Abstract:
BACKGROUND:A retinal image performance distorted by an asymmetric or irregular corneal surface cannot be compensated for with spherocylindric glasses completely. The best-corrected visual acuity is markedly decreased and contact lens fitting often impossible. The purpose of this study was to calculate the differential height between corneal topography raw data and any regular surface with mathematical methods in order to ablate the differential height with a computer-controlled laser beam, thereafter. METHODS:A Zernike decomposition of radial degree n = 16 was realized within a clinically relevant central corneal area of 8 mm in diameter based on corneal topography raw height data of a commercially available topographer (TMS-1, Tomey, Erlangen). Any target surface could be defined by varying weighting of the Zernike coefficients. The calculated differential height ablation between the raw data and the target surface given in a polar grid was transformed to a Cartesian grid to evaluate the sleeping time at each grid position considering the characteristic ablation curve for the intended ablation of the height difference. Subsequently, differential height ablation was simulated using an automated laser beam control for a modified excimer laser (MEL60, Aesculap-Meditec, Jena). We developed software tools for Zernike decomposition of corneal topography raw height data and time-regulated automatic laser beam control of the grid positions in the higher programming language C (Borland C++ 3.1, Borland Inc., München). RESULTS:Definition of a target surface can be realized alternatively by selecting a set of Zernike coefficients or defining a spherical or spherocylindrical surface by superposition of parabolic terms in a fixed proportion creating a best-fit target surface to the raw data. In originally "relatively flat" areas, the differential height profile indicates a "relatively deep" ablation resulting in relative steepening towards the periphery of the ablation zone. The resolution of the mechanical unit of the laser beam control consisting of two linear stepping motors is 9 microns in the focal plane with a reproducibility of 5 microns. The software unit is guiding the laser beam in a meandering fashion within the ablation area considering the calculated sleeping time for each grid position. Mean overlap of the 1 mm laser spots is 70%. The laser beam diameter of 1 mm effects a peripheral transition zone of 0.5 mm. CONCLUSIONS:Zernike decomposition of corneal topography height data is an efficient tool for localizing and quantifying superficial irregularities and for directly calculating an ablation profile from created differential height data. With an automatic laser beam control a well-defined laser ablation of superficial corneal irregularities is possible, subsequently.
journal_name
Klin Monbl Augenheilkdjournal_title
Klinische Monatsblatter fur Augenheilkundeauthors
Langenbucher A,Seitz B,Kus MM,van der Heyd GJdoi
10.1055/s-2008-1034963subject
Has Abstractpub_date
1998-09-01 00:00:00pages
132-40issue
3eissn
0023-2165issn
1439-3999journal_volume
213pub_type
杂志文章abstract::The value of a register of corneal grafts is that it can provide new data about the long-term outcome of corneal transplantation and may allow a more reasoned distribution of scarce donor corneas. The large numbers of cases and events can accommodate wide variations in practice patterns without losing statistical powe...
journal_title:Klinische Monatsblatter fur Augenheilkunde
pub_type: 杂志文章
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journal_title:Klinische Monatsblatter fur Augenheilkunde
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journal_title:Klinische Monatsblatter fur Augenheilkunde
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journal_title:Klinische Monatsblatter fur Augenheilkunde
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abstract::In addition to photopic visual acuity both mesopic vision and sensitivity to glare play an important role in road traffic safety. It is known since the comprehensive investigations by Harms and Aulhorn that mesopic vision and sensitivity to glare are subjected to interindividually different changes with increasing age...
journal_title:Klinische Monatsblatter fur Augenheilkunde
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abstract::Results of clinical observation over post-operative period and degree of exsudative reaction in 240 patients (262 eyes) with implantation of intraocular lenses are analysed. Three types of postoperative course are distinguished: a reactive, postoperative with early exsudative reaction and postoperative with late exsud...
journal_title:Klinische Monatsblatter fur Augenheilkunde
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journal_title:Klinische Monatsblatter fur Augenheilkunde
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journal_title:Klinische Monatsblatter fur Augenheilkunde
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journal_title:Klinische Monatsblatter fur Augenheilkunde
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journal_title:Klinische Monatsblatter fur Augenheilkunde
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journal_title:Klinische Monatsblatter fur Augenheilkunde
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journal_title:Klinische Monatsblatter fur Augenheilkunde
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更新日期:1991-12-01 00:00:00
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更新日期:2017-06-01 00:00:00
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journal_title:Klinische Monatsblatter fur Augenheilkunde
pub_type: 杂志文章
doi:
更新日期:1976-09-01 00:00:00
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journal_title:Klinische Monatsblatter fur Augenheilkunde
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journal_title:Klinische Monatsblatter fur Augenheilkunde
pub_type: 历史文章,杂志文章
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更新日期:1976-11-01 00:00:00
abstract::Clinical tests of visual acuity are an important measure of visual function. However visual acuity is usually determined only in narrow range of luminance levels between 160 and 320 cd/m2; therefore losses of visual acuity in other ranges of light intensity can not be detected. In a distance of 80 cm from the patients...
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pub_type: 杂志文章
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更新日期:1992-02-01 00:00:00