Björn Svedbergh

SCANNING ELECTRON MICROSCOPIC STUDIES OF THE TRABECULAR MESHWORK AND THE CANAL OF SCHLEMM - AN ATTEMPT TO LOCALIZE THE MAIN RESISTANCE TO OUTFLOW OF AQUEOUS HUMOR IN MAN

Chamber angle tissue from human eyes was investigated with scanning electron microscopy. The uveal and corneoscleral parts of the trabecular meshwork are described. The endothelial cells of the inner wall of Schlemms canal arc long and slender and, at most places, are oriented along the lumen of the canal. The average projected surface of a cell towards the canal is about 480 μm2. The total number of endothelial cells in the inner wall of the canal is about 23,000. The cells have pores with diameters up to 3(5) μm. The total number of pores is about 20,000. Calculations show that if all the observed pores exist in vivo, the resistance to outflow in the paths through the endothelial cells is a small fraction of the total resistance to outflow.

Passive silicon transensor intended for biomedical, remote pressure monitoring

Abstract A sensor is suggested for continuous monitoring of intraocular pressure and similar biomedical applications. The system consists of a capacitive pressure sensor determining the resonance frequency of a passive LC resonator. The resonance frequency is detected in a grid-dip configuration. The paper mainly deals with the capacitive sensor, which is fabricated in silicon, using a silicon fusion bond to seal the cavity. This process will minimize internal stress and provide the necessary conditions for a small temperature drift and stability over long periods of time. Experimentally, prototype sensors have been fabricated and evaluated in vitro . The results are promising and in accordance with theoretical expectations.

A system for wireless intra-ocular pressure measurements using a silicon micromachined sensor

A system for the continuous monitoring of intra-ocular pressure is described. The sensor is intended for permanent implantation, integrated with an artificial lens. The system consists of a capacitive pressure sensor, determining the resonance frequency of a passive LC network, and a detector, based on the grid-dip technique. The passive pressure sensing element is micromachined from two silicon wafers and connected to a gold-wire coil. Prototype sensors have been evaluated experimentally in vitro. Pressure has been measured remotely, with promising results.

EFFECTS OF ARTIFICIAL INTRAOCULAR PRESSURE ELEVATION ON THE CORNEAL ENDOTHELIUM IN THE VERVET MONKEY: (Cercopithecus ethiops)

Both eyes of anesthetized vervet monkeys were perfused with mock aqueous humor for 3–7 hours. By adjusting the height of a reservoir connected to the anterior chamber of each eye the intraocular pressure in one eye was maintained at 33–44 mmHg and in the other eye it was a few mmHg above the spontaneous level (12–15 mmHg). Morphologically the control eyes appeared normal, whereas pronounced changes were observed in the high pressure eyes. Thus the corneal endothelium showed an uneven surface towards the anterior chamber with vacuolization, blebbing and disruption of the cytoplasm. Pycnosis, excaryocytosis and even loss of whole endothelial cells were observed as well. The morphological changes were most pronounced in the peripheral part of the cornea and furthermore differed among neighbouring cells. During the healing process one could observe mitosis, amitosis and cell surface increase.

THE IOP-IOL. A PROBE INTO THE EYE

Abstract. The intraocular lens (IOL) implant can be looked upon as a probe into the space of the eye. Adapting that view, it is logical to furnish the IOL‐probe with biomedical sensors that would explore its environment. A sensor is presented for continuous monitoring of intraocular pressure (IOP), incorporated in the haptics of an IOL. The sensor consists of a capacitative spiral circuit, needing no energy, correlating its resonance frequency to the actual IOP. This resonance frequency is remotely and non‐invasively detected by an external device located in a spectacle frame.

EFFECTS OF ARTIFICIAL INTRAOCULAR PRESSURE ELEVATION ON THE OUTFLOW FACILITY AND THE ULTRASTRUCTURE OF THE CHAMBER ANGLE IN THE VERVET MONKEY (Cercopithecus ethiops)

Both eyes of anaesthetized vervet monkeys were perfused with mock aqueous humor for 3–7 hours. By adjusting the height of a reservoir connected to each eye the intraocular pressure in one eye was maintained at 33–48 mmHg and in the other eye it was a few mmHg above the spontaneous level. The facility of outflow in the high pressure eye increased by an average of 350% (160–630%), whereas the increase in the control eye was less than 40%. Morphologically the control eyes appeared normal, whereas pronounced changes were observed in the high pressure eyes. The endothelial cells in the trabecular meshwork were swollen and demonstrated loss of cytoplasm. Cell debris and “blebs” were observed in the intertrabecular spaces. The endothelial meshwork and the endothelium of the inner wall of Schlemms canal were partly disrupted. The outflow facility was normalized within 1 day but marked morphological changes were still present.

