Biomedical subjects

Theo Seiler

Publications and source records attributed to Theo Seiler.

26 records · Page 2Linked to original sources

PubMedDate not supplied

Corneal myxoma.

BACKGROUND: Myxomas are rare benign tumors that can be found most frequently in the heart. We report the clinical and histological findings in a very rare case of corneal myxoma, which is only the sixth case in the literature. CASE: A whitish elevated tumor of the anterior cornea developed in the left eye cornea of a 46-year-old man 2 years after luxation of the patient's lens into the anterior chamber and subsequent endothelial decompensation. The tumor covered the entire surface of the cornea except for the outer limbal periphery at Schwalbe's line. OBSERVATIONS: Histologically, the hypocellular tumor was characterized by scattered spindle- and stellate-shaped cells with wavy, randomly oriented collagen fibers in a myxomatous ground substance staining positively for acid mucopolysaccharides. Bowman's layer was absent. Immunohistochemically, the tumor cells were positive for vimentin. Ultrastructurally, the tumor cells had features characteristic of keratocytes with no basement membrane, much rough endoplasmic reticulum and vacuoles containing mucoid-like material. CONCLUSIONS: The ultrastructural observations support the hypothesis of a cellular origin of the myxoma from keratocytes. The tumor growth was most probably stimulated by chronic endothelial failure and bullous keratopathy.

Corneal Diseases↗

PubMedDate not supplied

Thermomechanical behavior of collagen-cross-linked porcine cornea.

PURPOSE: Collagen cross-linking using combined riboflavin/UVA treatment has been shown to increase the biomechanical rigidity of the cornea and has been used successfully for the treatment of progressive keratoconus. From morphological and biochemical investigations, a different degree of cross-linking for the anterior and posterior stroma by the treatment is suggested. The present study was undertaken to better evaluate this effect by testing the thermomechanical behavior. METHODS: Ten 10 x 5 mm corneal strips from porcine cadaver eyes enucleated within 5 h post mortem were cross-linked using the photosensitizer riboflavin and UVA irradiation (370 nm, irradiance = 3 mW/cm(2)) for 30 min and compared to ten untreated corneal strips and ten corneal strips cross-linked with 0.1% glutaraldehyde. The temperature in a water bath was raised from 60 to 95 degrees C with temperature increments of 1 degrees C per minute. The hydrothermal shrinkage of the corneal strips was measured in 2.5 degrees C steps using a micrometer. In addition, six 10-mm whole corneal buttons were cross-linked with riboflavin/UVA and immersed into water at 70 or 75 degrees C. RESULTS: The maximal hydrothermal shrinkage for the untreated control specimens and the posterior portion of the riboflavin/UVA-treated corneas was at 70 degrees C, for the anterior portion of the cornea cross-linked by riboflavin/UVA at 75 degrees C and for glutaraldehyde-cross-linked cornea at 90 degrees C. In the cross-linked corneal buttons, a typical mushroom-like shape was observed at 70 degrees C and a cylinder shape at 75 degrees C. CONCLUSIONS: The different degree of collagen cross-linking in the corneal stroma after riboflavin/UVA treatment is reflected by the differences in the maximal shrinkage temperature of the anterior and posterior portion. Therefore, in the corneas cross-linked with riboflavin/UVA a higher shrinkage temperature was observed for the anterior portion of the cornea (75 degrees C) compared to the posterior stroma (70 degrees C) due to the higher degree of cross-linking of the anterior stroma. The anterior localization of the cross-linking effect is advantageous for the endothelium and for the preservation of the anterior corneal curvature.

Animals↗

PubMedDate not supplied

Aberration-sensing and wavefront-guided laser in situ keratomileusis: management of decentered ablation.

PURPOSE: To clarify the feasibility of aberration-sensing and wavefront-guided laser in situ keratomileusis (LASIK) to manage grossly decentered ablation and to discuss the limitations of the technology. METHODS: Three patients with previous decentrations of the ablation zone between 1.5 to 2.0 mm were scheduled for wavefront-guided LASIK. All patients reported monocular diplopia and halos. Wavefront aberrations were measured with a Tscherning-type aberrometer. Laser ablation was done with a WaveLight Allegretto in a one-step procedure with ablation profiles calculated only from the individual wavefront map. Decentrations were determined from corneal topography. RESULTS: Three months after surgery, patient WM and patient SU had gained uncorrected and best spectacle-corrected visual acuity. The root mean square-wavefront error decreased up to 61% and 33%, respectively, for total and higher order aberrations (Zernike modes of 3rd order and higher). There was significant enlargement of the optical zone determined by corneal topography, and both patients no longer reported diplopia and halos at 3 months postoperatively. The optical aberration of the third patient (RE), after a 5.00-D overcorrection with a 2-mm decentration, was too high for aberration-sensing; retinal images obtained from the wavefront device were too smeared and not of sufficient contrast. In addition, this patient had a residual corneal thickness of 416 microm and thus wavefront-guided LASIK was not done. CONCLUSIONS: Wavefront-guided LASIK offers a new way of managing grossly decentered laser ablations. Unfortunately, there are still patients who have aberrations too large for wavefront sensing or with other clinical limitations such as a residual corneal thickness too thin for further treatment.

Adult↗

PubMedDate not supplied

Experimental results of preparing laser-shaped stromal implants for laser-assisted intrastromal keratophakia in extremely complicated laser in situ keratomileusis cases.

