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

Morphological changes to Schlemm's canal and the distal aqueous outflow pathway in monkey eyes with laser-induced ocular hypertension

Though roughly 30-50% of aqueous outflow resistance resides distal to Schlemm's canal (SC), the morphology of the conventional outflow pathway distal to SC has not been thoroughly evaluated. This study examined the morphological changes along proximal and distal aspects of the conventional aqueous outflow pathway and their association with decreased outflow facility in an experimental model of glaucoma in cynomolgus macaques. Nd:YAG laser burns were made to 270-340 degrees of the trabecular meshwork (TM) of one eye (n = 6) or both eyes (n = 2) of each monkey to induce ocular hypertension. Distinct regions of the TM were left unlasered. Contralateral eyes (n = 5) were not lasered and were utilized as controls. Monkeys were sacrificed ≥58 months after their last laser treatment. All eyes were enucleated and perfused at 15 mmHg for 30 min to measure outflow facility. Two pairs of eyes were also perfused with fluorescein to examine segmental outflow. All eyes underwent perfusion-fixation for 1 h. Anterior segments were cut into radial wedges and processed for light and electron microscopy. Width, height, and cross-sectional area (CSA) of SC were compared between high- and low-flow regions of control eyes, and between non-lasered regions of laser-treated eyes and control eyes. Number and CSA of intrascleral veins (ISVs) were compared between non-lasered and lasered regions of laser-treated eyes and control eyes, and between high- and low-flow regions of control eyes. Scleral collagen fibril diameter was compared between control eyes and lasered and non-lasered regions of laser-treated eyes. Median outflow facility was significantly decreased in laser-treated eyes compared to control eyes (P = 0.02). Median CSA and height of SC were smaller in high-flow regions than low-flow regions of control eyes (P < 0.05). Median width of SC was not significantly different between high- and low-flow regions of control eyes (P > 0.05). Median CSA, width, and height of SC were not different between non-lasered regions and control eyes (P > 0.05). SC was partially or completely obliterated in lasered regions. Median number of ISVs was significantly decreased in lasered regions compared to non-lasered regions (P < 0.01) and control eyes (P < 0.01). Median CSA of ISVs did not differ between these groups (P > 0.05). Median number and CSA of ISVs were not significantly different between high- and low-flow regions of control eyes (P > 0.05). Lasered regions displayed looser scleral stroma and smaller median diameter of collagen fibrils adjacent to the TM compared to non-lasered regions (P < 0.05) and control eyes (P < 0.05). Dense TM, partial to complete obliteration of SC, and a decreased number of patent ISVs may account in part for the decreased outflow facility in monkey eyes with laser-induced ocular hypertension. The significance of changes in scleral structure in laser-treated eyes warrants further investigation.

Tissue-based multiphoton analysis of actomyosin and structural responses in human trabecular meshwork

The contractile trabecular meshwork (TM) modulates aqueous humor outflow resistance and intraocular pressure. The primary goal was to visualize and quantify human TM contractile state by analyzing actin polymerization (F-actin) by 2-photon excitation fluorescence imaging (TPEF) in situ. A secondary goal was to ascertain if structural extracellular matrix (ECM) configuration changed with contractility. Viable ex vivo human TM was incubated with latrunculin-A (Lat-A) or vehicle prior to Alexa-568-phalloidin labeling and TPEF. Quantitative image analysis was applied to 2-dimensional (2D) optical sections and 3D image reconstructions. After Lat-A exposure, (a) the F-actin network reorganized as aggregates; (b) F-actin-associated fluorescence intensity was reduced by 48.6% (mean; p = 0.007; n = 8); (c) F-actin 3D distribution was reduced by 68.9% (p = 0.040); (d) ECM pore cross-sectional area and volume were larger by 36% (p = 0.032) and 65% (p = 0.059) respectively and pores appeared more interconnected; (e) expression of type I collagen and elastin, key TM structural ECM proteins, were unaltered (p = 0.54); and (f) tissue viability was unchanged (p = 0.39) relative to vehicle controls. Thus Lat-A-induced reduction of actomyosin contractility was associated with TM porous expansion without evidence of reduced structural ECM protein expression or cellular viability. These important subcellular-level dynamics could be visualized and quantified within human tissue by TPEF.

