Photokinetic Drug Delivery: Near infrared (NIR) Induced Permeation Enhancement of Bevacizumab, Ranibizumab and Aflibercept through Human Sclera

PURPOSE

Permeation studies, with near infrared (NIR) light and anti-aggregation antibody formulation, were used to investigate the in vitro permeation of bevacizumab, ranibizumab and aflibercept through human sclera.

METHODS

A vertical, spherical Franz cell diffusion apparatus was used for this scleral tissue permeation model. A photokinetic ocular drug delivery (PODD) testing device accommodated the placement of NIR LEDs above the donor chambers. An adjustable LED driver/square wave generator provided electrical energy with a variable pulse rate and pulse width modulation (duty cycle).

RESULTS

Exposure to non-thermal NIR light had no effect on mAbs with regard to monomer concentration or antibody binding potential, as determined by SE-HPLC and ELISA. The optimal LED wavelength was found to be 950 nm. Duty cycle power of 5% vs 20% showed no difference in permeation. When compared to controls, the combination of non-aggregating antibody formulation and NIR illumination provided an average transscleral drug flux enhancement factor of 3X.

CONCLUSION

Narrow wavelength incoherent (non-laser) light from an NIR LED source is not harmful to mAbs and can be used to enhance drug permeation through scleral tissue. The topical formulation, combined with pulsed NIR light irradiation, significantly improved scleral permeation of three anti-VEGF antibody drugs.

Use of the Toric Surgical Marker to Aid in Intraoperative Plaque Placement for the USC Eye Physics Plaques to Treat Uveal Melanoma: A New Surgical Technique

BACKGROUND AND OBJECTIVE

To describe a new surgical technique for intraoperative placement of Eye Physics (EP) plaques for uveal melanoma using a toric marker.

PATIENTS AND METHODS

A toric marker is designed for cataract surgery to align the axis of astigmatism; its use was modified in this protocol to mark the axis of suture coordinates as calculated by Plaque Simulator (PS) software.

RESULTS

The toric marker can be used to localize suture coordinates, in degrees, during intraoperative plaque placement. Linear marking using the toric marker decreases potential inaccuracies associated with the surgeon estimating 'clock-hours' by dot placement.

CONCLUSION

Use of the toric marker aided surgical placement of EP plaques. The EP planning protocol is now designed to display the suture coordinates either by clock-hours or degrees, per surgeon preference. Future research is necessary to determine whether routine use of the toric marker improves operative efficiency. [Ophthalmic Surg Lasers Imaging Retina. 2015;46:866-870.].

[Morphologically reasonable application of 1.44 microm Nd:YAG laser in ocular surgery for distant hemostasis in conjunctival and episcleral vessels]

The article discusses morphological changes in bulbar conjunctiva and episclera after experimental exposure to Nd:YAG laser radiation at 1.44 pm in comparison to the effect of diathermal coagulator Mira TR4000. The results proved the use of 1.44 microm Nd:YAG laser in ocular surgery for distant hemostasis morphologically reasonable. Non-contact and directional laser treatment is more delicate as it produces smaller irradiated area. The depth of penetration and tissue heating is very limited. Neither excessive reparation, nor scarring is found in the exposed area. On the contrary, diathermy is a contact procedure associated with irregular distribution of heat, which causes large tissue burns and necrosis with subsequent adherent scar formation.

Rod-like microglia are restricted to eyes with laser-induced ocular hypertension but absent from the microglial changes in the contralateral untreated eye

In the mouse model of unilateral laser-induced ocular hypertension (OHT) the microglia in both the treated and the normotensive untreated contralateral eye have morphological signs of activation and up-regulation of MHC-II expression in comparison with naïve. In the brain, rod-like microglia align to less-injured neurons in an effort to limit damage. We investigate whether: i) microglial activation is secondary to laser injury or to a higher IOP and; ii) the presence of rod-like microglia is related to OHT. Three groups of mice were used: age-matched control (naïve, n=15); and two lasered: limbal (OHT, n=15); and non-draining portion of the sclera (scleral, n=3). In the lasered animals, treated eyes as well as contralateral eyes were analysed. Retinal whole-mounts were immunostained with antibodies against, Iba-1, NF-200, MHC-II, CD86, CD68 and Ym1. In the scleral group (normal ocular pressure) no microglial signs of activation were found. Similarly to naïve eyes, OHT-eyes and their contralateral eyes had ramified microglia in the nerve-fibre layer related to the blood vessel. However, only eyes with OHT had rod-like microglia that aligned end-to-end, coupling to form trains of multiple cells running parallel to axons in the retinal surface. Rod-like microglia were CD68+ and were related to retinal ganglion cells (RGCs) showing signs of degeneration (NF-200+RGCs). Although MHC-II expression was up-regulated in the microglia of the NFL both in OHT-eyes and their contralateral eyes, no expression of CD86 and Ym1 was detected in ramified or in rod-like microglia. After 15 days of unilateral lasering of the limbal and the non-draining portion of the sclera, activated microglia was restricted to OHT-eyes and their contralateral eyes. However, rod-like microglia were restricted to eyes with OHT and degenerated NF-200+RGCs and were absent from their contralateral eyes. Thus, rod-like microglia seem be related to the neurodegeneration associated with HTO.

