Search PubMed⌕ Search

Biomedical subjects

P Janknecht

Publications and source records attributed to P Janknecht.

31 records · Page 2Linked to original sources
PubMed1994

[The Heidelberg Retina Tomograph: reproducibility and measuring errors in different pupillary widths using a model eye].

BACKGROUND: We measured the reproducibility and relative error of the Heidelberg Retina Tomograph (HRT) in a model eye with various widths of the pupil. METHODS: We put diaphragms of various diameters in front of the lens of a model eye. The volume of an artificial papilla which was inserted into the model eye was measured three times. The coefficient of variation (standard deviation/mean value) was taken as a measure of the reproducibility. The relative error was defined as the absolute value of the quotient of the difference between measured and real value. RESULTS: The relative error for diaphragms of 1.5 to 5 mm was 7% to 18.4%, for a diaphragm of 1 mm 19.8%, and for a diaphragm of 11 mm 21.3%. The coefficient of variation ranged from 0.49% to 1.95% for diaphragms of 1.5 to 11 mm diameter, and was 8.1 for a diaphragm of 1 mm diameter. CONCLUSION: The HRT is capable of measuring volumes with a reasonable accuracy. The accuracy does not depend on the width of the pupil over a wide range of pupil diameters. In cases of very small or very much dilated pupils the accuracy and reproducibility declines.

Eye, Artificial↗
PubMed1994

Optic nerve head analyser and Heidelberg retina tomograph: accuracy and reproducibility of topographic measurements in a model eye and in volunteers.

The accuracy and reproducibility of the optic nerve head analyser (ONHA) and the Heidelberg retina tomograph (HRT) were compared and the performance of the HRT in measuring fundus elevations was evaluated. The coefficient of variation of three repeated measurements in a model eye and in volunteers and the relative error in a model eye was calculated. With ONHA measurements the pooled coefficient of variation in volunteers was 9.3% in measuring cup areas and 8.4% in measuring the cup volume. In a model eye the pooled coefficient of variation was 7.6% for the parameter 'cup area' and 9.9% for the parameter 'cup volume'. The pooled relative error in the model eye was 6.6% for the parameter 'cup area' and 5.1% for the parameter 'cup volume'. With HRT measurements in volunteers the pooled coefficient of variation of both the parameters 'volume below contour' and 'volume below surface' was 6.9%. In the model eye the pooled coefficient of variation was 2.4% for the 'volume below contour' and 4.1% for the parameter 'volume below surface'. The pooled relative error in the model eye was 11.3% for the 'volume below contour' and 11% for the 'volume below surface'. The pooled relative error in measuring retinal elevations in the model eye was 3.8%. The coefficient of variation was 3.5%. The accuracies of the HRT and ONHA were similar. However, as the ONHA 'cup volume' is unreliable in patients because of the design of the ONHA whereas the HRT volume parameters are reliable it seems reasonable to assume that the HRT is superior to the ONHA. Only the HRT is capable of quantifying retinal elevations.

Adult↗
PubMed1993

[Isovolemic hemodilution in central retinal vein occlusion in patients less than 50 years of age].

AIM--Aim of the study was investigation of the effect of isovolemic hemodilution in patients younger than 50 years on the course of central retinal vein occlusion (CRVO) and to compare these results with those of older patients with CRVO. PATIENTS AND METHODS--We performed a prospective study on 35 patients younger than 50 years who were suffering from a central retinal vein occlusion. These patients were all treated by isovolemic hemodilution and compared to a group of older patients with CRVO with the same treatment. RESULTS--About 66% of the younger patients were men compared to only 46% in older patients. At least two cardiovascular risk factors were present in 8.5% of the younger and 54% of the older patients. 16 eyes showed the ischemic, 19 the nonischemic type of CRVO, a similar distribution as in older patients. The course of the disease was more favourable in younger patients, although ocular complications may occur in ischemic CRVO. Isovolemic hemodilution did not change the initial visual acuity of eyes with nonischemic CRVO, but led to an improvement in 56% of the eyes with ischemic CRVO. This means only a minor difference to the course of CRVO in hemodiluted older patients. CONCLUSION--In general, there is no principal difference between the CRVO in younger and older patients, but the course is more favourable in younger patients. On the basis of these findings we recommend isovolemic hemodilution in younger patients with ischemic CRVO.

Combined Modality Therapy↗
PubMed1993

[Effect of pterygium operation on preoperative astigmatism. Prospective study].