The Effect of Laser Trabeculoplasty on Posture-Induced Intraocular Pressure Changes in Patients with Open Angle Glaucoma

Purpose

To investigate the effect of argon laser trabeculoplasty (ALT) on posture-induced intraocular pressure (IOP) changes in patients with open angle glaucoma (OAG).

Methods

Thirty eyes of 30 consecutive patients with OAG who underwent ALT were prospectively analyzed. The IOP was measured using Icare PRO in the sitting position, supine position, and dependent lateral decubitus position (DLDP) before ALT and at 1 week, 1 month, 2 months, and 3 months after ALT.

Results

Compared to the baseline values, the IOP in each position was significantly decreased after ALT (all P < 0.001). During follow-up, the mean percentage of IOP reduction was similar in the sitting and supine positions, but was significantly lower in DLDP than in the sitting or supine positions (all P < 0.05). In terms of postural IOP changes, the IOP in the supine position and DLDP was significantly higher than that in the sitting position at the same time points during the follow-up period (all P < 0.001). The difference between the IOP in the supine position and DLDP during follow-up was significant (all P < 0.001). The extent of IOP differences between any positions did not show significant changes during the follow-up period (all P > 0.05).

Conclusions

ALT appears to be effective in lowering the IOP in various body positions, but the degree of this effect was significantly lower in DLDP. In addition, ALT seemed to have limited effects on posture-induced IOP changes.

Histologic findings after argon laser trabeculoplasty in glaucomatous eyes

The purpose of the study was to determine histologic findings after successful laser trabeculoplasty in eyes with glaucoma. Previous studies have examined eyes in which laser did not lower intraocular pressure, or examined only the region of the laser burn itself. Nineteen autopsy eyes from 14 donors with either primary open angle or pseudoexfoliative glaucoma that had undergone laser trabeculoplasty during life were studied. Clinical records were used to determine the effect of laser in lowering intraocular pressure (IOP). For comparison, 49 glaucomatous eyes that had not undergone laser, and 55 normal eyes were studied as control eyes. Histologic sections from multiple quadrants of each eye were studied by light microscopy, selecting regions between laser spots when the spots were visible. Meshworks from lasered eyes frequently had regions of an expanded juxtacanalicular region associated with numerous superimposed giant vacuoles partially filling Schlemm's canal. This finding was more common in eyes fixed by posterior chamber perfusion, occurring in 90% (9/10) of lasered eyes, while it was found in only 20% (3/15) of glaucomatous control eyes (p=0.01) and 33% (14/43) of normal eyes (p=0.01). The mean decrease in IOP caused by laser was 34%+/-14%, with mean follow-up time before death of 2.7+/-1.7 years. In eyes fixed by immersion the expanded JCT finding was less common, occurring in 22% (2/9) of lasered eyes, but only 9% (3/34) of glaucomatous control eyes and 8% (1/12) of normal eyes. The mean decrease in IOP in these eyes was 39%+/-10%, with mean follow up of 2.3+/-1.0 years until death. Downgrowth of Descemet's membrane over the meshwork was observed in portions of two of the 19 lasered eyes. In conclusion, laser trabeculoplasty associated with decreased IOP appears to cause a remodeling of the juxtacanalicular region of the meshwork. This may be a dynamic, flow dependent finding, as it was more common in eyes fixed by perfusion. Downgrowth of Descemet's membrane over the meshwork was uncommon.

