Journal of Refractive Surgery

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New Idea 

Asymmetric Radial Keratotomy for the Correction of Keratoconus

Massimo Lombardi, MD; Marco Abbondanza, MD

Abstract

We have had 10 years of successful experience with asymmetric radial keratotomy in keratoconus, designed to flatten the steeper central and paracentral areas of the cornea. We think the procedure is the treatment of choice for types I, II, and selected cases of type III keratoconus. The procedure does not adversely affect the results of subsequent surgery such as aphakic epikeratoplasty, corneal transplantation, cataract extraction with implantation of an intraocular lens, or glaucoma or retinal and vitreous procedures.

SURGICAL PROCEDURE

Before surgery, pachymetry, keratometry, cycloplegic refraction, and endothelial specular microscopy, including endothelial cell count and study of the cellular morphology, were performed, and intraocular pressure and corneal diameters were measured. In addition, shape section analysis, evaluation of central corneal clarity, and videokeratography with profile comparison using the Topographic Modeling System (Computed Anatomy Inc., New York, NY) and the Keratron (Optikon 2000, Rome, Italy) were performed.

The procedure is contraindicated in patients with less than 300 µm of corneal thickness on the apex of the cornea, in those with a keratometry reading of more than 60.00 diopters (D), and in those with central thick corneal leucomas as determined by slitlamp microscopy. Clinical contraindications include recurring corneal or mycotic infections, severe dry eye syndrome, and psychological instability.

Preparation for asymmetric radial keratotomy consists of designating the clear zone, delimiting the extent of treatment (30° to 270°) in accordance with the videokeratography, and calculating the number and depth of incisions based on pachymetry.

The procedure itself consists of placing three to twelve centripetal radial incisions in the inferior cornea (keeping them shallow enough to reduce the risk of perforating the apex of the cornea), with as large a central clear zone as possible (from 4.0 to 5.5 mm), always keeping within the ectatic area.

RESULTS

Results in 63 eyes after at least 60 months followup showed that the procedure stopped keratoconus progression and successfully corrected spherical and cylindrical ametropia (Tables 1-3, Figs 1-2). Nine eyes (12%) had a spectacle-corrected visual acuity of 20/20, and more than 25% approximately 20/25. After 6 months, keratometry and pachymetry readings were stable, except in three eyes with type III keratoconus that subsequently underwent corneal transplantation. These three were among the first in whom we performed the procedure, before we clearly understood its limitations. The subsequent penetrating keratoplasty was not adversely affected by this previous surgery.

Immediately after surgery, some patients experienced photophobia and fluctuation of visual acuity, but these problems resolved after 10 to 60 days.

Unwanted microperforations were rare, seldom required treatment (one eye required suturing with a 10/0 nylon), and had no significant effect on the final result. They tended to occur in eyes in which the corneal thickness was substantially irregular, especially in those with type III keratoconus. To help prevent such microperforations, incisions should be no more than 80% of corneal thickness.

DISCUSSION

In radial keratotomy, symmetric and radial corneal incisions flatten the central part of the cornea, with the effect increasing as the incisions become longer and deeper. With asymmetric radial keratotomy in keratconus, the steeeper central and paracentral cornea are flattened. The mechanism by which the procedure benefits patients with keratoconus is that the flattened corneal profile eliminates corneal ectasia, allowing a more even distribution of pressure in the anterior chamber. Also, the gradual healing of the incisions in tissues rich with fibrin creates a strong support for corneal stroma, which, before the procedure was tectonically relatively thin and weak. Thus, the original defect is unlikely to recur. Professor Fyodorov has demonstrated these effects in radial keratotomy, and they have been supported by a wealth of cytological and histological data, and…

We have had 10 years of successful experience with asymmetric radial keratotomy in keratoconus, designed to flatten the steeper central and paracentral areas of the cornea. We think the procedure is the treatment of choice for types I, II, and selected cases of type III keratoconus. The procedure does not adversely affect the results of subsequent surgery such as aphakic epikeratoplasty, corneal transplantation, cataract extraction with implantation of an intraocular lens, or glaucoma or retinal and vitreous procedures.

SURGICAL PROCEDURE

Before surgery, pachymetry, keratometry, cycloplegic refraction, and endothelial specular microscopy, including endothelial cell count and study of the cellular morphology, were performed, and intraocular pressure and corneal diameters were measured. In addition, shape section analysis, evaluation of central corneal clarity, and videokeratography with profile comparison using the Topographic Modeling System (Computed Anatomy Inc., New York, NY) and the Keratron (Optikon 2000, Rome, Italy) were performed.

The procedure is contraindicated in patients with less than 300 µm of corneal thickness on the apex of the cornea, in those with a keratometry reading of more than 60.00 diopters (D), and in those with central thick corneal leucomas as determined by slitlamp microscopy. Clinical contraindications include recurring corneal or mycotic infections, severe dry eye syndrome, and psychological instability.

