Case 1. A 33-year-old woman presented with progressive bilateral keratoconus that appeared at the age 17 years. She had a radial keratotomy performed on her left eye 23 months earlier, with six incisions and a clear zone diameter of 3.00 mm. During the operation, she sustained a macroperforation in the inferotemporal semimeridian which required closure with two perlón sutures. During the first few postoperative weeks, visual acuity reached 3/10 (Snellen 20/70, Parinaud 10), before decreasing considerably. Before surgery, the patient could wear hard contact lenses for a few hours in the morning but could not tolerate them after surgery. Examination revealed a stage III keratoconus. Her visual acuity on the left was 2/10 (Snellen 20/100), with a pinhole. Near the clear zone, we noted two rupture lines in Descemet's membrane, in addition to the scars of the two sutures. Keratometry showed an irregular astigmatism of 61.00 diopters at 30° and 63.00 D at 120°. The 8-millimeter penetrating keratoplasty was performed 23 months later, at which time the radial scars remained intact. The graft was attached by six interrupted sutures placed between the old radial incisions.
Case 2. A 25-year-old woman had radial keratotomy performed on both eyes, with satisfactory functional results. The initial operation involved 16 radial incisions with a clear zone diameter of 3 mm, and a transverse incision at 12 o'clock, to correct an associated astigmatism. In the left eye, a microperforation occurred during surgery. Sixteen months later, she had spontaneous opening of the three o'clock incision followed by a corneal abscess and a hypopyon. Peripheral deepening of the incision had been performed, which was evident from the presence of a double scar at the eight o'clock incision. An epithelial cyst was also noticed at the seven o'clock incision. The three o'clock incision was open its entire length, revealing a fistula, an incarcerated iris, and an aqueous leak. At this level, there was a huge stromal abscess. The fistula closed and the hypopyon disappeared after intravenous administration of phosphomycin and fluoroquinolone antibiotics.
We performed a penetrating keratoplasty 20 months after the radial keratotomy. During the trephining process, the radial incisions remained intact. The graft was easily sutured with a running suture of 20 bites.
Figure 1: Light microscopy of eye with keratoconus, examined 23 months after radial keratotomy. The epithelial cells are more adherent at the incision level than at other sites, where they were removed during surgery and histological preparation. There is no difference of fibrillogenesls and keratocytic reorganization between this keratoconus cornea and a normal cornea (staining HPS, original magnification x 10).
A corneal button, 8 mm in diameter, was obtained from each eye during penetrating keratoplasty. Both buttons were cut in half, one for light microscopy and the other for transmission electron microscopy.
Case 1. Under light microscopy, the characteristics of keratoconus were found. The epithelium was more adherent at the incision sites where Bowman's layer was retracted and where the basal epithelial cells were in direct contact with the stroma. At this level, the cells appeared cylindrical and elongated in the direction of the corneal surface (Fig 1). The differentiation of the epithelial cell layers was poor. The epithelial plug was small and included on average four cells in length and four cells in width. Bowman's layer was irregular. The stromal connective tissue fibers were disorganized, most likely indicating the site of an important retraction phenomenon. There was no neovascularization. It was difficult to determine precisely the depth of the incision; it appeared to be about half of the corneal thickness.
On transmission electron microscopy, we noticed that the epithelial plug cells were adherent to the stroma, due to cytoplasmic expansion anchoring points. This explains the strong epithelial adhesions at that level. The basal epithelial cells had numerous intracellular and intercellular vacuoles (Fig 2). They were separated from the stroma by a basement membrane, 30 to 70 nm thick, and were attached by hemidesmosomes. There was moderate fibroblastic activity around and under the epithelial plug. Fibroblasts contained increased numbers of mitochondria and granular endoplasmic reticulum. Their nuclei were irregular. Descemets membrane and the endothelium appeared normal.
Case 2. Under light microscopy, on most sections, a huge epithelial plug was noticed, with a round regular aspect, eight cells in height and 11 in width. Some epithelial cells appeared well anchored in the stroma. At other sites, the epithelial plug cells were enlarged. The epithelium was relatively thick and the cellular differentiation between the layers looked normal. An epithelial cyst was noted under one of the incisions. At other sites, the healing process appeared complete; a discrete thickening of the epithelium was noticed and the stroma was reorganized and contained no epithelial cells. Intrastromal neovascularization was evident at all incision sites, extending to a depth of two-thirds of the corneal thickness and demonstrating approximately ten new vessels. We estimated the depth of incisions to be approximately 70% of the corneal thickness.
Figure 2: Transmission electron microscopy shows that epithelial cells (E) at the plug level have formed a basement membrane (BA). They adhere to it by hemidesmosomes (He, between arrows). This adherence is strengthened by multiple digitations (D1). Bowman's layer is absent and the tissue underneath is formed by collagen fibrils and keratocytes (K) (original magnification x 2700).
Under transmission electron microscopy, epithelial cells appeared to have normal cytoplasmic components (Golgi apparatus, granular endoplasmic reticulum, ribosomes, cytoplasmic filaments) and fine chromatin was evident in the nuclei. Some sections performed at the abscess level showed inflammatory cells containing filled lysosomes within the incision. These cells were found 9 months after clinical healing of the abscess. The new vessels had a classical capillary structure, with endothelial cells and a basement membrane. Their sizes ranged from 6 to 12 µ in diameter.
The process by which radial incisions produce a flattening of the central cornea has been the subject of mathematical and experimental studies.1-2 Due to the nature of the unsutured incision, the healing process is slow. Several authors have noticed a persistence of an epithelial plug 6 months and3 IV2,4 2,5 and 4 years6 after surgery. One must wait 5 years7 for a complete reorganization of the stromal collagen fibrils to take place. The progressive disappearance of the epithelial plug and the presumed retraction within the fibrous scar may lead to an undercorrection. Inversely, the persistence of a hypertrophic epithelial plug and stretching of the scar could lead to the phenomenon of a progressive refractive shift in the hyperopic direction. Bowman's layer presumably contributes to the corneal shape and is cut at the incision, allowing changes in corneal curvature. We also noticed a large variability in the amount of wound healing in different incisions within the same cornea. Such asymmetry could explain induced astigmatism, which is sometimes irregular.
Finally, the microperforations that sometimes occur during radial keratotomy, thought by some surgeons to be evidence of adequate depth of incision, may in fact increase the risk of infection and complications several years later.
1. Schachar RA, Black TD, Huang T. Understanding Radial Keratotomy. Denison, Tex: LAL Publishing; 1981: 25-26.
2. Vito RP, Shin TJ, McCarey BE. A mechanical model of the cornea: the effects of physiological and surgical factors on radial keratotomy surgery. Journal of Refractive Surgery. 1989;5:82-88.
3. Stainer GA, Shaw EL, Binder PS, Zavala EY, Akers P. Histopathology of a case of radial keratotomy. Arch Ophthalmol. 1982;100:1473-1477.
4. Ingraham HJ, Guber D, Green WR. Radial keratotomy. Clinicopathologic case report. Arch Ophthalmol. 1985;103:683-688.
5. Binder PS, Waring GO, Arrowsmith P, Wang C. Histopathology of corneal rupture after radial keratotomy. Arch Ophthalmol. 1988;106:1584-1590.
6. Deg JK, Zavala EY, Binder PS. Delayed corneal wound healing following radial keratotomy. Ophthalmology. 1985;92:734-740.
7. Binder PS, Nayak SK, Deg JK, Zâvala EY, Sugar J. An ultrastructural and histochemical study of longterm wound healing after radial keratotomy. Am J Ophthalmol. 1987;103:432-440.