Histopathologic findings in two cases with history of intrastromal corneal ring segments insertion.

Intrastromal corneal ring segments (INTACS) implantation for mild myopia or keratoconus is simple and effective in most cases. Rarely, major complications can occur due to implantation. In this case report, we present two examples of possible intraoperative and postoperative complications of INTACS. The first case had histopathologic documentation of Descemet's membrane perforation as an intraoperative complication and the second case had accumulation of foamy histiocytes along the lamellar channels which has not been previously reported. These complications suggest further study is required on the long term effect of INTACS implantation on corneal tissue.

INTRODUCTION

Intrastromal corneal ring segments (INTACS, Addition Technologies Inc., Des Plaines, IL, USA) are approved for the treatment of simple myopia and more recently for keratoconus and post-refractive surgery ectasia.1 The procedure is considered a simple and safe intervention; however it can still be associated with complications. Complications such as corneal perforation can occur intraoperatively or postoperative complications can occur. In this case report, we present two examples of INTACs complications in keratoconus. One of the cases had an accumulation of foamy histiocytes along the lamellar channels, a finding that has not been previously reported in the peer-reviewed literature.

CASE REPORTS

Case 1

A 21-year-old male with keratoconus presented with a history of successful INTACS implantation in the left eye. INTACS implantation was aborted in the right eye because of intra-operative anterior chamber perforation. The vision in the right eye was 20/200 that improved to 20/50 with pinhole. Slit lamp examination of the right eye showed a focal corneal scar at the 12 o’clock position. The anterior chamber was deep with a clear lens. Posterior segment examination was unremarkable. Fifteen months after presentation, the patient underwent penetrating keratoplasty (PKP). The histopathologic appearance of the right corneal button that was removed during PKP was consistent with keratoconus. We were able to document the focal area of perforation on histopathologic examination of the right corneal button. Migrating endothelial cells with an underlying thin basement membrane were observed outlining the stroma around the area of attempted ring segment insertion [Figure 1]. The endothelium along the remaining Descemet's membrane away from the perforation was slightly attenuated.

Figure 1

Case 1 histopathologic documentation of a ruptured Descemet's membrane with migrating endothelial cells (arrows) outlining the stroma around the area of attempted ring segment insertion (Periodic acid schiff, ×200)

Case 2

A 27-year-old male with keratoconus presented to us with hard contact lens intolerance in both eyes. He underwent INTACS implantation in both eyes without intraoperative complications. The INTACS segments were 450 μm thick (Addition Technology, Inc. Ref # ISK-450-150). His vision in his first post-operative visit was hazy with a complaint of diplopia, 3 weeks following the procedure. The second post-operative visit, 4 months post surgery showed a best corrected visual acuity (BCVA) of 20/60 in the right and 20/70 in the left eye. His corneas remained clear around the segments for 4 months and subsequently developed whitish intrastromal deposits along the INTACS tunnels with clear central cornea and no effect on BCVA [Figure 2a]. These were first noted on his third post-operative visit, 5 months following the ring segments insertion.

Figure 2a

The clinical appearance of the intrastromal deposits around the ring segment (right eye) which was identical in both eyes

Penetrating keratoplasty (PKP) was performed for optical correction of the left eye vision in the fourth post-operative visit 8 months following the procedure. PKP was then performed after a total period of 16 months post-INTACS implantation on the left [Figure 2b]. The cornea was sent for histopathologic examination after the removal of INTACS. Histopathologic examination showed features consistent with keratoconus and revealed the presence of intrastromal foamy histiocytes around the INTACS channels [Figures Figure 2c, d].

Figure 2b

The left eye clinical appearance following penetrating keratoplasty

Figure 2c

The histopathologic appearance of foamy histiocytes (arrows) in the same area (Periodic acid schiff, ×200)

Figure 2d

Immunohistochemical staining of the cells (CD68, ×200)

DISCUSSION

INTACS are used in the management of simple myopia, keratoconus, and post-refractive surgery ectasia. They consist of two hexagonal semi-circular segments measuring 150° in arc length, with an inner diameter of 6.80 mm and an outer diameter of 8.10 mm. INTACS are made of poly(methyl methacrylate) or (PMMA) and are available in various thicknesses.1 Complications of INTACS may seen in the intraoperative period and includeanterior chamber perforation and Descemet's membrane detachment in cases where the femtosecond laser (Intralase, Abbott Laboratories Inc., Abbott Park, IL, USA) is used to create channels.2 Popstoperative complications include segment extrusion, keratitis, neovascularization, and collection of abnormal deposits along the lamellar channels.12

The procedure in our first case was performed with mechanical insertion of the ring segment. The scar at the perforation site was identified clinically at the 12 o’clock position which was opposite the thinnest part of the cornea (inferonasally). Hence, we believe the intraoperative perforation occurred due to inaccurate pachymetry.

In the second case, deposits along the lamellar channels appeared less than 6 months postoperatively. Ruckhofer and colleagues1 reported that deposits occur clinically in up to 74% of cases within the first 2 years, peaking within the first 6 months. The incidence and density of the deposits were higher with increasing segment thickness and duration of implantation.1 Our second patient underwent implantation of thick segments (0.45 mm) which might have been a predisposing factor. Central crystalline deposits and similar deposits along the channels have been clinically observed 4 years following INTACS implantation with no effect on vision.3

Histologic stromal changes in response to corneal inserts in rabbits include keratocyte activation, intracellular lipid accumulation, and new collagen formation.4 Based on animal models, some authors believed that keratocytes can produce lipid as a nonspecific response to mechanical or metabolic factors.5 In humans, corneal implants may also precipitate intracellular and extracellular production of lipids as a result of stress by degenerating cells.6 This lipid production presents clinically as crystalline deposits and has been even reported to occur at site other than the ring segment insertion.3 A recent theory using histopatholgic studies suggests accumulation of fibrotic extracellular matrix components and proteinases due to keratocyte apoptosis.78 However, there was no evidence of an inflammatory response or foreign-body granuloma in any of these reports. The presence of foamy histiocytes in case 2 is a new unexplained histopathologic finding. The long term effect of INTACS-induced tissue reactions needs to be determined with specific attention directed toward the possible keratoconus progression and acceleration of corneal thinning.5