Modern treatment options for the therapy of keratoconus

1. Introduction 

With the aid of modern surgical techniques, implantation of intrastromal corneal ring segments (ICRS, Intacs®) and postoperative treatment with special contact lenses, a possible keratoplasty can sometimes be delayed or even avoided altogether in patients with progressing keratoconus. Intrastromal procedures can be performed with extreme precision by the technology of the femtosecond laser (Femtec®, Perfect Vision, Heidelberg). The new femtosecond laser technology has proved itself in the meantime in different indications and allows distinctly less traumatic surgery compared to mechanical techniques [1], [2], [3]. At our clinic these special surgical procedures have been performed since December 2004 in progressing keratoconus patients with preoperative contact lens intolerance.

After femtosecond laser assisted surgery and the aid of ICRS, contact lens fitting could be performed again and the initially planned keratoplasty postponed [4], [5]. The procedures with ICRS and keratoconus have also been substantiated by other authors [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16] with mechanical instruments whereas the treatment spectrum in regard to thinner corneae could be expanded with the femtosecond laser “Femtec”.

2. Baseline findings 

In July 2005 a 42-year-old patient with bilateral progressing keratoconus, which was more pronounced in the left eye, presented to our clinic. The patient was unable to continue wearing contact lenses as his visual acuity was declining and the lenses no longer tolerable. He had been wearing RGP contact lenses for 8 years. The contact lens (four-curve design with an aspheric bevel) parameters were right base curve 6.9mm power −11.25D diameter 9.2mm and left base curve 6.5mm power −15.00D diameter 9.6mm. Best corrected visual acuity with these lenses preoperative was 6/18 in the right and 6/12 in the left eye. Fitting contact lenses with different designs except scleral lenses was tried without success. Subjective refraction resulted in right −9.75/−2.75×85 and left −15.25/−6.50×70 with visual acuities of right 6/24 and left 6/18. The patient had an intraocular pressure of 16mmHg bilaterally. The lens was clear and the fundus without pathological changes. Examination of corneal topography (Orbscan® II) (Fig. 1, Fig. 2) which we used alongside the Scheimpflug camera (Fig. 3, Fig. 4) as basis for the calculation of femtosecond laser treament gave the following results:

•O.D.: K values 52.8D in 8° and 48.0D in 98°. Pachymetry at the thinnest point was 418μm.

•O.S.: K values 56.3D in 178° and 50.4D in 88°. Pachymetry at the thinnest point was 360μm.

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Fig. 1. Orbscan O.D. preoperative.

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Fig. 2. Orbscan O.S. preoperative.

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Fig. 3. Pentacam O.D. preoperative.

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Fig. 4. Pentacam O.S. preoperative.

3. Treatment 

In September 2005 surgery on the worse left eye was conducted first. The location of the implantation tunnel was determined as baseline parameters by means of the corneal topography data. The implantation tunnel was then created in 70% depth (350μm) of the cornea with 1.05mm width, a spacing of 8μm and an energy of 3μJ. In the Femtec laser treatment the cornea is flattened to 35D by a patented synthetic so-called “interface” located between cornea and laser. Following laser preparation the opening of the canal is carried out from intrastromal to epithelial via the femtosecond laser. After opening the implantation tunnel is examined for microperforations and irrigated with an antibiotic with the help of a special spatula and a irrigation canula with define flow direction towards the opened site. We observed that by utilising an antibiotic (Lavasept® (polihexanide)) possible deposits on the ICRS could be significantly reduced. After this the implantation of ICRS into the implantation tunnel was performed. The epithelial access was sewed up for 4 weeks with a single button suture and a therapeutic contact lens was inserted. As medication we chose 4× Floxal® EDO® (ofloxacin) and 4× Dexa-sine® AT (dexamethasone) with decreasing frequency.

The same procedure was chosen for the right eye which was operated in November 2005 with the following parameters: canal depth 70% (380μm), spacing 8μm, energy 3μJ, canal width 1.05mm, and access 1.5mm.

4. Postoperative care 

Two months after the implantation of intrastromal corneal ring segments the patient was treated with custom-made mini-scleral contact lenses as a corneal lens geometry was not accepted. The following visual acuity, cornea and tear film values were determined during contact lens fitting:

•Uncorrected vision: O.D.<6/60; O.S.<6/60.

•Refraction and corrected visual acuity (spectacles): O.D.: −2.00/−6.00×60 (6/18); O.S.: −5.00/−5.50×120 (6/18); BVD: 12.00mm.

•Corneal topography (Fig. 5, Fig. 6): O.D.: K values 46.7D in 75° and 46.1D in 165°; O.S.: K values 42.8D in 74° and 41.6D in 164°.

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Fig. 5. Orbscan O.D. postoperative.

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Fig. 6. Orbscan O.S. postoperative.

•Corneal diameter: 13.00mm.

•Tear film: tear meniscus height ∼0.2mm; tear break-up time 6s; thin lipid layer.

Based on performed corneal topography the patient was fitted with high Dk rigid gas permeable rotational symmetric mini-scleral contact lenses (Fig. 7, Fig. 8). These contact lenses have a newly developed geometry which can be individually altered and are therefore indicated in all atypical corneal shapes such as following keratoplasty (Fig. 9). The diameters of these lenses are normally between 13 and 16mm in contrast to regular scleral lenses. We prefer to try this lens type first for physiological and handling reasons. The scleral profile was matched by slit lamp examination according to the corneo-scleral profile measurement procedure first published by Gaggioni and Meier in 1987 [17], [18].

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Fig. 7. Contact lens O.D.

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Fig. 8. Contact lens O.S.

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Fig. 9. Contact lens design.

The fitting related advantages of these lenses lie in the good centration, relatively easy interpretation of the fluorescein pattern as well as the good visual acuity achievable in conjunction with a satisfactory subjective and objective tolerance.

•Contact lens parameters: O.D.: base curve 7.3mm power −7.12D peripheral curve 7.0mm diameter 14.5mm; O.S.: base curve 7.3mm power −9.62D peripheral curve 7.0mm diameter 14.5mm.

•Material Boston XO white: Falco Kontaktlinsen, Switzerland.

•Contact lens care system: Boston Advance®.

•Corrected visual acuity (contact lenses): O.D.: 6/6; O.S.: 6/6.

The improvement in visual acuity compared to the prior RGP corneal lenses was a result of the stable fit and excellent physiological and mechanical acceptance.

5. Conclusion 

The implantation of corneal ring segments in combination with a postoperative contact lens treatment is sometimes an alternative to an otherwise required corneal transplantation in cases of keratoconus. Femtosecond laser technology for the implantation of corneal ring segments allows significantly less traumatic surgery compared to mechanical techniques. Intrastromal ring segment induced corneal flattening facilitates contact lens treatment which is required to achieve adequate visual acuity. Rigid gas permeable contact lenses or sometimes silicone hydrogel soft lenses are indicated depending on postoperative corneal shape. Sometimes custom mini-scleral contact lenses are indicated in cases of keratoconus where corneal shape is atypical.