Biphasic intraocular pressure response to Q-switched Nd:YAG laser irradiation of the iris and the apparent mediatory role of prostaglandins

In rabbits, laser irradiation of the iris causes an immediate rise in intraocular pressure (IOP), with a concomitant increase of prostaglandins (PGs) in the aqueous humor. We studied IOP responses to Q-switched Nd:YAG laser application to the iris in unanesthetized rabbits, and found that a prolonged IOP reduction lasting for 6-24 hr invariably followed the transient IOP rise of 0.5-2 hr duration. The magnitude of both the IOP rise and reduction was dependent on the level of laser energy. A masked, randomized study revealed that the intraperitoneal administration of indomethacin (50 mg kg-1) prior to laser application significantly reduced the ocular hypertensive and hypotensive responses to laser irradiation (energy: 24 mJ). The maximum IOP rise from baseline was 5.4 +/- 3.0 mmHg (n = 10) with the intraperitoneal vehicle and 1.5 +/- 4.2 mmHg (n = 10) with intraperitoneal indomethacin administration. Thus, the difference was statistically significant (P less than 0.025, Student's t-test). The maximum IOP reduction from baseline was -8.5 +/- 2.6 mmHg (n = 10) with the intraperitoneal vehicle and -4.0 +/- 2.4 mmHg (n = 10) with intraperitoneal indomethacin (P less than 0.001, Student's t-test). The concentration of PGE2 in the aqueous humor, as determined by radioimmunoassay on samples obtained at 2 and 4 hr after laser application, was found to be significantly increased in rabbits that received the vehicle solution but not in animals that were pretreated with intraperitoneal injection of indomethacin. This suggests that this PG or other cyclooxygenase products are involved with mediation of the initial IOP increase and the prolonged decrease in IOP that follows laser irradiation of the iris.

Apraclonidine effects on ocular responses to YAG laser irradiation to the rabbit iris

Apraclonidine (p-aminoclonidine) ophthalmic solution effectively reduces the rise in intraocular pressure (IOP) following anterior segment laser surgery. We tested the effect of topical 0.5% apraclonidine on intraocular pressure and on protein and prostaglandin (PG) E2 concentrations in aqueous humor following Q-switched Nd:YAG laser irradiation to the iris of albino rabbits, at an energy level of 2 to 200 mJ. IOP was measured prior to and for 24 hr after irradiation. Aqueous humor was withdrawn before and 1 hr after laser irradiation for determining protein (Lowry method) and PGE2 (radioimmunoassay). Four to seven rabbits were used for each experiment. The increase in IOP and protein concentration following laser irradiation was demonstrated to be dependent on the amount of laser energy. Apraclonidine completely abolished the IOP rise, and significantly reduced the elevation of protein content. Apraclonidine failed to affect the increase in PGE2.

[Krypton laser coagulation in idiopathic macular holes]

Twenty-six eyes with acute idiopathic senile macular holes and visual acuity of between 0.02 and 0.5 were treated by laser coagulation with krypton red. The laser burns were placed in a ring around the hole, at the border of the retinal detachment. A few weeks after treatment marked regression of the detachment was seen. During the follow-up period (3-18 months) visual acuity improved in 18 eyes, deteriorated in 1 and was unchanged in 7.

Clinical, structural and molecular phototherapy effects of laser irradiation on the trabecular meshwork of human glaucomatous eyes

The effects of argon laser trabeculoplasty (LTP) on intraocular pressure (IOP), outflow facility, the morphology of the trabecular meshwork (TM), and the pattern of extracellular glycoprotein fibronectin in trabeculum were studied in 46 eyes of patients with primary open-angle glaucoma (POAG). The LTP was done with informed consent, anticipating that trabeculectomy would be carried out at a scheduled time (2 h to several months following laser therapy). We found that the magnitude of IOP reduction and the improvement in the facility of outflow achieved are directly dependent on the time course after LTP and laser-induced structural changes in trabecular tissue. Light microscopic and immunohistochemical evaluations of the TM specimens at earlier intervals after LTP revealed evidence of heat effects, with disruption and shrinkage of the TM collagenous components and accumulation of fibronectin deposits in the aqueous drainage channels as compared with the TMs of matched patients with POAG who did not receive laser treatment. Within 24 h after LTP, proteins of glaucomatous TMs excised from patients incorporated increased amounts of [3H]-leucine radioactive label; however, the amount of [3H]-leucine-labeled material was significantly depressed in later periods of evaluation. The specimens obtained at longer intervals after LTP showed partial or total occlusion of the intertrabecular spaces by extracellular debris; however, the amount of trabecular fibronectin was not significantly different from that measured 24 h after LTP. At least two potential mechanisms are proposed for the TM tissue response to laser treatment, including heat-induced stretching of the collagen in lamellae and fibronectin-mediated attachment of beams supporting an adhesive tightening of the trabecular components caused by LTP. The changes in laser-induced tissue responses appear to be the result of morphological repair of irradiation-injured trabecular tissue.

