von enim » 17.06.2015, 05:57
Ich fand diesen Artikel hier sehr hilfreich:
Auszug:
If a patient’s epithelium is thinner than the treated profile, stromal tissue will be wasted, and often, it will not exceed 10 μm in a previously unoperated, healthy eye.5 If the epithelium is thicker, contrary to what many would think, no undercorrection ensues. Instead, a decrease in the effective optical zone occurs (Figure 1). Therefore, it is important to enlarge the planned optical zone to ensure an adequate effective optical zone. This would seem clinically unacceptable in moderate to high myopes, as such a measure would consume precious stromal tissue. Interestingly, however, the more myopia to be treated, the lower the decrease in the optical zone, should the patient’s epithelium be thicker than planned (Figure 2). The planned optical zone would need to be only marginally larger than the expected effective one.
On the other hand, for patients with low myopia, the optical zone can significantly shrink if the epithelium is thicker than planned; however, based on computer modeling, it seems that the larger the planned optical zone, the less the change in optical zone, should the epithelium be thicker (Figure 3). Particularly in low myopes, significantly enlarging the optical zone (to 7.3 mm, for instance) will not remove appreciable stromal tissue. As for the fact that the epithelium is thicker nasally than temporally and inferiorly than superiorly,5 computer modeling shows that the result would be tilt, which is well tolerated optically.7 Astigmatism, however, can be induced if one meridian has a steeper or flatter epithelial profile than the other. Again, taking into account corneal epithelial thickness data in virgin eyes from the literature and using computer modeling, the induced astigmatism should be +0.75 D at worst. Data suggest that this scenario is not important in the clinical setting.8,9
Gemessen werden kann die Epitheldicke zum gegenwärtigen Zeitpunkt nur mit dem RTVue OCT-Gerät und dem Artemis VHF Ultraschall-Biomikroskop. Wobei von letzterem bisher nur ein paar Exemplare produziert worden sind. Dazu auch sehr empfehlenswert:
Ich fand diesen Artikel hier sehr hilfreich:
[list]
[b]Single-Step Transepithelial PRK[/b]
[i]Shady T. Awwad, MD, & Samuel Arba Mosquera, MSC, PhD[/i]
HTML: [url]http://crstoday.com/2014/10/single-step-transepithelial-prk/[/url]
PDF: [url]http://crstoday.com/pdfs/crst1014_tech.pdf[/url][/list]
Auszug:
[size=85][i]If a patient’s epithelium is thinner than the treated profile, stromal tissue will be wasted, and often, it will not exceed 10 μm in a previously unoperated, healthy eye.5 If the epithelium is thicker, contrary to what many would think, no undercorrection ensues. Instead, a decrease in the effective optical zone occurs (Figure 1). Therefore, it is important to enlarge the planned optical zone to ensure an adequate effective optical zone. This would seem clinically unacceptable in moderate to high myopes, as such a measure would consume precious stromal tissue. Interestingly, however, the more myopia to be treated, the lower the decrease in the optical zone, should the patient’s epithelium be thicker than planned (Figure 2). The planned optical zone would need to be only marginally larger than the expected effective one.
On the other hand, for patients with low myopia, the optical zone can significantly shrink if the epithelium is thicker than planned; however, based on computer modeling, it seems that the larger the planned optical zone, the less the change in optical zone, should the epithelium be thicker (Figure 3). Particularly in low myopes, significantly enlarging the optical zone (to 7.3 mm, for instance) will not remove appreciable stromal tissue. As for the fact that the epithelium is thicker nasally than temporally and inferiorly than superiorly,5 computer modeling shows that the result would be tilt, which is well tolerated optically.7 Astigmatism, however, can be induced if one meridian has a steeper or flatter epithelial profile than the other. Again, taking into account corneal epithelial thickness data in virgin eyes from the literature and using computer modeling, the induced astigmatism should be +0.75 D at worst. Data suggest that this scenario is not important in the clinical setting.8,9[/i][/size]
Gemessen werden kann die Epitheldicke zum gegenwärtigen Zeitpunkt nur mit dem RTVue OCT-Gerät und dem Artemis VHF Ultraschall-Biomikroskop. Wobei von letzterem bisher nur ein paar Exemplare produziert worden sind. Dazu auch sehr empfehlenswert:
[list]
[b]Epithelial Mapping with the RTVue SD-OCT and Future Clinical Applications in Corneal Refractive Surgery[/b]
[i]Dr. Dan Z. Reinstein[/i]
Video: http://cnpg.comparenetworks.com/113967-Epithelial-Mapping-with-the-RTVue-SD-OCT-and-Future-Clinical-Applications-in-Corneal-Refractive-Surgery/[/list]
