Biomedical subjects

M Kohlhaas

Publications and source records attributed to M Kohlhaas.

At least 19 recordsLinked to original sources

PubMed2006

[The role of pachymetry in routine glaucoma diagnosis].

The influence of corneal thickness on the precision of Goldman applanation tonometry is highly disputed. Goldmann and Schmidt assumed that the physiological variation of corneal thickness does not influence the measurement. But they indicated that an "abnormal" deviation of corneal thickness can lead to a false measurement. In the last 30 years many investigations have reliably demonstrated that thick corneas produce elevated applanation values and thin corneas lower values. The correction value is 1 mm Hg per 25 microm change in corneal thickness. The accuracy of intraocular pressure measurement is important for the detection and monitoring of glaucoma. Therefore it is necessary to recalculate applanation values based on corneal thickness in every patient, especially after refractive surgery. It is also necessary to keep in mind that with applanation tonometry we measure a force. From the force readings we deduce the value of the intraocular pressure. This conclusion is only correct if the theory of Goldmann applanation tonometry is right. But between force measurement and intraocular pressure there is the individual cornea with special properties like thickness, rigidity and astigmatism which can influence the correctness of the measurement. So we can understand why knowledge of corneal thickness can improve the deduction from force measurement of intraocular pressure. It is also reasonable that other individual corneal properties we do not measure or do not know so far can influence the deduction. This means that the corneal thickness is not the only variable. Pachymetry allows us to estimate the intraocular pressure with higher precision. Therefore it should be clinically used.

Artifacts↗

PubMed2005

[Glaucoma diagnostics and corneal thickness].

In recent years the role of pachymetry in the correction of applanation tonometry values was controversially disputed. At the present time it is undoubtedly proven that central corneal thickness affects the accuracy of applanation tonometry. The dimension of this influence is 1 mmHg of pressure per 25 microm of change in corneal thickness. It is important to remember that Goldmann and Schmidt calibrated the applanation tonometer according to the central corneal thickness of their population by using the optical method. Therefore, it is first necessary to determine the corneal thickness for each examiner and his methods. The linear correction formula should be used only in the range of corneal thickness in which the formula was determined. The correction according to Orssengo and Pye and further developments in tonometry may offer alternatives for better estimation of intraocular pressure.

Cornea↗

PubMed2005

[A new treatment of keratectasia after LASIK by using collagen with riboflavin/UVA light cross-linking].

BACKGROUND: Keratectasia is one of the most severe complications after refractive laser surgery. Usually penetrating keratoplasty is the treatment of choice to achieve an optical rehabilitation in such cases. PATIENTS AND METHODS: We report on a female patient who developed keratectasia in both eyes 4 weeks after LASIK. Due to a severe keratectasia 10 months after LASIK, a treatment with riboflavin/UVA cross-linking was performed. RESULTS: Due to the induced collagen cross-linking the biomechanical status of the cornea was stabilized and a progression of the keratectasia was prevented. The postoperative refraction and corneal topography have been stable for 18 months. CONCLUSION: Collagen cross-linking leads to a stiffening of the anterior parts of the corneal stroma. The increase of biomechanical stability can stop the progression of a keratectasia after LASIK by means of a simple procedure.

Adult↗

PubMed2005

[Applanation tonometry in "normal" patients and patients after LASIK].

BACKGROUND: Until now it was thought that morphological parameters of the eye such as corneal thickness, corneal curvature and axial length do not affect tonometry results. However, the aim of this study was to find out whether there actually is an influence of these parameters on applanation tonometry. PATIENTS AND METHOD: In this prospective study we examined 125 eyes of 125 normal patients with a corneal thickness of 568.8 +/- 43.79 microm, a corneal curvature of 7.72 +/- 0.27 mm and an axial length of 23.62 +/- 2.05 mm. Before performing a phacoemulsification, the anterior chamber was temporarily punctured. With a closed system the intraocular pressure (IOP) was manometrically set at 20, 35 and 50 mmHg using an H (2)O column. The IOP was then measured with a Perkins tonometer. With these patients we compared 102 eyes that had undergone LASIK due to a myopia of 6.3 +/- 2.17 D. Before and 6 months after surgery, IOD, k-values and central corneal thickness of these patients were measured. RESULTS: At all set pressure levels there was a highly significant correlation of measured IOP and corneal thickness. At all set pressure levels the measured IOP significantly depended on corneal thickness (r(2) = 0.78 - 0.83). After LASIK, IOP was reduced from 16.5 +/- 2.1 to 12.9 +/- 1.9 mmHg. There was a significant correlation between IOP and corneal curvature as well as corneal thickness (r(2) = 0.631; P < 0.001). The biomechanical characteristics of the cornea are changed so that the measured IOP has to be corrected by an additional 0.75 mmHg. CONCLUSION: Since corneal thickness does affect Goldmann applanation tonometry we recommend to use the "Dresden Correction Table" (Tab. ) to achieve the real IOP. Pressure measurements after LASIK are inaccurate because of a change in corneal biomechanics, corneal thickness and curvature and they should be corrected as follows: IOP (real) = IOP (measured) + (540 - CCT)/71 + (43 - K-value)/2.7 + 0.75 mmHg.

