Clinical studies on the efficiency of high power laser radiation upon some structures of the anterior segment of the eye. First experiences of the treatment of some pathological conditions of the anterior segment of the human eye by means of a Q-switched laser system

Laser-induced cavitation in plasmonic nanoparticle solutions: A comparative study between gold and titanium nitride

In this work, we present an extensive comparative study between novel titanium nitride nanoparticles (TiN NPs) and commercial gold nanorods (GNR), both dispersed in water and exposed to a pulsed laser-induced cavitation process. The optical density, shockwave emission, and bubble formation of these solutions were investigated using shadowgraphy, spatial transmittance modulation, and acoustic measurements. TiN nanoparticle solutions exhibited high stability undser a periodic nanosecond pulsed-laser irradiation, making these nanomaterials promising agents for high-power applications. In addition, they demonstrated a stronger nonlinear absorption compared to the GNR solutions, and plasma formation at lower laser energies. This study advances our understanding of the optical properties of TiN and discusses significant differences compared to gold, with important implications for future applications of this material in water treatment, nonlinear signal converting, and laser-induced cavitation for medical implementations, among others.

Contributions to Progress in Ophthalmology from Switzerland: From the 16th to the 21st Century

There are numerous contributions to the development of ophthalmology from Switzerland, a country that holds a very special place in the history of medicine from the age of Paracelsus and Vesal to the current time. This review gives an overview over these contributions and the pioneers, among them Johann Friedrich Horner, Hans Goldmann, Jules Gonin, and Walter Rudolf Hess, one of only two ophthalmologists ever awarded the Nobel Prize for Medicine. A leading role in this evolution of modern ophthalmology has been played by physicians from Basel, home of Switzerland's oldest university.

[Retinal changes after laser interventions on anterior segment of the eyeball]

Laser surgery of the cornea, iris, angle of the anterior chamber and other parts of anterior segment of the eye sees wide application in clinical practice. The adverse effects it can cause in the anterior segment are well known and understood. At the same time, changes the treatment method can cause in the posterior segment of the eye - primarily, in macular area of the cornea, which is of great importance, have not been studied sufficiently. Purpose of the review - to consolidate previously published data on changes in the retina after laser intervention on the anterior segment of the eye.

Induction of oxidative stress in human aqueous and vitreous humors by Nd:YAG laser posterior capsulotomy

AIM

To evaluate whether the Q-switched Nd:YAG laser treatment applied in routine capsulotomy elicits oxidative stress in aqueous and vitreous humors.

METHODS

Thirty-six patients who had to undergo a 25 gauge pars plana vitrectomy due to vitreoretinal disorders were enrolled, 15 of them underwent a Q-switched Nd:YAG laser capsulotomy 7d before vitrectomy due to posterior capsule opacification (PCO) (Nd:YAG laser group) while the remaining 21 patients were not laser treated before vitrectomy (no Nd:YAG laser group). Samples of the aqueous and vitreous humors were collected during vitrectomy from all patients for the assessment of oxidative parameters which were compared between the Nd:YAG laser group and no Nd:YAG laser group. Thiobarbituric acid reactive substances (TBARS), a product of membrane lipid peroxidation, nitrite levels, the antioxidative activities of SOD and catalase, the 4-HNE-protein conjugate formation, indicating structural modifications in proteins due to lipoperoxidation, were assessed in aqueous and vitreous samples.

RESULTS

In the human vitreous humor TBARS levels are significantly higher in the Nd:YAG laser group compared to the no Nd:YAG laser group and importantly, there is a significant correlation between the TBARS levels and the total energy of Nd:YAG laser used during capsulotomy. Moreover the anti-oxidative activities of SOD and catalase were significantly decreased by Nd:YAG laser treatment, both in aqueous and vitreous humors. In accordance with the TBARS data and anti-oxidative enzyme activities, significantly higher levels of proteins were conjugated with the lipoperoxidation product 4-HNE in the aqueous and vitreous humors in the Nd:YAG laser-treated group in comparison to no Nd:YAG laser group.

CONCLUSION

These data, clearly suggest that any change that Q-switched Nd:YAG photo disruption may cause in the aqueous and vitreous compartments, resulting in a higher level of oxidative damage might be of considerable clinical significance particularly by accelerating the aging of the anterior and posterior segments of the eye and by worsening the intraocular pressure, the uveal, the retinal (especially macular) pathologies.

