Georg Schuele

Femtosecond laser capsulotomy.

PURPOSE: To evaluate a femtosecond laser system to create the capsulotomy. SETTING: Porcine and cadaver eye studies were performed at OptiMedica Corp., Santa Clara, California, USA; the human trial was performed at the Centro Laser, Santo Domingo, Dominican Republic. DESIGN: Experimental and clinical study. METHODS: Capsulotomies performed by an optical coherence tomography–guided femtosecond laser were evaluated in porcine and human cadaver eyes. Subsequently, the procedure was performed in 39 patients as part of a prospective randomized study of femtosecond laser‐assisted cataract surgery. The accuracy of the capsulotomy size, shape, and centration were quantified and capsulotomy strength was assessed in the porcine eyes. RESULTS: Laser‐created capsulotomies were significantly more precise in size and shape than manually created capsulorhexes. In the patient eyes, the deviation from the intended diameter of the resected capsule disk was 29 μm ± 26 (SD) for the laser technique and 337 ± 258 μm for the manual technique. The mean deviation from circularity was 6% and 20%, respectively. The center of the laser capsulotomies was within 77 ± 47 μm of the intended position. All capsulotomies were complete, with no radial nicks or tears. The strength of laser capsulotomies (porcine subgroup) decreased with increasing pulse energy: 152 ± 21 mN for 3 μJ, 121 ± 16 mN for 6 μJ, and 113 ± 23 mN for 10 μJ. The strength of the manual capsulorhexes was 65 ± 21 mN. CONCLUSION: The femtosecond laser produced capsulotomies that were more precise, accurate, reproducible, and stronger than those created with the conventional manual technique. Financial Disclosure: The authors have equity interest in OptiMedica Corp., which manufactures the femtosecond laser cataract system.

Femtosecond Laser–Assisted Cataract Surgery with Integrated Optical Coherence Tomography

An image-guided, femtosecond laser can create precisely placed, accurate cuts in the eye to improve cataract surgery. The Power of Light As Star Wars fans know, a lightsaber fares better against the Dark Force than does a metal sword. Ophthalmologists, who battle the darkening forces of eye disease, have also learned this lesson, replacing steel scalpels with lasers for creating precise, controlled incisions in the eye. Laser-assisted in situ keratomileusis—commonly known as LASIK surgery—corrects myopia (nearsightedness) and other refractive errors in millions of people each year. Now, Palanker et al. used this approach to devise a more precise, reproducible and automated way to remove cataracts. The authors combine the precise cuts of a laser with the imaging sophistication of optical coherence tomography, a method that uses interference of coherent light scattered by biological tissues to create three-dimensional images of their internal structure. On the basis of the individual patient’s eye anatomy, the laser system calculates the optimal set of cutting patterns for cataract removal and directs the laser to execute these slices, resulting in fast, clean surgery. Two light-based methods made this surgical advance possible. The first, the femtosecond laser, is ideal for use deep inside a fragile eye. Unlike longer pulse lasers, which melt and boil their targets away, producing significant collateral damage to adjacent structures, femtosecond light pulses can turn the material in the focal spot into ionized plasma, allowing dissection of transparent tissues without heat accumulation and minimal disturbance to the surroundings. The resulting cut is smooth and precise. The second method—optical coherence tomography (OCT)—takes advantage of slight variations in the refractive properties of living tissues. Coherent light scattered by structures within the eye allows reconstruction of a 3D image of the live tissue. Palanker et al.’s instrument uses this imaging technique to map the cornea, iris and crystalline lens within the patient’s eye and precisely position the various laser cuts. The laser makes a circular opening in the lens capsule (the membrane that surrounds the lens itself), sections the opaque lens into small pieces that are easily removed, and carves a partial incision in the cornea for later completion of surgery and insertion of the artificial lens under sterile conditions. The laser-created edges in the lens capsule are stronger than those made manually, so they better resist damage when the opaque lens is removed or the new lens is implanted. All the laser cuts are produced without perforating the cornea, so that the procedure can be performed outside the operating room. The laser can also be used to cut the corneal surface for correction of astigmatism and for creating a port for surgical instruments in the operating room. Although the new instrument plans and performs incisions much more accurately than do currently available tools, a surgeon still must remove the lens manually. The benefits of the more precise surgical incisions on visual acuity in patients with various types of intraocular lenses will need to be ascertained in a larger prospective trial, although the preliminary data in the paper are promising and indicate that the laser procedure is safe for ocular tissues. This new instrument will arm surgeons with a precise and automated lightsaber with which to battle the darkening forces of cataracts. About one-third of people in the developed world will undergo cataract surgery in their lifetime. Although marked improvements in surgical technique have occurred since the development of the current approach to lens replacement in the late 1960s and early 1970s, some critical steps of the procedure can still only be executed with limited precision. Current practice requires manual formation of an opening in the anterior lens capsule, fragmentation and evacuation of the lens tissue with an ultrasound probe, and implantation of a plastic intraocular lens into the remaining capsular bag. The size, shape, and position of the anterior capsular opening (one of the most critical steps in the procedure) are controlled by freehand pulling and tearing of the capsular tissue. Here, we report a technique that improves the precision and reproducibility of cataract surgery by performing anterior capsulotomy, lens segmentation, and corneal incisions with a femtosecond laser. The placement of the cuts was determined by imaging the anterior segment of the eye with integrated optical coherence tomography. Femtosecond laser produced continuous anterior capsular incisions, which were twice as strong and more than five times as precise in size and shape than manual capsulorhexis. Lens segmentation and softening simplified its emulsification and removal, decreasing the perceived cataract hardness by two grades. Three-dimensional cutting of the cornea guided by diagnostic imaging creates multiplanar self-sealing incisions and allows exact placement of the limbal relaxing incisions, potentially increasing the safety and performance of cataract surgery.

