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Biomedical subjects

E van der Zypen

Publications and source records attributed to E van der Zypen.

At least 19 recordsLinked to original sources
PubMed1997

Transconjunctival application of mitomycin C in combination with laser sclerostomy ab interno: a long-term morphological study of the postoperative healing process.

The precise mechanism whereby mitomycin C enhances IOP reduction in glaucoma filtering surgery still eludes us. Ten rabbits received full-thickness Nd:YAG laser sclerostomy ab interno and adjunctive intraoperative treatment with mitomycin C (MMC) applied topically over the intact conjunctiva (0.5 mg ml-1 for 5 min). A systematic ultrastructural analysis of the fistulas and surrounding tissue was then conducted in conjunction with clinical observations, over the ensuing 10 weeks. In order to investigate also the extent to which MMC impedes fistula occlusion in the absence of percolating aqueous humour, we created non-perforating ('half-thickness') sclerostomies ab interno in three additional rabbits, one with and two without MMC therapy. Transconjunctival MMC application resulted in no serious complications. Eight of the ten full-thickness fistulas remained patent throughout the study, maintaining significant IOP reduction; the other two sclerostomies were compromised by iris incarceration. The MMC-treated, half-thickness canal remained as a tissue-free cul de sac; the two non-treated ones became completely occluded within one week without having recourse to extraocular cell populations. MMC suppressed the migration and proliferation of fibroblasts, macrophages and clump cells from the episclera, sclera, ciliary body and iris root. Repolymerization of heat-damaged collagen was abortive; neosynthesis was not observed. Myofibroblasts were encountered in the vicinity of the sclerostomy canals, and, after the fifth week, these cells were also found to be deployed as a canal-lining layer, delimiting the lumen from the surrounding stroma along most of the fistula length. Towards the external ostium, this layer of myofibroblasts was incomplete or absent. Near the internal ostium, lining cells were derived from the corneal endothelium. The transconjunctival mode of applying MMC appears to be efficient. This antifibrotic drug exerts its inhibitory influence by suppressing not only cell migration and proliferation, but also phagocytic and synthetic activities. However, exposed tissues are not acellular, and amongst the populations present, myofibroblasts are found to dominate the scene. The canal-delimiting cellular lining may play a role in maintaining fistula patency in MMC-treated eyes.

Administration, Topical↗
PubMed1997

Morphological changes elicited in skeletal muscle by a Nd:YAG laser scalpel and electrocautery during surgical reduction of the human tongue.

A Nd:YAG laser scalpel was used for the surgical reduction of a human hyperplastic tongue. This instrument combines a fine cutting precision with haemostatic properties, whereby loss of blood is minimized and the surgeon's field of view unimpeded by flooding from the damaged capillary bed. The coagulative properties of Nd:YAG laser light are, however, insufficient to effect blood flow stasis in larger calibre vessels (arteries > 2 mm; veins > 3-5 mm), such as those located at the base of the tongue. For this purpose, bipolar diathermy (electrocautery) was employed. The ultrastructural changes incurred by skeletal muscle fibres using these two "heat" sources were compared. The damage profile elicited using each modality was similar: coagulation of myofilamentous proteins leads to destruction of fibrillar architecture with concomitant loss of periodic banding; on moving away from the wound margin, characteristic features are gradually restored. As the severity of these heat-induced effects decreases, there is a corresponding increase in superimposed dislocation and tearing phenomena induced by post-treatment swelling.

Adult↗
PubMed1995

[Healing of laser-induced sclerostomy channels in the rabbit].

BACKGROUND: Obliteration of sclerostomy canals during the course of healing is of course undesirable, but before interference with the process can hope to be successful, a stepwise ultrastructural delineation of the course of events provoked by surgucal intervention is essential. In the current study, such an analysis is undertaken, and the changes in tissue morphology discerned correlated with observed modulations in IOP. METHODS: Two cw-Nd:YAG laser sclerostomies were created ab interno on one eye in each of ten rabbits; the unoperated fellow-eyes served as controls. IOP was monitored daily over a twelve-day period. Changes incurred within the canals and to collaterally damaged scleral tissue were analyzed at two-day intervals by light and electron microscopy. RESULTS: The development of well-defined filtering blebs demonstrated the success of the procedure. IOP was significantly lowered during the entire course of the observation period, but after the fifth postoperative day, the blebs had disappeared. Within five days of surgical intervention, morphological analysis revealed the canal to be invaded by macrophages originating from both the iris root and episcleral tissue; these were actively engaged in the phagocytosis of intensely damaged collagen abutting on the lumen. A few days later, the lumen had become occluded by fibroblasts and a dense capillary network. The course of regeneration observed within scleral tissue which had undergone moderate thermal insult, suggests that collagen fibrils undergo a process of repolymerization. CONCLUSIONS: Although the time course of repair is more rapid in rabbits than in humans, the data gleaned nonetheless yield valid information respecting the sequence of events involved in the scarification process. The loose nature of the tissue occluding the canal lumen apparently permits the percolation of fluid through it, thus accounting for the clinical discrepancy between a continuing decrease in IOP and the disappearance of a filtering bleb.