Pars plana posterior capsulectomy with a 27-gauge microincision vitrectomy system for dense posterior capsule opacification

We describe a surgical technique of pars plana posterior capsulectomy using a transconjunctival sutureless 2-port 27-gauge microincision vitrectomy system to deal with dense posterior capsule opacification (PCO). The technique was used successfully in 5 eyes of 5 patients with dense PCO that had been unsuccessfully treated by neodymium:YAG laser photodisruption.

Cavitation in medicine

We generally think of bubbles as benign and harmless and yet they can manifest the most remarkable range of physical effects. Some of those effects are the stuff of our everyday experience as in the tinkling of a brook or the sounds of breaking waves at the beach. But even these mundane effects are examples of the ability of bubbles to gather, focus and radiate energy (acoustic energy in the above examples). In other contexts that focusing of energy can lead to serious technological problems as when cavitation bubbles eat great holes through ships' propeller blades or cause a threat to the integrity of the spillways at the Hoover Dam. In liquid-propelled rocket engines, bubbles pose a danger to the stability of the propulsion system, and in artificial heart valves they can cause serious damage to the red blood cells. In perhaps the most extraordinary example of energy focusing, collapsing cavitation bubbles can emit not only sound, but also light with black body radiation temperatures equal to that of the sun (Brennen 1995 Cavitation and bubble dynamics). But, harnessed carefully, this almost unique ability to focus energy can also be put to remarkably constructive use. Cavitation bubbles are now used in a remarkable range of surgical and medical procedures, for example to emulsify tissue (most commonly in cataract surgery or in lithotripsy procedures for the reduction of kidney and gall stones) or to manipulate the DNA in individual cells. By creating cavitation bubbles non-invasively thereby depositing and focusing energy non-intrusively, one can generate minute incisions or target cancer cells. This paper will begin by briefly reviewing the history of cavitation phenomena and will end with a vision of the new horizons for the amazing cavitation bubble.

The Effect of ND:YAG Laser Posterior Capsulotomy Size on Refraction, Intraocular Pressure, and Macular Thickness

Purpose. The aim of this study is to examine the influence of capsulotomy size on, spherical equivalent (SE), intraocular pressure (IOP), and macular thickness. Materials and Methods. Sixty-eight patients were examined preoperatively and 1, 4, and 12 weeks after Nd:YAG capsulotomy. Patients were divided into two groups based on the postoperative capsulotomy size. Changes in SE, IOP, and macular thickness were compared between two groups. Results. We found a higher hyperopic shift in large capsulotomy group. In both groups 1 and 2, IOP increased 1 week postoperatively. Intraocular pressure rise in group 2 was higher than in group 1. Both groups had increased macular thickness at 1 week postoperatively. The degree of macular thickening was similar in group 1 and group 2. Comment. Patients who underwent a larger capsulotomy have a higher hyperopic shift and IOP elevation. Rise in macular thickness was similar in large and small capsulotomy groups.

Nd:YAG laser capsulotomy: a survey of UK practice and recommendations

PURPOSE

To determine national trends in YAG laser capsulotomy practice in the NHS.

METHODS

A total of 300 consultants were randomly selected, based on a list from the Royal College of Ophthalmologists, to receive a postal questionnaire. It included 10 questions about YAG capsulotomy technique and postcapsulotomy management.

RESULTS

A total of 158 (53%) replies were received; 132 (83.5%) questionnaires were completed correctly. Most consultants dilate the pupil prior to treatment (98.5%) and use contact lens (87.9%), with 63.5% reporting using contact lenses for more than one indication. Nearly half of the consultants used cruciate laser pattern (47.0%). Most aimed for capsulotomy size larger than undilated pupil size (64.4%). A total of 42.4% used postoperative steroid drops, 61.8% for 1 week. Half used postlaser intraocular pressure-lowering drops with the majority used as 1-stat dose (85.1%). A total of 60% are not reviewing cases. Cases reviewed are mostly seen by doctors, with 50% reviewed 1 month postlaser.

CONCLUSIONS

Though commonly practiced, there is still considerable variation in YAG laser capsulotomy practice among NHS consultant ophthalmologists. Evidence-based guidelines are warranted to lessen any unnecessary complications.

Perception of difficulties with vision-related activities of daily living among patients undergoing unilateral posterior capsulotomy

OBJECTIVES

To assess the influence of Nd:YAG (neodymium: yttrium-aluminum- garnet) laser unilateral posterior capsulotomy on visual acuity and patients' perception of difficulties with vision-related activities of daily life.

