Biomedical subjects

A Frohn

Publications and source records attributed to A Frohn.

At least 19 recordsLinked to original sources

PubMed2001

Late opacification of the foldable hydrophilic acrylic lens SC60B-OUV.

OBJECTIVE: To investigate the cause of severe central opacification in 41 foldable acrylic intraocular lenses (IOLs) requiring explantation. Another IOL was opacified in the original sealed vial. DESIGN: Case series and laboratory analysis. TESTING: Light microscopy, high performance liquid chromatography, sodium dodecyl sulfate polyacoylamide gel electrophoresis, spectrometric analysis, and autoclaving. RESULTS: Neither fatty acids nor proteins could be identified within the IOLs. Spectrometric analysis yielded absorption peaks in the ultraviolet spectral range. CONCLUSIONS: The spectroscopic findings indicate premature aging of the ultraviolet blocking agent. The source of the opacification is a change in the IOL material itself.

Acrylic Resins↗

PubMed2001

Beam-deflection method of diagnosing impaired vision.

We describe a simple method to assign a diagnosis of cataract to patients with obscurely impaired vision as well as to those with mild lens opacities. When the narrowest slit is used in a slitlamp examination, a small beam of light appears on the macula. Routine fundoscopy with the 78.0 diopter lens or a 3-mirror glass is appropriate. If a cataract is present, the beam of light is scattered into several straight lines, distorted lines, or both. This has proved a useful diagnostic tool when the lens appears clear but the patient's vision is impaired, and extensive examinations such as computer tomography or nuclear magnetic resonance tomography for impaired vision may be avoided. The beam-deflection method uses devices that are generally available and can detect cataract in the early stages of development.

Adolescent↗

PubMed2000

Ultrasonic transmission in viscoelastic substances.

PURPOSE: To study the propagation of ultrasonic shock waves in viscoelastic agents and the resulting corneal load. SETTING: University Siegen, Institute for Mechanics and Control Engineering, Siegen, Germany. METHODS: The anterior chamber of a manufactured artificial eye was constructed according to anatomic dimensions. Three openings were drilled--for the phaco tip, for the exchange of a viscoelastic agent or water, and for the shock-wave sensor. The sensor was fixed to the area corresponding to the corneal apex. The sensor signal was analyzed using a direct oscilloscope that measured the amplitude reaching the corneal apex. Shock-wave propagation in several viscoelastic agents was compared with that in balanced salt solution. RESULTS: In hydroxypropyl methylcellulose, the shock wave was amplified or influenced slightly. In hyaluronic-acid preparations, acoustic dampening occurred. CONCLUSION: Removal of hyaluronic-acid derivatives prior to phacoemulsification is not necessary.

Anterior Chamber↗

PubMed1999

Implantation of a toric poly(methyl methacrylate) intraocular lens to correct high astigmatism.

A 57-year-old man experienced a decrease in visual function because of cataract formation. Corneal astigmatism was 13.4 diopters (D) because he had had a penetrating keratoplasty 27 years before. Cataract surgery was planned, and biometric data for toric intraocular lens (IOL) implantation were collected for the manufacture of a custom IOL. After phacoemulsification, a toric poly(methyl methacrylate) (PMMA) IOL of +19.0 D spherical and +12.0 D cylindrical power was implanted via a sclerocorneal tunnel incision. Three months postoperatively, corneal astigmatism was 14.3 D and best corrected visual acuity (BCVA), 20/25. Postoperative refraction (+1.5 -3.0 x 90) and BCVA remained stable for 7 months. No significant IOL rotation was observed. Implantation of a toric PMMA IOL corrected high corneal astigmatism. Toric IOL technology with high cylindrical power allows enhancement of IOL surgery.

Astigmatism↗

PubMed1998

[Axial displacement of IOL and visual impairment].

BACKGROUND: After a cataract surgery procedure with vitreous loss a vitreous strand remained in the wound. An unusual visual impairment was observed. PATIENT: A shift in refraction depending on the pupillary diameter was observed. In miosis the refraction was estimated to +1.0 sph, in mydriasis -1.0 sph/ -0.5 cyl, respectively. METHOD: We presumed that the vitreous strand between the iris and the intraocular lens caused an axial displacement of the IOL during the change from miosis to mydriasis and v.v. Therefore the vitreous strand was surgically eliminated. After surgery the refractive changes by pupillary actions were overcome. In a computer simulation (ray tracing), the amount of axial displacement of the IOL was estimated to 1.5 mm. CONCLUSION: This paper reminds of considering other reasons for loss of VA than CME, e.g. axial displacement of IOL. An adequate method of examination is the measurement of refraction in miosis and mydriasis.

Aged↗

PubMed1998

Diode array as fixation light to reduce unwanted globe movements.

In ocular surgery complications can occur from eye movements during topical anesthesia or insufficient retrobulbar anesthesia. To minimize eye movements during surgery a fixation light was designed consisting of a diode array embedded in an eye patch, and a keyboard, which will be positioned on the patient's thorax. The patient focuses with the unoperated eye at a flashing diode which is part of the diode array. The operated eye is guided by conjugated eye movements. With the keyboard, the surgeon can change the diode signal all over the array. As a result, the eye is kept still or moved in the appropriate direction to facilitate the surgical process. The flat and lightweight design of the device enables its use under sterile surgical covers or in an upright position of the patient during laser applications.

