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 Post subject: CX-L Corneal Collagen Crosslinking with Riboflavin
PostPosted: Wed Mar 21, 2007 4:52 pm | Post{ VIEW_SINGLE_POST } 

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Há um novo tratamento em estudo, essa nova técnica chama-se C3-R e seria a aplicação de colágeno na córnea cruzado com riboflavina, em forma de colírio e com a aplicação de luz ultravioleta C para fortalecer a córnea. Essa técnica tem sido utilizada em combinação com o implante de anéis intraestromais, no caso as Intacts. Aos poucos alguns centros de oftalmologia estão estudando e experimentando o tratamento com C3-R após o implante de segmentos de anéis intraestromais (anéis de Ferrara e outros) e eventualmente com a aplicação de cirurgia refrativa por excimer laser. Estas técnicas conjuntas aplicadas de forma sequencial ainda são muito novas, e devem ser feitas com muita cautela.

A córnea fica mais forte e pode aplanar um pouco, especialmente quando utilizada em conjunto com o implante de anéis intracorneanos, mas não assegura de fato tirar todas as irregularidades da córnea. Estudos mais recentes indicam que o procedimento é contraindicado em córneas com espessura menor que 400 µ (micras). Apesar de não ser indicada cirurgia refrativa por excimer laser em cima de uma cornea tratada com está técnica, há essa possibilidade. Creio que no futuro a combianação das três técnicas será uma realidade. Entretanto, se a técnica for utilizada em casos mais avançados, é possível que a adaptação de lentes de contato especiais pode ser feita mais facilmente, especialmente nos casos onde há ceratocones muito avançados, córnea fina e pontuda, sem presença de nébula (leucoma) que ocorre geralmente em casos de hidropsia aguda da córnea. A córnea rompe e cicatriza rapidamente, deixando no local uma aparência esbranquiçada, com bem menor transparência, o que pode diminuir a qualidade da visão, nestes casos severos de hidropsia, conforme a solução seria a ceratoplastia penetrante ou lamelar (transplante de córnea).

Já existem profissionais no Brasil estudando o C3-R, atualmente já em conjunto com implante de anéis e eventualmente cirurgia refrativa por excimer laser. O IOSB (Instituto de Olhos Dr. Saul Bastos) em Porto Alegre está com planos de aprofundar os estudos nessa área. Nos EUA e na Europa, apenas alguns centros apenas estão trabalhando com esta técnica ainda em estudos. Os estudos tem mostrado que essa técnica, embora ainda em testes, quando utilizada com anéis intra-estromais (Intacts, Ferrara, etc) pode aplanar o ceratocone. É algo novo, em testes, mas que tem demonstrado bons resultados por enquanto. É importante ressaltar que a técnica é absolutamente experimental e que apesar dos resultados promissores, carece ainda de análise de resultados a longo prazo.


Pelo que li exaustivamente sobre essa técnica, ela não faz com que a córnea perca a sua irregularidade, ou seja, não cura o ceratocone, mas pode baixá-lo a níveis aceitáveis quando usada em conjunto com implante de anéis. Provavelmente ainda haverá a necessidade de adaptação de lentes de contato RGPs especiais para o paciente, principalmente nos casos mais avançados, entretanto não resta dúvidas de que esta é uma alternativa para que os pacientes com casos mais avançados, onde a córnea está muito fina, para que não necessitem de um transplante de córnea.

Esta técnica está atualmente disponível em seletos centros oftalmológicos no mundo, realizada sob um estrito comitê de ética ou acompanhados pelo protocolo de estudo aprovado pela Institutional Review Board (IRB). Nos EUA esta técnica está sendo feita apenas quando há o termo de consentimento, exigido pelo FDA (Food and Drug Administration).

Mais sobre a técnica nos links abaixo:

"The 30-minute CrossLinking treatment is performed in the doctor's office. During the treatment, custom-made riboflavin eye drops are applied to the cornea, which is then activated by ultraviolet light. This amazingly simple process has been shown in laboratory and clinical studies to increase the amount of collagen cross-linking in the cornea and strengthen the cornea. In published European studies, such treatments were proven safe and effective in patients."

