual responses, can help in evaluating patients for suitability for receiving a permanent microelectronic retinal implant. Further study is warranted.

Blindness↗
PubMed2002

Inferior limited macular translocation for subfoveal choroidal neovascularization secondary to age-related macular degeneration: 1-year visual outcome and recurrence report.

PURPOSE: To report the 1-year visual outcomes and incidence of persistent and recurrent choroidal neovascularization (CNV) after limited macular translocation (LMT) for subfoveal CNV in patients with age-related macular degeneration (ARMD). DESIGN: Interventional case series. METHODS: Retrospective review of 102 consecutive eyes of 101 patients that had the inferior limited macular translocation procedure for subfoveal choroidal neovascularization secondary to ARMD. The outcome measures were visual acuity at 12 months after surgery, change in visual acuity from baseline, the proportion of eyes with moderate (3 or more lines) or severe (6 or more lines) visual acuity loss, and cumulative incidence of persistent or recurrent CNV and its impact on visual acuity. Cumulative incidence was estimated using Kaplan-Meier survival analysis methods. Association between persistence and recurrence of CNV and the Snellen visual acuity recorded at each follow-up visit was evaluated using the Wilcoxon rank-sum test. RESULTS: Eighty-six (84.3%) of 102 eyes completed the 1-year follow-up. By 12 months postoperatively, 35 (40.7%) of the 86 eyes achieved visual acuity of 20/100 or better while 34 (39.5%) of the 86 eyes experienced 2 or more Snellen lines of visual improvement. In the 52 eyes with effective translocation and complete laser photocoagulation of the CNV complex with sparing of the sensory fovea, the estimated incidence of recurrence was 34.6% at 12 months (95% confidence interval of 21%-48%). Sixty-five percent of the recurrences were subfoveal and caused a decrease in visual acuity. There was a trend toward worse median change in visual acuity in eyes with persistent or recurrent CNV. CONCLUSIONS: Limited macular translocation for the treatment of subfoveal CNV secondary to ARMD is associated with improvement in visual acuity in approximately 39.5% of eyes and enables complete laser photocoagulation of the neovascular complex with sparing of the sensory macula in approximately 60.4% of eyes that complete 1 year follow-up. Persistence and recurrence of CNV are common after LMT and are important causes of vision loss. Further studies are warranted to more precisely evaluate the risks and benefits of LMT in ARMD.

Choroidal Neovascularization↗
PubMed2002

Initial experience using the transconjunctival sutureless vitrectomy system for vitreoretinal surgery.

OBJECTIVE: To describe the initial experience and to evaluate the safety and feasibility of using the 25-gauge Transconjunctival Sutureless Vitrectomy System (TSV) for a variety of vitreoretinal procedures. DESIGN: Retrospective review of a consecutive interventional case series. PARTICIPANTS: Thirty-five eyes of 33 patients, including cases of idiopathic epiretinal membrane (12 cases), retinal detachment (6 cases), macular hole (5 cases), branch retinal vein occlusion (4 cases), retinopathy of prematurity (4 cases), persistent diabetic macular edema (1 case), diabetic vitreous hemorrhage (1 case), retained lens material after cataract extraction (1 case), and Norrie disease (1 case). INTERVENTION: All patients underwent surgery using the 25-gauge TSV. MAIN OUTCOME MEASURES: Intraocular pressure, visual acuity, and postoperative complications. RESULTS: The median preoperative intraocular pressure was 16 mmHg (range, 10-21 mmHg), whereas the median intraocular pressure on the first postoperative day was 12 mmHg (range, 6-28 mmHg). The median intraocular pressure at 1 week and 1 month were both 16 mmHg (range, 10-30 mmHg). Overall, the median preoperative visual acuity was 20/100 (range, 20/30 to hand motions), and the median postoperative visual acuity after a mean follow-up of 14 weeks (range, 1-60 weeks) was 20/60 (range, 20/20-20/150). One eye developed a postoperative retinal detachment. CONCLUSIONS: The 25-gauge TSV seems to be practical and safe for a variety of vitreoretinal procedures. The concept of transconjunctival surgery has the potential to increase the efficiency of a variety of vitreoretinal surgeries and possibly hasten the postoperative recovery and outcomes in several conditions by simplifying the surgical procedure; minimizing surgically induced trauma; and decreasing the convalescence period, the operating time, and the postoperative inflammatory response.

Adult↗
PubMed2002

Patient selection for macular translocation surgery using the scanning laser ophthalmoscope.