METHODS

We conducted an interventional survey that included 48 patients between 40 and 80 years of age with uni- or bilateral pseudophakia, posterior capsule opacification, and visual acuity <or=0.30 (logMAR) in one eye who were seen at a Brazilian university hospital. All patients underwent posterior capsulotomy using an Nd:YAG laser. Before and after the intervention, patients were asked to complete a questionnaire that was developed in an exploratory study.

RESULTS

Before posterior capsulotomy, the median visual acuity (logMAR) of the included patients was 0.52 (range 0.30-1.60). After posterior capsulotomy, the median visual acuity of the included patients improved to 0.10 (range 0.0-0.52). According to the subjects' perceptions, their ability to perform most of their daily life activities improved after the intervention (p<0.05).

CONCLUSIONS

After patients underwent posterior capsulotomy with an Nd:YAG laser, a significant improvement in the visual acuity of the treated eye was observed. Additionally, subjects felt that they experienced less difficulty performing most of their vision-dependent activities of daily living.

Franz Fankhauser: the father of the automated perimeter

Franz Fankhauser is known as the father of automated perimetry and of the q-switched Nd:YAG laser knife. His 15-year journey to computerize perimetry started in 1958 with unsuccessful attempts to automate kinetic perimetry. The switch to using static perimetry resulted in a breakthrough in 1973, and in 1975 the OCTOPUS perimeter came on the market. At the same time Fankhauser was working on the use of light sources for the treatment of ocular tissues. During his career, Fankhauser worked in very close collaboration with mathematicians, physicists, engineers. One of the most astonishing characteristics of Fankhauser was his ability to find and to motivate young scientists to work as a cohesive group for his projects.

Use of Nd:YAG laser capsulotomy

Surgery for cataract removal has become successively refined such that posterior capsular opacification is the most common problem presenting after modern cataract extraction. Various techniques and treatments exist to manage patients with posterior capsular opacification using Nd:YAG capsulotomy. There are many possible variations in initial assessment, pre-laser treatments, laser techniques, and follow-up routines. The literature on the use of Nd:YAG laser for capsulotomy was reviewed and interpreted. This article presents the currently available knowledge in a format that allows the practitioner to tailor an evidence-based protocol for treating patients with symptomatic posterior capsule opacification.

Initial clinical experience with the picosecond Nd:YLF laser for intraocular therapeutic applications

AIMS/BACKGROUND

Compared with nanosecond (ns) pulses of conventional Nd-YAG lasers, picosecond (ps) laser pulses allow intraocular surgery at considerably lower pulse energy. The authors report initial clinical experiences using a Nd:YLF ps laser for the treatment of various indications for photodisruption.

METHODS

A Nd:YLF laser system (ISL 2001, wavelength 1053 nm) was used to apply pulse series of 100-400 microJ single pulse energy at a repetition rate of 0.12-1.0 kHz. Computer controlled patterns were used to perform iridectomies (n = 53), capsulotomies (n = 9), synechiolysis (n = 3), and pupilloplasties (n = 2). Other procedures were vitreoretinal strand incision (n = 2) and peripheral retinotomy (n = 1). For comparison, 10 capsulotomies and 20 iridotomies were performed with a Nd:YAG ns laser. The ps laser cut of an anterior capsule was assessed by scanning electron microscopy (SEM).

RESULTS

Open, well defined iridectomies (mean total energy 4028 mJ, mean diameter 724 microns), were achieved at first attempt in 92% of the cases. In 64% an iris bleeding and in 21% an IOP increase of > 10 mm Hg occurred. All capsulotomies were performed successfully (mean energy 690 mJ/mm cutting length) but with a high incidence of intraocular lens damage. The attempted vitreoretinal applications remained unsuccessful as a result of optical aberrations of the eye and contact lens. Although ps laser capsulotomies and iridectomies required much higher total energy than ns procedures, the resulting tissue effects of the ps pulses were more clearly defined. SEM examination of a ps incision of the anterior lens capsule demonstrated, nevertheless, that the cut was more irregular than the edge of a continuous curvilinear capsulorhexis.

CONCLUSION

Series of ps pulses applied in computer controlled patterns can be used effectively for laser surgery in the anterior segment and are considerably less disruptive than ns pulses. The ps laser is well suited for laser iridectomies while the ns laser is preferable for posterior capsulotomies. As vitreoretinal applications remained unsuccessful, the range of indications for intraocular photodisruption could not be extended by the ps laser.