Structural and biomechanical effects of photooxidative collagen cross-linking with photosensitizer riboflavin and 370 nm UVA light on human corneoscleral tissues

This study quantitatively investigated the immediate effects of a photooxidative collagen cross-linking treatment with photosensitizer riboflavin (RF) and 370 nm UVA light in in vitro human corneoscleral collagen fibrils using histology, thickness, scanning electron microscopy, and atomic force microscopy analyses. Twenty 8 x 2 mm corneoscleral strips were dissected sagittally from donor tissue using a scalpel. Four parameters were investigated, including the density, thickness, adhesion force, and stiffness of corneoscleral tissues before and after the collagen cross-linking treatment. The RFUVA-catalyzed collagen cross-linking treatment led to an increase in the density of both corneal (8%) and scleral (23%) stromal collagens. However, there was no difference in corneoscleral thickness. Furthermore, RFUVA-catalyzed collagen cross-linking treatment led to an increased biomechanical response of corneosclera: 25 and 8% increases in corneoscleral stiffness, and 24 and 22% increases in corneoscleral adhesion force. The collagen cross-linking treatment through RF-sensitized photoreaction may cause structural and biomechanical changes in the collagen fibril network of the cornea and the sclera. This is due to narrowing of the interfibrillar spacing and the stromal edema.

Optical characteristics of the cornea and sclera and their alterations under the effect of nondestructive 1.56-μm laser radiation

Optical properties of cornea and sclera of the eye and their alterations under the effect of 1.56-μm laser radiation are studied. The laser settings corresponded to the laser treatment regimens used (1) to correct the shape of the cornea and change the refraction of the eye and (2) to improve the hydraulic permeability of the sclera in glaucoma cases. A fiber-optical system to investigate the dynamics of the reflected and transmitted scattered laser radiation and a setup with a double integrating sphere to determine the optical properties of the ocular tissues on the basis of the Monte-Carlo simulation of the propagation of light was used. When the radiation characteristics corresponded to the treatment regimens for correcting the shape of the cornea, no noticeable changes were detected in its optical properties. When irradiating the sclera in conditions corresponding to the treatment regimens for improving its hydraulic permeability, the optical characteristics of the tissue showed definite changes. The results obtained as to the dynamics of the optical signals during the course of laser irradiation of the cornea and sclera create prerequisites for designing test systems to be used with novel medical laser techniques for correcting visual abnormalities.

[The study of opportunity of aqueous humor filtration increase after nondestructive laser exposure of sclera in the site of pars plana projection (experimental study)]

Increase of scleral water permeability due to formation of porous structure after exposure of pulsed periodic radiation of erbium-glass optical fiber laser with wave length 1,56 pm was demonstrated in experimental study of cadaver human eyes in vitro and eyes of experimental animals (rabbits) in vivo. Simultaneous complex laser exposure of pars plana and ciliary processes results in summation of morphological changes that provide decrease of aqueous humor secretion, uveal drainage and extension of suprachoroid space. A base for new noninvasive technology of nondestructive laser exposure in glaucoma treatment is established.

Effect of cross-linking with riboflavin and ultraviolet A on the chemical bonds and ultrastructure of human sclera

This study examined the effect of the cross-linking with riboflavin-ultraviolet A (UVA) irradiation on the chemical bonds and ultrastructural changes of human sclera tissues using Raman spectroscopy and atomic force microscopy (AFM). Raman spectroscopy of the normal and cross-linked human sclera tissue revealed different types of the riboflavin-UVA and collagen interactions, which could be identified from their unique peaks, intensity, and shape. Raman spectroscopy can prove to be a powerful tool for examining the chemical bond of collagenous tissues at the molecular level. After riboflavin-UVA treatment, unlike a regular parallel arrangement of normal collagen fibrils, the AFM image revealed interlocking arrangements of collagen fibrils. The observed changes in the surface topography of the collagen fibrils, as well as in their chemical bonds in the sclera tissue, support the formation of interfibrilar cross-links in sclera tissues.

Long-term biomechanical properties of rabbit sclera after collagen crosslinking using riboflavin and ultraviolet A (UVA)

PURPOSE

Scleral crosslinking by the photosensitizer riboflavin and ultraviolet A (UVA) has been shown to increase significantly the scleral biomechanical rigidity and might therefore become a possible sclera-based treatment modality for progressive myopia. In the present study, the long-term effect of the new crosslinking method on biomechanical properties was investigated in the rabbit sclera.

METHODS

A 10 x 10 mm sector of the equatorial sclera of nine Chinchilla rabbit eyes was treated in vivo using a UVA double diode of 370 nm with a surface irradiance of 3 mW/cm(2) and application of 0.1% riboflavin-5-phosphate drops as photosensitizer for 30 min. Three days, 4 months and 8 months postoperatively, biomechanical stress-strain measurements of the treated scleral strips were performed and compared to contralateral control sclera using a microcomputer-controlled biomaterial tester. In addition, routine histological controls were performed.

RESULTS

Following the crosslinking treatment, Young's modulus was increased by 320% after 3 days, 277% after 4 months and 502% after 8 months, and ultimate stress by 341% after 3 days, 131% after 4 months and 213.8% after 8 months versus the controls. The decrease in ultimate strain was between 24% and 44.8%. On histology, no tissue damage was detected.

CONCLUSION

Our new method of scleral collagen crosslinking proved very effective and constant over a time interval of up to 8 months in increasing the scleral biomechanical strength. Therefore, the new treatment might become an option for strengthening scleral tissue in progressive myopia and other conditions associated with weakened sclera. There were no side-effects on the retina or retinal pigment epithelium. The new crosslinking treatment could now be tested in a suitable myopia model (like the tree shrew) and finally in human eyes.