Animals↗
PubMed1995

Irradiation of rabbit retina with diode and Nd:YAG lasers.

AIMS: This study was carried out to compare the effects of continuous wave infrared laser radiation on pigmented and albino rabbit retinas at two wavelengths: 810 nm (diode) and 1064 nm (Nd:YAG). METHODS: Transpupillary laser pulses were applied with a spot size of 200 microns and durations of 200 ms (pigmented rabbits) and 0.5-1 s (albino rabbits). Light and electron microscopic analyses were performed immediately after exposure. RESULTS: In pigmented rabbits, threshold lesions were induced using a power of 100 mW with the diode and 200 mW with the Nd:YAG lasers. Damage was incurred by the retinal pigment epithelium with extension into the superficial and mid choroid posteriorly and into the outer retina anteriorly. In albino rabbits, lesions of comparable anteroposterior extension were identified using a power of 10 W with the Nd:YAG laser. Using diode laser irradiation, a maximum power output of 1.2 W failed to produce discernible lesions. CONCLUSIONS: The observed patterns of morphological damage are produced by complex tissue radiation interactions. In pigmented animals, this was primarily related to absorption of radiant energy by melanin within the retinal pigment epithelium and the choroidal melanocytes. In albino rabbits, laser induced effects occurred as a consequence of multiple scattering, together with absorption within haemoglobin and possibly also within tissue water. The data obtained provide further insight into the biological mechanisms arising from retinal photocoagulation with near infrared lasers.

Acute Disease↗
PubMed1995

Sclerostomy ab interno using long-wave laser modalities: acute morphological effects.

Sclerostomy fistulas were created ab interno in cadaver porcine eyes by an active contact method using a 200-microns-diameter silica optical fiber in conjunction with either Ho:YAG-, Nd:YAG-, or diode-laser light, and a qualitative comparison of the degree of collateral thermal damage induced in each case was undertaken at the light and electron microscopic levels. The apparent breadth of coagulated tissue observed in association with cross-sectioned fistula profiles exhibited considerable local variation, irrespective of the radiation source employed; no intrinsic difference in either the intensity or the extent of the thermal insult incurred was noted between the three laser modalities.

Animals↗
PubMed1994

[Sclerostomy using various laser modalities. Ultrastructure of acute effects].

The effects of Ho:YAG- (free-running mode), Nd:YAG- (continuous wave mode) and diode- (continuous wave mode) laser radiation on the degree of collateral thermal damage realized during the creation of sclerostomy canals ab interno (by an active contact method) were compared morphologically: Both the nature and extent of coagulation occurred by scleral collagen fibrils were found to be independent of the laser modality employed.

Animals↗
PubMed1993

[Surgery with the laser scalpel. Physical principles and clinical effectiveness].

BACKGROUND: The conventional surgical method for cutting vascularized tissue with scalpel and scissors may now be improved by use of the laser scalpel. In particular, the frequent interruption necessitated and the poor visibility caused by bleeding may be mitigated owing to the haemostatic properties of laser light. This instrument may be of particular value for tasks involving extrabulbar structures, such as extraocular muscles and lacrimal tissue, as well as for facial surgery. MATERIALS AND METHODS: The mode of action and physical properties of a new laser scalpel are described and its characteristics compared with those of other instruments on the market. The probe consists of a clad, sculptured silica fibre with a core diameter of 0.6 mm and a conical 0.15 mm-diameter cutting tip. Radiation generated by a low cw-Nd:YAG laser module is fed into the probe, at the exit point of which a maximal power density of 57 kW/cm2 is attained. Radiated laser energy penetrates the tissue as an incision is made, thereby inducing an efficient blood flow stasis which is amplified by thermal energy diffusing from the immediate surroundings of the scalpel tip. RESULTS: In this report, the laser scalpel is implemented for the excision of a vascularized, amelanotic, facial naevus. Both the cutting and haemostatic effects were found to be excellent, occurrence of the latter phenomenon being supported by ultrastructural findings. The healing response was comparable to that observed after conventional surgery. CONCLUSION: The new laser scalpel represents an inexpensive and effective cutting and haemostatic tool powered by a standard cw Nd:YAG laser module, with a wide spectrum of potential applications.

