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Biomedical subjects

T Kohnen

Publications and source records attributed to T Kohnen.

At least 37 records · Page 2Linked to original sources
PubMed2001

[Scheimpflug photographic imaging following implantation of anterior and posterior chamber phakic intraocular lenses: preliminary results].

BACKGROUND: For the correction of refractive errors lenticular procedures are increasingly used in addition to corneal refractive surgery. One of those techniques is the implantation of intraocular lenses into phakic eyes (pIOL). Due to the close neighborhood of the implant to delicate intraocular structures, exact positioning and high postoperative stability are required. Scheimpflug photography has been shown to be a suitable instrument for the biometry of the anterior eye segment and the examination of IOL position. PATIENTS AND METHODS: Four anterior chamber phakic IOLs (pIOLs) (Bausch & Lomb NuVita) and 7 posterior chamber pIOLs (Staar ICL) were examined 1 week, 1 month and 3-6 months following implantation. At each examination 1 Scheimpflug slit image and 1 infrared retroillumination image were taken using the anterior eye segment analysis system EAS-1000 (Nidek Co., Gamagori, Japan). Evaluation of the images was performed with a personal computer and the software provided by the manufacturer. The distance of the pIOL to cornea and human lens was calculated and incidence and amount of pIOL rotation around the optical axis and potential crystalline lens opacification were assessed. RESULTS: The distance between the anterior chamber pIOL and the cornea 1 week after implantation was 1.61 +/- 0.10 mm. The distances between the myopic posterior chamber pIOL and the human lens were 0.34 +/- 0.11 mm and between the hyperopic posterior chamber pIOL and the human lens 0.26 and 0.29 mm, respectively. The values were constant over a period of 3-6 months. The pIOL showed no movement or change of position around the optical axis. There was no detectable cataract formation in the human lens. CONCLUSIONS: All implanted phakic anterior and posterior chamber IOLs showed a stable position in the eye within the observation period. Scheimpflug photography is proved to be a useful technique for the postoperative evaluation of the positioning of phakic IOLs.

Anterior Chamber↗
PubMed2000

[Intra-individual comparison of intraocular lenses of highly refractive silicone (Allergan SI40NB) and hydrophobic acrylate (Alcon Acrysof MA60BM). 1-year follow-up].

BACKGROUND: A prospective, randomized study was performed to evaluate intra-individually the biocompatibility of foldable, highly refractive silicone and hydrophobic acrylic intraocular lenses (IOL). MATERIALS AND METHODS: We studied 35 patients who underwent phacoemulsification using a self-sealing tunnel incision. In a randomized fashion one eye received a 6-mm optic IOL made of high-refractive index silicone (Allergan SI40NB) and the other eye a hydrophobic acrylic 6-mm optic IOL (Alcon AcrySof MA60BM). All patients were examined 7 days, 1-3 and 6 months, and 1 year postoperatively. RESULTS: The mean best-corrected visual acuity (BCVA) was 0.9 +/- 0.12 vs. 0.89 +/- 0.13 (SI40NB vs. MA60BM) after 1-3 months. One-year postoperatively BCVA was still 0.9 +/- 0.12 vs. 0.87 +/- 0.14. The flare values (photon counts/ms) increased slightly 7 days after surgery (14.2 +/- 8.68 vs. 15.49 +/- 7.2, n.s.). Three months after surgery these values were again in the normal range. The mean IOL decentration was 0.29 +/- 0.14 vs. 0.3 +/- 0.15 mm 1 year postoperatively. Scheimpflug slit photography showed 40% of MA60BM IOLs to have "glistenings." No significant difference regarding posterior capsular opacification was found. CONCLUSION: One year after implantation of foldable, highly refractive silicone and hydrophobic acrylic IOLs using a self-sealing tunnel incision and phacoemulsification, no significant functional or morphological differences between the two IOL types were observed.

Acrylates↗
PubMed2000

Comparison of changes in manifest refraction and corneal power after photorefractive keratectomy.

