Akuter Keratokonus beim Down-Syndrom

Zusammenfassung Es wird über 10 Patienten mit Down-Syndrom berichtet, die einen akuten Keratokonus entwickelten. Die Ergebnisse wie Alter bei Krankheitsbeginn, Geschlechtsverteilung, Befund des Partnerauges und histologische Veränderungen der Hornhaut werden mit denen der Literatur verglichen. — Eine eigene Theorie zur Ätiopathogenese des akuten Keratokonus bei Trisomie 21 und anderen Krankheitsbildern mit generalisierter Bindegewebsschwäche wird vorgestellt und diskutiert.

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Acute keratoconus in mongolism

Ten cases of mongolism are reported in which acute keratoconus developed. The results according to age and sex distribution, onset of the disease, status of the fellow eye, and histology of the cornea are compared with former reports. Our theory of the etiopathogenesis of acute keratoconus in patients with trisomy 21 and other diseases with generalized weakness of the connective tissue is presented and discussed.

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Herrn Prof. Dr. F. Schmid, Aschaffenburg, zum 60. Geburtstag gewidmet     

Intrakorneale Ringsegmente beim Keratokonus

Introduction

The spectrum of stage-related therapy of keratoconus has been broadened through surgical implantation of intracorneal ring segments (INTACS) as a possible method of reducing irregular astigmatism, leading to a reduction of corneal grafts especially in young, working-aged patients with keratoconus. The purpose of the present study was to evaluate the preoperative and postoperative results of femtosecond laser-assisted implantation of INTACS in ectatic corneal diseases.

Patients and methods

From August 2011 to January 2013, 20 eyes from 16 patients with a clear cornea in the visual axis suffering from hard contact lens intolerance underwent surgery in the Homburg/Saar Keratoconus Center (HKC) by the same surgeon (MEH). Among these were 16 keratoconus eyes, 1 eye with pellucid marginal degeneration und 3 eyes with post-LASIK iatrogenic keratectasia. The insertion of the INTACS ring segments was achieved by a femtosecond laser-assisted procedure that created a precise 360° tunnel at a depth of 80?% of the corneal thickness (395.8?±?38.5 μm) in the 6–7 mm zone.

Results

At 6 months follow-up mean uncorrected distance visual acuity improved from 0.07?±?0.07 preoperatively to 0.6?±?0.26 postoperatively. Mean best-corrected distance visual acuity changed from 0.4?±?0.15 preoperatively to 0.9?±?0.29 postoperatively. Mean sphere decreased from ??7.6?±?6.1 dpt to ??1.4?±?2.8 dpt. Astigmatism decreased from ??6.0?±?2.8 dpt preoperatively to ??4.3?±?2.0 dpt postoperatively. There was also a reduction in the mean flat K from 47.8?±?4.7 dpt preoperatively to 44.2?±?5.0 dpt postoperatively and in mean steep K from 51.9?±?5.0 dpt to 48.4?±?6.6 dpt. The central eccentricity index in the Pentacam was reduced to around 50?%. Neither intraoperative nor postoperative complications (including non-responders) were observed.

Conclusions

The femtosecond laser-assisted INTACS implantation provides a valid alternative to early keratoplasty for keratoconus patients with a clear central cornea and contact lens intolerance. It is a minimally invasive and reliable method for stage-related surgical management of keratoconus.     

Narbenbildung nach Hornhautvernetzung beim Keratokonus

Background

Corneal scar development after riboflavin-UVA-induced corneal collagen cross-linking (CXL) was retrospectively evaluated.

Patients and methods

A total of 163 CXL-treated eyes in 127 patients with stage 1–3 keratoconus according to Krumeich’s classification were included in this retrospective analysis. The follow-up period was 1 year. At the first and at all follow-up examinations uncorrected visual acuity (UCVA), best corrected visual acuity (BCVA), biomicroscopic findings, corneal topography and corneal thickness were recorded.