Effect of low fluence diode laser irradiation on the hydraulic conductivity of perfused trabecular meshwork endothelial cell monolayers

OBJECTIVE

To determine the effect of low-fluence diode laser irradiation upon the fluid perfusion characteristics of cultured human trabecular meshwork cell monolayers when placed in a specially designed testing apparatus and subjected to fluid flow driven by a hydrostatic pressure gradient.

METHODS

Two experimental series were conducted. In the first series, six low-fluence diode laser irradiation experiments were conducted using cultured human trabecular meshwork cell monolayers grown on filter supports. Upon reaching a steady state perfusion condition at approximately 5.0 mmHg, monolayers were irradiated at fluencies ranging from 0.2619 to 0.8571 J/cm2 using a diode laser (lambda=810 nm). Perfusion and data collection continued for 45 minutes post-irradiation, after which the monolayers were tested to determine post-experimental viability. Hydraulic conductivity values were analyzed for post-irradiation response in 2.5-minute intervals, grouped by viability. In the second series, a total of six irradiated experiments and six simultaneous nonirradiated control experiments were conducted. Fluence values of 0.3571 J/cm2 (n=3) and 0.4286 J/cm2 (n=3) were used. Hydraulic conductivity values were analyzed for post-irradiation response in 2.5-minute intervals, grouped by irradiated vs. nonirradiated control groups.

RESULTS

In the first series, analysis showed that the viable monolayers exhibited a statistically significant increase in hydraulic conductivity (p<0.001) from 10 minutes post-irradiation onward. The non-viable monolayers exhibited a statistically significant decrease in hydraulic conductivity. In the second series, irradiated groups showed a significant difference (p<0.001) from nonirradiated controls from 10 minutes post-irradiation onward.

CONCLUSION

Low-fluence diode laser irradiation increases hydraulic conductivity in viable perfused TM cell monolayers when compared to baseline values or simultaneous nonirradiated controls while decreasing hydraulic conductivity in nonviable monolayers.

Management of glaucoma: focus on pharmacological therapy

Glaucoma represents a major cause of vision loss throughout the world. Primary open-angle glaucoma, the most common form of glaucoma, is a chronic, progressive disease often, though not always, accompanied by elevated intraocular pressure (IOP). In this disorder, retinal ganglion cell loss and excavation of the optic nerve head produce characteristic peripheral visual field deficits. Patients with normal-tension glaucoma present with typical visual field and optic nerve head changes, without a documented history of elevated IOP. A variety of secondary causes, such as pigment dispersion syndrome and ocular trauma, can result in glaucoma as well. Treatment of all forms of glaucoma consists of reducing IOP. With proper treatment, progression of this disease can often be delayed or prevented. Treatment options for glaucoma include medications, laser therapy and incisional surgery. Laser techniques for the reduction of IOP include argon laser trabeculoplasty and selective laser trabeculoplasty. Both techniques work by increasing outflow of aqueous humour through the trabecular meshwork. Surgical options for glaucoma treatment include trabeculectomy, glaucoma drainage tube implantation and ciliary body cyclodestruction. While each of these types of procedures is effective at lowering IOP, therapy usually begins with medications. Medications lower IOP either by reducing the production or by increasing the rate of outflow of aqueous humour within the eye. Currently, there are five major classes of drugs used for the treatment of glaucoma: (i) cholinergics (acetylcholine receptor agonists); (ii) adrenoceptor agonists; (iii) carbonic anhydrase inhibitors (CAIs); (iv) beta-adrenoceptor antagonists; and (v) prostaglandin analogues (PGAs). Treatment typically begins with the selection of an agent for IOP reduction. Although beta-adrenoceptor antagonists are still commonly used by many clinicians, the PGAs are playing an increasingly important role in the first-line therapy of glaucoma. Adjunctive agents, such as alpha-adrenoceptor agonists and CAIs are often effective at providing additional reduction in IOP for patients not controlled on monotherapy. As with any chronic disease, effective treatment depends on minimising the adverse effects of therapy and maximising patient compliance. The introduction of a variety of well tolerated and potent medications over the past few years now allows the clinician to choose a treatment regimen on an individual patient basis and thereby treat this disorder more effectively.

