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Biomedical subjects

N Ehlers

Publications and source records attributed to N Ehlers.

At least 19 recordsLinked to original sources
PubMed1995

Effect of excimer laser keratectomy on the mechanical performance of the human cornea.

Enucleated human eye globes were set-up for measurements of pressure (2-100 mmHg) induced tangential epithelial and endothelial side corneal strain, and for measurements of central corneal thickness and central radius of curvature. In one experimental group (N = 6), a shallow ablation (15-20 microns deep) removing Bowman's layer was performed in the central 7 mm diameter zone of the cornea. The fellow eye served as control (N = 6). In another experimental group (N = 6) a 70% deep keratectomy was performed in the central 7 mm diameter zone. The pressure induced central corneal strain was 5-10% higher in corneas without Bowman's layer compared with intact corneas. The epithelial side tangential corneal strain in eyes with a 70% deep keratectomy increased to twice as much as that of intact corneas, but the endothelial side strain was similar. In all groups of eyes Young's modulus of elasticity increased rapidly with the corneal stress level up to testing loads of 25 mmHg. At higher loads the degree of stress-stiffening was smaller. The differences in average corneal strain between the 3 groups could be explained by the induced changes in central corneal thickness, as there were no statistically significant differences in stress-normalized Young's modula of elasticity between the 3 groups. The central radius of curvature did not change significantly with increasing pressure in intact eyes or in eyes without Bowman's layer. In deep keratectomized corneas the corneal radius of curvature decreased approximately 1% when the intraocular pressure was increased from 2 to 100 mmHg.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1995

Recurrence and rejection rates following corneal transplantation for herpes simplex keratitis.

Seventy-two penetrating primary keratoplasties for herpes simplex keratitis performed from 1970 to 1993 were reviewed. Postoperative follow-up periods ranged from 6 months to 16 years with 2 years median. Epithelial herpetic recurrence occurred in 25% of the transplants the first year and in 44% during the first 2 years. Primary allograft rejection was observed in 29% of the grafts the first year and in 46% during the first 2 years. Preoperative inflammation was a risk factor for preservation of a clear cornea (p < 0.10). The degree of corneal vascularization prior to operation did not influence the survival of the grafts. The overall one-year survival rate of a clear graft was 84% and the 2-year survival rate was 67%. Prophylactic antiviral treatment is discussed.

Adolescent↗
PubMed1995

Healing velocity of corneal epithelium evaluated by computer. The effect of topical steroid.

To objective determine the area of corneal abrasion, a video camera was connected to a slit-lamp. The videosignal was digitized and analyzed by a computer program. The maximal horizontal and vertical diameters were measured as well as the total abraded area. The algorithms of calculating healing velocity of corneal epithelium are discussed, and this system was tested on patients treated for myopia with a 193 nm ArF excimer laser. It was shown that topical steroid application did not impair corneal epithelial healing velocity.

Administration, Topical↗
PubMed1995

A three-dimensional study of the human corneal keratocyte density.

The population of stromal keratocytes represents a rarely examined topic. In the present paper we investigated the three-dimensional distribution of keratocytes in human donor corneas. The keratocyte density was calculated from biochemical measurements of the DNA content in samples of the corneal (and scleral) stroma obtained from well-defined regions. The DNA content of the central stroma (0-2 mm from apex) had a mean (+/- SD) of 1.25 +/- 0.30 micrograms DNA/mg dry tissue weight, corresponding to a cellularity of 4.6 +/- 1.1 x 10(4) cells/mm3 (n = 13). Towards the corneal periphery, the cellularity gradually increased to a 60-70% higher cell density at limbus. In the central stroma, an anterior-posterior cell gradient was found with a 30% lower cellularity in the subendothelial region compared to the subepithelial stroma (n = 8). In the four main quadrants of the central stroma, a uniform cell density was found while the peripheral areas showed a 10% higher cellularity in the superior quadrant. A close intraindividual correlation was observed between data obtained from 40 paired corneas ('cornea 1' versus 'cornea 2'); the stromal cellularity within 0-3.75 mm from apex (r = 0.81), the stromal cellularity within 3.75-5.5 mm (r = 0.92), the stromal cellularity within 5.5-8.0 mm (r = 0.85), and the endothelial cell density (r = 0.84). However, within a given cornea no correlation was found between the density of endothelial cells and keratocytes. These data define normal values for the regional density of keratocytes in the human cornea.

Adult↗
PubMed1994

[Excimer laser therapy of recurrent corneal erosions].

