Importance of radiofrequency in ophthalmology

Abstracts

Este trabalho revisa e faz uma análise crítica da radiofrequência em oftalmologia. O aquecimento da córnea tem sido realizado desde 1889 com diferentes finalidades terapêuticas e cirúrgicas. O princípio do aquecimento da córnea causa um enrugamento do colágeno que muda a curvatura da córnea. Após a aprovação da FDA em 2004, iniciou-se um estudo multicêntrico no Brasil coordenado pela Faculdade de Medicina do ABC que resultou na análise de 258 pacientes. Como conclusão o estudo mostrou que o procedimento tem um resultado temporário e que os melhores resultados foram obtidos em pacientes entre 45 e 55 anos de idade sem correção óptica para longe. Acreditamos que o problema ainda não foi resolvido e que novas pesquisas devem ser realizadas.

Ondas de rádio; Oftalmopatias; Topografia da córnea

REVIEW ARTICLE

^IDepartment of Ophthalmology, ABC Medical School (FMABC), Santo André/SP, Brazil

^IICornea and External Diseases Unit, Department of Ophthalmology, ABC Medical School (FMABC), Santo André/SP, Brazil

^IIIRefractive Surgery Unit, Department of Ophthalmology, ABC Medical School (FMABC), Santo André/SP, Brazil

Correspondence

ABSTRACT

This paper reviews and makes a critical analysis of radiofrequency in ophthalmology.

Localized heating of the cornea has been apllied since 1889 for different therapeutic and surgical objectives.The principle that heating corneal tissue causes shrinking of the collagen that changes the corneal curvature. After the approval of FDA in 2004, we initiated a multicenter study in Brazil coordinated by ABC School of Medicine that resulted in an analyses of 258 patients. Inconclusion the study showed that the procedure had a temporary result and the best results were obtained in patients between 45 and 55 years old without optical correction for far.We believe that the problem has not been solved yet and a great deal of research effort should be focused.

Keywords: Radio waves/therapeutic use; Eye diseases/therapy; Corneal topography

Introduction

The first studies on radiofrequency date back to 1864, when the Scottish scientist James Clerk Maxwell, after observing the experiments made by Faraday, managed to produce an electromagnetic radiation that travelled through space with wave-like features and calculated that those waves propagated at the speed of light.^(1-4)

The properties of electromagnetic radiation were confirmed in 1888 by the experiments of Heinrich Hertz, who used oscillating charges to produce high frequencies, around 500 Mc/s, for the first time. Due to the importance of Hertz's experiments, the unit c/s (cycles per second) was named after him (Hz).

Further technological developments made it possible to produce higher frequencies up to 300 GHz (300 x 10⁶ kHz). Such frequencies, classified as SHF (Super High Frequencies) and EHF (Extremely High Frequencies), can be used for communication and also have the property of being absorbed by water (H₂O) or oxygen (O₂) molecules.^(3.4)

Studies on the absorption of electromagnetic waves by water and oxygen showed that waves of shorter wavelength and higher frequency produce heat in the irradiated area.

In ophthalmology, radiofrequency was initially used for refractive surgery in 1980 with the works of Rowsey et al. and Doss and Rowsey, who used it to treat keratoconus. The technology was later used for several conditions, such as ocular plastic surgery, conjunctival surgery, glaucoma surgery and complications of cataract surgery.^(5-18)

Radiofrequency for treating refractive errors

In the United States of America, after approval by the Federal Drug Administration (FDA) on April 11, 2002, a device named "ViewPoint™ CK System", from Refractec, Inc., California, was launched in the market. The system, based on the concepts of thermokeratoplasty, applies a high frequency, low energy electrical current to the corneal stroma, producing a temperature sufficient to shrink collagen fibres (Figure 1). The device has been approved by the FDA for the treatment of hyperopia from +0.75 to +3.25D with astigmatism < -0.75 D and a difference up to 0.50D between visual acuity with and without cycloplegia in persons over 40 years of age.^{(19 -31)}

Figure 1:
Collagen shrinking

On February 6, 2004 the FDA approved the same technology for the correction of presbyopia, aiming at balanced vision.

For the adoption of the technology in Brazil, the Department of Ophthalmology of ABC Medical School, with the approval of the Ministry of Health, prepared a National Protocol for the Study of Radiofrequency in Ophthalmology. The protocol began in 2002 with 300 operations using an animal model. This study established the criteria for optimal power and application time to obtain the best effects on the corneal stroma - a power of 0.6W, with 0.60 seconds per pulse (Figures 1, 2 and 3).

Figure 2:
Applying saline solution

Figure 3:
Corneal topography

Figure 4: Corneal topographic map

In the second stage of the protocol 40 volunteers were selected, 20 of them hyperopic and 20 presbyopic. The volunteers underwent radiofrequency therapy at the Eye Institute of the ABC Medical School.

After this pilot phase, having established the optimal radiofrequency parameters for the correction of refractive errors, a multicenter study was conducted on the treatment of presbyopia in 45 reference centres throughout Brazil.^(27,28,32)

The study, concluded in 2010, assessed the anatomical behaviour of the cornea in 258 patients and showed that, after undergoing radiofrequency therapy, all patients had an abrupt increase in corneal curvature (Chart 1). After this initial peak increase, the curvature decreased over time, with a loss of therapeutic effect.

Chart 1

Average keratometry

The desired effects on near vision were observed in 88% of operated eyes 90 days after the procedure and were maintained in 70% after 360 days (Charts 2 and 3).