Primary argon laser trabeculoplasty vs. pilocarpine Short-term effects

Abstract This is a prospective study of 82 newly discovered patients with simplex or capsular glaucoma from two centres, collected between 1984 and 1989 and selected at random for primary treatment by either laser or pilocarpine. Preliminary two‐year follow‐up shows that primary laser treatment gives a significantly higher number of patients where the intraocular pressure is successfully controlled. Primary argon laser trabeculoplasty has been carried out in 40 patients. The first treatment was given to either the upper or to the lower half of the trabecular meshwork. In the second treatment after one month the other half was treated. In both groups the first treatment gave the highest pressure reduction. The somewhat higher pressure reduction after upper treatment versus lower was insignificant. The degree of trabecular pigmentation did not influence the two month follow‐up result, neither did the type of glaucoma. Of the eyes treated with laser, peripheral anterior synechiae could be seen in 18%. Acute intraocular pressure rises greater than 5 mmHg occurred in 21% of the eyes after the first treatment and in 37% after the second treatment. Pressure rises greater than 10 mmHg occurred in 5% after the first and in 10% after the second treatment. No pressure‐lowering substances were given. Considering that 16% of the eyes had an intraocular pressure that was higher than baseline pressure even 6 h after either first or second treatment, it is recommended that a pressure‐lowering medication on the day of treatment should be administered.

Primary argon laser trabeculoplasty vs pilocarpine. II: Long-term effects on intraocular pressure and facility of outflow. Study design and additional therapy.

Abstract In a prospective study 82 patients recently diagnosed with simple or capsular glaucoma were randomized to receive primary argon laser trabeculoplasty or pilocarpine treatment. A 2‐year follow‐up showed a better success rate in the laser group, with less need for additional therapy. The average intraocular pressure and peak pressure was lower and the daytime pressure variation was significantly less in the laser group. The better increase in facility of outflow in the laser group was not statistically significant. In capsular glaucoma, laser treatment resulted in a significantly lower average pressure than with medication. In simple glaucoma the effect was about the same in the two treatment groups. Increase in facility of outflow was significantly better in simple glaucoma than in capsular glaucoma. High initial intraocular pressure gave a significantly lower success rate. Primary argon laser trabeculoplasty as a single glaucoma treatment seems advantageous in comparison to medication with pilocarpine for regulating intraocular pressure.

Protrusions of the Inner Wall of Schlemm's Canal

Large specific protrusions of the trabecular meshwork into Schlemms canal (hernias) have been suggested to be the main drainage routes for aqueous humor, similar to the function of the arachnoid villi in draining the cerebrospinal fluid. My quantitative study in cynomolgus monkeys does not support such a hypothesis. The drainage routes of the aqueous humor, evaluated from the number and sizes of the pores observed by scanning electron microscopy, were as common through the hernias as through other parts of the inner wall of Schlemms canal at different levels of intraocular pressure. The total surface of the hernias was a small percentage of the total surface of the inner wall.

RETROLENTAL FIBROPLASIA OR CONGENITAL ENCEPHALO-OPHTHALMIC DYSPLASIA?

ABSTRACT: Svedbergh, B. (Department of Ophthalmology, University of Uppsala, Uppsala, Sweden). Retrolental fibroplasia or congenital encephalo‐ophthalmic dysplasia? Acta Paediatr Scand, 64: 891, 1975.–Congenital encephalo‐ophthalmic dysplasia (CEOD) is described in 2 cases. The eye signs, clinically identical to the cicatricial stage of retrolental fibroplasia (RLF), are combined with brain maldevelopment and occurred without oxygen treatment. RLF in a strict sense should be reserved for oxygen‐induced retinopathy in prematures.