Results

At 1 year following CXL, 149 eyes (91.4%) of 114 patients had a clear cornea without corneal scar (control group), while 14 eyes (8.6%) of 13 patients developed clinically significant corneal scar (scar group). Preoperatively, the mean K value of the apex was 62.1 ± 13.8 D in the control group and 71.1 ± 13.2 D in the scar group (P=.02). The mean value of corneal thickness before the procedure was 478.1 ± 52.4 μm in the control group and 420.0 ± 33.9 μm in the scar group (P=.001). The UCVA and BCVA, which were preoperatively similar between groups (P=.59, P=.75 respectively), were postoperatively improved in the control group (P=.023, P=.001 respectively), but reduced in the scar group (P=.012, P=.004 respectively).

Conclusion

K-values and corneal thickness could be considered as predictive factors for the possible development of corneal scarring after riboflavin-UVA-induced CXL. Advanced keratoconus appears to be associated with a higher risk of corneal scar development due to lower corneal thickness, greater curvature and intrinsic tissue characteristics.     

Kollagen-Crosslinking mit Riboflavin und UVA-Licht beim Keratokonus

Reduced corneal mechanical stability in keratoconus and similar corneal diseases can be treated by photooxidative crosslinking of the corneal collagen. This method is currently undergoing clinical evaluation worldwide. To achieve high absorption of the irradiation energy in the cornea, riboflavin at a concentration of 0.1% and UVA light at a wavelength of 370 nm corresponding to the relative maximum of absorption of riboflavin (vitamin B2) is used. These therapeutic parameters were experimentally tested and have been proven clinically. Current data demonstrate that the therapeutic crosslinking procedure is safe when the important theoretical and clinical parameters are observed, and that progression of keratoconus can be prevented. In all, 80% of the published cases show a decrease in corneal curvature of about 2 D, which leads not only to stabilisation but also to an increase in visual acuity.     

Neues zur Biomechanik der Kornea beim Keratokonus

Keratoconus is a bilateral, progressive, non-inflammatory corneal degeneration characterized by a conical protrusion of the cornea which leads to marked corneal thinning thereby inducing severe visual impairment due to increasingly irregular astigmatism. Current corneal imaging technology provides an accurate anatomical and topographical analysis of the cornea which is the ‘gold standard for the diagnosis of keratoconus and preoperative screening in refractive surgery. Until recently evaluation of corneal biomechanics was feasible only in vitro as the technology required for in vivo analysis was not available. However, in recent years methods have been developed which enable an accurate in vivo analysis of corneal biomechanics thereby enhancing the early detection of keratoconus and improving the safety profile of corneal refractive procedures.     

Haze-Bildung nach Vernetzungstherapie bei Keratokonus

The aim of cross-linking therapy is to prevent keratoconus progression and stabilize the present refractive situation. A 41-year-old man was treated with collagen cross-linking in one eye. Postoperatively there were a diffuse subepithelial opacification and a paracentral corneal thinning. This superficial scarring in the sense of a "haze" disappeared only gradually despite intensive therapy.     

Wellenfrontanalyse zur Diagnose des subklinischen Keratokonus

BACKGROUND: The entity of subclinical keratoconus (SKC) has not been defined sufficiently yet. The aim of the study was to describe ocular wavefront aberrations of clinically inconspicuous fellow eyes in patients with early keratoconus (KC) as a model of SKC and to assess the feasibility of higher-order wavefront analysis to discriminate eyes with SKC from normal eyes. METHODS: This prospective study included eight clinically inconspicuous fellow eyes of eight patients with newly detected KC in the contralateral eye and a paracentral inferior-superior difference (PISD) <1.4 D. In total, 15 eyes of 12 patients with newly diagnosed KC and a PISD >1.4 D were included as positive controls and 71 healthy eyes of 40 patients served as negative controls. The wavefront error was measured in all eyes with a Hartmann-Shack sensor. Discriminant analysis was performed with input from ocular HOA data and PISD. Receiver operating characteristic (ROC) curves were plotted for PISD, single Zernike coefficients, and for the output values of the discriminant functions to investigate their usefulness for discrimination between SKC eyes, early KC eyes, and healthy controls. RESULTS: There were significant differences between inconspicuous fellow eyes (group 2) and controls (group 3) for PISD, for the coefficients Z3(-3), Z3(-1), Z4(0) and Z5(-1), and for the output values of the discriminant functions. The latter discriminated between groups 2 and 3 with maximum sensitivity and specificity (A(z) ROC=1), whereas discriminative ability was considerably lower for single Zernike coefficients. CONCLUSION: Single Zernike coefficients did not appear to be useful for the detection of SKC. Using discriminant analysis, from PISD and higher-order Zernike coefficients a metric with very high discriminative ability between normal and SKC eyes could be constructed.     