LINKS:

http://www.keratoconusinserts.com/cornea.html

http://www.keratoconusinserts.com/research.htm

http://www.allaboutvision.com/condition ... oconus.htm

http://www.pr.com/press-release/27461

http://www.indiaprwire.com/pressrelease ... 181611.htm

Atenciosamente,

_________________
Luciano Bastos
Diretor & Instrutor Clínico de LC IOSB / Diretor Ultralentes
Membro:
Scleral Lens Education Society (US)
British Contact Lens Association (UK)
Contact Lens Society of America (US)
Contact Lens Manufacturer Association (US)


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 Post subject: C3-R Crosslink: Resultados a Longo Prazo
PostPosted: Thu May 15, 2008 8:53 am | Post{ VIEW_SINGLE_POST } 

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Joined: Thu Apr 27, 2006 7:45 pm
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ESTE ARTIGO SERÁ TRADUZIDO EM BREVE.

Collagen crosslinking with riboflavin and ultraviolet-A light in keratoconus: Long-term results.

Raiskup-Wolf F, Hoyer A, Spoerl E, Pillunat LE.
From the Department of Ophthalmology, C.G. Carus University Hospital, Dresden, Germany.

PURPOSE: To prove the long-term dampening effect of riboflavin- and ultraviolet-A-induced collagen crosslinking on progressive keratoconus. SETTING: Department of Ophthalmology, C.G. Carus University Hospital, Dresden, Germany. METHODS: Four hundred eighty eyes of 272 patients with progressive keratoconus were included in this long-term retrospective study. The maximum follow-up was 6 years. At the first and all follow-up examinations, refraction, best corrected visual acuity (BCVA), corneal topography, corneal thickness, and intraocular pressure were recorded. RESULTS: The analysis included 241 eyes with a minimum follow-up of 6 months. The steepening decreased significantly by 2.68 diopters (D) in the first year, 2.21 D in the second year, and 4.84 D in the third year. The BCVA improved significantly (>/=1 line) in 53% of 142 eyes in the first year, 57% of 66 eyes in the second year, and 58% of 33 eyes in the first year or remained stable (no lines lost) in 20%, 24%, and 29%, respectively. Two patients had continuous progression of keratoconus and had repeat crosslinking procedures. CONCLUSIONS: Despite the low number of patients with a follow-up longer than 3 years, results indicate long-term stabilization and improvement after collagen crosslinking. Thus, collagen crosslinking is an effective therapeutical option for progressive keratoconus.

PMID: 18471635 [PubMed - in process]

_________________
Luciano Bastos
Diretor & Instrutor Clínico de LC IOSB / Diretor Ultralentes
Membro:
Scleral Lens Education Society (US)
British Contact Lens Association (UK)
Contact Lens Society of America (US)
Contact Lens Manufacturer Association (US)


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 Post subject: Re: C3-R Corneal Collagen Crosslinking with Riboflavin
PostPosted: Tue Jun 24, 2008 7:04 pm | Post{ VIEW_SINGLE_POST } 

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Joined: Thu Apr 27, 2006 7:45 pm
Posts: 326
Location: Porto Alegre
Obs. Este artigo será traduzido em breve


CORNEAL COLLAGEN CROSS-LINKING TECHNIQUE

THE PROCEDURE

The procedure is typically performed under sterile conditions using topical anesthetics. The surgeon debrides the central 7 mm of the corneal epithelium with a blunt spatula to allow for better diffusion of the riboflavin. As a photosensitizer, 0.1% riboflavin solution (10 mg of riboflavin-5–phosphate in 10 mL of dextran-T–500 20% solution) is applied to the de-epithelialized cornea 5 minutes before and during the irradiation, and the surgeon keeps the cornea moist with a drop of balanced salt solution every 2 minutes. The irradiating source (Figure 1) is placed 1 cm from the cornea's center and applied for 30 minutes using an ultraviolet-A double diode (370 nm, with a potentiometer in series to regulate the voltage and an irradiance of 3 mW/cm²), which corresponds to a dose of 5.4 J/cm². The desired irradiance can be measured with an ultraviolet-A light meter and adjusted accordingly via the potentiometer. Postoperatively, the eye wears a bandage contact lens and receives a topical antibiotic until corneal re-epithelization is complete, followed by a 6-week course of a topical steroid.


LABORATORY STUDIES

A study was performed to quantify the effects of the treatment. According to the study's results, maximal cross-linking occurs within the anterior 300 µm of the cornea. Histological evidence of apoptosis following the administration of ultraviolet-A light and topical riboflavin was found within the anterior 300 µm of the stroma. In rabbit corneas, the diameter of collagen fibers increased by 12.2% in the anterior stroma compared with 4.6% in the posterior stroma. Ultraviolet-A light with riboflavin therapy has been shown to increase corneal rigidity by 71.9% in porcine corneas and by 328.9% in human corneas. Corneas cross-linked with riboflavin and ultraviolet-A rays required a higher temperature for hydrothermal shrinkage and showed a greater resistance to collegenase digestion compared with controls, particularly in the anterior stroma.