A randomised prospective comparison of operative peripheral iridectomy and Nd:YAG laser iridotomy treatment of acute angle closure glaucoma: 3 year visual acuity and intraocular pressure control outcome

AIM

To compare visual acuity and intraocular pressure outcomes 3 years after treatment of acute angle closure glaucoma (AACG) by operative peripheral iridectomy (PI) or Nd:YAG laser iridotomy (YAG PI).

METHODS

A prospective study of consecutive patients presenting to one ophthalmology department with uniocular AACG during a 2 year period. Following informed consent patients were randomised to bilateral PI or bilateral YAG PI. Three years after treatment the mean Snellen visual acuity converted to logMAR scores of the two groups was compared using the unpaired Student's t test. The number of patients with normal intraocular pressure with no further treatment in each group was compared using the chi 2 test with Yates's correction.

RESULTS

21 patients underwent bilateral PI and 27 bilateral YAG PI. Three years after treatment visual acuity was 0.30 (SD 0.28) log MAR units for PI eyes and 0.57 (0.67) logMAR units for YAG PI eyes (p = 0.08, NS). 15 (70.4%) PI eyes and 19 (71.8%) YAG PI eyes had an intraocular pressure less than 21 mm Hg with no further treatment (NS).

CONCLUSIONS

There was no significant difference in visual acuity or intraocular pressure control 3 years after treatment of AACG with PI or YAG PI.

Shielding properties of laser-induced breakdown in water for pulse durations from 5 ns to 125 fs

The shielding effectiveness of laser-induced breakdown from focused, visible laser pulses from 5 ns to 125 fs is determined from measurements of transmission of energy through the focal volume. The shielding efficiency decreases as a function of pulse duration from 5 ns to 300 fs and increases from 300 fs to 125 fs. The results are compared with past studies at similar pulse durations. The results of the measurements support laser-induced breakdown models and may lead to an optimization of laser-induced breakdown in ophthalmic surgery by reduction of collateral effects.

Nonlinear absorption: intraocular microsurgery and laser lithotripsy

The paper reviews the principles of nonlinear absorption with reference to the present major clinical applications of plasma-mediated effects: intraocular microsurgery and laser lithotripsy. Emphasis is laid on the analysis of the working mechanisms, sources of collateral damage, and on strategies for both the optimization of efficacy and the minimization of side effects.

Intraocular laser surgical probe for membrane disruption by laser-induced breakdown

A fiber probe has been designed as a surgical aid to cut intraocular membranes with laser-induced breakdown as the mechanism. The design of the intraocular laser surgical probe is discussed. A preliminary retinal damage distance has been calculated with breakdown threshold, spot size, and shielding measurements. Collateral mechanical-damage effects caused by shock wave and cavitation are discussed.

Ultrastructure of Picosecond Laser Intrastromal Photodisruption

PURPOSE

To investigate the ultrastructure of the corneal stroma after picosecond intrastromal photodisruption with a neodymium-doped yttrium-lithium-fluoride (Nd:YLF) laser.

METHODS

We performed picosecond intrastromal photodisruption on six human eye-bank eyes using a lamellar technique. Thirty picosecond pulses at 1000 Hz and 20 to 25 mJ per pulse were placed in an expanding spiral pattern, the pulses separated by 15 microns. Three layers were placed in the anterior stroma, separated from each other by 15 microns. In addition, intrastromal radial and arcuate incisions were generated in two living rabbit eyes in a plane perpendicular to the corneal surface. After the procedure, the corneas were processed for scanning and transmission electron microscopy.

RESULTS

Scanning electron microscopy of the eye-bank eyes demonstrated multiple, coalescing intrastromal cavities forming a layer oriented parallel to the corneal surface. These cavities had smooth inner walls. Transmission electron microscopy demonstrated tissue loss surrounding some cavities, with the terminated ends of collagen fibrils clearly evident. Other cavities were formed by separation of lamellae, with little evidence of tissue loss. A pseudomembrane was present along the margin of some cavities. Although there was occasional underlying tissue disruption along the border of a cavity, there was no evidence of thermal damage or tissue necrosis. The perpendicular photodisruptions demonstrated intrastromal cleavage of corneal collagen similar to diamond-knife incisions, with the exception of intact overlying Bowman's and epithelial layers.