Aged↗
PubMed1993

Versatility of the cw-Nd:YAG and diode lasers in ocular surgery.

The effectiveness of cw-Nd:YAG and diode laser light in performing transscleral chorioretinal coagulation is demonstrated in cadaver porcine eyes using a new contact probe that facilitates irradiation of these layers. Both radiation sources also may be viable alternatives to argon laser light in effecting chorioretinal and cycloendocoagulation.

Animals↗
PubMed1992

Induction of vascular haemostasis by Nd:YAG laser light in melanin-rich and melanin-free tissue.

Haemostasis was effected in vessels of melanin-rich (MR: choroid) and melanin-free (MF: mesentery) rabbit tissue irradiated with a cw-Nd:YAG laser. The following parameters were employed: - pulse duration: 200 ms (MR) and 100 ms (MF); focal spot diameter: 200 microns (MR) and 80 microns (MF); pulse energies: 100-250 mJ (MR) and 0.5-1 J (MF); irradiances: 1.6-4.0 kW cm-2 (MR) and 1-2 x 10(2) kW cm-2 (MF). In melanin-rich tissue, laser energy is absorbed principally by melanin granules contained within the stromal melanocytes. The heat generated in these structures radiates into the surrounding tissue where it is dissipated. The damage thus incurred by the endothelium of blood vessels encompassed within this field triggers the haemostatic mechanism whereby blood flow is arrested. This effect is realized by the formation of an occluding plug of platelets, which is stabilized by the deposition of fibrin, particularly in capillaries, and to a lesser degree in larger vessels of the vascular lamina. In melanin-free tissue, haemoglobin serves as the primary site of energy absorption, which is thus shifted from the stroma to the vessel lumen. Irradiation of vessels in such tissue leads to thermocoagulation of plasma proteins and consequent stasis of blood flow.

Animals↗
PubMed1992

Ultrastructural localization of hyaluronan in myelin sheaths of the rat central and rat and human peripheral nervous systems using hyaluronan-binding protein-gold and link protein-gold.

Neural tissue of central (rat spinal cord) and peripheral origin (rat sciatic nerve, nerve fascicles of rat skin and iris and of human conjunctiva) was processed by osmium tetroxide/microwave fixation and embedded in epoxy resin. Hyaluronan-binding proteins and link proteins coupled to 15-20-nm gold particles were used as markers in a one-step post-embedding procedure for identifying hyaluronan (hyaluronic acid) at the ultrastructural level. All myelin sheaths in both rat and human material were found to be intensely labelled. The specificity of the hyaluronan-binding probes was demonstrated by the total loss of labelling following treatment of sections with hyaluronidase or by preincubating either the probes with hyaluronan oligosaccharides or the sections with unlabelled hyaluronan-binding protein. The identified hyaluronan appears to be located extracellularly, but is precise role here remains to be elucidated.

Animals↗
PubMed1992

[Hemostatic effect of the Nd:YAG laser in cw function].

The Nd:YAG laser may be effectively employed to induce blood flow stasis and vessel closure in rabbits. The mechanism by which these effects are achieved depends upon the nature of the primary absorbing structures in the irradiated tissue, as well as upon the energy level of radiation. Vascular wall damage occasioned in consequence of energy absorption in melanin granules triggers blood flow stasis according to the classic clotting cascade, defects in the endothelial cell wall being closed by aggregated platelets. In tissue lacking melanin pigmentation, energy is absorbed primarily by the haemoglobin of erythrocytes, and blood flow is arrested by coagulation of plasma proteins, platelets being absent from the impact centre. The portent of these different haemostatic mechanisms upon repair of the endothelial cell wall and neovascularization have yet to be determined.

Animals↗
PubMed1992

Laser cyclocoagulation.

Since its introduction in 1973 by Beckman and Sugar, cycloablation, using Nd: YAG laser energy has gained increasing attention. Nd: YAG laser energy may both be delivered in the contact and non-contact mode and the energy source may both work in the pulsed or cw mode. The physical and clinical effects of the various design principles differ. A short survey of the present state of the art is presented.