Aged↗

PubMed2001

[Lacrimal duct treatment with ring intubation in injuries of the upper and lower eyelids].

BACKGROUND: Treating injuries of the lacrimal system with a silicon intubation is an approved method to prevent post-traumatic epiphora. MATERIALS AND METHODS: Between 1990 and 1999, operations were carried out on 44 patients with injuries of the canaliculi with silicon ring intubations. Interesting for us were the age distribution, causes of injuries, localisation and mid- to long-term postoperative complications. RESULTS: The age of the patients was between 1.75 and 74 years, 48% of the injuries were caused by household accidents, 23% by violence, 20% by traffic accidents and 9% by job-related accidents. The canaliculus inferior was injured in 68% of all patients. We found 10 postoperative complications, e.g. ectropia, a too long silicon ring or granuloma. We found a positive anatomical readapted lacrimal system in 88% and 12% of our patients complained of distinct to severe epiphora. CONCLUSIONS: The treatment of lacrimal laceration with a silicon intubation is an excellent method but special care should be taken with correct positioning of the lid margin.

Accidents, Home↗

PubMed2000

[Ultrasound biomicroscopy in pigmentary glaucoma].

PURPOSE: To evaluate the anatomical relationships of the iris in pigmentary glaucoma before and after laser iridotomy and to evaluate the effect on intraocular pressure. METHODS: Ultrasound biomicroscopy (UBM, Humphrey-Zeiss) of the anterior segment was performed in 28 eyes of 28 patients (20 male, 8 female, mean age 43 years, mean untreated IOP 24.3 mmHg) with pigmentary glaucoma before and after laser iridotomy. The slope of intraocular pressure was documented. Mean follow-up was 9 months. For statistical analysis the Wilcoxon test was used. RESULTS: Ten out of 28 eyes showed iridozonular contact and concavity of the midperipheral iris. Laser iridotomy resulted in a significant pressure drop (P < 0.05) in these 10 eyes (24.6 mmHg to 18.3 mmHg). Eighteen eyes, however, did not show iridozonular contact and intraocular pressure did not drop sufficiently (P > 0.05; 25.1 mmHg to 23.1 mmHg) after laser iridotomy. CONCLUSION: The results show that iridozonular contact does not exist in every patient with pigmentary glaucoma. Therefore, it seems possible that more than one pathogenic mechanism is involved in pigmentary glaucoma. In patients with iridozonular contact, however, laser iridotomy significantly reduces intraocular pressure.

Adult↗

PubMed1998

[Primary orbital implant dislocation. A retrospective study].

BACKGROUND: To compensate the orbital volume deficit after enucleation orbital implants are used. METHOD: Between 1986 and 1996, 449 enucleations were performed. One hundred and fifty-five orbital implants were used: 96 hydroxylapatite-ceramic-silicon (HAK-silicon), 29 hydroxylapatite-ceramic (HAK), 26 Kiel bone chips, 3 Walser and 1 Bangerter implant. RESULTS: Ten orbital implants (6.45%) had to be explanted. Seven of the 96 HAK-silicon implants were explanted: four could be changed, two of them with a smaller and two with a same diameter. We observed a complication rate of 7.29% and a rate of total loss of 3.13%. One luxated HAK-implant could be refixated (3.45%), and one implant (3.85%) of the Kiel bone chip implants was explanted. CONCLUSION: Using different types of orbital implants after enucleation, we observed a complication rate of 7%. However, to avoid the post-enucleation-syndrome and to achieve better motility of the prosthesis, orbital implants should be used.

Adolescent↗

PubMed1998

[Experiences with "reversed tip and snip" phacoemulsification].