Optical patient interface in femtosecond laser-assisted cataract surgery: Contact corneal applanation versus liquid immersion

Purpose To compare 2 optical patient interface designs used for femtosecond laser–assisted cataract surgery. Setting Optimedica Corp., Santa Clara, California, USA, and Centro Laser, Santo Domingo, Dominican Republic. Design Experimental and clinical studies. Methods Laser capsulotomy was performed during cataract surgery with a curved contact lens interface (CCL) or a liquid optical immersion interface (LOI). The presence of corneal folds, incomplete capsulotomy, subconjunctival hemorrhage, and eye movement during laser treatment were analyzed using video and optical coherence tomography. The induced rise of intraocular pressure (IOP) was measured in porcine and cadaver eyes. Results Corneal folds were identified in 70% of the CCL cohort; 63% of these had areas of incomplete capsulotomies beneath the corneal folds. No corneal folds or incomplete capsulotomies were identified in the LOI cohort. The mean eye movement during capsulotomy creation (1.5 sec) was 50 μm with a CCL and 20 μm with an LOI. The LOI cohort had 36% less subconjunctival hemorrhage than the CCL cohort. During suction, the mean IOP rise was 32.4 mm Hg ± 3.4 (SD) in the CCL group and 17.7 ± 2.1 mm Hg in the LOI group. Conclusions Curved contact interfaces create corneal folds that can lead to incomplete capsulotomy during laser cataract surgery. A liquid interface eliminated corneal folds, improved globe stability, reduced subconjunctival hemorrhage, and lowered IOP rise. Financial Disclosure Drs. Talamo, Culbertson, Batlle, Feliz, and Palanker are consultants to and Messrs. Gooding, Angeley, Schuele, Marcellino, and Andersen, and Ms. Essock‐Burns are employees of Optimedica Corp., Sunnyvale, California, USA.

Optoacoustic real-time dosimetry for selective retina treatment

The selective retina treatment (SRT) targets retinal diseases associated with disorders in the retinal pigment epithelium (RPE). Due to the ophthalmoscopic invisibility of the laser-induced RPE effects, we investigate a noninvasive optoacoustic real-time dosimetry system. In vitro porcine RPE is irradiated with a Nd:YLF laser (527 nm, 1.7-micros pulse duration, 5 to 40 microJ, 30 pulses, 100-Hz repetition rate). Generated acoustic transients are measured with a piezoelectric transducer. During 27 patient treatments, the acoustic transients are measured with a transducer embedded in an ophthalmic contact lens. After treatment, RPE damage is visualized by fluorescein angiographic leakage. Below the RPE damage threshold, the optoacoustic transients show no pulse-to-pulse fluctuations within a laser pulse train. Above threshold, fluctuations of the individual transients among each other are observed. If optoacoustic pulse-to-pulse fluctuations are present, RPE leakage is observed in fluorescein angiography. In 96% of the irradiated areas, RPE leakage correlated with the optoacoustic defined threshold value. A noninvasive optoacoustic real-time dosimetry for SRT is developed and proved in vitro and during patient treatment. It detects the ophthalmoscopically invisible laser-induced damage of RPE cells and overcomes practical limitations of SRT for use in private practice.

Selective retinal therapy with microsecond exposures using a continuous line scanning laser.

Purpose: To evaluate the safety, selectivity, and healing of retinal lesions created using a continuous line scanning laser. Methods: A 532-nm Nd:YAG laser (PASCAL) with retinal beam diameters of 40 μm and 66 μm was applied to 60 eyes of 30 Dutch-belted rabbits. Retinal exposure duration varied from 15 μs to 60 μs. Lesions were acutely assessed by ophthalmoscopy and fluorescein angiography. Retinal pigment epithelial (RPE) flatmounts were evaluated with live-dead fluorescent assay. Histological analysis was performed at 7 time points from 1 hour to 2 months. Results: The ratios of the threshold of rupture and of ophthalmoscopic visibility to fluorescein angiography visibility (measures of safety and selectivity) increased with decreasing duration and beam diameter. Fluorescein angiography and live-dead fluorescent assay yielded similar thresholds of RPE damage. Above the ophthalmoscopic visibility threshold, histology showed focal RPE damage and photoreceptor loss at 1 day, without inner retinal effects. By 1 week, photoreceptor and RPE continuity was restored. By 1 month, photoreceptors appeared normal. Conclusion: Retinal therapy with a fast scanning continuous laser achieves selective targeting of the RPE and, at higher power, of the photoreceptors without permanent scarring or inner retinal damage. Continuous scanning laser can treat large retinal areas within standard eye fixation time.