The effect of topical dexamethasone and preoperative beta irradiation on a model of glaucoma fistulizing surgery in the rabbit

We studied the effect of topical dexamethasone (1%) and preoperative beta irradiation on a model of glaucoma fistulizing surgery in the rabbit. Intraocular pressure and gross facility of aqueous outflow following surgery were not influenced by either treatment, although blebs persisted longer in the irradiated eyes. Steroids reduced clinically observable inflammation as well as the number of inflammatory cells identifiable by microscopy. Fibroblast production temporarily slowed, and ultra-structural examination demonstrated lipid-filled vacuoles and dilated mitochondria in these eyes. Also, the scar was thinner at 24 days. Beta irradiation delayed wound healing and the scar was thinner in the early postoperative stages, but the light microscopic appearance of the scar was unaltered at 59 days. Inflammation was more pronounced initially, with abundant fibrin in the wound. Recovery of the conjunctival epithelium was delayed. The delay in fibroblast recruitment and wound contraction, the thinner scar tissue, and the increased survival of the bleb are all factors that suggest that beta irradiation may be a useful adjunct to glaucoma surgery.

Platelet-activating factor and laser trauma of the iris

Local application of platelet-activating factor (PAF) on the rabbit eye caused a dose-dependent significant increase in intraocular pressure (IOP). After laser irradiation of the iris the IOP showed a hypertensive phase of about 3 hr. Prophylactic treatment with the PAF antagonist BN 52021 but not with indomethacin abolished the hypertensive phase. Elevated levels of protein (10.6 +/- 0.9 g/l) and prostaglandin E2 (PGE2, 1.7 +/- 0.2 ng/ml) were measured in the aqueous humor 2 hr after laser irradiation of the iris. Prophylactic treatment with BN 52021 showed lower levels of protein (6.1 +/- 0.7) and PGE2 (1.1 +/- 0.02); with indomethacin pretreatment the level of protein was 3.4 +/- 0.7 g/l and of PGE2 0.10 +/- 0.02 ng/ml. A role of PAF as a mediator in ocular inflammatory response is suggested.

A comparison of CW Nd:YAG contact transscleral cyclophotocoagulation with cyclocryopexy

The cyclodestructive and inflammatory effects of CW Nd:YAG contact laser were compared to those of conventional cryopexy. CW Nd:YAG light transmitted by fiber optic cable and sapphire crystal was applied transsclerally to the ciliary body of pigmented and albino rabbits. Cyclocryopexy was given to a comparable second group. The intraocular pressure (IOP), flare, iritis, cells and conjunctival hyperemia were monitored clinically up to 3 weeks. The breakdown of the blood-aqueous barrier and time course of ocular inflammation was similar for both modalities and IOP was -12.2 +/- 4.2 mm Hg for laser cyclopexy and -15.1 +/- 5.4 mm Hg for cyclocryopexy at 3 weeks. Ciliary body lesions were noted in both groups. Overall, albino rabbits showed less histological damage and faster recovery of IOP. Contact cyclophotocoagulation and cyclocryopexy can be considered models of ocular injury. The similarities in ocular irritative response suggest a similar pathophysiologic mechanism underlying the pressure behavior in both thermal mode injuries.

The effect of therapeutic ultrasound on the average of multiple intraocular pressures throughout the day in therapy-resistant glaucoma

The effect of therapeutic ultrasound was evaluated in 17 patients with therapy-resistant glaucoma by comparing average intraocular pressure (IOP) curves measured before and 3-4 months after insonification. The insonification regimen was standardized; the medication was identical during both pressure curve measurements. The average IOP decrease was 44% +/- 24 SD (range, 73% decrease to 6% increase). In 82% of the patients the IOP decrease was more than 34%. There was no correlation between the percentage of IOP decrease and the average IOP before insonification (correlation coefficient, 0.21; P = 0.41).