UNLABELLED: The endothelial cell count after phacoemulsification serves as a sensitive indicator for the level of corneal traumatization caused by different phacoemulsification techniques concerning the used phacotime and phacoenergy/s. PATIENTS: In a prospective and randomized study, the "reversed tip and snip" technique and the "divide and conquer" technique were performed in groups of 30 patients each. The corneal endothelial cell count was measured preoperatively as well as 4 weeks and 3 months postoperatively. In a second study the phacotime and phacoenergy used/second and the endothelial cell loss were compared between patients 1-30 and 31-60 who were operated on with the "reversed tip and snip" technique, demonstrating the learning curve of this technique. RESULTS: The endothelial cell count showed significant (P < 0.001) reduction by about 10% after the "reversed tip and snip" technique and by about 15% after the "divide and conquer" technique. The latter produced significantly greater cell loss. The phacotime (mean: 22-17) and phacoenergy/s (mean: 23-16) were reduced significantly (P < 0.05) when patients 1-30 were compared with 31-60. CONCLUSION: The "reversed tip and snip" phacoemulsification technique produces less endothelial cell loss than the "divide and conquer" technique. There is a short learning curve by using the "reversed tip and snip" technique.

Aged↗

PubMed1998

Corneal sensation after cataract and refractive surgery.

Most surgical procedures involving the anterior segment of the eye disrupt the normal organization of corneal innervation. Since denervation of the cornea results in impaired epithelial wound healing, increased epithelial permeability, decreased epithelial metabolic activity, and loss of cytoskeletal structures associated with cellular adhesion, it is important to identify the factors that determine the extent of neural regeneration. Mechanisms of corneal nerve damage and studies of corneal nerve fiber loss and reinnervation after cataract and refractive surgery--epikeratophakia, cryokeratomileusis, keratomileusis in situ, photorefractive keratectomy, laser in situ keratomileusis, and phacoemulsification--are reviewed and the decrease in corneal sensitivity, as a measure of corneal destruction and corneal metabolism, after these surgical procedures is compared.

Animals↗

PubMed1998

[Type I lattice corneal dystrophy. Clinical and molecular genetic study of a large family].

BACKGROUND: Lattice corneal dystrophy type I is one of the frequent forms of stromal dystrophies following autosomal dominant inheritance. The beta-IG-h3 gene encoding keratoepithelin on the long arm of chromosome 5 has recently been described as disease gene for lattice corneal dystrophy type I as well as for three other corneal dystrophies with autosomal dominant pattern of inheritance. PATIENTS AND METHODS: Ten family members in three generations of a large family with autosomal dominant lattice corneal dystrophy were analyzed clinically by slit-lamp biomicroscopy. Mutation analysis in the beta-IG-h3 gene was carried out at the mRNA level by RT-PCR and cDNA sequencing. RESULTS: A heterozygous single-base substitution (417C-->T) in exon 4 of the beta-IG-h3 gene was detected predicting the replacement of arginine-124 by cysteine. Analysis of 10 family members showed perfect cosegregation of the mutation and lattice corneal dystrophy type I. The investigation excluded this mutation in one family member previously classified as potentially affected. CONCLUSIONS: The investigation confirmed autosomal dominant inheritance with complete penetrance in the family described. The mutation 417C-->T has already been found earlier in another family of different geographic origin. These results suggest a mutation hot spot at position 417. In addition, no evidence of genetic heterogeneity of lattice corneal dystrophy type I was detected. Molecular genetic analysis (in conjunction with genetic counselling) therefore may be useful in routine diagnostics as the confirmation of the diagnosis by histological examination is possible only after keratoplasty. The common pathomechanism in lattice corneal dystrophy type I may facilitate development of new therapeutic concepts; the easy accessibility of the target organ may provide new possibilities e.g. for gene therapy.

Adult↗

PubMed1998

Endothelial cell loss secondary to two different phacoemulsification techniques.

BACKGROUND AND OBJECTIVE: The endothelial cell count after phacoemulsification serves as a sensitive indicator for the level of corneal damage caused by different phacoemulsification techniques. PATIENTS AND METHODS: In a prospective and randomized study, the "Reversed Tip and Snip" technique and the "Divide and Conquer" technique were performed in groups of 30 patients each. The corneal endothelial cell count was measured preoperatively as well as 4 weeks and 3 months postoperatively. RESULTS: The endothelial cell count showed significant (P < .001) reduction by approximately 10% after the "Reversed Tip and Snip" technique and by approximately 15% (P < .001) after the "Divide and Conquer" technique. The latter produced a significantly (P < .001) greater cell loss. CONCLUSIONS: The "Reversed Tip and Snip" phacoemulsification technique produces less endothelial cell loss than the "Divide and Conquer" technique.