Evaluierung der dynamischen Konturtonometrie bei Keratokonus

Purpose

The gold standard for measuring intraocular pressure (IOP) until now has been Goldmann applanation tonometry (GAT), which depends on the central corneal thickness (CCT) and curvature. In patients with keratoconus who have an abnormal corneal geometry and thickness, measurement of pressure with GAT is often difficult and not very reproducible. We compared the impact of the central corneal thickness (CCT) on the IOP measured with dynamic contour tonometry (DCT), a digital method which is adapted to the corneal geometry, and GAT in patients with keratoconus.

Methods

IOP was measured in 54 patients (38 men and 16 women, mean age of 36±9.9 years) with GAT and DCT in randomized order. All patients had a keratoconus which was assured by topography. In addition central corneal thickness (CCT) was measured with the Pentacam. For statistical analysis the Pearson correlation was calculated and a Bland-Altman diagram plotted.

Results

Mean corneal thickness was 486.2±45.5 μm. DCT measured the IOP at a mean value of 14.9±2.6 mmHg and GAT at 13.3±2.9 mmHg. With a mean difference of 1.6±2.4 mmHg DCT measured significantly higher than GAT (p≤0.05) Neither IOP measurements with GAT (r=?0.03; p>0.05) nor those with DCT (r=0.08; p>0.05) showed a significant correlation to central corneal thickness.

Conclusion

The example of keratoconus confirms that IOP measured by GAT is lower than if measured by DCT. Because both methods are independent of the CCT they are equally acceptable for IOP follow-up in eyes with keratoconus, which may result in progressive corneal thinning in the long term.     

DALK und perforierende Laserkeratoplastik bei fortgeschrittenem Keratokonus

Background

In cases of contact lens intolerance and/or central corneal scars, corneal transplantation is indicated for advanced keratoconus. This can be performed as deep anterior lamellar keratoplasty (DALK) or as penetrating keratoplasty (PKP). The German keratoplasty registry shows that the proportion of anterior lamellar grafts in Germany has remained stable at approximately 5?% in recent years.

Methods

Up to now DALK has not been technically standardized but can result in a good visual acuity using the big bubble technique if Descemet’s membrane is laid bare intraoperatively. In 10–20?% a conversion to PKP is required if perforation of Descemet’s membrane occurs. In cases of advanced keratoconus PKP is still the method of first choice especially after corneal hydrops due to rupture of Descemet’s membrane. Non-contact excimer laser trephination seems to be especially beneficial for eyes with iatrogenic keratectasia after LASIK and those with repeat grafts in cases of keratoconus recurrence due to the graft being too small. For donor trephination from the epithelial side, an artificial chamber is used. Wound closure is achieved by a double running cross-stitch suture according to Hoffmann. Graft size is adapted individually depending on corneal size (as large as possible and as small as necessary). Limbal centration is given priority intraoperatively due to optical displacement of the pupil.

Results

Prospective clinical studies have shown that the technique of non-contact excimer laser PKP improves donor and recipient centration, reduces vertical tilt and horizontal torsion of the graft in the recipient bed, thus resulting in significantly less all-sutures-out keratometric astigmatism (2.8 D versus 5.7 D), higher regularity of the topography (SRI 0.80 vs. 0.98) and better visual acuity (0.80 vs. 0.63) in contrast to the motor trephine. The stage of the disease does not influence functional outcome after excimer laser PKP.