PURPOSE: To determine which corneal curvature values most closely correlate to change in manifest refraction after excimer laser photorefractive keratectomy. METHODS: In a prospective study at the Cullen Eye Institute, excimer laser photorefractive keratectomy was performed on 27 eyes of 27 patients (mean age, 38.07+/-6.65 years). Preoperative refractive errors ranged from -2.25 diopters to -8.75 diopters (mean, -5.74+/-2.09 diopters). Preoperatively and 1 month postoperatively, we determined the spherical equivalent of the subjective manifest refraction (corrected for a 12-mm vertex distance) and measured corneal power using standard keratometry (Bausch & Lomb Keratometer; Rochester, New York) and computerized videokeratography (EyeSys Corneal Analysis System; Premier Laser Systems Inc, Houston, Texas). We collected 15 corneal values: standard keratometry and 14 computerized videokeratography values calculated using the axial, instantaneous, and refractive formulas. All calculations were performed with 1.3375 and 1.376 for the refractive index of the cornea. For each of the corneal values, we subtracted the change in corneal power from the change in manifest refraction and calculated for this difference the means, SDs, correlations, and regressions. RESULTS: Mean differences between change in refraction and change in corneal power were lower when for a refractive index of 1.376 than for 1.3375, were lowest for the most central measurement points, and displayed a high SD. A value of 1.408 for the refractive index would be required to optimize the correlation between change in manifest refraction and effective refractive power of the central 3 mm of the cornea. CONCLUSIONS: For individual patients who have undergone photorefractive keratectomy, changes in corneal values determined by computerized videokeratography or by standard keratometry do not reliably predict change in manifest refraction.

Adult↗
PubMed2000

Scanning electron microscopic characteristics of phakic intraocular lenses.

OBJECTIVE: To analyze the surface quality of new generation phakic intraocular lenses (IOLs). DESIGN: Experimental materials study. MATERIALS: Three different new generation phakic IOLs: angle-fixated anterior chamber lens Chiron Vision NuVita MA20 (polymethylmethacrylate [PMMAD, iris-fixated anterior chamber lens Ophtec Artisan Iris-Claw (PMMA), posterior chamber lens Staar ICM (polymer from porcine collagen and 2-hydroxyethyl methacrylate [HEMA]). METHODS: Representative samples of three different phakic IOLs underwent surface and edge-finish examination with light microscopy (LM). The phakic IOLs were then examined by use of scanning electron microscopy (SEM), and particular attention was given to optic surface quality, edge finish, haptic, and optic/haptic junction. RESULTS: In all IOLs the LM examination showed a smooth and homogeneous surface. No irregularities, particularly at the optic front and back surface, optic edge, haptic, and the optic/haptic junctions, were detected by SEM. One exception was a minor surface roughness at the claws of an Artisan iris-fixated anterior chamber IOL. CONCLUSIONS: Phakic IOLs are implanted either in the anterior or posterior chamber of healthy eyes, and high standards for their surface quality are required. The evaluation of surface properties with LM and SEM did not reveal any defects that contraindicate the implantation of phakic IOLs.

Biocompatible Materials↗
PubMed2000

Scotopic measurement of normal pupils: Colvard versus Video Vision Analyzer infrared pupillometer.

PURPOSE: To prospectively measure the scotopic pupil diameter in a normal population and to compare 2 infrared pupillometers for these measurements. SETTING: Johann Wolfgang Goethe-University, Department of Ophthalmology, Frankfurt am Main, Germany. METHODS: The Colvard infrared pupillometer was compared to the Video Vision Analyzer (VIVA) infrared pupillometer under scotopic light conditions in 33 participants (aged 19 to 55 years). Reliability was assessed by 2 independent examiners (E1, E2). Statistical analysis was performed using a comparison method by Bland and Altman. RESULTS: Mean pupil diameter was 6.16 mm +/- 1.20 (SD) (range 3.20 to 9.00 mm) with all measurements taken under scotopic illumination. The mean scotopic pupil diameter was 6.08 +/- 1.16 mm (range 3.2 to 8.4 mm) with the Colvard pupillometer and 6.24 +/- 1.28 mm (3.5 to 9.0 mm) with the VIVA pupillometer. The mean differences between the Colvard and VIVA were -0.27 mm (E1) and -0.05 mm (E2). Limits of agreement ranged from 1.4 (Colvard) to 2.4 (VIVA). The coefficients of repeatability ranged from 0.7 (Colvard) to 1.1 (VIVA). CONCLUSIONS: A mean scotopic pupil diameter of 6.15 mm with a maximal pupil size of 9.00 mm can be expected in a normal population; this should be considered in refractive corneal and refractive lens surgery. Measurements with the Colvard pupillometer were more reliable and precise than those with the VIVA pupillometer.

Adult↗
PubMed2000

Incision sizes with 5.5 mm total optic, 3-piece foldable intraocular lenses.