Aged↗

PubMed1997

[Biomechanical study of corneal stability after photorefractive keratectomy].

BACKGROUND: Photorefraktive keratectomy (PRK) is the most frequent refractive surgical procedure worldwide. The central corneal thickness is reduced due to removal of the anterior stroma, including Bowman's layer, with a laser beam. This procedure results in considerable alterations of the corneal structure. What does this mean for the mechanical properties of the cornea? METHODS: Intraocular pressure was increased via a 180 degrees tilt. Before and during this procedure, corneal topography was measured by photokeratoscopy. We examined 26 patients after PRK and 25 controls who had not undergone any surgical procedure. RESULTS: The corneal center flattened by 0.038 +/- 0.05 dpt (P > 0.05) in the PRK patients and by 0.187 +/- 0.045 dpt (P < 0.05) in the control group. PRK patients within 1 year after operation showed a minimal central corneal steepening, whereas PRK patients after more than 1 year showed a reaction similar to that in normal corneas (P < 0.05). CONCLUSION: Corneal stability is altered after PRK. After 1 year corneal stability seems to normalize due to stromal remodelling.

Adult↗

PubMed1997

[Change in corneal sensitivity after topical dorzolamide administration. A comparative study].

BACKGROUND: The new antiglaucoma drug, dorzolamide, mainly evokes local side effects like eye burning, pruritus, blurred sight and a foreign-body sensation. A clinical study was conducted to determine it dorzolamide has any influence on corneal sensitivity. SUBJECTS AND METHODS: We examined three different groups of substances. We used sodium chloride solution 0.9% and the local anesthetic oxybuprocaine 0.4% as control groups, each in two subgroups aged 23-40 years or 60-86 years. Corneal sensitivity was measured in the corneal center with Draeger's electronic optic aesthesiometer. We took the measurements directly before and 1,5,10,15 and 20 min after applying one eye drop. RESULTS: The control groups with sodium chloride solution showed no significant (P > 0.05) corneal hyposensitivity. The local anesthetic caused corneal asensitivity (P < 0.05) until the 10-min measurement. Twenty minutes after giving the anesthetic, with 12.10(-5) N corneal sensitivity nearly reached the starting value. At this time corneal sensitivity in the older subgroup was still decreased with 627.10(-5) N. In the younger subgroup dorzolamide only caused slight, but significant (P < 0.05), hyposensitivity of the cornea 1 and 5 min after application of the eye drop. CONCLUSION: Although dorzolamide decreases corneal sensitivity only a little, people with glaucoma using contact lenses should not insert them until at least 15 min after applying the dorzolamide.

Adult↗

PubMed1997

[Effect of various ablation levels on endothelial density in the enucleated pig eye. Experimental study with the 193 nm Excimer laser].

UNLABELLED: The effects of deep excimer laser ablations on the corneal endothelial cell count are still unknown. MATERIALS AND METHODS: In an in-vitro study the endothelial cell counts of 125 pig corneas were examined after excimer laser ablation. Five groups of 25 eyes reach, one control group and four groups with 3, 10, 20, and 35 D of ablation were examined. After the laser treatment, a corneoscleral disc was prepared and stored for up 5 days in an organ culture medium. The endothelial cell density of 5 corneas in each group was measured in a period of 5 days with a phase contrast microscope. RESULTS: Significant cell loss, 13-25%, was measured in each group after 5 days. There were no significant differences between the ablated corneas and the control group. CONCLUSION: Deep excimer laser ablations do not significantly reduce the endothelial cell count.

Animals↗

PubMed1997

[Changes in corneal thickness and endothelial cell density after cataract extraction using phacoemulsification].

UNLABELLED: Corneal metabolism is reduced after cataract extraction. PATIENTS AND METHODS: In a prospective study the corneal thickness and endothelial cell count of 48 patients were examined after phacoemulsification. Corneal thickness was measured with an ultrasound pachymeter and the endothelial cell count with a contact endothelial camera at the 12 o'clock position and in the corneal center before and 4 weeks, 4 months and 1 year after operation. RESULTS: One year after the operation, corneal thickness increased about 9% in the 12 o'clock position and about 12% in the corneal center. The endothelial cell count decreased about 27% in the 12 o'clock position and about 18% in the corneal center. We measured a significant correlation between cell loss and age at both points. Concerning the corneal thickness, no significant correlation was found. CONCLUSION: After cataract extraction corneal metabolism is reduced. The endothelial cell count or corneal thickness can be used as an indicator of the corneal trauma resulting from the operation.