[Comparative analysis between sclera treated with glycerin and sclera treated with gamma irradiation, alkali and glycerin in the reconstruction of anophthalmic socket: experimental study in rabbits]

PURPOSE

To compare two sclera decontamination methods: treatment with glycerin versus treatment with gamma irradiation, alkali and glycerin, aiming to detect the clinical and histological alterations in rabbit anophthalmic sockets reconstructed with sclera-involved polymethylmethacrylate spheres.

METHODS

Thirty-nine New Zealand-breed rabbits were divided into two groups: group I, whose animals were submitted to enucleation of one eye and reconstruction with a polymethylmethacrylate sphere involved in glycerin-treated sclera; group II, where there was enucleation, and reconstruction performed with a polymethylmethacrylate sphere involved in sclera treated with gamma irradiation, alkali and glycerin. The two groups were observed at four moments, at 7, 21, 42 and 84 days after surgery. Preset times elapsed, the rabbits were euthanized, sockets were exenterated, the material was processed for embedment in paraffin, cut into 5 microm sections thick and stained with hematoxylin-eosin and Masson's trichrome techniques. The scleras were submitted to morphometric and semiquantitative analysis. Results were compared by Mann-Whitney's non-parametric test.

RESULTS

Comparative analysis of vascularization of the surgical interface pointed out a significative difference in the evaluation done 21 days after the implant (P<0.001), with group II showing greater neovascularization. Comparison of the fibrous capsule thickness displayed a significative difference at moments corresponding to 21 days (P<0.001) and 42 days (P<0.001). At both moments, group II presented a thicker fibrous capsule than group I. Likewise, there was variation in sclera thickness, being thicker in group II, at the 21-day post-implant (P=0.003) moment, and at the 42-day moment (P=0.024), as well. Along the experimental period, when groups were analyzed we could observe statistically significative diminution of vascularization in the surgical interface, in group I, as well as in group II, at the moment of 7, 21, 42 and 84 days.

CONCLUSION

When used as coating on the polymethylmethacrylate implant for the reconstruction of rabbit anophthalmic socket, the sclera treated with gamma irradiation, alkali and glycerin reacted similarly to the traditionally used glycerin-treated sclera. The two treatments induced a similar inflammatory response. The formation of neovessels, thickness of fibrous capsule and of sclera developed differently in the two groups. Nevertheless, they presented similar results at the end of the 84-day observation period. There was no significant difference between the two groups, with regard to sclera preservation.

Evaluation of a KTP (potassium-titanyl-phosphate) 532 nm laser for endovaporization of choroidal melanomas

BACKGROUND AND OBJECTIVES

The purpose of this in vitro study is to evaluate the use of the KTP (potassium-titanyl-phosphate) 532 nm laser for future use in endovaporization of large choroidal melanomas.

STUDY DESIGN/MATERIALS AND METHODS

A KTP 532 nm green laser coupled to a 0.3 mm fiberoptic probe was used to perform in vitro studies on human cadaver eyes and on one enucleated melanoma eye. The specimens were examined by histological staining (Masson-Trichrome) and scanning electron microscopy (SEM).

RESULTS

Histological analysis of sclera, choroid, retina, and melanoma revealed different zones of collateral thermal tissue damage. These zones were analyzed quantitatively. We determined the best suitable laser parameters and the time for sclera penetration.

CONCLUSIONS

The KTP-laser showed good potential in intraocular vaporization of choroidal melanomas. However, great differences in laser absorption between sclera and melanoma can cause significant complications such as perforation.

Cross-linking of scleral collagen in the rabbit using riboflavin and UVA

PURPOSE

Scleral biomechanical weakness and thinning is known to be one of the main factors in the pathogenesis of progressive myopia. We tried to strengthen rabbit sclera by cross-linking scleral collagen using ultraviolet A (UVA) and the photosensitizer riboflavin.

METHODS

Circumscribed 10 x10 mm sectors of the posterior--equatorial sclera of six chinchilla rabbit eyes were treated in vivo using a UVA double diode with 4.2 mW/cm(2) UVA at 370 nm and applying 0.1% riboflavin-5-phosphate drops as photosensitizer for 30 min. 1 day postoperatively biomechanical stress--strain measurements of three treated scleral strips were performed using a microcomputer-controlled biomaterial testing device and compared to non-treated contralateral control sclera. In addition, three treated eyes were examined histologically by light microscopy, TUNEL staining and electron microscopy to evaluate side-effects.

RESULTS

Following the cross-linking treatment, the ultimate stress was 11.87+/-1.8 MPa versus 3.63+/-0.40 in the controls (increase of 227.9%, p=0.014), Young's modulus 27.67+/-4.16 MPa versus 4.9+/-.15 MPa in the controls (increase of 464.7%, p=0.021) and ultimate strain 92.2+/-7.43% versus 165.63+/-19.09% in the controls (decrease of 54.52%, p=0.012). Histologically, serious side-effects were found in the entire posterior globe with almost complete loss of the photoreceptors, the outer nuclear layer and the retinal pigment epithelium (RPE).

CONCLUSIONS

Our new method of scleral collagen cross-linking proved very effective in increasing the scleral mechanical strength; the new treatment may represent an option for strengthening scleral tissue in progressive myopia. However, serious side-effects were observed in the outer retina. In future studies these side-effects could be avoided by reducing the irradiation dose below the cytotoxic level of the retina. Before its clinical application, the new method should be tested in a myopia animal model.