CONCLUSION

Intrastromal photodisruption with a Nd:YLF picosecond laser induced no thermal necrosis or coagulative change in the region of tissue interaction. Lamellar intrastromal photodisruption demonstrated both tissue loss and lamellar separation when performed with the current treatment parameters, possibly limiting ablation efficiency and predictability.

Time-resolved observations of shock waves and cavitation bubbles generated by femtosecond laser pulses in corneal tissue and water

BACKGROUND AND OBJECTIVE

Photodisruption in ocular media with high power pulsed lasers working at non-absorbing frequencies have become a well established surgical tool since the late seventies. Shock waves and cavitation bubbles generated by the optical breakdown may strongly influence the surgical effect of photodisruptive lasers. We have investigated the shock wave and cavitation bubble effects of femtosecond laser pulses generated during photodisruption in corneal tissue and water. The results are compared to those obtained with longer laser pulses.

STUDY DESIGN/MATERIALS AND METHODS

Laser pulses with 150 fs duration at approximately 620 nm wavelength have been focused into corneal tissue and water to create optical breakdown. Time-resolved flash photography has been used to investigate the dynamics of the generated shock waves and cavitation bubbles.

RESULTS

A rapid decay of the shock waves is observed in both materials with similar temporal characteristics and with a spatial range considerably smaller than that of shock waves induced by picosecond (or nanosecond) optical breakdown. Cavitation bubbles are observed to develop more rapidly and to reach smaller maximum diameter than those generated by longer pulses. In corneal tissue, single intrastromal cavitation bubbles generated by femtosecond pulses disappear within a few tens of seconds, notably faster than cavitation bubbles generated by picosecond pulses.

CONCLUSIONS

The reduced shock wave and cavitation bubble effects of the femtosecond laser result in more localized tissue damage. Therefore, a more confined surgical effect should be expected from a femtosecond laser than that from picosecond (or nanosecond) lasers. This indicates a potential benefit from the applications of femtosecond laser technology to intraocular microsurgery.

Neodymium: YAG membranectomy for pupillary membranes on posterior chamber intraocular lenses

PURPOSE

To evaluate the effectiveness of neodymium: YAG laser for the removal of membranes from the anterior surface of intraocular lenses.

METHODS

Seven patients had reduced vision due to a membrane on the anterior surface of a posterior chamber intraocular lens (PC IOL). Six of the membranes developed after extracapsular cataract surgery and PC IOL combined with trabeculectomy and one after pars plana vitrectomy. Six of the membranes developed in the early postoperative period in association with a fibrinous reaction of the anterior chamber. One formed 7 months after surgery in an eye with iris capture behind the IOL. The membranes persisted despite intensive topical steroid therapy. A neodymium: YAG (Nd:YAG) laser was used to remove the membranes from the anterior of the IOL in all the seven cases.

RESULTS

The Nd:YAG laser effectively severed the peripheral connections of the membranes to the iris and lens, creating a clear central zone within the visual axis. The settings were fundamental mode, 1.2-to 3.1-mJ energy per shot and 48.3 +/- 20.1 single pulses. Vision improved significantly in six patients, whereas elevated intraocular pressure was observed in one patient.

CONCLUSION

Postoperative pupillary membranes may be successfully lysed with use of the Nd:YAG laser.

Lasers in ophthalmology

This article reviews the principle uses of ophthalmic lasers, providing historical background with an emphasis on new applications and areas of investigation. Ophthalmic photocoagulation was the first medical laser application and has restored or maintained vision in millions of people. More recently, photodisruption and, increasingly, ablation have gained prominence for treating a wide range of ocular pathology. The unique properties of lasers have also been harnessed for diagnostic purposes, with optical coherence tomography representing a significant improvement over existing imaging methods. Many ophthalmic applications of lasers have been developed, but the field is a dynamic one which continues to evolve along with laser technology itself.

Intraocular microsurgery with a picosecond Nd:YAG laser

We investigated the use of picosecond Nd:YAG laser pulses for intraocular microsurgery. With a pulse duration of 100 picoseconds, only 70 microJ of pulse energy is required to consistently produce optical breakdown in the deep vitreous. This pulse energy is nearly two orders of magnitude less than the typical pulse energies used in conventional (nanosecond) photodisruptors. The reduced pulse energy results in a smaller zone of tissue damage, an important consideration when operating close to the retina or other sensitive ocular structures. Efficient cutting action is achieved by applying multiple pulses at a moderately high repetition rate of 50-200 Hz. An in vitro model was developed to assess axial confinement of picosecond photodisruption. In vivo vitreous membrane surgery was performed in experimental rabbit eyes to demonstrate a potential clinical application of picosecond laser-induced optical breakdown.