PURPOSE: To determine incision sizes for 5.5 mm total optic, foldable intraocular lenses (IOLs) made of silicone or hydrophobic acrylic. SETTING: Johann Wolfgang Goethe-University, Department of Ophthalmology, Frankfurt am Main, Germany. METHODS: In a prospective randomized clinical study including 40 cataract procedures with a temporal limbal tunnel approach, incision sizes for 5.5 mm optic, 3-piece foldable IOLs were measured before and after phacoemulsification and before and after IOL implantation using calipers. Three 5.5 mm optic, 3-piece foldable IOLs were used: 2 silicone (Pharmacia CeeOn 912, Allergan SI-55NB) and 1 hydrophobic acrylic (Alcon AcrySof MA30BA). Ten lenses of each model were implanted with a forceps, and 10 SI-55NB IOLs were implanted with the AMO Unfolder injector. Measurements of the tunnel incisions at various times were statistically evaluated using an analysis of variance and the Tukey-Kramer multiple comparison test. RESULTS: Mean tunnel width before and after implantation, respectively, was 3.32 mm+/- 0.06 (SD) and 3.42+/- 0.06 mm for the CeeOn 912 using a Nichamin implantation forceps, 3.28+/- 0.09 mm and 3.42+/- 0.09 mm for the AcrySof MA30BA using a Buratto implantation forceps, 3.00+/- 0.07 mm and 3.10+/- 0.05 mm for the SI-55NB using a Fine Universal II Folder, and 2.66+/- 0.08 mm and 2.81+/- 0.11 mm for the SI-55NB using the AMO Unfolder. Incision sizes before and after implantation were statistically different between 2 IOLs (CeeOn 912 and MA30BA) and the SI-55NB groups. Implantation of the SI-55NB with the Unfolder was associated with significantly smaller incision sizes before and after implantation than implantation with the Fine folder. CONCLUSIONS: Incisions sizes of 2.8 to 3.4 mm were associated with 5.5 mm total optic, 3-piece foldable IOLs. The Allergan SI-55NB high-refractive-index silicone IOL implanted with the AMO Unfolder system provided the smallest postimplantation incision; however, the refractive optic of this IOL is 5.0 mm versus 5.5 mm for of the CeeOn 912 and AcrySof MA30BA.

Acrylic Resins↗
PubMed2000

Optic neuropathy associated with laser in situ keratomileusis.

PURPOSE: To report 4 cases of optic neuropathy following laser in situ keratomileusis (LASIK). SETTING: Tertiary Care ophthalmic practices. METHODS: In this retrospective observational case series, 4 patients who developed acute visual loss following LASIK are reported. All had clinical evidence of optic neuropathy. Two had optic disc edema and 2 had normal appearing optic discs initially. None of the patients experienced significant visual recovery, and all developed optic atrophy in the affected eye. RESULTS: All patients had evaluations for alternative etiologies of their optic neuropathy, with negative results. All patients were therefore presumed to have experienced an ischemic optic neuropathy following LASIK. CONCLUSIONS: Patients who have LASIK may experience an acute anterior or retrobulbar optic neuropathy. The etiology is unknown but may be related to the marked increase in intraocular pressure that occurs during a portion of the procedure.

Adult↗
PubMed1999

Ocular biocompatibility testing of intraocular lenses: a 1 year study in pseudophakic rabbit eyes.

PURPOSE: To evaluate the appropriate duration for conducting ocular biocompatibility studies with an intraocular lens (IOL) in the pseudophakic rabbit model. SETTING: Alcon Laboratories, Inc., Fort Worth, Texas, USA. METHODS: A single-piece biconvex poly(methyl methacrylate) (PMMA) IOL was implanted in the capsular bag of 18 eyes of New Zealand white rabbits; 8 eyes received sham surgeries. Rabbits were monitored clinically and then sacrificed 6 or 12 months after surgery for histopathological examination of ocular tissues. RESULTS: Biomicroscopic examination revealed mild ocular changes in all surgical eyes during the first 3 months postoperatively. After that, there was a high incidence of posterior synechias, flare, and posterior capsule opacification (PCO) in eyes with PMMA IOLs. Posterior synechias and flare scores remained mild to moderate throughout the study, whereas PCO severity increased over time. Similar findings were observed in sham eyes. In addition, several eyes with PMMA IOLs developed IOL dislocation, hyphema, iris bombe, and a fibrous membrane covering the IOL. No discernible differences in biomicroscopic scores were observed in eyes at 6 or 12 months. Intraocular pressures and morphology of the corneal endothelium were normal in both groups. Results from histopathological analysis of the ocular tissues were consistent with observations from the biomicroscopic examinations. CONCLUSION: The results suggest that IOL implantation studies in the pseudophakic rabbit eye should be conducted for 3 or fewer months. Regulatory guidelines requiring longer ocular implantation studies should be revised to reflect the inherently rapid and extensive ocular response in the rabbit model.

Animals↗