Collagen crosslinking of human and porcine sclera

PURPOSE

To develop methods of collagen crosslinking the sclera to increase its biomechanical strength for the treatment of progressive myopia.

SETTING

Department of Ophthalmology, Technical University of Dresden, Dresden, Germany.

METHODS

Sagitally oriented scleral strips of 4.0 mm x 8.0 mm were prepared from 5 human postmortem eyes and 50 porcine cadaver eyes and treated with various crosslinking methods including physical crosslinking by combined riboflavin-ultraviolet A (UVA) or rose bengal/white-light irradiation and chemical crosslinking by incubation with glucose, ribose, glyceraldehyde, and glutaraldehyde solutions. Parallel scleral strips from the same eye were used as untreated controls. After crosslinking, stress-strain measurements of the treated and control scleras were performed using a microcomputer-controlled biomaterial tester.

RESULTS

A statistically significant increase in scleral rigidity was found after crosslinking with riboflavin-UVA, with a rise in stress in treated porcine (157%) and human (29%) sclera, and after treatment with glyceraldehyde, with a rise in stress in treated porcine (487%) and human (34%) sclera, and with glutaraldehyde, with a rise in stress in treated porcine (817%) and human sclera (122%) at 8% strain. The other crosslinking methods proved ineffective. The untreated human sclera had a 4-fold higher stiffness than porcine sclera.

CONCLUSIONS

Collagen crosslinking induced by riboflavin-UVA, glyceraldehyde, and glutaraldehyde led to a significant increase in biomechanical strength in human and porcine sclera. Using these methods, collagen crosslinking might become a treatment possibility for progressive myopia. Future animal and clinical studies must determine the best application methods and the long-term effects of increased crosslinking on scleral rigidity and prevent potential toxicity or serious side effects.

Eyelid and scleral necrosis following bare iridium-192 seed for retinoblastoma

A 2 1/2-year-old girl with a history of bilateral retinoblastoma underwent primary enucleation of the right eye and was referred for further management of persistent tumor in the fellow eye. Previous treatment of the left eye included external beam radiotherapy, systemic chemotherapy, laser photocoagulation, cryotherapy, and direct scleral application of a bare iridium-192 radioactive seed. Examination revealed focal full-thickness necrosis of the left upper and lower eyelid and a large inferonasal viable retinoblastoma tumor with overlying retinal detachment. Systemic chemotherapy and direct laser photocoagulation were administered. Four months after presentation, the patient developed focal scleral necrosis with 360 degrees hemorrhagic choroidal detachment. Enucleation was performed and histopathologic examination demonstrated full-thickness scleral necrosis with adjacent viable retinoblastoma tumor cells. Follow-up examinations showed no evidence of recurrent or metastatic tumor. This case is the first report of scleral necrosis following combined modality treatment of retinoblastoma.

[Experimental and morphological as well as physical and chemical interaction of laser radiation of a close infrared range with the fibrous eye membrane]

Experimental-and-morphological as well as physical-and-chemical changes occurring in the eye fibrous coat tissues, i.e. the cornea and sclera, at non-ablation impact of fiber laser radiation (Er-glass) with a wavelength of 1.56 mcm were analyzed. Necrobiotic or necrotic changes occur in the tissues with regard for laser radiation capacity and impact duration; subsequently, the regenerative process involving a retraction of the sclera and a flattening of the cornea takes place in the end. When the cornea is heated by fiber laser radiation with a minimally possible intensity (up to 0.3 Wt), a temporary weakening is observed in the corneal rigidity. Should it be accompanied by a simultaneous occurrence of retraction forces coming from the sclera (at its coagulation), it can be used to change, in the clinical controllable mode, the corneal curvature radius.

Transscleral thermotherapy: short- and long-term effects of transscleral conductive heating in rabbit eyes

OBJECTIVE

To determine the highest safe treatment temperature, at 30- and 60-second exposure durations, for transscleral thermotherapy (TSTT) of choroidal melanoma.

METHODS AND DESIGN

Transscleral conductive heating was performed in 15 rabbits at 50 degrees C to 70 degrees C for 30 or 60 seconds. The thermal lesions in the ocular fundus were monitored for 4 months with ophthalmoscopic, photographic, and fluorescein angiographic examination. Histologic examination included polarized light microscopy.

RESULTS

The effect of TSTT was similar for both exposure durations. Vascular occlusion in the retina and choroid developed at temperatures of 55 degrees C and higher. After heating at 60 degrees C, scleral collagen fibers developed a minimal undulation; at 65 degrees C, they became clearly undulated. The undulation resolved in the 3 to 4 months after heating. Heating at 70 degrees C caused persistent severe damage to the sclera. Retinal tears developed after heating at 65 degrees C and 70 degrees C.

CONCLUSIONS

A temperature of 65 degrees C was found to be the highest temperature that did not cause permanent damage to the sclera at both exposure durations. A temperature of 60 degrees C may be the optimal temperature for TSTT of choroidal melanoma because retinal tears may develop at 65 degrees C.

CLINICAL RELEVANCE

In TSTT, the temperature levels reached are cytotoxic for choroidal melanoma as well as intrascleral tumor cells. Occlusion of choroidal vessels induced by TSTT may contribute to tumor necrosis because these vessels serve as feeder vessels for the tumor.