In addition, comparisons of microkeratome-created flaps of the anterior and posterior cornea after ultraviolet-A and riboflavin treatment have provided further evidence that significant stiffening occurs in the anterior stroma.

CLINICAL STUDIES

Wollensak et al1 pioneered the technique of using riboflavin and ultraviolet-A light to cross-link collagen in keratoconic eyes. In their study, the disease ceased to progress in all 23 eyes with previous clinical evidence of advancing keratoconus during a follow-up period of 3 months to 4 years. Furthermore, and more significantly, regression was observed with a decrease in keratometric values by 2.01 D in 70% of eyes. The investigators did not observe significant changes in corneal and lenticular transparency, endothelial cell counts, and IOP. Given that collagen turns over every 2 to 3 years, it is unclear how long the effects of cross-linking will last or if ultraviolet-A with riboflavin therapy will need to be repeated periodically. None of the patients in the study by Wollensak et al required another treatment.

Caporossi et al also reported a decrease in mean keratometric values by 2.10 D in eyes treated with ultraviolet-A with topical riboflavin as well as an improvement in UCVA by 3.6 lines. They demonstrated a significant decrease in corneal coma and a trend toward more topographic symmetry. According to Caporossi et al and Mazzotta et al, confocal microscopy achieved an initial reduction in anterior and intermediate stromal keratocytes after treatment with a gradual repopulation. A demarcation line in the corneal stroma is visible at the slit lamp as early as 2 weeks following treatment and represents a change in the index of refraction and/or reflective properties induced by the collagen cross-linking in the anterior cornea. This may aid in surgeons' assessment of the depth of collagen cross-linking achieved.

There was one short-term, retrospective, nonrandomized study using riboflavin-ultraviolet-A–induced corneal collagen cross-linking as an adjunct to inferior-segment Intacs (Addition Technology, Inc., Des Plaines, IL), which showed an additive effect when compared to the group receiving Intacs alone.


RISKS AND SIDE EFFECTS

The deleterious effects of ultraviolet light on ocular structures have been well documented. With the use of riboflavin as a photosensitizing agent, however, there is an ultraviolet-A transmission rate of only approximately 7% across the cornea, thus limiting ultraviolet-A irradiance of the lens and retina. Nevertheless, concern remains about ultraviolet-A cytotoxicity to the corneal endothelium. In rabbits, the cytotoxic level for corneal endothelial damage induced by ultraviolet-A light was 0.36 mW/cm². Using the aforementioned surgical technique, this level could be reached in corneas with a central thickness of less than 400 µm, so it is imperative that surgeons measure corneal pachymetry preoperatively to ascertain that at least this threshold is met. The lens receives 0.65 J/cm² of ultraviolet-A irradiance, which is far less than the amount needed to produce a cataract (70 J/cm²).19 As for retinal damage, research with rhesus monkeys has shown a threshold level of 81 mW/cm², which, again, is not achieved with a standard treatment.


THE BOTTOM LINE

Treating keratoconus with ultraviolet-A light and riboflavin to cross-link corneal collagen is a noninvasive procedure with promising preliminary results. Long-term studies are needed to determine the stability of the cross-linked cornea. It should be noted that the ultraviolet-A device and riboflavin-facilitated collagen cross-linking procedure have not yet been evaluated in FDA-monitored clinical trials and are not FDA approved.

As this treatment modality undergoes further long-term clinical investigations, it may develop not only into a primary treatment option for patients with progressive keratoconus but also a prophylactic measure in forme fruste keratoconus and/or ectasia following photorefractive surgery to prevent further progression. To avoid seriously harmful side effects, it is important to strictly adhere to the surgical protocol, perform preoperative pachymetry to exclude patients with a corneal thickness of less than 400 µm, and closely monitor ultraviolet-A irradiance with an ultraviolet meter.



Source > http://www.crstoday.com/PDF%20Articles/ ... 707_PR.php

_________________
Luciano Bastos
Diretor & Instrutor Clínico de LC IOSB / Diretor Ultralentes
Membro:
Scleral Lens Education Society (US)
British Contact Lens Association (UK)
Contact Lens Society of America (US)
Contact Lens Manufacturer Association (US)


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