Aged↗

PubMed1997

[Measuring intraocular pressure in keratoconus. Effect of the changed biomechanics].

BACKGROUND: Keratoconus is associated with changes in the corneal structure, such as defects of Bowman's layer, a decrease of corneal thickness etc. They result in alterations of some of the biomechanical parameters of the cornea, namely, rigidity and elasticity. The present study was performed to examine how impression tonometry and applanation tonometry for determination of intraocular pressure (IOP) are affected by the changed biomechanical parameters associated with keratoconus. PATIENTS AND METHODS: We examined 20 normal subjects (40 eyes) and 17 keratoconus patients (25 eyes). The corneal thickness was measured by ultrasound pachymetry in the corneal center. In the keratoconus patients, an additional measurement was made at the conus peak. The corneal curvature was determined using the TMS keratoscope. The IOP measurements were made with the Schiötz tonometer (10 g). For comparison, additional IOP measurements in the corneal center and, in the keratoconus group, on the conus peak were made with the applanation tonometer. RESULTS: The normal subjects had a central corneal thickness of 548 +/- 30 microns, compared to 505 +/- 42 microns in the corneal center and 425 +/- 41 microns on the conus peak in keratoconus patients. The average corneal curvature was 43.3 +/- 1.8 D in the normal subjects and 47.8 +/- 4.1 D in keratoconus patients. Applanation tonometry produced results on 11.33 +/- 1.43 mm Hg in the normal group (corneal center) compared to values of 12.00 +/- 2.55 mm Hg (corneal center) and 7.30 +/- 1.95 mm Hg (conus peak) in the keratoconus cohort. The coefficient of rigidity was 0.0236 +/- 0.0026 microliter-1 in the normal subjects, compared to 0.0173 +/- 0.0050 microliter-1 in the keratoconus patients. CONCLUSION: The morphological changes associated with keratoconus may cause tonometry errors.

Adult↗

PubMed1997

[Endothelial cell loss after phacoemulsification with the "reversed tip and snip" technique compared with the "divide and conquer" technique].

BACKGROUND: The endothelial cell count after phakoemulsification is a sensitive parameter to compare different phakoemulsification techniques. PATIENTS AND METHOD: In a prospective study 30 patients in each group were operated upon the "Reversed Tip and Snip" and with the "Divide and Conquer"-Technique. The corneal endothelial cell count was measured before surgery and 4 weeks and 3 months after the operation. RESULTS: The endothelial cell count was reduced significantly about 10% after the the "Reversed Tip and Snip" and about 15% after the "Divide and Conquer"-Technique. The first mentioned technique had a significantly reduced cell loss than the latter. CONCLUSION: The "Reversed Tip and Snip" phakoemulsification technique causes less endothelial cell loss than the "Divide and Conquer"-Technique.

Aged↗

PubMed1997

[Development of corneal sensitivity after phacoemulsification with scleral tunnel incision].

BACKGROUND: after anterior segment surgery the anatomical structures and in particular corneal metabolism and corneal trophic are reduced. The corneal wound healing might be monitored by measuring corneal sensitivity. MATERIAL AND METHOD: In a prospective study of 1 year corneal sensation of 26 patients, age = 72.49 +/- 11.09 years, after phacoemulsification with scleral tunnel is examined. Corneal sensitivity is measured with the Draeger aesthesiometer in the corneal center, in the 6 o'clock and 12 o'clock position before and 4 weeks, 4 months and 1 year after the operation. RESULTS: The preoperative corneal sensitivity thresholds before the operation are with 11.61 +/- 10.49 x 10(-5) N in the 12 o'clock position, in the center with 2.43 +/- 2.57 x 10(-5) N and in the 6 o'clock position with 11.86 +/0 10.37 x 10(-5) N normal. Even 1 year after surgery corneal sensitivity is markedly reduced with 257.08 +/- 306.71 x 10(-5) N, 107.77 +/- 246.76 x 10(-5) N and 82.81 +/- 140.77 x 10(-5) N in the 6 o'clock position. CONCLUSION: Even 1 year after phacoemulsification corneal sensitivity is definitely hyposensitive in the center and descretely hypotensitive in the periphery at the 6 o'clock.

Adult↗