Phacoemulsification and thermal wound injury

The technique of lens nucleus phacoemulsification has revolutionized cataract surgery. However, the production of ultrasound energy is associated with heat generation that can result in damage to ocular tissue, in particular the corneoscleral wound site. Thermal damage to the corneoscleral wound site may result in difficulty with wound closure and consequent risk of wound leakage, as well as damage to the adjacent corneal stroma and endothelium, fistula formation, and the induction of high degrees of post-operative astigmatism. The loss of adequate flow of irrigation fluid around the phacoemulsification tip is the key factor in the development of phacoemulsification-induced thermal injury. Use of excessive ultrasound power and production of excessive frictional forces generated by contact of the vibrating phacoemulsification needle with the irrigation sleeve are also factors involved. In the event of a "phacoburn," a specialized "gape suture" may help minimize surgically-induced astigmatism. The degree of induced astigmatism tends to wane over time; astigmatic keratotomy is an option in the setting of high degrees of residual astigmatism.

Cellular photoablation to control postoperative fibrosis in filtration surgery: in vitro studies

The purpose of this study was to evaluate the feasibility of cellular photoablation using fluorescence-generated photoreaction products as a method to control postoperative fibrosis in filtration surgery. The fluorescent probe, 2', 7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, acetoxymethyl ester (BCECF-AM) is a cell membrane permeable compound rendered membrane-impermeable and fluorescent upon cleavage by intracellular esterases. Human scleral and Tenon's capsule fibroblasts were cultured and used as the target cells. Uptake and retention of the probe were determined with a fluorescence multi-well plate reader. Fibroblasts with or without intracellular probe were irradiated under conditions of fluorescence microscopy with diffuse blue light (450-490 nm, 1.68x10(2)mW m(2-1)). The viability of cells was examined by trypan blue exclusion and crystal violet test. To better mimic a wound healing process the effect of cellular photoablation was verified in artificial lesions produced in cultured monolayers loaded with different concentrations of the probe. Uptake and retention of BCECF-AM is dependent on ambient concentration. When incorporated the probe is lethal to those cells exposed to the appropriate photo-irradiation. Cells exposed to BCECF-AM (for 45 min) at a concentration of approximately 10 microm and irradiated for 1 min resulted in 100% cell death. Cellular photoablation in contrast to chemotherapeutic agents acts only on the targeted cells. This method shall be pursued as an alternative therapy to control postoperative fibrosis in filtration surgery.

Comparison of episcleral plaque and proton beam radiation therapy for the treatment of choroidal melanoma

PURPOSE

To compare the efficacy of iodine-125 (125I) and ruthenium-106 (106Ru) episcleral plaque radiation therapy and proton beam radiation therapy (PBRT) in the treatment of choroidal melanoma.

DESIGN

A retrospective, nonrandomized comparative study.

METHODS

Charts of patients treated with 125I, 106Ru, and PBRT for choroidal melanoma between January 1988 and June 1996 at St. Bartholomew's Hospital and Moorfields Eye Hospitals were reviewed.

MAIN OUTCOME MEASURE

Local control of choroidal melanomas after 125I, 106Ru, or PBRT.

RESULTS

A total of 597 patients were identified (125I = 190, 106Ru = 140, PBRT = 267). Patients treated with 106Ru had a significantly greater risk of local tumor recurrence than did patients treated with either 125I (P = 0.0133; confidence interval [CI], 1.26-7.02; risk ratio, 2.97) or PBRT (P = 0.0097; CI, 1.30-6.66; risk ratio, 2.94). A stepwise Cox proportional hazard model found maximal basal diameter to be a significant covariate (P = 0.0033).

CONCLUSION

Patients treated with 106Ru had a significantly greater risk of local tumor recurrence than did those patients treated with either 125I or PBRT.

Distribution of photon absorption rates across the rat retina

1. An investigation into the distribution of light intensity across the rat retina was carried out on excised, intact rat eyes exposed to Ganzfeld illumination from a helium-neon laser (543 nm). 2. Some of the light entering the eyes exits through the sclera where its intensity can be monitored with an optical 'pick-up' that samples the intensity coming from a small region of external sclera and underlying retina. The spatial resolution of the pick-up is such that it samples light that has passed through ca 2 % of the rods in the rat eye. 3. Some of the laser light is absorbed by the rod pigment, rhodopsin, which gradually bleaches. Bleaching in the retina, in turn, causes an exponential increase in intensity emanating from the sclera. By monitoring this intensity increase, we are able to measure two important parameters in a single bleaching run: the local rhodopsin concentration and the local intensity falling on the rods. 4. With an ocular transmission photometer, we have measured both the local intensity and the local rhodopsin concentration across wide regions of rat retina. Both pigmented and albino rats were studied. 5. The distributions of rhodopsin and intensity were both nearly uniform; consequently, the product, (rhodopsin concentration) x (intensity), was similarly nearly equal across the retina. This means that the initial rate of photon absorption is about the same at all retinal locations. 6. Interpreted in terms of photostasis (the regulation of daily photon catch), this means that the rate of photon absorption is about the same in each rod, viz. 14 400 photons absorbed per rod per second. Since this rate of absorption is sufficient to saturate the rod, one possible purpose of photostasis is to maintain the rod system in a saturated state during daylight hours.

Results of histo-pathologic examination of three enucleated eyes with a choroidal melanoma after strontium-90 irradiation

Three patients with a choroidal melanoma, treated with HDR (High Dose Rate) Strontium-90 brachytherapy, underwent an enucleation. Radiation effect was only visible at the irradiation zone with a brisk transition to normal tissue. Tumour was replaced by necrotic and scar tissue. The underlying sclera had a markedly reduced number of fibrocytes, but no structural alteration of the collagen stroma.