Chart 2

Efficacy in 90 days Near visual acuity without correction preoperative x Near visual acuity without correction preoperative

Chart 3

Efficacy in 360 days Near visual acuity without correction preoperative x Near visual acuity without correction preoperative

Safety analysis showed that 96.8% of patients maintained their preoperative binocular distance vision after 90 days, and 88% did so after 360 days (Charts 4 and 5).

Chart 4

Safety in 90 days Near visual acuity without correction preoperative x Near visual acuity without correction preoperative

Chart 5

Safety in 360 days Near visual acuity without correction preoperative x Near visual acuity without correction preoperative

In some cases (26.5%) distance vision improved without correction. It is important to note that in all cases distance vision worsens abruptly in the immediate postoperative period, but as the corneal curvature decreases, distance vision improves progressively without the expected loss of near vision.

The patients who had a greater loss of distance vision were the ones with higher degrees of latent hyperopia.

In the near vision chart (Chart 6) the percentage of patients with vision between J1 and J3 during the period of analysis remained high.

Chart 6

Binocular, uncorrected near visual acuity

It was therefore concluded that the treatment of presbyopia with radiofrequency is safe and effective and that it produces a temporary effect.

Regarding the surgical technique, it is clear that the best results are obtained when the corneal surface is kept dry during the procedure and that centralisation and visualisation of corneal marks is facilitated when performed under a microscope with coaxial illumination (microscopes coupled with excimer laser devices hinder marking).

Furthermore it can be stated that this procedure is "surgeon dependent", i.e. the position of the probe and its depth of penetration, as well as corneal compression during application, are important factors for achieving best results, because bad centralisation of corneal marking leads to worse refractive outcomes, with high astigmatism and lower visual acuity.

Regarding the results of the procedure, distance visual acuity tends to be low in the immediate postoperative period, causing discomfort to most patients. On average, this discomfort decreases after 30 days with the stabilisation of corneal curvature. A partial loss of the therapeutic effect occurs approximately 6 months after the procedure, when the patient reports a decrease in near visual acuity. There is also a phenomenon of decoupling between postoperative refraction and visual acuity in operated eyes, i.e., the measured refraction for distance vision does not match the visual acuity. This finding supports the theory of the "blend" effect described by Holladay where a multifocal corneal effect would occur due to the prolate central cornea which would be responsible for the improvement in near vision, and not the initially induced myopia.

With respect to the indications of radiofrequency for the correction of presbyopia, ideally patients should have a preoperative visual acuity of 20/20 in both eyes without correction. Occasional hyperopia with cycloplegia should not exceed +0.50SD with +0.50CD in both eyes, to prevent any loss of distance vision postoperatively. The ideal age for the procedure is between 45 and 55 years due to the progressive nature of presbyopia and accommodative properties. Patients with very functional or completely ineffective accommodation should not undergo the procedure.

The temporary effect should be considered a positive feature of the procedure, because presbyopia may still be progressing at this age, therefore definitive procedures are contraindicated.

Reoperation may be indicated only when the therapeutic effect has remitted completely and, according to the literature, should be performed at the same sites as in the previous procedure.

Definite loss of corneal tissue does not occur with the procedure, the optical centre of the cornea is preserved, and the resulting monovision provides satisfactory distance visual acuity.

Several studies have also assessed the use of thermokeratoplasty with radiofrequency to correct astigmatism. Wen Xuet al. concluded in 2010 that the nomogram for conductive keratoplasty provides good results in the treatment of hyperopic astigmatism.⁽²⁶⁾

Other Ophthalmic Indications

In modern medicine, many therapeutic techniques can be used for different purposes. The various types of lasers, as well as the various radiofrequency devices, can be used for cauterisation, coagulation, tissue contraction, vaporisation, and cutting.^(33-39)

Radiofrequency can often be used to obtain results similar to lasers, but at lower costs, by simply modulating the frequency, power, exposure time and pulse and by using uni-, bi- or tripolar probes.^{(25,26,38,39)}

Ocular plastic surgery

In ocular plastic surgery, radiofrequency has been used for blepharoplasty, excision of tumours, treatment of xanthelasma, trichiasis, and recanalisation of the nasolacrimal duct.^(9.18)

Conjunctiva

In the conjunctiva, radiofrequency is used for coagulation, to treat pterygium and to remove tumours.⁽¹⁰⁾

Extrinsic ocular muscles

In strabismus, radiofrequency can be used to weaken medial or lateral extrinsic muscles in cases of mild strabismus and even to cut muscles during surgery.

Cornea

In external diseases, radiofrequency is used to treat keratoconus and bullous keratopathy.^{(11,12,24,30,33-37,40-45)}

Cataract surgery

In cataract surgery, radiofrequency is more frequently used to perform anterior capsulorhexis and also posterior capsulorhexis in congenital cataract.^(13,14)

Glaucoma

For glaucoma, several studies have shown that radiofrequency can be used to create transconjunctival fistulas in the trabecular meshwork with a device called the trabectome.

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Importance of radiofrequency in ophthalmology

José Ricardo Carvalho Lima Rehder^I; Leonardo Verri Paulino^II; Eduardo Paulino^III

Publication Dates

• Publication in this collection
  28 June 2013
• Date of issue
  Apr 2013

History

• Received
  07 Oct 2011
• Accepted
  26 July 2012