Recurrent corneal erosions have been recognized as a clinical problem for many years. Many patients with erosions do not respond satisfactorily to the standard treatment. In this paper we present a study of treatment of 24 patients with recurrent corneal erosions with the excimer laser, where 75% of the patients reported the treatment as a success.

Adult↗
PubMed1994

The keratocyte density of human donor corneas.

The cellularity of the human corneal stroma has not been described in the literature. In the present study we calculated the density of keratocytes in human donor corneas using a new method for biochemical measurement of the stromal DNA content (sDNA). The DNA measurements were compared to morphological counts of the number of keratocyte nuclei per area (KNPA) obtained from histological sections. A significant correlation was found between the data achieved by the two methods (r = +0.52, p < 0.001, n = 46). No significant change in either sDNA or KNPA was found during 28 days of organ culture, and no influence of donor age, sex, or post mortem time was found on either sDNA or KNPA. Both sDNA and KNPA approximated a normal distribution with a mean sDNA of 1.10 +/- 0.25 micrograms DNA/mg dry tissue weight and an average KNPA of 200 +/- 53 nuclei/mm2 (n = 35). Between paired corneas the sDNA were closely correlated (r = +0.83, p < 0.005, n = 11 pairs) with an intra-individual variation of only 0.5%. Using the sDNA data, the keratocyte density in the central region of human donor corneas was calculated to be 129,000 +/- 29.000 per mg dry tissue weight (n = 35). Thus, when corneal grafting is performed (using a 7 mm trephine) an average of 818,000 +/- 186,000 donor keratocytes are transplanted. Assuming a uniform cellularity throughout the stroma, the average number of keratocytes was calculated to be 2,430.000 +/- 551,000 per human donor cornea.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1992

Excimer laser treatment of pterygium.

Primary experience with the use of excimer laser in pterygium therapy is presented. Twenty-two pterygia (11 primary and 11 recurrent) were surgically removed using the bare-sclera technique followed by excimer laser ablation to smooth the corneal surface. As recurrence was observed in 20 eyes (91%) during the first year, supplementary excimer laser treatment of a pterygium does not seem to reduce the recurrence rate. The high recurrence rate in this series may to a certain extent reflect the surgical technique used (bare-sclera).

Adult↗
PubMed1992

Excimer laser refractive keratectomy for high myopia. 6-month follow-up of patients treated bilaterally.

Both eyes of twenty patients were treated for myopia with refractive keratectomy using an excimer laser (193 nm), and followed for six months. The 40 eyes were divided into Group I (22 eyes) with an attempted refraction change of 5-8 diopters; and Group I (18 eyes) with 9-12 diopters of attempted refraction change. In Group I the corrected visual acuity improved or was unchanged in 16/22 eyes. Two eyes with high preoperative corrected visual acuity had experienced a significant loss in corrected visual acuity after 6 months. In Group II, the corrected visual acuity decreased in 10/18 eyes, in 4 eyes significantly. Among the 40 eyes, 39 had a refraction change less than intended after 6 months. Overcorrection was seen in only 1 eye. In Group I, 20/22 eyes were corrected up to 2.5 diopters less than attempted. In Group II, 9/18 eyes were more than 2.5 diopters from the attempted correction. All eyes developed subepithelial opacification ('haze'), which, in spite of steroid treatment, was still present after 6 months. The haze was more severe in eyes treated with 9-12 diopters of attempted refraction change. The achieved refraction change in the two eyes of the same patient was found to be correlated, possibly due to an individual factor in corneal wound healing.

Adolescent↗
PubMed1991

Epikeratophakia for high myopia.

A cryo-technique for production of corneal epi-lenses has been developed. During the manufacturing procedure the anterior surface of the tissue is moulded and the posterior surface cut with a microtome. After cutting, the epi-lenses are stored for days to weeks in an organ culture medium. Twelve eyes in 10 patients have been treated with epikeratophakia for high myopia (greater than -7 D). In all eyes, epithelialization was complete within one week, and at follow-up 3-18 months after the operation all epi-lenses were clear. The average refractive change in spherical equivalents was 9.7 +/- 4.4 D. All eyes obtained better uncorrected visual acuity, and no eyes lost more than one line of the best corrected visual acuity. At the time of follow-up, the patients' native cornea had regained normal hydration, whereas the epi-lenses did not thin as much as expected.

Adult↗
PubMed1991

HLA-DR/RFLP compatible corneal grafts.