Transscleral ciliary body photodynamic therapy using phthalocyanine and a diode laser: functional and morphologic implications in albino rabbits

BACKGROUND AND OBJECTIVES

To evaluate the morphologic and functional effects of ciliary body photodynamic therapy (PDT) using phthalocyanine and a diode laser.

MATERIALS AND METHODS

The upper half of the left eye ciliary body of 16 albino rabbits was irradiated transsclerally using a 670-nm diode laser (400 mW/cm2) after intravenous injection of phthalocyanine (6 mg/kg). The animals were observed for a maximum of 2 months by means of tonometry, biomicroscopy, and fundus examination. At the end of the follow-up period, they were killed and their eyes were prepared for light and electron microscopy.

RESULTS

Transscleral PDT resulted in intraocular pressure (IOP) reduction in the treated eye, which lasted about 2 weeks. During this time, the treated eye had IOP values that were significantly lower than its baseline IOP values and the IOP values of the untreated eye (P < .05). One month after the procedure, the IOP had returned to baseline values. Histologic examination revealed vascular endothelial cell damage causing vascular thrombosis in the treated areas. The architecture of the two ciliary epithelium layers showed a significant abnormality. Disappearance of epithelial apical junction complexes and loss of the normal b-cytomembrane enfolding were observed in the course of electron microscopic examination. Large intercellular spaces between epithelial cells were noticed. All of these changes had subsided by the end of the second postoperative month.

CONCLUSION

Transscleral phthalocyanine-mediated PDT with the parameters used in this experiment results in significant but temporary functional and morphologic alterations in the ciliary bodies of albino rabbits.

Hyperbaric oxygen therapy for beta-radiation-induced scleral necrosis

BACKGROUND

Beta-radiation has been used since 1950 as a postoperative measure to reduce the recurrence of pterygia. Scleral necrosis has been a major complication after radiotherapy that has led to perforation of the globe, endophthalmitis, and visual loss in some cases.

METHOD

A patient is presented in whom scleral necrosis developed 25 days after a pterygiectomy with bare sclera technique followed by 3000 cGy in 3 weekly, divided doses of strontium 90. After a conjunctival graft failure, the patient was treated with hyperbaric oxygen therapy.

RESULTS

The sclera revascularized and returned to nearly normal thickness after 14 sessions of hyperbaric oxygen therapy.

CONCLUSION

Hyperbaric oxygen therapy may be an effective treatment for acute scleral necrosis after postoperative beta-radiation.

Microwave cyclodestruction: evaluation on human eyes

AIMS

The study was set up to evaluate the effect of microwave cyclodestruction on human eyes.

METHODS

Two human eyes were studied. For treatment a horn shaped 5.8 GHz microwave applicator and fibre optic thermometry were used. Just before enucleation, the rectangular (2 x 3 mm) microwave aperture was placed onto the conjunctiva at a position 1-2 mm posterior to the corneal scleral limbus. Each of three to four treatment spots was targeted to receive a thermal dose of 54 degrees C for 1 minute. Clinical, gross, and histopathological evaluations were performed.

RESULTS

Clinical evaluations of the treatment sites (immediately after microwave application) revealed no evidence of conjunctival or scleral damage. Trace fluorescein 2% uptake was noted within the targeted zones. The first eye was sectioned along the equatorial axis. Examination of the ciliary body and pars plana revealed whitening of the ciliary processes and depigmentation. Histopathological evaluations revealed ciliary epithelial necrosis with pigment dispersion. The vascularity of the ciliary processes showed focal disruption and haemorrhage. The underlying ciliary muscle and sclera appeared to be unaffected. No other findings could be attributed to microwave cyclodestruction.

CONCLUSION

The results of this phase I toxicity study suggest that microwave heating can be used to damage preferentially the epithelial layers of the human ciliary body.

Optical and thermal mechanisms related to the design of laser sclerostomy

Collateral, thermally induced structural damage during laser sclerostomy ab interno or ab externo was investigated theoretically and compared with experimental results. We show that collateral heat damage in contact strategies using fiber delivery is mainly due to heat conductivity following explosive ablation. Electron micrographs of perforated porcine eyes show that the damage is only weakly dependent on the laser wavelength. The experiments also demonstrate that simultaneous application of laser irradiation and pressure with the fiber tip yield efficient perforation of scleral tissue even when the weakly absorbed radiation of Nd:YAG or diode lasers is employed.

Bilateral streptococcal corneoscleritis complicating beta irradiation induced scleral necrosis

Images

Microwave-induced retinal destruction with sparing of sclera and choriocapillaris

We studied the effect of short-term hyperthermia on sclera, choroid, and retina by delivering microwave radiation (2.45 GHz) for 1 minute to 12 eyes of Dutch belted pigmented rabbits. Four eyes each were treated with 43 degrees C, 45 degrees C, and 47 degrees C and followed for 4 weeks. The 43 degrees C group showed minimal disruption of retinal pigment epithelium and outer retina, with pigment migration; the 45 degrees C and 47 degrees C groups showed complete retinal and RPE damage, pigment migration, and glial proliferation. At the same time, the sclera and choroid in all of the eyes remained essentially unchanged. We conclude that microwave-induced hyperthermia can create retinal scarring without significant damage to sclera and choriocapillaris. The next experimental step will be to refine the microwave delivery system to ensure predictable and reproducible lesions.