High-grade corneal astigmatism is considered to be an indication for pterygium surgery. However, no prospective studies have been carried out to determine whether a pterygium operation really reduces preoperative astigmatism. Therefore, we prospectively examined 23 patients who were operated on for pterygia at the University Eye Clinic in Freiburg in 1991. Pre- and postoperative corneal astigmatism was measured by ophthalmometry or retinoscopy. Preoperative astigmatism after pterygium surgery was reduced or unaltered in 19 patients. In 4 patients, the postoperative astigmatism was increased. The mean preoperative astigmatism was 2.41 D in the horizontal meridian, the postoperative astigmatism 1.29 D. The reduction was statistically significant (P < 0.0001, Wilcoxon test). The higher the preoperative astigmatism, the higher the difference between pre- and postoperative astigmatism (r2 = 0.88, P = 0.0001). Our technique of pterygium surgery (free conjunctival transplant after polishing the cornea, limbus, and sclera) reduces preoperative astigmatism. Thus, high-grade astigmatism can be regarded as an indication for pterygium surgery.

Astigmatism↗
PubMed1993

[Do scars grow despite successful laser coagulation of subretinal neovascularization?].

After successful laser coagulation of subretinal neovascularization, we examined 9 patients to see if laser scar growth (which can be expected according to the literature) is accompanied by an increase in associated scotoma. We used a specially designed visual field program. Laser scars had grown by 23% 107 days after therapy and by 32% after 409 days. The changes in our patients were at the lower range of the data reported in the literature. The increase in the laser scar was statistically significant in just one patient. Mean sensitivity and two further parameters for describing visual fields, which we introduced, all hinted at an improvement in the central visual field, although the laser scars had grown. The mean sensitivity increased by 4.9% and 7.5% after 107 and 409 days, respectively.

Adult↗
PubMed1993

Postoperative refraction and anterior chamber depth after complicated cataract surgery with vitreous loss and transscleral suture fixation of posterior chamber lenses.

The postoperative refraction and anterior chamber depth of 50 eyes that had complicated cataract extraction with vitreous loss were compared with those of 25 fellow eyes (that had uncomplicated cataract extraction) of the same patients. Transscleral suture fixation of the posterior chamber intraocular lens (PC-IOL) was required in 34 of the 50 study eyes; the lens was implanted onto the remaining defective capsule in the remaining 16. The anterior chamber depth was significantly deeper after transscleral suture fixation of the PC-IOL (mean, 0.54 mm; P < .01). The difference between the refraction of the eyes with transscleral suture fixation and that of the control eyes was +0.58 diopters. Although each surgeon should assess specific results and modify the lens calculations accordingly, we have found that with our technique, for eyes that have required transscleral suture fixation of a PC-IOL, +0.50 D should be added to the calculated IOL power.

Aged↗
PubMed1992

[Surgical aspiration of secondary cataract. Success quotas and complications].

Cataracta secundaria ("Elschnig pearls") following extracapsular cataract extraction with IOL implantation can be treated by Neodymium-YAG laser capsulotomy or by surgical peeling. The major benefit of the peeling technique is the preservation of an intact posterior capsule. We retrospectively reviewed the peeling procedures (n = 224, mean age: 67 years) performed in our hospital from 1987 to 1990. The results were as follows: (1) In almost all cases (214/224) visual acuity was improved by the operation (mean improvement 0.16-->0.54); (2) major complications were: rupture of the posterior capsule in 9% (20 eyes), mostly (11 cases = 5%) associated with vitreous prolapse; retinal detachment in 1% (2 cases, one with, one without preceding rupture of the posterior capsule); persistnt corneal edema caused by endothelial decompensation in 1 case; (3) recurrence of cataracta secundaria after the first peeling was observed in 26%. Surgical peeling of cataracta secundaria improves visual acuity to about the same extent as Neodymium-YAG laser capsulotomy. It is not without risk, however, and complications occur, including retinal detachment. The possibility that a secondary cataract can reform must be taken into account.

Aged↗
PubMed1991

[Automatic perimetry of the central visual field in diseases of the macula].

We developed a program for testing the central 12 degrees of the visual field with a spatial resolution of 1.6 degrees that was easy to operate. The program was designed for the Octopus computer-perimeter and created by means of the SARGON-utility. Our way of examining differed slightly from the standard Octopus procedure. We tested 16 normal eyes and 13 eyes of patients with various diseases of the central retina. Our normal values of differential threshold sensitivities were about 1.8 dB below the normal values of the Octopus system. Sensitivity and specificity of the program were nearly identical irrespective of using our normal values or the Octopus normal values for the calculation of the above mentioned parameters. Sensitivity was 84.6%, specificity 87.5%. The ability of the program to correctly localize retinal defects was shown. The program was designed for follow-up of patients having undergone paramacular lasercoagulation.

