Study of optical and structural changes of the eye after refractive surgery with phakic posterior intraocular lens implantation

Tese de doutoramento em CiênciasKeratorefractive surgeries, such as photorefractive keratectomy and LASIK, have limitations when used for the correction of high refractive errors. Wound healing and biomechanical responses can occasionally lead to poor refractive predictability, prolonged visual recovery, and instability of refraction, loss of vision from corneal irregularity or scarring and when too much corneal tissue is removed with the laser it can induce progressive corneal ectasia. As understanding of these limitations has become more recognized, indications for corneal refractive surgery have narrowed. Intraocular refractive procedures offer many potential advantages such as reversibility, fast visual recovery and preservation of accommodation. The risks and benefits of pIOL implantation in appropriate patients may be more advantageous than other refractive surgery techniques; however, complications relating to pIOLs can be more disabling than those from keratorefractive surgery. Glaucoma, angle closure, cataract formation, corneal decompensation and endophthalmitis are potential complications after pIOL insertion. The main goal of this work was the evaluation and characterization of several parameters, including refractive and visual status, effectiveness, predictability, stability and safety, after posterior chamber pIOL (Visian ICL) implantation as well as the potential and factors that may be associated with the onset of complications with this type of pIOL implant. Therefore, the present Thesis is divided into four main issues, each of one reporting on important aspects on ICL implantation. 1) The first issue that includes chapters 2 to 5, concern to the measurement of separation between the central posterior surface of the ICL and the anterior crystalline lens surface (vault), comprising several methods of measurement and evaluation of that distance and their postoperative behavior over time. As observed, this distance is crucial on safety and success of ICL implantation. Postoperative vault shows a tendency to decrease overtime and it is frequently associated with the most related post-ICL complications. Parameters such as age, anterior chamber depth or white to white distance could potentially affect the amount of this postoperative distance.2) The second issue evaluates the long-term results of the ICL for myopia correction as well the effectiveness and safety of the toric ICL implantation among different refractive ranges of astigmatism, being covered by chapters 6 to 9. The results are very good; the implantation of ICL for moderate to high myopia as well for moderate to high astigmatism is safe and effective and provides long-term predictable, stable refractive results, supporting the US FDA outcomes. The rotational stability of the toric ICL seems to be excellent. 3) The third issue evaluated the efficacy of the combination of procedures, including ICL implantation plus corneal laser treatment, for the correction of myopia with astigmatism and hyperopia (chapter 10 and 11). The ICL implant showed to be very stable when a second surgical procedure is applied and residual refractive error has been successfully addressed with a bioptics approach involving secondary LASIK or PRK. 4) The fourth issue (chapter 12) included an overview of the major complications often associated with phakic ICL implantation. The major complications are cataract formation, typically anterior subcapsular cataract. Whether the cataract is age-related or associated with the surgical procedure or the implant itself, in some cases it became visually significant enough to require cataract extraction. Surgeon learning curve and most inadequate vaulting over the natural crystalline lens, has been identified as the major causes of this induced cataract. Accurately measurement of the sulcus diameter and selecting the correct ICL size is important to ensure proper vaulting and avoid surgically related cataract formation. In conclusion, phakic IOL surgery is an efficacious technique for correcting refractive error in patients who would otherwise be poor candidates for corneal refractive surgery. The designs of pIOLs have progressed over many years. Most early designs have been abandoned because of high rates of complications. At present, Visian ICL is the only posterior-chamber pIOL that have received FDA approval in the United States, but several other lenses are undergoing trials. Many of the studies discussed in this thesis, suggest that their visual and refractive outcomes are, in the aggregate, very encouraging. However, as with any new surgical technology, significant challenges remain. Future preoperative assessment will likely combine increased skills of biometry, increased knowledge of lens vaulting dynamics, and preoperative computer simulation of pIOL position and thus improve ICL safety. All the information provided and new data that will become available rapidly the next years in this area of active research on pIOLs, will probably speed-up the learning curve for the surgeon and increase the knowledge about the behavior of the ICL, therefore making the outcomes f the procedure more safe and predictable and less surgeon-dependent