The effect of varying wavelength on subconjunctival scleral laser suture lysis in rabbits

We studied laser suture lysis of subconjunctival scleral sutures in a rabbit eye using selected wavelengths from a dye and diode laser to determine which wavelength caused the least conjunctival damage. We found an oval shaped area of coagulation necrosis surrounding the suture track in the conjunctival substantia propria measuring in depth 61.0 mu for 488 + 514 nm (blue-green), 105.7 mu for 514 nm (green), 148.3 mu for 630 nm (red), and 29.0 mu with 780 + 830 nm (infrared) wavelengths. No observable damage was noted with 585 nm (yellow) or 610 nm (orange) wavelengths. The energy intensity required for suture lysis was similar across each wavelength studied. No damage was observed in the sclera or conjunctival epithelium. These findings suggest that using the yellow or orange wavelength, when performing laser suture lysis clinically, potentially may limit conjunctival damage.

Laser sclerostomy by pulsed-dye laser and goniolens

We describe an ab-interno laser sclerostomy procedure using the method termed dye-enhanced ablation with a slit-lamp delivery system and special goniolens such that only the laser light beam penetrates the anterior chamber. The procedure uses a microsecond-pulsed-dye laser emitting at 666 nm and iontophoresis of methylene blue dye (absorption of 668 nm) into the sclera at the limbus to enhance the absorption of the laser light. We compared the number of pulses needed to perforate excised human sclera at pulse durations of 1.5, 20, and 300 microseconds. Pulse durations of 1.5 and 20 microseconds required 20 pulses or fewer to perforate excised human sclera with pulse energies of 75 to 100 mJ. The ab-interno laser sclerostomy procedure was performed in 54 eyes of Dutch-belted rabbits with pulse durations of 1.5 or 20 microseconds and a 100- or 200-microns incident spot diameter delivered using a CGF goniolens. Full-thickness fistulas were successfully created at both pulse durations in approximately 80% of eyes treated. A range of three to 25 pulses was required to perforate sclera with slightly fewer pulses and lower pulse energies at 1.5 microseconds compared with 20 microseconds. There were no significant complications from the procedure. This technique could permit filtration surgery to be performed on an outpatient basis.

Transscleral microwave cyclodestruction

A 4.6-gigahertz (GHz) microwave applicator was used to ablate the ciliary body in rabbit eyes. High-frequency electromagnetic radiation provides a favorable dose distribution to induce local heating of the ciliary body. For treatment, a 3-mm diameter disc-shaped applicator was placed on the conjunctiva and over the ciliary body. Conjunctival temperatures were monitored during treatment with a built-in thermocouple thermometer located at the center of the disc-shaped antenna. This allowed direct measurement (dosimetry) of the conjunctival temperature during treatment. Using this microwave-based heat-delivery system, doses in a range of 60 degrees for 30 or 60 seconds appeared to cause ciliary body damage with relative sparing of the conjunctiva and sclera.

Effect of transscleral neodymium: YAG cyclophotocoagulation on intraocular lenses

A neodymium: YAG laser operating in the thermal mode was used to irradiate isolated intraocular lenses (IOLs) and to perform transscleral cyclophotocoagulation on pseudophakic autopsy eyes to investigate the potential damage to IOL haptics such irradiation may cause. In the isolated IOLs, 70 mJ of energy deformed and partially melted both polymethylmethacrylate (PMMA) and polypropylene haptics. One of the capsular-fixated PC-IOL haptics in an autopsy eye partially melted when irradiated with the maximum energy level (8.8 J), with the aiming beam focused 1 mm posterior to the limbus and maximal posterior focus offset.

Recurrent pterygia: results of postoperative treatment with Sr-90 applicators

Recurrent pterygia in 42 patients (48 eyes) were treated locally with strontium-90 irradiation from May 1967 to May 1988. The 31 male patients had an average age of 52 years; the 11 female patients, 46 years. All patients underwent surgical resection of the recurrent pterygia with use of the bare-sclera technique. During the immediate postoperative period the surgical site was treated with an Sr-90 applicator (beta irradiation). Doses ranged from 10 to 70 Gy (average, 50 Gy). Follow-up times ranged from 8 to 136 months (median, 14 months). The local control rate was 89%. Four of the five recurrences were in patients treated with doses of 1,000-1,500 cGy (P less than .0002). None of the patients developed cataracts or any other serious complications.

Stimulation of cell division by argon and Nd:YAG laser trabeculoplasty in cynomolgus monkeys

Although laser treatment of the trabecular meshwork is the most common form of surgery for glaucoma, the tissue response to this therapy is still incompletely understood. We applied argon or Nd:YAG laser to the trabecular meshwork of six monkeys. Cell division was identified by injecting tritiated thymidine into the anterior chamber 24 hr after laser application. Autoradiography of tissue sections revealed significantly more labelled cells in eyes treated with laser than in the untreated controls. In addition, cells in neighboring tissues such as iris, ciliary body and sclera showed labelling in association with laser application. Furthermore, comparison of argon-induced lesions with those caused by pulsed Nd:YAG suggests that there are quantitative and qualitative differences in the response of trabecular meshwork and surrounding tissues to these two forms of laser energy.