Effect of melatonin on intraocular pressure

We studied the effect of orally administered melatonin on intraocular pressure in humans. We suppressed serum melatonin levels by exposing our subjects to bright light. Our experiments suggest that melatonin lowers intraocular pressure in man. This may prove to be a therapeutically useful agent since melatonin appears to be relatively free of side effects and is effective in small quantities.

A controlled five-year follow-up study of laser trabeculoplasty as primary therapy for open-angle glaucoma

We followed up 32 eyes of 32 patients with early glaucoma (22 with capsular glaucoma and ten with simple glaucoma) who received laser trabeculoplasty as a primary therapy. These eyes were compared with a matched control group of 32 eyes treated with medication initially. The success rate (intraocular pressure below 22 mm Hg with laser alone or medication alone) at five years was 50% (16 of 32 eyes) in the laser-treated group and 22% (seven of 32 eyes) in the control group (P less than .02). The control group required more modifications of their therapy to control intraocular pressure. The neuroretinal rim area in the control eyes decreased 2.5 times as much as in the laser group (P = .017). Changes in the Friedmann visual fields did not differ significantly between the two groups.

Factors affecting the results of argon laser trabeculoplasty in open-angle glaucoma

Argon laser trabeculoplasty (ALT) was performed in 232 eyes of 180 patients affected by uncontrolled primary open-angle glaucoma (POAG), exfoliation syndrome glaucoma (ESG) or pigment dispersion syndrome glaucoma (PDSG). Mean follow-up was 9 months (3-22). Mean IOP change was -21.6% (+/- 19) from the initial value. The effect of IOP was larger in patients with ESG, PDSG, and in POAG cases with more pigmented trabecular meshwork. No relationship was found between IOP changes and age or refraction of patients; the association with iridoplasty did not influence final results. An Octopus computerized perimeter was used for pre and post-treatment visual field tests. In 113 eyes Octopus exams met the requirements for quantitative analysis. In this group 17% of visual field improved, 64% remained stable and 19% worsened. A good functional response was more frequent among the eyes with less advanced disease.

Treatment of glaucoma with high-intensity focused ultrasound

This report is a summary of results for 170 eyes of patients with refractory glaucoma treated with high-intensity focused ultrasound. The results are analyzed in terms of the effectiveness of various treatment regimens, complications, and classifications of the patient population according to such factors as age and etiology. The mean pretreatment intraocular pressure (IOP) for the ensemble of patients treated with optimal intensity levels was 38.6 mmHg. Whereas only 10% of these patients had an IOP of 25 mmHg or less prior to treatment, 90% had an IOP of 25 mmHg or less within 3 months of treatment. At 1 year after a single treatment, 65% of patients still maintained intraocular pressures of 25 mmHg or less, and 56% had pressures of 22 mmHg or less. The effectiveness of retreatment of failed or unresponsive cases was also investigated and found to have a degree of success comparable to that of initial treatments.

Q-switched neodymium: YAG laser surgery of the vitreous

Fifty-nine eyes underwent vitreous surgery (vitreolysis) with the Q-switched Nd: YAG laser. This was used to cut vitreoretinal bands and membranes in 16 eyes and to clear persistent vitreous opacities in 25 eyes. The use of appropriate specialized contact lenses and modification of the standard slit-lamp delivery system were essential for vitreous YAG laser surgery. Successful results occurred in eyes where the target tissues were located at distances greater than 2 mm from the crystalline lens and the retina. Vision was improved in 18 eyes, unchanged in 40 eyes, and worse in 1. Complications included focal opacities of the crystalline lens in 5 eyes, retinal holes with detachment in 1 eye, and minor retinal hemorrhages in 4. Methods of preventing complications are discussed.

The effect of argon laser trabeculoplasty on the rate of filtering surgery

We examined the impact of argon laser trabeculoplasty (ALT) on the overall rate of filtering surgery on a resident service. From 1981 through 1984, 121 eyes underwent ALT for treatment of uncontrolled primary open-angle glaucoma despite maximum tolerated medical therapy. Mean intraocular pressure decreased from 27 +/- 4 mmHg to 20 +/- 5 mmHg (median follow-up, 9 months). From 1978 through 1981, the mean annual rate of filtering surgery was 16. Only one filtering procedure was performed in 1982, the first full year of ALT use. However, 15 filtering procedures were performed in 1983 and 18 were performed in 1984. Despite a large number of apparently effective ALT treatments and despite an overall reduction in outpatient visits of 20%, the rate of filtering surgery has returned to the pre-ALT level. This suggests that ALT may be effective in delaying the need for surgery, but in many cases it probably does not prevent surgery.

