Phakic intraocular lenses part 1: historical overview, current models, selection criteria, and surgical techniques

In this 2-part overview, the current status of phakic intraocular lens (pIOL) surgery to correct refractive errors is reviewed. Three types of pIOLs, categorized by their intraocular position, are included: angle-supported anterior chamber, iris-fixated anterior chamber, and posterior chamber (usually fixated in the ciliary sulcus). Part 1 reviews the main models of each pIOL type, the selection criteria, and the surgical techniques, with emphasis on currently available pIOLs. Bioptics, adjustable refractive surgery, and enhancements are addressed, and applications of the new anterior segment imaging techniques are reviewed.     

Accommodation and presbyopia : part 2: surgical procedures for the correction of presbyopia

There are two basic approaches for the surgical correction of presbyopia: increasing depth of focus (e.g. by means of multifocal laser abrasion of the cornea), Or restoring accommodation in the sense of a dynamic change in ocular refraction (accommodative intraocular lenses, scleral expansion). Pseudoaccommodative procedures are able to achieve satisfactory near vision, albeit at the price of lower performance in the intermediate range and decreased image quality. The restoration of accommodation remains problematic, partly because the mechanism of accommodation and the development of presbyopia are still not fully understood. Some surgical procedures are based on concepts, the validity of which is not confirmed or which even contradict experimental evidence. Thus, it is necessary to assess the results and presumed mechanisms critically and objectively.     

Einfluss der stromalen Restdicke nach myoper LASIK auf die Messung des Augeninnendrucks

Purpose

The purpose of this study was to compare the influence of residual bed thickness after myopic ablation on intraocular pressure measurements using Goldmann applanation tonometry and dynamic contour tonometry.

Methods

Intraocular pressure using Goldmann tonometry and dynamic contour tonometry was measured in 50 eyes before, 1 and 3 months after LASIK for myopia. LASIK surgery reduced the central corneal thickness by 71±27 µm. During surgery, corneal thickness was measured by optical coherence pachymetry (Online OCP, 4optics AG) prior to flap creation, after flap lifting, and after laser ablation.

Results

Postoperative measurements with Goldmann tonometry were reduced by ?3.7 mmHg (p<10^?6) and mean measurements with dynamic contour tonometry were reduced by ?1.5 mmHg (p<10^?6). Differences in measurements with Goldmann tonometry were significantly correlated with thickness of residual bed after ablation, whereas measurements with dynamic contour tonometry were not.

Conclusions

Thickness of residual bed appears to influence readings with Goldmann tonometry more than readings with dynamic contour tonometry after myopic LASIK.     

Zyklorotation des Auges bei wellenfrontgeführter LASIK mit statischem Iriserkennungstracker

PURPOSE: Centration of the ablation zone decisively influences the result of wavefront-guided LASIK. Cyclorotation of the eye occurs as the patient changes from the sitting position during aberrometry to the supine position during laser surgery and may lead to induction of lower and higher order aberrations. METHODS: Twenty patients (40 eyes) underwent wavefront-guided LASIK (B&L 217z 100 excimer laser) with a static eyetracker driven by iris recognition (mean preoperative SE: -4.72+/-1.45 D; range: -1.63 to -7.00 D). The iris patterns of the patients' eyes were memorized during aberrometry and after flap creation. RESULTS: The mean absolute value of the measured cyclorotation was -1.5+/-4.2 degrees (range: -11.0 to 6.9 degrees ). The mean cyclorotation was 3.5+/-2.7 masculine (range: 0.1 to 11.0 degrees ). In 65% of all eyes cyclorotation was >2 masculine. CONCLUSIONS: A static eyetracker driven by iris recognition demonstrated that cyclorotation of up to 11 degrees may occur in myopic and myopic astigmatic eyes when changing from a sitting to a supine position. Use of static eyetrackers with iris recognition may provide a more precise positioning of the ablation profile as they detect and compensate cyclorotation.