Transpupillary irradiation of the rabbit retina with the cw-Nd:YAG laser. I. Acute morphologic effects produced using two different pulse forms

The retinas of six pigmented rabbits (12 eyes) were irradiated with a cw-Nd:YAG laser using two different pulse forms, in conjunction with a constant pulse duration of 200 msec and a retinal focus diameter of 200 microns. The first pulse form (a) was characterized by an initial transient, lasting 15-20 msec, with a peak power twice that of the ensuing plateau phase of 180-185 msec. The second pulse form (b) was almost rectangular in shape. Although the average energies (and powers) for each pulse form were identical, almost 20% of this entity was delivered within the first 20 msec for the first pulse form. Impact lesions were examined at the biomicroscopic, light, and electron microscopic levels, and the characteristic morphologic features described for the cw-mode in general. Comparison of the effects produced using each pulse form revealed a number of differences. At low pulse energies (less than 150 mJ) the rectangular pulse form produced a photocoagulation reaction within the outer sensory retina, but when using the pulse form with the initial transient, this effect was superimposed by a degree of mechanical disruption. Ruptures produced within the elastic component of Bruch's membrane first appeared at lower pulse energies (ie, at 75 mJ, as opposed to 150 mJ for the rectangular pulse form) and were more frequent, and choroidal macrohemorrhaging (observed at pulse energies greater than or equal to 200 mJ) occurred only, when this latter pulse form was employed. Each of these phenomena may be attributed to the higher power and energy densities attained during the initial transient, which has disruptive properties. In order to avoid the risk of severe bleeding, these irradiation parameters should be maintained below approximately 6.4 X 10(3) W/cm2 and approximately 0.13 X 10(3) J/cm2.

Focal irradiation of perforating eye injuries

Plaques constructed with 125I were used to irradiate the sites of perforating ocular injuries in rabbits. An approximate dose of 16Gy given over a period of 6 days was shown to significantly reduce intraocular cellular proliferation when irradiation was commenced within 24 hours after injury. If irradiation was delayed until day 5, this reduction in cellular proliferation and intraocular membrane formation did not occur. Smaller radiation doses of approximately 6Gy given within 24 hours post-injury and administered over 6 days also reduced the extent of cellular proliferation but was not as effective as the 16Gy dose.

The role of inflammation in CW Nd:YAG contact transscleral photocoagulation and cryopexy

Cyclodestructive modalities in humans have been shown to be effective when applied 3.5 mm or more posterior to the limbus. Therefore, CW Nd:YAG contact transscleral laser and cryopexy were applied 6 mm posterior to the limbus of pigmented rabbits. The intraocular pressure (IOP), flare, iritis, cells and conjunctival hyperemia were monitored clinically up to 3 weeks. The pressure lowering effect was -7.5 +/- 7.7 mm Hg for laser retinopexy and -14.2 +/- 6.0 mm Hg for retinocryopexy at 3 weeks and was comparable to application of the same modalities directly over the ciliary body. Similarly, induction of intraocular inflammation by injecting 10 micrograms of endotoxin intravitreally lowered IOP significantly. These findings suggest that hypotension may not be directly due to cyclodestruction but may be related to the ocular irritative response and extent of neuroepithelial defect, irrespective of its distance from the limbus.

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 Nd:YAG laser 1.3 u wavelength: in vitro effects on ocular structures

We evaluated the in vitro effects of the 1.3 u wavelength of a Nd:YAG laser using a fiberoptic delivery system, with or without sapphire tips on ocular tissue. Conjunctival and retinal adhesions were achieved best with a noncontact technique compared with a contact method.

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.

Pseudomonas endophthalmitis associated with scleral necrosis

Three cases of pseudomonas endophthalmitis associated with scleral necrosis 3 to 10 years after pterygium excision and beta irradiation are described. The value of prophylactic repair of radiation-induced scleral necrosis and early aggressive management of pseudomonas endophthalmitis are emphasized.

Sterilization of scleral homografts with ionizing irradiation

We devised a method of sterilization and preservation of sclera that we have found reliable and convenient. Gamma irradiation is a highly effective method of sterilization. Airtight, watertight, plastic packaging of frozen irradiated sclera allows for safe long-term storage and for convenient use in the operating room.

Morphological studies about the efficiency of laser beams upon the structures of the angle of the anterior chamber. Facts and concepts related to the treatment of the chronic simple glaucoma

Working at a power density above optical breakdown threshold, irradiation effects upon the angle of the anterior chamber of the Macaca speciosa monkey by a Nd glass Q-switched laser, have been analysed with scanning electron microscopy. Two different damage effects can be identified: openings of Schlemm's canal and the creation of a cyclodialysis, that is opening the uveoscleral outflow routes; the latter may be a more effective one than the former. Also a third mechanism, namely a structural alteration of the trabecular meshwork, at the molecular level by laser action, has been inferred. The physical effects leading to optically induced mechanical damage are discussed. Applicability of such effects upon the morphological findings described here, is limited and to a greater part speculative. A better definition of the physical parameters, required for optimal therapeutical damage effects in the treatment of the wide angle glaucoma may be obtained by trial and error methods, which are guided by the results of electron microscopical analyses of samples obtained from in vivo and in vitro experiments.

Proton irradiation of simulated ocular tumors

Silicone sponges were sutured to the sclera of owl monkeys to create an indentation which would simulate a tumor of the posterior segment of the eye. A tantalum clip inserted in the silicone sponge served as a marker for radiographic localization of the simulated tumors. The acute lesions obtained on the retina and choroid after moderately high doses of proton irradiation suggest that this method of aiming the proton beam will be adquate for human clinical trials.