Preparation for asymmetric radial keratotomy consists of designating the clear zone, delimiting the extent of treatment (30° to 270°) in accordance with the videokeratography, and calculating the number and depth of incisions based on pachymetry.

The procedure itself consists of placing three to twelve centripetal radial incisions in the inferior cornea (keeping them shallow enough to reduce the risk of perforating the apex of the cornea), with as large a central clear zone as possible (from 4.0 to 5.5 mm), always keeping within the ectatic area.

RESULTS

Results in 63 eyes after at least 60 months followup showed that the procedure stopped keratoconus progression and successfully corrected spherical and cylindrical ametropia (Tables 1-3, Figs 1-2). Nine eyes (12%) had a spectacle-corrected visual acuity of 20/20, and more than 25% approximately 20/25. After 6 months, keratometry and pachymetry readings were stable, except in three eyes with type III keratoconus that subsequently underwent corneal transplantation. These three were among the first in whom we performed the procedure, before we clearly understood its limitations. The subsequent penetrating keratoplasty was not adversely affected by this previous surgery.

Immediately after surgery, some patients experienced photophobia and fluctuation of visual acuity, but these problems resolved after 10 to 60 days.

Unwanted microperforations were rare, seldom required treatment (one eye required suturing with a 10/0 nylon), and had no significant effect on the final result. They tended to occur in eyes in which the corneal thickness was substantially irregular, especially in those with type III keratoconus. To help prevent such microperforations, incisions should be no more than 80% of corneal thickness.

Figure 1 : Asymmetric radial keratotomy for keratoconus. A) Videokeratograph shows type I keratoconus with inferior steepening. B) Postoperative videokeratograph shows resolution of the inferior steepening, with a central steep zone surrounded by a bowtie pattern of flattening.

Figure 1 : Asymmetric radial keratotomy for keratoconus. A) Videokeratograph shows type I keratoconus with inferior steepening. B) Postoperative videokeratograph shows resolution of the inferior steepening, with a central steep zone surrounded by a bowtie pattern of flattening.

The final results depended on diameter of the clear zone, number of incisions, depth of incisions, deepening of incisions, size of the treated asymmetric corneal area (from 30° to 180° to 270°), quality of the diamond knife blade, the surgeon's ability to perform a regular and constant 80% incision depth, and the surgeon's incisional surgery experience.

All patients with bilateral keratoconus chose to have the procedure performed on their second eye.

Figure 2: Asymmetric radial keratotomy for keratoconus. A) Videokeratograph shows keratoconus in the right eye with inferonasal steepening. B) After surgery, a large area of steepening is replaced by a focal area of flattening, with a residual central steep zone.

Figure 2: Asymmetric radial keratotomy for keratoconus. A) Videokeratograph shows keratoconus in the right eye with inferonasal steepening. B) After surgery, a large area of steepening is replaced by a focal area of flattening, with a residual central steep zone.

Table

Table 1Asymmetric Radial Keratotomy in 22 Eyes with Type I Keratoconus

Table 1

Asymmetric Radial Keratotomy in 22 Eyes with Type I Keratoconus

Table

Table 2Asymmetric Radial Keratotomy in 25 Eyes with Type II Keratoconus

Table 2

Asymmetric Radial Keratotomy in 25 Eyes with Type II Keratoconus

Table

Table 3Asymmetric Radial Keratotomy in 16 Eyes with Type III Keratoconus

Table 3

Asymmetric Radial Keratotomy in 16 Eyes with Type III Keratoconus

DISCUSSION

In radial keratotomy, symmetric and radial corneal incisions flatten the central part of the cornea, with the effect increasing as the incisions become longer and deeper. With asymmetric radial keratotomy in keratconus, the steeeper central and paracentral cornea are flattened. The mechanism by which the procedure benefits patients with keratoconus is that the flattened corneal profile eliminates corneal ectasia, allowing a more even distribution of pressure in the anterior chamber. Also, the gradual healing of the incisions in tissues rich with fibrin creates a strong support for corneal stroma, which, before the procedure was tectonically relatively thin and weak. Thus, the original defect is unlikely to recur. Professor Fyodorov has demonstrated these effects in radial keratotomy, and they have been supported by a wealth of cytological and histological data, and by histopathology. The healing of incisions in patients with keratoconus requires more time.

Table 1

Asymmetric Radial Keratotomy in 22 Eyes with Type I Keratoconus

Table 2

Asymmetric Radial Keratotomy in 25 Eyes with Type II Keratoconus

Table 3

Asymmetric Radial Keratotomy in 16 Eyes with Type III Keratoconus

10.3928/1081-597X-19970501-18

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