Diode laser iridotomy in rabbit and human eyes

We investigated the use of an infrared diode laser to perform iridotomies in 20 eyes of ten rabbits and 40 eyes of 24 patients with primary angle-closure glaucoma. We used a two-stage method with initial circular stretch burns and subsequent penetrating multiple burns. The iris was perforated in one session and remained patent through ten months in rabbits, and seven to nine months in humans. Transitory clinical complications included intraocular pressure increase of more than 10 mm Hg (20%, eight of 40 eyes), corneal endothelial changes (5%, two of 40 eyes), clouding of lens surface (60%, 24 of 40 eyes), localized cataract (5%, two of 40 eyes), and pupillary distortion (70%, 28 of 40 eyes). No retinal damage was observed. Diode laser can be used for peripheral iridotomy.

A randomised, prospective comparison of Nd:YAG laser iridotomy and operative peripheral iridectomy in fellow eyes

A prospective, randomised comparison of Nd:YAG laser iridotomy and operative peripheral iridectomy in the fellow eye of 52 patients presenting with acute angle closure glaucoma has been undertaken. Nd:YAG laser iridotomy resulted in a significantly higher incidence of iris bleeding at the time of treatment (p less than 0.05), higher intraocular pressure one hour (p less than 0.02) and three hours (p less than 0.02) following treatment, and a higher incidence of focal corneal oedema 24 hours following treatment (p less than 0.001). One laser treated patient developed acute angle closure glaucoma two weeks following treatment despite the presence of a small patent iridotomy. After a mean follow-up period of 11.8 months there was no significant difference between the two groups in visual acuity, or intraocular pressure. It is concluded that Nd:YAG laser iridotomy is a satisfactory alternative to operative peripheral iridectomy in the prophylactic treatment of fellow eyes.

How large must an iridotomy be?

Four cases of acute angle closure glaucoma in eyes with a small but patent Nd-YAG laser iridotomy are presented, and similar cases in the literature are reviewed. Theoretically a 15 microns diameter iridotomy should be large enough to prevent angle closure glaucoma due to pupil block. Mechanisms by which larger iridotomies fail to prevent angle closure glaucoma, and the role of provocation tests following iridotomy, are discussed. An iridotomy should be at least 150-200 microns in diameter if acute angle closure glaucoma is to be reliably prevented.

Optically coupled technique for photorefractive surgery of the cornea

A novel optically coupled laser probe and method that achieve noninvasive in vivo refractive flattening of the cornea of experimental eyes is described. This new refractive surgery concept is based on the highly localized photodisruption and/or photoablation of tissue within the stromal layer of the cornea without other layers' being affected. This is accomplished by a microscope probe that is optically index matched to the corneal surface, thereby achieving high numerical apertures. The sharp focal volume ensures highly localized energy deposition. Preliminary results in rabbit, primate, and human eye-bank eyes indicate significant permanent refractive changes with an exceptionally small amount of tissue modification.

Q-switched neodymium YAG laser vitreolysis in the therapy of posterior segment disease

We describe our experience of ten cases of posterior segment vitreolysis, using the short-pulse neodymium YAG (Yttrium Aluminium Garnate) laser. Eight patients had proliferative diabetic retinopathy, one patient had had an intraocular foreign body removed and one patient had had uveitis. Of the ten, five patients had macular traction retinal detachments, three patients had progressive traction retinal detachments threatening the macula and two patients had recurrent vitreous haemorrhages from mechanical traction on areas of fibrovascular proliferation. Eight of the patients were successfully treated. One macular retinal detachment failed to flatten and a tear was found which may have been iatrogenic. In one patient with a traction retinal detachment significant traction was relieved but the detachment failed to flatten completely. We discuss the indications, techniques, difficulties and complications. Our experience suggests that this technique has an important role in the treatment of selected patients, sparing patients conventional vitrectomy, or making possible the treatment of those for whom vitrectomy has been contraindicated or refused. Anterior defocusing of the YAG would be a useful modification of current laser systems and improved aiming systems desirable for the future.