Conclusions

In cases with optimal course DALK achieves the same visual outcome as mechanical PKP but the healthy endothelium can be preserved and endothelial immune reactions are prevented in keratoconus. In contrast to the undisputed clinical advantages of excimer laser keratoplasty with orientation teeth/notches in keratoconus, the major disadvantage of femtosecond laser application is still the necessity of suction and applanation of the cone during trephination.     

Modellierung der Hornhauttopographie mit einem Subdivisionsschema bei Keratokonus

Problemstellung. Bei irregul?ren Hornhautoberfl?chen k?nnen Topographiesysteme oftmals nur unvollst?ndige Daten liefern. Subdivisionsschemata finden breite Anwendung in der Computergrafik zum Vervollst?ndigen und Gl?tten von Oberfl?chen. Ausgehend von einem Netz aus Dreiecksfacetten soll durch Iterationen eine “glatte” und vollst?ndige Oberfl?che aus Hornhauttopographiedaten in einem Standardkoordinatensystem berechnet werden.     

Modellierung der Hornhauttopographie mit einem Subdivisionsschema bei Keratokonus

BACKGROUND: Videokeratoscopy is often unable to obtain complete data sets in cases of irregular or asymmetric corneal topography. Subdivision schemes are very common in computer graphics for completion and smoothing of surfaces. Based on a network of triangular facets a smooth and complete surface in a standard coordinate system can be derived from topographic raw data. PATIENTS AND METHODS: We examined 88 patients with keratoconus and 40 normal controls. Polygons and polyhedra were defined from videokeratoscopic height data, and a surface was modeled using a modified butterfly subdivision scheme for a nonuniform sampled grid.To assess the model quality topographic raw data were changed to missing values centrally (at the apex of the cone) and in four midperipheral quadrants. The target value was the root mean square error, comparing the remodeled value of the subdivision scheme to the raw data at the position of the missing values for each group. RESULTS: Due to the nonuniform mesh of our Placido-based topographer we used a dynamic adaptive model and the governing dynamic differential equation.With a single missing value, no difference was detected between normals and patients with keratoconus. For a missing area consisting of 13 raw data points, the remodeling error was significantly higher in patients with keratoconus than in normals.With the neighborhood of 13 missing data points, the apex of the cone was remodeled in both groups of patients with less precision than with the peripheral missing data. CONCLUSION: The locality of the equation systems to be solved and the easy calculation of explicit formulas for the normals may simplify ray-tracing techniques and make subdivision attractive for large datasets in corneal topography even with irregular patterns.     

Ulcus corneae durch MRSA nach UV/Riboflavin-Crosslinking bei Keratokonus

Riboflavin/UV cross-linking is a surgical method for stabilizing a progressive form of keratoconus which was developed in Germany and is now used worldwide. The procedure is considered to be safe and rarely results in complications. In this article we report the case of a 40-year-old male patient with a severe infection due to methicillin-resistant Staphylococcus aureus (MRSA) after uneventful cross-linking in the better eye. Despite intensive local and oral therapy the ulcer did not heal completely and penetrating keratoplasty had to be performed.     

Beidseitiges Einschmelzen der Hornhaut nach beidseitigem simultanen Kollagen-Crosslinking bei Keratokonus und Down-Syndrom

Corneal cross-linking is one of the options for treatment of progressive keratoconus. Following the published standards regarding indication and treatment schedules, it seems to be a highly safe and effective operation. Only a very few severe complications, such as stromal scarring and bacterial keratitis, have been reported. We describe a patient with keratoconus and Down syndrome who was treated with corneal cross-linking on both eyes simultaneously. One week after the operation he developed central corneal melting without signs of infection in his right eye, and 1 month after the operation in his left eye. Penetrating keratoplasties had to be performed on both eyes and were successful. A possible reason for the corneal melting might have been a corneal stroma that was thinner than the proposed limit of 400 µm at the centre. The published recommended standards should be met.