Membrane formation in the chamber angle after failure of argon laser trabeculoplasty: analysis of risk factors

AIM

Membrane formation in the chamber angle induced by argon laser trabeculoplasty (ALT) can be a cause of treatment failure. Identification of risk factors for membrane formation was the primary aim of this retrospective study.

METHODS

Semithin sections of trabeculectomy specimens obtained in a 2 year period were examined by light microscopy. 122 eyes which were treated with one or more ALTs before trabeculectomy were identified. In 46 eyes, a sufficient amount of trabecular meshwork was obtained to permit morphological analysis.

RESULTS

Eyes treated with ALT had a significantly higher incidence of membrane formation (p=0.001). In 23/46 specimens a cellular and collagenous membrane was observed covering the entire trabecular meshwork. In 14/23 specimens (61%), this membrane was readily visible at low power magnification (x40). Comparison of these eyes with those without membrane formation revealed a significant difference in the number of ALTs (mean 2.07 (SD 0.73) v 1.48 (0.59); p=0.026) and in preoperative IOP (32.0 (9. 7) v 26.2 (8.4) mm Hg; p=0.04).

CONCLUSIONS

Membrane formation in the chamber angle is a frequent cause of ALT failure. The major risk factor is the number of ALTs performed.

Ocular hypotensive effect of pilocarpine before and after argon laser trabeculoplasty

PURPOSE

The purpose of this study was to compare the hypotensive response of human glaucomatous eyes to 1% pilocarpine solution before and after argon laser trabeculoplasty.

METHODS

We designed a prospective, 'repeated measures' study comparing the ocular hypotensive effect of acutely administered 1% pilocarpine solution in 30 medically uncontrolled glaucomatous eyes, before and after argon laser trabeculoplasty.

RESULTS

The pilocarpine-induced IOP decrease was 3.6 +/- 0.59 mmHg before argon laser trabeculoplasty, and 1.8 +/- 0.53 mmHg after laser therapy. In both instances, the pilocarpine hypotensive effect was significantly correlated with pretreatment IOP (p = 0.02, r = 0.41 before argon laser trabeculoplasty, and p = 0.003, r = 0.52 after argon laser trabeculoplasty). We built a 'repeated measurements ANCOVA' model, and found no statistically significant difference between the pilocarpine IOP lowering effect before and after argon laser trabeculoplasty (p = 0.4).

CONCLUSION

Argon laser trabeculoplasty does not modify the IOP lowering effect of 1% pilocarpine solution.

Laser trabeculoplasty for primary open-angle glaucoma

The purpose of the Committee on Ophthalmic Procedure Assessments is to evaluate on a scientific basis new and existing ophthalmic tests, devices, and procedures for their safety, efficacy, clinical effectiveness, and appropriate uses. Evaluations include examination of available literature, epidemiological analyses when appropriate, and compilation of opinions from recognized experts and other interested parties. After appropriate review by all contributors, including legal counsel, assessments are submitted to the Academy's Board of Trustees for consideration as official Academy policy.

Argon and low energy, pulsed Nd:YAG laser trabeculoplasty. A prospective, comparative clinical and morphological study

