Ophthalmologe最新文献

Background: Corneal cross-linking (CXL) is used to treat corneal ectatic diseases. The aim is to improve the reduced consolidation of the cornea in order to halt further corneal protrusion and therefore subsequent deterioration of the optical imaging proportions.

Material and methods: In this article the principles of corneal cross-linking based on riboflavin and UV light are presented including recent research results. Furthermore, the most important treatment protocols including standard CXL (S-CXL), accelerated CXL (A-CXL), transepithelial CXL (TE-CXL) and the approach of the CXL procedure for thin corneas are explained.

Results: The CXL method depends on four major components, the riboflavin solution, oxygen, UV light and the availability of cross-linking sites on the collagen tissue. According to the present state of knowledge, the photochemical process of the CXL method induces covalent bonds between the fibrils and proteoglycans and thus stabilizes the collagen fibers, resulting in corneal consolidation. In addition to the S‑CXL, which has proven its effectiveness and safety in a large number of studies, there are other treatment protocols that have been developed based on the Bunsen-Roscoe law of reciprocity. The A‑CXL protocol has the advantage of having a shorter irradiation time but it seems to be less effective than the S‑CXL protocol concerning the increase in corneal stiffness. The use of TE-CXL has so far not yet gained acceptance in the clinical practice.

Conclusion: The CXL procedures primarily aim to stabilize the cornea. In the future, in addition to stabilization of the cornea, simultaneous improvement of visual acuity will be the main focus.

Background: Melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGC) area third class of photoreceptors in the retina in addition to rods and cones. They are a small heterogeneous population of cells primarily mediating non-image-forming visual functions.

Objective: This article provides an overview of the current understanding of the functions and the diversity of ipRGCs. It moreover gives an insight into clinically and translationally relevant aspects and treatment options.

Material and methods: Narrative review article.

Results: ipRGCs make up ~1-2% of all retinal ganglion cells and are divided into 6 specialized subtypes. With the photopigment melanopsin they can trigger light responses without rod or cone input and can relay irradiance information to various centers of the brain. Depending on the subtype, ipRGCs mediate non-image-forming tasks, such as the pupillary light reflex or synchronizing the circadian clock, and image-forming tasks, such as contrast optimization. ipRGCs exhibit differential resilience against optic nerve damage, making them an interesting study object for the development of neuroprotective strategies. In addition, melanopsin is an attractive optogenetic tool for vision restoration.

Conclusion: Knowledge on ipRGC physiology is indispensable for understanding frequent clinical observations. Their functional and morphological features are the subject of active research, which highlights novel translational strategies.

Background: Corneal crosslinking (CXL) is used in keratoconus to strengthen and stabilize the cornea and to prevent further progression with subsequent visual loss and the possible need for keratoplasty. Correct treatment indications is crucial in this context. Since the introduction of the initial Dresden protocol, other modified CXL protocols have been proposed to optimize treatment success.

Objective: The relevant parameters for treatment indications are explained and the clinical results of new CXL protocols are presented.

Methods: The currently valid criteria with respect to the indications for CXL in keratoconus, PubMed search for relevant publications and own experiences with different CXL protocols are presented.

Results: The reproducibility of topographic parameters depends on the stage of the keratoconus. Accelerated CXL as well as transepithelial CXL with a hyperoxic environment show comparable efficiency with shorter surgery time and possibly lower complication rates. Customized CXL with an individualized UV irradiation profile provides improved results with faster epithelial healing. Lower UV energy doses enable CXL to be conducted in eyes with minimal stromal pachymetry of less than 400 µm before irradiation. The combination of CXL with photorefractive keratectomy (PRK) provides visual acuity improvements but also increases the risk of visual loss.

Conclusion: Current indication rules for CXL neglect the reduced reproducability of topographic and tomographic measurements in keratoconus. The latest CXL protocols presented here provide a safe alternative with similar and/or better efficacy compared to standard CXL. The combination of CXL with PRK offers an option for visual rehabilitation in patients with contact lens intolerance.