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INCISIONAL ASTIGMATISM CORRECTION

 

Increasing Importance of Astigmatism Correction
Due to the rising expectations of patients and the competition of the surgical centers, the importance of patient satisfaction increases. Thus the surgical correction of astigmatism gets a growing importance even in the standard cataract surgery.

Surgically induced astigmatism
All formulas for calculating the IOL to be implanted requires the input of the expected surgically induced astigmatism. The influence of surgical technique on the outcome is not completely predictable.
Every cut in the cornea will change the corneal topography. The surgically induced astigmatism in principle is unavoidable. Low is the risk of sclerocorneal incision, temporal localization and cut length less than 2 mm. [1] A survey in Germany in 2010 came to the conclusion that only 2% of cataract surgeries with micro incisions (< 2mm ) are astigmatism neutral. [2] With 66% the standard inzisions dominate (2.6 to 3.1 mm). [3] Giansanti et al. showed in their study [4] that even cutting widths of 2.75 mm causes an astigmatic change of 0.65 diopters.

Optimization of clear cornea inzisions
The aim of cataract surgery should be an minimal  MTR astigmatism or a astigmatism free cornea. In any case, in terms of patient satisfaction, the astigmatism should be increased. The temporal accesses induce the slightest surgical astigmatism.
If the astigmatism should be reduced, the incision must be made in the steep corneal meridian. Here the intraoperative aberrometry on phakic and pseudophakic eye supports the surgeons as a navigation system and tool to minimize incisional astigmatism.

Limbal relaxing incisions (LRI, AK)
Compared to the implantation of toric lenses, the correction of corneal astigmatism by relaxing limbal incisions (LRI) for moderate astigmatism, astigmatic ceratotomy (AK) for severe astigmatism> 5 diopters requests a lower financial effort.
Due to lack of alternatives the LRI are performed by nomograms, based on the preoperative determination of the cylinder and axis position.
The success of LRI depends on the experience of the surgeon and is hardly to monitor and to rate during the surgery. These two factors give the process variability, which makes it difficult to predict accurately the postoperative result.

Research and Development
Our development efforts for the surgical navigation system aimed at simulating changes in corneal topography and increase the degree of automation and reproducibility of incisional astigmatism correction.

 

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Literature

 

[1]

C. Hoffmann, „Analysis of biometry and prevalence data for corneal astigmatism in 23239 eyes,“ J Cataract Refract Surg, Bd. 36, pp. 1479-1485, 2010.

[2]

M. Wenzel, T. Kohnen, A. Scharrer und e. al., „Ambulate Intraokularchirurgie 2011: Ergebnisse der Umfrage von BDOC, BVA, DGII und DOG,“ Ophthalmo-Chirurgie, Nr. 24, pp. 205-214, 2012.

[3]

M. Müller und T. Kohnen, „Inzisionen für die Biaxiale und koaxiale mikroinzisionale Kataraktchirurgie,“ Ophthalmologie, Nr. 107, pp. 108-115, 2010.

[4]

F. Giasanti, E. Rapizzi, G. Virgili, R. Mencucci, A. Bini, L. Vannozzi und U. Menchini, „Clear cornea incision of 2.75 mm for cataract surgery induces little change of astigmatism in eyes with low preoperative corneal cylinder.,“ Eur J Ophthalmol, pp. 16: 385-393, 2006.