Fifty-one elective high risk transplantations were matched according to HLA/DR antigens and RFLP-subtypes. The 18 months survival of the grafts are 93% in the matched group compared to 50% in a non-matched compatible historical control group.

Adolescent↗
PubMed1991

A clinical comparison of optical and ultrasonic pachometry.

Central corneal thickness (CCT) of normal and oedematous corneae was measured in a study comparing a modified Haag-Streit optical pachometer and an ultrasonic pachometer (Teknar Ophthasonic, preset velocity 1630 m/s). Sixty-eight patients were examined before and after cataract extraction with implantation of an anterior chamber lens. Mean values of CCT before operation were 531 +/- 4.9 (SEM) micron by optical pachometry and 524 +/- 4.7 microns when measured by ultrasound (not significantly different). On the first post-operative day the values were 618 +/- 8.4 and 602 +/- 7.6 microns for optical and ultrasonic measurements, respectively (significantly different, 2P less than 0.001). Correlation analysis showed a high dependence between the methods with coefficients of correlation being 0.955 before and 0.958 after the operation. Linear regression analysis revealed small, but significant differences between the techniques. The difference between the two methods increased with increasing corneal hydration, whereas it could not be ascribed to sex, age, or intraocular pressure. It is concluded that for clinical purposes optical and ultrasonic pachometry techniques are comparable.

Aged↗
PubMed1990

Effect of near normoglycemia for 5 years on progression of early diabetic retinopathy and renal involvement.

The effect of strict metabolic control for 5 years on renal function and retinal morphology was estimated in 24 insulin-dependent diabetic individuals (age 29 +/- 8 years, diabetes duration 10 +/- 6 years) with albustix negative urine and minimal or no background retinopathy before the study. They were randomized to conventional insulin treatment (CIT) or continuous subcutaneous insulin infusion (CSII) with a portable pump. During CSII treatment the metabolic status was significantly improved. HbA1c fell from 8.9 +/- 2.0 to 7.4 +/- 1.3% (p less than 0.01) whereas HbA1c was unchanged during CIT treatment. The mean value of urinary albumin excretion (UAE) was not statistically significantly changed (from 12 +/- 10 mg/24 h to 13 +/- 5 mg/24 h in CSII patients and from 14 +/- 12 to 11 +/- 6 mg/24 h in CIT patients (p greater than 0.1). On the other hand, the elevated GFR values were significantly reduced in both CSII and CIT patients, 129 +/- 17 to 120 +/- 9 and 129 +/- 18 to 119 +/- 12 ml/min.1,73m2, respectively (p less than 0.05). Both the number of microaneurysms, haemorrhages and exudates tended to increase mor in CIT patients than in CSII patients during the 5 year study period, but the differences did not reach statistically significance (p greater than 0.1). Pump treatment did not induce proliferations or "cotton wool" exudates. We conclude that no statistically significantly differences between GFR values, UAE rates, and progression of background retinopathy was observed between normoalbuminuric IDDM patients treated for 5 years with CIT and CSII, respectively. However, due to the size of the material a type II error must be taken into consideration.

Adult↗
PubMed1989

[Control of refraction in cataract surgery].

The optical problems associated with cataract surgery are reviewed and methods to control the refractive state of the eye after the operation are presented. The clinical benefit of a calculation of intraocular lens (IOL) power from measurements of corneal curvature and eye length is demonstrated in a series of operated patients from two Danish eye departments. It is concluded, that the postoperative refraction can be controlled with a reasonable accuracy. Large and unexpected deviations in the postoperative refraction are avoided in this way, and in a number of cases it is possible to reduce the need for spectacles after the operation.

Cataract Extraction↗
PubMed1989

Exogenous, ocular, and systemic factors associated with keratitic ulceration.

Information on type and frequency of empirically observed exogenous, ocular, and systemic predisposing factors for keratitic ulceration is important for clinical identification of groups at risk and may form a basis for planning experimental studies on the pathogenesis of ulceration. Therefore a retrospective study comprising 104 patients with 25 herpetic and 79 non-herpetic corneal ulcerations was performed. Patients with herpetic ulcerations were mainly males and were younger than patients with non-herpetic corneal ulceration. Keratoplasty and steroid treatment was found as frequent co-existing predisposing factors in the herpetic group. In the non-herpetic group an exogenous factor was found in 56%, an ocular factor in 56%, and a systemic predisposing factor in 46% of the patients. In only 2.5% of these patients was there found no predisposing factor. Pathogenetic mechanisms of predisposing factors for non-herpetic corneal ulceration is discussed.

Adolescent↗