Timolol and intra-ocular pressure elevation following neodymium: YAG laser surgery

The intra-ocular pressure in 76 patients, undergoing Neodymium: YAG laser surgery was measured just before treatment, and one and two hours afterwards. The fellow eye served as a control. Serious elevation of the intra-ocular pressure was demonstrated, especially in capsulotomy in the aphakic eye, to a lesser extent in pseudophakic eyes. Intra-ocular pressure elevation of more than 20 mm was seen in iridectomies. Timolol 1/2% eyedrops given before Neodymium: YAG laser treatment minimized the elevation of the intra-ocular pressure. Prolonged follow-up of the intra-ocular pressure is recommended.

Laser iridectomy. A controlled study comparing argon and neodymium: YAG

Laser peripheral iridectomies were performed on both eyes of 38 patients with acute or chronic primary angle-closure glaucoma or with narrow angles capable of closure. The right eye was treated with the neodymium YAG laser (Nd:YAG) and the left eye with the argon laser. Patients were followed for a minimum of eight months. The mean number of applications to produce iris penetration was six with the Nd:YAG laser and 73 with the argon laser. Visual acuity, postoperative intraocular pressure (IOP), corneal changes, and pigment dispersion were similar in the two groups. Microhyphema was more prevalent in the Nd:YAG iridectomy group. Pupillary distortion, iritis, and late failure of patency were more frequent in the argon laser group. Nd:YAG laser iridectomies require fewer applications and produce less inflammation. This controlled study demonstrates that when properly and carefully performed, the Nd:YAG laser is at least as effective and appears to be as safe as the argon laser for performing peripheral iridectomies.

Use of the YAG laser with a seven-micron spot in pseudophakic eyes

We report on 216 cases of posterior capsulotomy performed with a LASAG Microruptor II YAG laser in patients with posterior chamber intraocular lenses. In 108 cases, the YAG laser was used in multimode with a 70-micron spot and 3.5 mJ to 5.0 mJ of energy; in the other 108 cases, the laser was used in fundamental mode with a 7-micron spot and 0.7 mJ to 1.2 mJ of energy. In the first group, IOL damage was seen in 10.2% of cases, uveitis developed in 0.4% of patients, and transient eye pressure elevation was noted in 6.5% of patients. In the second group, neither IOL damage nor uveitis occurred, and only two cases (1.8%) developed transient pressure elevation.

Secondary surgical and neodymium-YAG laser discissions

Between November 1978 and June 1984, 161 surgical and 102 neodymium-YAG laser discissions were performed. The incidence of discission in patients with a mean three-year follow-up after extracapsular surgery was 22.1% (39 of 176 eyes) after extracapsular cataract extraction alone and 14.5% (81 of 558 eyes) after extracapsular cataract extraction with intraocular lens implantation (P less than .02); the incidence was 25.5% (47 of 184 eyes) with the transiridectomy clip lens and 9.1% (33 of 364 eyes) with the posterior chamber lens (P less than .001). The average interval between cataract surgery and the discission was 2.4 years. The intraocular pressure was increased in 51% (48 eyes) of the eyes two to five hours after YAG laser discission and was unpredictable in most patients. After surgical discission, the intraocular pressure was increased on the first postoperative day in 13% (18 eyes) of the eyes. With surgical discission, significant complications included vitreous manipulation, wound leak, and intraocular inflammation. Intraocular lens pitting occurred in 20 patients undergoing YAG laser discission. Complications with both procedures included cystoid macular edema, retinal detachment, glaucoma, and closure of a previously adequate discission opening.

Complications associated with the use of the neodymium:YAG laser

The neodymium:YAG laser was used in a consecutive series of 93 eyes. Diagnosis was opacified posterior capsule in 81 eyes of which 52 were pseudophakic, with cystoid macular edema and vitreous strands in eight eyes, pigmented anterior hyaloid in two eyes, opacified anterior capsular flap in one eye and vitreous strand blocking an anterior chamber tube shunt to an encircling band tube in one eye. Despite significant visual improvement and reduction of cystoid macular edema, a variety of complications were seen. These included pitting of the implant in 26 eyes and cracks in four, two of which developed a vitreitis. These occurred more frequently in our earlier cases. Also seen was elevated IOP in six eyes, pupillary block in two, vitreous face rupture in five, cystoid macular edema in four, hyphemas in four, corneal injury in two and acute peripheral retinal hemorrhage in one eye.