Picosecond optical breakdown: tissue effects and reduction of collateral damage

The effects of picosecond laser-induced optical breakdown on tissue were investigated using high-intensity 40 ps Nd:YAG laser pulses at 1.06 microns. Tissue damage was evaluated using the corneal endothelium in vitro as a model system. Systematic studies were performed to determine the scaling of the tissue damage and damage range with pulse energy. For suprathreshold lesions, the radius of the damage zone varies as the cube root of the pulse energy, in agreement with simple physical scaling laws. A minimum damage range of less than 100 microns was observed for pulse energies of 8 muJ. Damage morphology was investigated by scanning electron microscopy. Three different damage patterns were observed; cell damage, cell removal, and rupture of Descemet's membrane. Different irradiation geometries were used to study damage mediated by either the shock wave or the cavitation bubble. Comparative studies using 10 ns pulses demonstrated that picosecond pulses yielded a significant reduction in collateral tissue damage.

Study of the temporal and spatial dynamics of plasmas induced in liquids by nanosecond Nd:YAG laser pulses. 1: Analysis of the plasma starting times

We report on a theoretical and experimental study of the temporal and spatial dynamics of plasmas produced in liquids by single Nd:YAG laser pulses of nanosecond duration. This study was motivated by the increasing attention paid to the phenomenon of optical breakdown and to its related effects on tissues and media in connection with microsurgical techniques developed for ophthalmology and urology. Streak camera recordings of the emission from laser-induced plasmas were taken in distilled and tap water in controlled irradiation conditions. From streak recordings, plasma starting times as a function of the axial distance from focus, the overall length of the plasma column, plasma lifetimes, and plasma absorption were derived and analyzed. In this first paper we analyze the curves of plasma starting time, as a function of the irradiation parameters and of the properties of the medium. We show that a model obtained by upgrading the theory of the moving breakdown allows accurate interpretation of the experimental observations.

Long-term follow-up of neodymium: YAG laser angle surgery for open-angle glaucoma

Seventy-nine eyes (61 patients) with open-angle glaucoma and uncontrolled intraocular pressure (IOP) of 23 mmHg or more despite maximal tolerated medical therapy and prior argon laser trabeculoplasty (75 eyes) were treated with neodymium: YAG (Nd: YAG) laser angle surgery and followed for at least 1 year. Ten pulses of 10 mJ were applied to the midtrabecular meshwork over 40 degrees in the most visible portion of the angle. The IOP was controlled successfully (less than or equal to 22 mmHg) in 60 eyes (76%) 1 month after treatment and in 36 of 78 eyes (46%) 1 year after treatment. Long-term complications included two eyes with advanced glaucoma that lost central fixation despite good IOP control after treatment.

Low-energy linear-incision neodymium: YAG laser iridotomy versus linear-incision argon laser iridotomy. A prospective clinical investigation

When the Q-switched neodymium: YAG (Nd: YAG) laser is focused through the Wise 103-diopter (D) iridotomy-sphincterotomy lens (103-D lens) at low energy levels, the peripheral iris fibers can be cut individually across the iris tension lines to produce large iridotomies of controllable size. Thirty patients had linear-incision Nd:YAG laser iridotomy in one eye and linear-incision argon laser iridotomy in the other. Two-hour post-laser IOP rises averaged 7.33 mmHg for the Nd:YAG laser and 8.64 mmHg for the argon laser. The argon laser produced lens burns in 9 of 30 eyes, including 7 of 9 blue eyes. No lens damage occurred with the Nd:YAG laser. No corneal or retinal damage was seen with either laser. Local oozing of blood inhibited optical breakdown and required a pause before completion in 5 of 30 eyes with Nd:YAG iridotomy, including 4 of 6 dark brown thick irides. Because the iris fibers must be cut by direct contact with the laser plasma, serial cutting of iris fibers by multiple low-energy plasmas is safer than a single-shot, high-power plasma occupying the full thickness of the iris. Because it is effective and because it avoids the hazards of argon laser iridotomy and of high-power Nd:YAG laser iridotomy, linear incision Nd:YAG laser iridotomy is recommended as the safest method of iridotomy.

Neodymium:YAG laser iridotomy

During the past several years the Neodymium:YAG laser has become increasingly popular for performing peripheral iridotomy. Using energy levels of 2-8 millijoules per shot and 1-3 shots per treatment, most irides can be penetrated in one sitting. Nd:YAG laser iridotomies show very little tendency to close, except in patients with active intraocular inflammation. A small amount of hemorrhage is common following YAG laser iridotomy, but clinically significant hyphema is rare. Significant lenticular or corneal damage is extremely rare. Although longterm follow-up of large numbers of patients is lacking, Nd:YAG laser iridotomy appears to be a safe and effective alternative to Argon laser iridotomy in selected patients.