Argon laser trabeculoplasty (ALT; 1.0 W, 0.1 sec, 50 microns) was performed in right eyes, and low energy, Q-switched Nd:YAG laser trabeculoplasty (Nd:YAGLT; 1.1-4.8 mJ/pulse) in left eyes of 14 patients with primary open-angle glaucoma and in one patient with juvenile glaucoma. The pre-laser intraocular pressure (IOP) was medically uncontrollable (IOP > 21 mmHg). The interocular pressure difference varied between 0 and 3 mmHg. In 9 patients IOP decreased to less than 22 mmHg (success) in both eyes. No statistically significant difference has been revealed with paired t-test in the degree of IOP decrease between ALT and Nd:YAGLT treated eyes during the 1-18 months' follow-up. Treatment variables of Nd:YAGLT had no statistically significant effect on the duration of the post-laser success with Cox-regression. In 4 patients both treatments were ineffective (IOP > 21 mmHg). In 2 patients ALT was successful but Nd:YAGLT was ineffective. In three cases of early bilateral laser failure (IOP > 21 mmHg at the first month visit) trabeculectomy was performed on both eyes in the third post-laser month. Following ALT the uveoscleral meshwork was severely destroyed in the area of the laser spots, and the surrounding collagen fibres were heat-damaged. The meshwork between the laser spots was covered by a membrane formed by migrating endothelial cells. In the uveoscleral meshwork Nd:YAGLT induced severe focal damage surrounded by circumscript shrinkage and scarring. The juxtacanalicular tissue remained free of laser induced damage. No endothelial membrane was present. The results suggest that low energy, Q-switched Nd:YAGLT may represent an alternative method of glaucoma laser surgery.

Immunohistochemical monitoring of the effect of a synthetic fibronectin-like peptide (Arg-Gly-Asp) on the age-related changes in the isolated human corneoscleral tissue of glaucomatous eyes

Fibronectin, an adhesion glycoprotein has been detected and localized in samples of the trabecular meshwork from eight normotensive and 30 glaucomatous human eyes of various ages by means of the indirect immunoperoxidase staining technique. Fibronectin concentration in the trabecular meshwork tissue was evaluated by morphometric analysis. Deposits of the adhesion glycoprotein fibronectin were shown to be spread in the ocular drainage outflow system from patients along with progressive primary open-angle glaucoma (POAG). The fibronectin level quantitatively evaluated in serial cross-sections of trabecular meshwork, appeared to be increased during ageing and more rapidly in the event of POAG development. The active amino acid sequence in fibronectin is an arginine-glycine-aspartic acid tripeptide (Arg-Gly-Asp) and it was shown that the synthetic Arg-Gly-Asp peptide specifically inhibited the adhesive function of fibronectin in trabecular meshwork samples when incubated for 30 min at a concentration of 1-2 mg/ml. The peptide concentration necessary for a 50% decrease of the maximal fibronectin level in the trabecular meshwork specimen derived from patients with moderately advanced POAG stage, was about 1 mg/ml. Immunohistochemical staining exhibited a fainter fibronectin staining in trabecular tissues including the external trabecular layers and subendothelial region of Schlemm's canal, in samples incubated with the synthetic peptide compared with the same tissue explants before peptide treatment. It may be concluded that the adhesion control system is likely to play an important role in development and maintenance of tissue architecture and specialization of the normal human trabecular meshwork.

Skin-derived antileukoproteinase (SKALP), an elastase inhibitor from human keratinocytes. Purification and biochemical properties

Recently we reported a preliminary characterization of anti-elastase activity which is found in cultured keratinocytes and in epidermis from psoriasis patients, but not in normal human epidermis. Here we present evidence that this inhibitory activity is derived from a cationic protein with a molecular mass of 18 kDa. In psoriatic scales the inhibitor is mainly present as a biologically active 11 kDa fragment. Inhibition of human leukocyte elastase is strong (Ki = 2 x 10(11) M) and fast (kon = 10(7) M-1.s-1). Using chromatofocusing, affinity chromatography and gel-permeation FPLC, the 11 kDa fragment was purified from psoriatic scales. This preparation was reduced and carboxymethylated, blotted onto poly(vinylidene difluoride) membrane and subjected to N-terminal gas-phase sequencing. Within a stretch of 16 amino acids a 40% homology was found with the active site of antileukoproteinase (ALP) a known serine proteinase inhibitor present in mucous secretions. We therefore propose the acronym SKALP (skin-derived antileukoproteinase) as a name for this elastase inhibitor.