Anesthesia, Local↗

PubMed1996

[Visual image in high ametropia. Computer-assisted simulation with optic ray calculation].

PURPOSE: A computer program developed by the authors allows to calculate the path of light rays coming from an object through all the refractive surfaces of a Gullstrand model eye until it reaches the retina. METHOD: The program calculates several hundred light rays for every point of a given object. A menue allows to modify optical and morphological parameters in an interactive way. For instance, the indices of refraction, the radii of the cornea and of the cristalline lens, as well as the length of the bulbus can be modified. Further, one can add seeing aids such as eye glasses or a contact lens, or implant an artificial intraocular lens. The seeing aids may be decentered and/or tilted. RESULTS: The code calculates also the visual impression by projecting the image from the retina back to a screen at the distance of the object, where the human brain "sees" the object. For image interpretation we use a normal Gullstrand eye with a very small aperture stop. In this way we can simulate the visual mapping (visual impression) of a corrected or uncorrected ametropia. CONCLUSIONS: In this paper we present two nontrivial examples: we calculate the regional polyopia ("Bildverdoppelung") and the annular scotoma which appear whenever a high myopia or aphakia are corrected by eye glasses.

Computer Simulation↗

PubMed1996

A ray tracer for ophthalmological applications.

Ray tracing with a personal computer allows realistic simulation of optical properties of the human eye. Patterns of point sources are used as objects. The path of light rays is calculated between the point source and the retina for a Gullstrand eye model with improved parameters; the normal eye model has a resolution limit close to the natural resolution limit of the human eye. The image formed on the retina is projected back to a screen at the distance of the object so as to simulate image interpretation by the brain. Refractive errors are modeled by a change in eye parameters and corrected by eyeglasses or/and contact lenses or by an artificial intraocular lens. For optic correction the parameters of seeing aids can be fitted automatically by a least-squares routine. The effect of faulty eye correction on image quality is visualized by using a photograph of a realistic scene as an object.

Aphakia↗

PubMed1995

[Tarantule hairs as corneal foreign bodies].

A 22 year-old-man and owner of several tarantulas visited his ophthalmologist because of red itchy eyes. Additionally to kerato-conjunctivitis epidemica, uncommon hairs were found especially in his left cornea. Corrected visual acuity was 0.8. According to literature these spider hairs can induce granulomas in the meaning of ophthalmia nodosa, and even migrate inside the eye. Therefore we removed as many hairs as possible, but we left two, not to cause iatrogen perforation. The penetration depth was measured by laser tomography. Local steroids successfully prevented further granuloma formation. Regular ophthalmological controls are important to early detect possible changes, and if necessary to remove these hairs even from deeper corneal layers, in case by keratectomy.

Adult↗

PubMed1993

[Eye burns caused by wolf's milk].

If the sap of Euphorbia inadvertently gets in the eye, it can cause conjunctivitis, keratitis or iritis. Therapy consists of rinsing, antibiotics, steroids and mydriatics when the anterior chamber is inflamed. It may also be necessary to protect the damaged eye from light, because photoallergic reactions are possible.

Burns, Chemical↗

PubMed1992

Intraocular pressure and anterior chamber depth before and after extracapsular cataract extraction with posterior chamber lens implantation.

Long-term intraocular pressure (IOP) was evaluated in 41 glaucoma patients after extracapsular cataract extraction (ECCE) with posterior chamber lens (PC-IOL) implantation. All patients were initially monitored for a mean of 19 days. Eight failed to return for reexamination, but follow up of the other 33 continued for a mean of 12 months. IOP dropped significantly and the need for medication was reduced in all patients (particularly in those with open-angle glaucoma and prior iridotomy and iris suturing). The reduction in pressure remained significant in patients with simple or exfoliation glaucoma even after long-term observation. Pressure also significantly dropped in patients who had undergone previous ophthalmic surgery. The pressure drop was possibly due to a surgical deepening of the chamber angle. (Using the laser tomographic scanner, we found the same phenomenon in 50 patients without glaucoma: following ECCE/PC-IOL, the anterior chamber angle widened 9.3 +/- 4.3 degrees.)

Aged↗

PubMed1991

[Validity and reproducibility of confocal corneal measurements].

In order to verify reproducibility and validity of confocal measurements of the cornea we examined a well known biological model: Increasing corneal thickness under hypoxic conditions during contact lens wear. The method verified increasing thickness with high significance. In addition, reproducibility was determined within a range of 5 mu. As a result, confocal measurements proof to be a powerful tool for topographical reconstruction of corneal shape.

Algorithms↗

PubMed1991

[Effect of anti-glaucoma eyedrops on cell differentiation of the conjunctiva].