Ciliary Body↗
PubMed1992

A new instrument for controlling pressure exerted on the sclera during contact Nd:YAG laser cyclodestruction.

We tested the device described by Rol et al in their article in this issue, designed to define and precisely control the pressure applied to the sclera during contact cyclodestruction with a cw-Nd:YAG laser. Since scleral transparency, and hence transmission of laser energy, depends on the pressure applied, control of this parameter represents an important advance toward the goal of standardizing the cyclodestructive procedure. In eight of nine cadaver pig eyes, pressure was exerted on the sclera using the pressure-controlling device, with a setting of 0.25 N for two of these eyes, and one of 0.4 N for the other six. In the remaining eye, pressure was controlled intuitively by an experienced surgeon. Applying forces of 0.25 or 0.4 N yielded similar success rates, although these fluctuated greatly even under constant pressure conditions (from 17% to 50% at 0.25 N; from 27% to 42% at 0.4 N). The highest success rate (55%) was achieved by the intuitively controlled pressure irradiations of the experienced surgeon. The variation in coagulation intensity that occurred despite constant pressure suggests that additional factors contribute to the results achieved. Nonetheless, this pressure-controlling probe represents an important achievement. It will permit not only the novice but even experienced operators to adhere unambiguously to a protocol of quantitative, reproducible parameters, and will also help researchers to better understand the relationship between energy delivered and intraocular pressure reduction achieved in contact cyclophotocoagulation.

Animals↗
PubMed1991

Blood flow stasis induced by cw-Nd:YAG laser irradiation: comparative morphology of mesenteric and choroidal vessels in pigmented rabbits.

cw-Nd:YAG laser radiation was effective in producing blood flow stasis within arteries (35-40 microns in diameter) of pigmented rabbit mesentery (beam spot size: 80 microns; fluence: 2 x 10(4) J cm-2) and choroid (beam spot size: 200 microns; fluence: 6 x 10(2) J cm-2). However, the mechanism by which this was achieved differed in each case, and depended upon the energy absorbing structures present in the irradiated tissue. In non-pigmented tissue, such as the mesentery, haemoglobin represents the primary absorption centre, and the temperature attained within the vessel lumen (as inferred from morphological changes) is sufficient to denature plasma proteins, in particular fibrinogen, which consequently occlude the vessel lumen and arrest bleeding. In pigmented tissue, such as the choroid, melanocyte granules represent the primary absorption centre, which is thus shifted from the vessel lumen to the stroma. The temperature rise achieved within the vessel lumen is consequently lower, as evidenced by the absence of plasma protein denaturation. Blood flow stasis nonetheless occurs, but is triggered according to the normal haemostatic mechanism.

Animals↗
PubMed1990

[Bruch's membrane and its significance for retinopexy following laser irradiation].

Retinopexy may be produced by either of two mechanisms following transpupillary irradiation of the retina with the Nd:YAG laser. Which of these mechanisms is operative will depend on the degree of disruption produced within the elastic component of Bruch's membrane. Small defects in the elastic component of Bruch's membrane are soon completely bridged by regenerated retinal pigment epithelium (RPE) cells. However, there is a risk of subretinal neovascularization in such defects. Large defects in the elastic component of Bruch's membrane are not completely bridged by regenerating RPE cells before proliferating Müller cells invade this region and spread from it, mushroom-like, within the choroid. In this case subretinal neovascularization does not occur. In the former instance (small defects) retinopexy is achieved by a process of interdigitation between the microvilli of Müller and RPE cells; and in the latter (large defects) via a press-stud-like anchorage of Müller cells within the choroid. It has not yet been established whether these two retinopexy phenomena, observed after irradiation of rabbit retinas, occur in the same way in man.

Animals↗
PubMed1990

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.

Animals↗
PubMed1989

The mechanism of aqueous outflow following trabeculectomy. A light and electron microscopic study.

The morphological effects of trabeculectomy, performed as therapy for a case of chronic simple glaucoma, are described in the two eyes of a patient ten and thirteen months after treatment. Ten months after surgery, a transscleral channel, extending from the position formerly occupied by Schlemm's canal to the conjunctiva, is found. This channel is formed from a network of extended fibroblasts and loosely-packed collagenous tissue, and a large number of vessels, including both dilated blood capillaries and lymphatic vessels, develop within it. The sclera and subconjunctiva react differently to the presence of the nylon sutures. The findings support the hypothesis that the formation of an intrascleral outflow route stimulated by surgical intervention plays an important role in lowering IOP after trabeculectomy.

Aged↗