PURPOSE: To evaluate the feasibility of laser-shaped stromal implants from a donor eye for correcting extreme high hyperopia with irregular astigmatism and an exceptionally thin corneal bed. METHODS: Thirty-one fresh enucleated porcine eyes were used. The procedure was initiated with mechanical de-epithelialization followed by a lamellar cut with a microkeratome, resulting in a hinged flap (thickness 150 microm, diameter 9.5 mm). The cornea was photoablated with PRK treatment for +8.00 D sphere (hyperopic lenticule group) and -5.00 D sphere (myopic group) by a scanning spot excimer laser. A customized scanning software algorithm was used to create a circumferential cut with a 6.5-mm internal diameter. The lenticule was removed from the stromal bed and measured by a surface profiling system. A clinical case was performed on a patient with previous LASIK and highly irregular hyperopic astigmatism to verify the clinical utility of the experimental setup. RESULTS: Under the microscope, lenticules seemed round, regular, and transparent. The average surface profile of porcine corneas demonstrated good parabolic shape with individual variations as large as 30 microm, probably due to the corneal size and curvature differences between the porcine eye and the human eye--for which the microkeratome is designed. The patient underwent a topography-guided treatment after laser-assisted intrastromal keratophakia (LAIK) and 1-month follow-up showed an increase of UCVA, BSCVA, and central corneal thickness. CONCLUSIONS: The use of modern scanning-spot excimer lasers and microkeratomes enabled us to produce stromal lenticules of good quality, which might be acceptable to implant into a human eye.

Adult↗

PubMedDate not supplied

Anterior lamellar keratoplasty with a microkeratome: a method for managing complications after refractive surgery.

PURPOSE: To demonstrate a technique of anterior lamellar keratoplasty with standardized and automated preparation of surface-parallel cuts in both donor and recipient appropriate for addressing several problems after laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). METHODS: We report a noncomparative series of ten eyes with complications after LASIK and PRK. Lamellar cuts were performed in donor and recipient eyes by means of an automated microkeratome. Lamellar grafts were fixed by only four single sutures. In two eyes, a re-lift LASIK was performed after 6 months. RESULTS: Surgery was uneventful and visual acuity was improved in all eyes. Residual irregular astigmatism and refractive error were corrected in two eyes by means of excimer laser computer-assisted ablation and resulted in a further improvement of uncorrected and best spectacle-corrected visual acuity. CONCLUSIONS: Anterior lamellar keratoplasty with a microkeratome can be used for the management of certain complications of PRK and LASIK.

Adult↗

PubMedDate not supplied

Correlation between corneal and total wavefront aberrations in myopic eyes.

PURPOSE: Corneal topography data expressed as corneal aberrations are frequently used to report corneal laser surgery results. However, the optical image quality depends on all optical elements of the eye, including the human lens. We investigated correlations between corneal and total wavefront aberrations and the relevance of corneal aberrations for representing the optical quality of the total eye. METHODS: Thirty-three eyes of 22 myopic patients were measured using a corneal topography system and a Tscherning-type wavefront analyzer. Pupils were dilated to at least 6 mm in diameter. All measurements were centered with respect to the line of sight. Corneal and total wavefront aberrations were calculated up to the 6th Zernike order in the same reference plane. RESULTS: Statistically significant correlations (P<.05) between corneal and total wavefront aberrations were found for astigmatism (C3,C5) and all 3rd Zernike order coefficients such as coma (C7,C8). No statistically significant correlations were found for 4th, 5th, or 6th order Zernike coefficients. On average, all Zernike coefficients for corneal aberrations were larger than the Zernike coefficients for total wavefront aberrations. CONCLUSIONS: Due to the lack of correlation between corneal and total wavefront aberrations in most of the higher order aberrations, measurement of corneal aberrations are of limited use for representation of the optical quality of the human eye, especially after corneal laser surgery. Corneal aberrations and optical elements within the eye are optically balanced. As a consequence, ideal customized ablations must take both corneal and total wavefront aberrations into consideration.

Adult↗

PubMedDate not supplied

Laser intrastromal keratoplasty--case report.

PURPOSE: To evaluate the feasibility of correcting high hyperopia by means of intrastromal implantation of a laser shaped corneal lenticule prepared from a human donor eye. METHODS: A female patient with high hyperopia and irregular astigmatism resulting from multiple laser in situ keratomileusis procedures and lamellar keratoplasty underwent laser intrastromal keratoplasty. Her preoperative uncorrected visual acuity (UCVA) was 20/300 and best spectacle-corrected visual acuity (BSCVA) was 20/100 with a refraction of +8.00 -1.00 x 130 degrees. Corneal topography showed a highly irregular corneal surface. Central corneal thickness was 398 microm. Lenticule preparation included mechanical de-epithelialization of a human donor eye, keratectomy with a microkeratome, user-designed software combining a photorefractive keratectomy (PRK) treatment for +8.00 D sphere, an ablation zone of 7.0 mm, and a circumferential cut (internal diameter of 6.5 mm) for tissue ablation. Implantation involved re-lifting the flap, positioning the lenticule onto the corneal bed, and repositioning of the flap. RESULTS: The operation was uneventful as was the early postoperative follow-up. BSCVA improved to 20/50 with +1.00 -2.25 x 120 degrees at 2 months postoperatively. Corneal topography showed a more regular cornea with increased curvature in all meridians. Central corneal thickness increased to 600 microm. CONCLUSION: Laser intrastroma keratoplasty may be an option for correcting high hyperopa and irregular astigmatism in eyes with a thin corneal bed.

Adult↗

PubMedDate not supplied

Transferring wavefront measurements into corneal ablations: an overview of related topics.

We give an overview of possible side effects that are specific for, or of particular relevance in, customized treatments. Certain processes involved in customized ablations have the potential to alter the quality of the optical correction. Professionals associated with customized treatment should be informed and trained with respect to possible sources of error.

Algorithms↗