Neodymium:YAG laser interaction with Alcon IOGEL hydrogel intraocular lenses: an in vitro toxicity assay

The objective of this study was to determine the potential toxicity generated by the interaction of the Nd:YAG laser and Alcon IOGEL intraocular hydrogel lens material. The IOGEL lens is composed of poly 2-hydroxyethylmethacrylate, containing 38% water, previously shown to be highly biocompatible in a wide range of tissue culture and implantation experiments. In this study, intraocular lenses (IOLs) immersed in serum-free cell culture medium were purposely exposed to exaggerated doses of laser energy to cause extensive damage. An IOLAB polymethylmethacrylate (PMMA) lens served as a control lens material. The resultant solutions were assayed for cytotoxicity in a bioassay system using fourth passage human corneal endothelial cells. No cytotoxicity was seen in the bioassay for the IOGEL hydrogel IOLs or the PMMA control IOL at any laser range/dosage tested over a 72-hour incubation period. Hydrogel lenses exhibited decreasing yellowing with decreasing energy levels, and no lens discoloration was apparent at the lowest level of irradiation, 5 mJ/50 laser bursts; the PMMA control lens exhibited moderate yellowing at 15 mJ/50 bursts. Lens marking was moderate for all IOGEL IOLs; the PMMA lens marking was severe at the power level tested.

Contact application of Nd:YAG laser through a fiberoptic and a sapphire tip

We evaluated the effects of Nd:YAG laser energy directly applied to ocular tissue through a fiberoptic and a sapphire tip. All ocular tissue could be easily cut with the maximum 4 watts of energy. The coagulated borders extended 20 to 200 mu into the healthy tissue depending on the speed with which the cutting was performed.

Clinical experience with Nd:YAG laser vitreolysis in the anterior segment

The clinical experience of two surgeons performing Nd:YAG laser anterior vitreolysis to disrupt vitreous strands adherent to surgical wounds with and without pupillary distortions and/or cystoid macular edema is presented. We describe our technique. The results indicate that vision improved in 50% of the cases, with visual acuity improving from 20/40 or better in three of 20 eyes preoperatively to 11 of 20 eyes postoperatively. No adverse effects or complications occurred in any of our 20 patients. Neodymium:YAG laser vitreolysis should be considered presently as the method of choice for initial treatment of vitreous strands incarcerated in the wound.

Intensity of the flash associated with laser-induced plasma in the eye

A bright flash of light is emitted by the plasma formed at the focus of an ophthalmic Nd: YAG laser. The purpose of this investigation is to determine whether the plasma flash constitutes a hazard to the operator. The intensity of the flash at the slit lamp eyepiece was measured and the experimentally derived value was verified by independent calculation. For hazard assessment purposes, the concept of a spectrally weighted maximum permissible exposure (MPE) is described in the paper. Based on the MPE and our measurements and calculations our conclusion is that viewing the flash in a patient's eye through the microscope would not be considered hazardous to the operator. In contrast, during technical procedures, targets in air are used to produce a plasma and in this situation eye protection is recommended when viewing the flash through the microscope.

Effects of an erbium: YAG laser on ocular structures

We evaluated the effects of the erbium:YAG laser (2.9 micron wavelength) on ocular structures. Energy was successfully transmitted through a fiberoptic bundle for intraocular and extraocular applications. The wavelength was strongly absorbed by ocular tissues, producing ablations with minimal thermal damage. Our results indicated that the erbium:YAG laser may have potential uses as a photoablative tool to reshape the corneal surface and as a surgical knife.

Safety of high-energy neodymium:YAG laser pulses in YAG sclerostomy

YAG sclerostomy was performed in 15 eyes of nine cynomolgus monkeys. Individual pulse energies ranged between 10 and 135 millijoules. Total pulse energy ranged between 2,000 and 36,000 millijoules in order to test the extreme range of energy that might be required. Both acute effects and chronic effects were studied in the corneal endothelium, the lens capsule, the iris, the ciliary body, the retina, and the sclera. Techniques included flat preparations of the corneal endothelium, paraffin sections for light microscopy, and scanning and transmission electron microscopy. Our conclusion is that individual pulse energies of up to 135 millijoules with a total of up to 36 joules of energy are safe in monkey eyes when performing YAG sclerostomy.