Investigation of Selective Retina Treatment (SRT) by Means of 8 ns Laser Pulses in a Rabbit Model

It has been shown that selective retina treatment (SRT) using a train of 1.7 microseconds laser pulses allows selective damage of the retinal pigment epithelium (RPE) while sparing the adjacent photoreceptors and thus avoiding laser scotoma. It was the purpose of this work to investigate SRT laser effects with Q‐switched pulses of only 8 nanoseconds in duration by evaluating the angiographic and ophthalmoscopic damage thresholds and the damage range by histology in a rabbit model.

Optical spectroscopy noninvasively monitors response of organelles to cellular stress

Fast and noninvasive detection of cellular stress is extremely useful for fundamental research and practical applications in medicine and biology. We discovered that light scattering spectroscopy enables us to monitor the transformations in cellular organelles under thermal stress. At the temperatures triggering expression of heat shock proteins, the refractive index of mitochondria increase within 1 min after the onset of heating, indicating enhanced metabolic activity. At higher temperatures and longer exposures, the organelles increase in size. This technique provides an insight into metabolic processes within organelles larger than 50 nm without exogenous staining and opens doors for noninvasive real-time assessment of cellular stress.

Patterned laser trabeculoplasty.

BACKGROUND AND OBJECTIVE A novel computer-guided laser treatment for open-angle glaucoma, called patterned laser trabeculoplasty, and its preliminary clinical evaluation is described. PATIENTS AND METHODS Forty-seven eyes of 25 patients with open-angle glaucoma received 532-nm laser treatment with 100-μm spots. Power was titrated for trabecular meshwork blanching at 10 ms and sub-visible treatment was applied with 5-ms pulses. The arc patterns of 66 spots rotated automatically after each laser application so that the new pattern was applied at an untreated position. RESULTS Approximately 1,100 laser spots were placed per eye in 16 steps, covering 360° of trabecular meshwork. The intraocular pressure decreased from the pretreatment level of 21.9 ± 4.1 to 16.0 ± 2.3 mm Hg at 1 month (n = 41) and remained stable around 15.5 ± 2.7 mm Hg during 6 months of follow-up (n = 30). CONCLUSION Patterned laser trabeculoplasty provides rapid, precise, and minimally traumatic (sub-visible) computer-guided treatment with exact abutment of the patterns, exhibiting a 24% reduction in intraocular pressure during 6 months of follow-up (P < .01).

Retinal safety of near-infrared lasers in cataract surgery

Abstract. Femtosecond lasers have added unprecedented precision and reproducibility to cataract surgery. However, retinal safety limits for the near-infrared lasers employed in surgery are not well quantified. We determined retinal injury thresholds for scanning patterns while considering the effects of reduced blood perfusion from rising intraocular pressure and retinal protection from light scattering on bubbles and tissue fragments produced by laser cutting. We measured retinal damage thresholds of a stationary, 1030-nm, continuous-wave laser with 2.6-mm retinal spot size for 10- and 100-s exposures in rabbits to be 1.35 W (1.26 to 1.42) and 0.78 W (0.73 to 0.83), respectively, and 1.08 W (0.96 to 1.11) and 0.36 W (0.33 to 0.41) when retinal perfusion is blocked. These thresholds were input into a computational model of ocular heating to calculate damage threshold temperatures. By requiring the tissue temperature to remain below the damage threshold temperatures determined in stationary beam experiments, one can calculate conservative damage thresholds for cataract surgery patterns. Light scattering on microbubbles and tissue fragments decreased the transmitted power by 88% within a 12 deg angle, adding a significant margin for retinal safety. These results can be used for assessment of the maximum permissible exposure during laser cataract surgery under various assumptions of blood perfusion, treatment duration, and scanning patterns.

Optoacoustic control system for selective treatment of the retinal pigment epithelium

The selective damage of the retinal pigment epithelium (RPE) is a new treatment method for several retinal diseases. By applying a train of microsecond(s) laser pulses it is possible to selectively damage these cells and simultaneously spare the adjacent photoreceptor and neural tissue. Due to the ophthalmologic invisibility of the RPE cell damage we investigate an optoacoustic (OA) control system to monitor the RPE cell damage. Setup: The irradiation was performed with a frequency doubled Nd:YLF laser by applying a train of +s laser pulses. In vitro, the OA transients were received by an ultrasonic broadband transducer. During treatment an OA contact lens with embedded transducer was used. In vitro: Freshly enucleated porcine RPE samples with CalceinAM as life/death staining were used. Below RPE cell damage threshold a classic thermoelastic transient was found. Above cell damage threshold the OA transient differs form pulse to pulse. This can be explained by microbubble formation around the strong absorbing melanosomes inside the RPE cells. In vivo: We found the same pulse to pulse deviations of the OA transient above the fluoresceine angiographic detectable RPE damage threshold during treatment. This system give us a new approach to non-invasively monitor the selective RPE treatment.