After local application of pilocarpine (minimum 1%), timolol (0.5%) or levobunolol (0.5%) to 6 patients, cell differentiation of the conjunctival epithelium was compared to that in 48 healthy persons. The least difference was found after pilocarpine application. The five ultrastructurally defined cell types were found to vary least when compared to the same cell types in normal subjects. The patients treated with timolol and levobunolol showed a reduction in secretory epithelial cells, especially within the conjunctiva bulbi, and a pronounced increase in cells with rough endoplasmatic reticulum. In addition to a loss of desmosomes and zonulae occludentes on the cell surface, a minimum 1-year application of the three antiglaucomatous medications leads to a reduction in the microvilli and microplicae and, particularly in patients treated with beta blockers, to intracellular changes, specifically increased vacuolization and dilation of the rough endoplasmatic reticulum. The latter may be attributable to the action of benzalkonium chloride (present as a preservative in all three eye drops studied) on the superficial epithelial cells. The cytotoxic action of the preservative may be intensified by the simultaneous application of beta blockers due to their destabilizing effect on the tear film.

Cell Differentiation↗

PubMed1991

[Image of the cornea with the scanning laser ophthalmoscope].

With a scanning laser ophthalmoscope (SLO), a hexagonal reflex phenomenon can be observed, which originates from the tear film and corneal tissue layers. Time motion analysis verifies that it is possible to discriminate between the cornea and tear film.

Cornea↗

PubMed1990

[Eye involvement in hyperimmunoglobulin E syndrome].

The Hyperimmunoglobulinemia-E-Syndrome (HIE) is characterized by high levels of serum-IgE, diminished counts of T-suppressor-cells, eosinophilia, and disturbed chemotactic functions of neutrophil granulocytes. An 8 years old female, suffering from hyperimmunoglobulinemia E (HIE), showed marginal corneal ulcera since five years. Positive conjunctival smears included several bacterias and chlamydia, but never local herpes virus. Inspite of treatment by antibiotics, virostatica, and therapeutical contact lens, a spontaneous corneal perforation occurred. A penetrating keratoplasty was successful for a short time, but soon ulceration rose again. At last a second penetrating keratoplasty was necessary. The early status showed tidy results, but some weeks later marginal ulceration occurred again. There was no clinical proof for herpetical genesis of the course, but evidence is conceivable for pathomechanisms similar to conjunctivitis vernalis.

Child↗

PubMed1990

[Laser scanning in ophthalmology].

The current state of the art for the major laser scanning methods, laser scanning ophthalmoscopy (LSO) and laser tomographic scanning (LTS) is discussed and the function principles are described. Experience with a prototype of each instrument from Rodenstock (LSO) and Heidelberg Instruments (LTS) is reported. LSO imaging of the cornea, vitreous, retina, and optic disc, as well as on-line processing is demonstrated with examples (nerve fibre colour coding and histograms). Measurement of the cornea, optic disc and retinal topography with LTS is also demonstrated with examples. An example of polarization optical imaging of the cornea's assumed interferometric "tension patterns" is shown. The current status and future possibilities of laser scanning, its expanded diagnostic potential with microperimetry, IR scanning angiography and polarization optic imaging and measurement (eg. nerve fibre thickness) is discussed extensively. The safety aspects of laser light exposure of the macula are also mentioned. Laser scanners as imaging and measuring sensors of unknown accuracy open a new area of possibly revolutionary diagnostic possibilities.

Cornea↗

PubMed1990

[Imaging the optic papilla with the laser scanning ophthalmoscope].

The laser scanning ophthalmoscope offers tissue examination and support of papillometrical evaluations as a result of different forms of illumination. Confocal, mixed, and Tyndall light are used in the differential diagnosis and identification of the scleral rim. With highpower mixed light under miotic conditions, imaging of the excavation is possible.

Glaucoma↗

PubMed1989

[Nonspecific eye autoantibodies in uveitis].

Under certain pathologic circumstances autoantigens lead to the formation of autoantibodies. In uveitis, autoimmunologic phenomena will also be discussed. We studied 149 sera of uveitis patients for various organ specific and non-organ specific autoantibodies. We found antisarcolemal autoantibodies (ASA) mainly in patients with acute iritis (59% positive) but also in panuveitis (40%) and iridocyclitis (29%). On the other hand antiendothelial antibodies (AEA) could be found in 43% of patients with chorioretinitis. Antisinusoidal antibodies (SA) have been detected in iritis and panuveitis patients more often than in the control group which show positive autoantibodies in 5% of all cases. Using ELISA we looked for antibodies against keratin, laminin and microsomes. Because antimicrosomal-, antilaminin- and antisarcolemal-antibodies recognize the same epitope, there was a good correlation of these three autoantibodies. Similar clusters of autoantibodies (ASA, AEA and SA) have been found in various infectious diseases and in chronic inflammatory diseases in which an infectious component is discussed. These results may indicate that iritis, iridocyclitis, chorioretinitis and panuveitis are secondary reactions of eye tissue following a systemic primary disease. Especially viruses are well-known for their production of autoantibodies. In patients with intermediate uveitis we could not demonstrate these autoantibodies more often than in the control group, favouring theories which believe in an autoimmune reaction against vitreous elements.

Antibodies, Antinuclear↗