OBJECTIVES: To evaluate the use of the scanning laser ophthalmoscope (SLO) as a predictor for potential visual improvement in eyes with subfoveal choroidal neovascularization (CNV) secondary to age-related macular degeneration (AMD) undergoing limited macular translocation. DESIGN: Retrospective noncomparative case series. PARTICIPANTS: Consecutive series of 71 eyes of 70 patients with subfoveal CNV secondary to AMD that underwent effective and uncomplicated limited macular translocation at the Wilmer Ophthalmological Institute. METHODS: Evaluation of the fundus microperimetry and fixation pattern was conducted on all patients using the Rodenstock scanning laser ophthalmoscope (G. Rodenstock Instrument GmbH, Munich, Germany) within 72 hours before surgery. MAIN OUTCOME MEASURES: Sensitivity and specificity in addition to positive and negative predictive values of SLO findings for visual outcome after macular translocation. RESULTS: Stable fixation presented the highest positive predictive value for visual acuity equal to or better than 20/100 (30 of 33 = 0.91), and predominantly eccentric fixation had the highest negative predictive value for visual acuity worse than 20/100 (7 of 9 = 0.78). Sensitivity was higher for the presence of predominantly central fixation (42 of 48 = 0.87), and specificity was higher for relatively unstable/unstable fixation (20 of 23 = 0.87). CONCLUSIONS: Eyes with stable and central fixation (without dense central scotoma) good preoperative visual acuity, and short length of symptoms are those with the greatest chance to achieve good vision after macular translocation. The knowledge of the fixation and microperimetry pattern enables better understanding of the macular function in eyes with AMD and may be useful for evaluation of baseline retinal cell viability. Incorporation of these testing modalities may help to optimize patient selection for macular translocation or other future techniques aimed at rescuing photoreceptors.

Aged↗
PubMed2002

A new 25-gauge instrument system for transconjunctival sutureless vitrectomy surgery.

OBJECTIVES: To introduce and evaluate the infusion and aspiration rates and operative times of the 25-gauge transconjunctival sutureless vitrectomy system (TSV) DESIGN: In vitro experimental and comparative interventional study. PARTICIPANTS AND CONTROLS: Twenty eyes of 20 patients underwent a variety of vitreoretinal procedures using the 25-gauge TSV, including idiopathic epiretinal membrane (n = 10), macular hole (n = 4), rhegmatogenous retinal detachment (n = 3), branch retinal vein occlusion (n = 2), diabetic vitreous hemorrhage (n = 1), and 20 cases similar in diagnosis and severity were matched to provide comparison between duration of individual portions of the surgical procedures with the existing 20-gauge vitrectomy system. METHODS: Description of the 25-gauge TSV is provided; infusion and aspiration rates of the 25-gauge and standard 20-gauge vitrectomy system were measured in vitro using balanced saline solution and porcine vitreous for several levels of aspirating power and bottle height, and operating times of individual portions of surgical procedures were measured for the 25-gauge and 20-gauge vitrectomy system. MAIN OUTCOME MEASURES: Infusion, aspiration rates, and operative times of the 20-gauge and 25-gauge vitrectomy system. RESULTS: Infusion and aspiration rates of the 25-gauge TSV system were reduced by an average of 6.9 and 6.6 times, respectively, compared with the 20-gauge system when balanced saline solution was used. The average flow rate of the Storz 25-gauge cutter (at 500 mmHg, 1500 cuts per minute [cpm]) was 40% greater than that of the 20-gauge pneumatic cutter (at 250 mmHg, 750 cpm) but about 2.3 times less than the 20-gauge high-speed cutter (at 250 mmHg, 1500 cpm). Mean total operative time was significantly greater for the 20-gauge high-speed cutter (26 minutes, 7 seconds) than for the 25-gauge vitrectomy system (17 minutes, 17 seconds) (P = 0.011). CONCLUSIONS: Although the infusion and aspiration rates of the 25-gauge instruments are lower than those for the 20-gauge high-speed vitrectomy system, the use of 25-gauge TVS may effectively reduce operative times of select cases that do not require the full capability of conventional vitrectomy.

Diabetes Complications↗
PubMed2002

Limited macular translocation: current concepts.

Macular translocation is a promising treatment modality that offers patients a chance to improve their vision, potentially to a level that may allow reading and driving. Proper patient selection avoids surgery in eyes with permanently damaged central retina and identifies eyes with the greatest potential for good visual outcomes. Functionally, those patients with recent-onset subfoveal CNV without permanent foveal neurosensory retina damage have the greatest likelihood of good visual outcome. Use of fixation evaluation by means of the SLO appears to greatly optimize patient selection. Anatomically, the best candidates have small minimum desired translocations and healthy RPE-Bruch membrane-choriocapillaris complex beyond the borders of the lesion. The exact role of limited macular translocation for the management of subfoveal CNV in this era of photodynamic therapy remains to be evaluated, and a pilot multicenter, randomized, clinical trial is under way to compare the efficacy of limited macular translocation with photodynamic therapy in eyes with subfoveal CNV secondary to AMD.

Choroidal Neovascularization↗