Adult↗
PubMed1991

[Chronic subgaleal abscess as a cause of eyelid swelling].

A 36 year-old female patient presented with a massive swelling of the eyelid, cheek, and neck. We could not explore any cause for those swellings. Finally, magnetic resonance imaging of the head showed a hugh subgaleal abscess. It was caused by minor scalp trauma.

Abscess↗
PubMedDate not supplied

Did the spectrum of endophthalmitis change? A study comprising 13 years experience with operative therapy of endophthalmitis.

PURPOSE: The authors wondered whether the spectrum of endophthalmitis and the type of therapy had changed. METHODS: Files of patients who were operated upon for endophthalmitis between 1988 and 2000 were retrospectively analyzed. They were divided into Group 1 (operated upon 1988 to 1994) and Group 2 (1995 to 2000). RESULTS: Group 1 consisted of 83 patients (43.4% female, mean age 63.9 years), Group 2 of 108 (38.9% female, mean age 64.6 years). Bilateral endophthalmitis occurred in 8.4% of Group 1 patients (3.7% of Group 2 patients). Patients in both groups took on average 1.2 drug types against various internal diseases. The mean interval between first symptoms and presentation in the clinic was 45.7 days in Group 1 (19 days in Group 2; difference statistically significant). There were 63% (Group 1) (70% [Group 2]) cases of postoperative endophthalmitis, among them 58% (Group 1) (63% [Group 2]) after cataract extraction, 6% (Group 1) (5% [Group 2]) after glaucoma surgery, 20% (Group 1) (17% [Group 2]) endogenous and 17% (Group 1) (13% [Group 2]) post traumatic. In Group 2 slightly more Gram-negative bacteria were found. As an initial procedure the following were performed: vitrectomy (70% [Group 1], 88% [Group 2]), removal of crystalline lens (11% [Group 1], 10% [Group 2]), removal of pseudophakos (2% [Group 1], 12% [Group 2]), opening of posterior capsule (1% [Group 1], 9% [Group 2]), and anterior chamber irrigation (36% [Group 1], 43% [Group 2]), often combining procedures. There were significantly more vitrectomies and openings of the posterior capsule in Group 2. Neither the spectrum of secondary and tertiary procedures nor the reasons for such surgery differed in both groups. Neither visual acuity at initial presentation (0.1) nor at final follow-up (0.3) differed between the two groups. The rate of enucleation was less in Group 2 (6% versus 11%) although not statistically significantly. CONCLUSIONS: In Group 2 there were slightly more Gram-negative bacteria and the time interval between initial symptoms and presentation in the clinic had decreased. This can be interpreted as an increase in the severity of the endophthalmitis cases. The final visual acuity was identical in both groups, the enucleation rate improved.

Adolescent↗
PubMedDate not supplied

Recurrent herpetic keratitis during topical acyclovir application.

Dendritic herpetic keratitis developed in a 49-year-old patient during topical acyclovir treatment. A positive herpes simplex culture was obtained. After acyclovir was replaced by trifluorothymidine and interferon, the dendritic lesion disappeared and herpes simplex culture became negative. Six months later a carcinoma of the larynx was diagnosed. The acyclovir-resistant herpetic keratitis may be associated with the carcinoma because resistant herpes simplex virus strains are predominantly described in patients suffering from immune deficiency.

Acyclovir↗
PubMedDate not supplied

Reduction of retinal exudates in diabetic retinopathy after heparin-induced extracorporal LDL-precipitation (HELP). A case report.

INTRODUCTION: Exudative diabetic retinopathy is difficult to treat. We describe a patient in whom we believe extracorporeal LDL-precipitation (HELP) improved visual acuity. METHODS: HELP is a variant of extracorporeal dialysis which reduces low-density lipoprotein and fibrinogen levels. CASE REPORT: A heavily overweight patient with massive exudative diabetic retinopathy was administered HELP. Four months after starting HELP, and after vitrectomy and panretinal photocoagulation, the massive exudation was drastically lower. Visual acuity improved from 0.03 (0.02) OD (OS) to 0.25 (0.13) OD (OS). DISCUSSION: The role of vitrectomy and panretinal photocoagulation is discussed. HELP seems to be the most probable explanation for our patient's gain in visual acuity.

Chemical Precipitation↗