John D. Goosey

Quantified Histopathology of the Keratoconic Cornea

Purpose. This study systematically investigated and quantified histopathological changes in a series of keratoconic (Kc) corneas using a physiologically formulated fixative to not further distort the already distorted diseased corneas. Methods. Twelve surgically removed Kc corneal buttons were immediately preserved and processed for light and transmission electron microscopy using an established corneal protocol. Measurements were taken from the central cone and peripheral regions of the host button. The sample size examined ranged in length from 390 to 2608 &mgr;m centrally and 439 to 2242 &mgr;m peripherally. Results. The average corneal thickness was 437 &mgr;m centrally and 559 &mgr;m peripherally. Epithelial thickness varied centrally from 14 to 92 &mgr;m and peripherally from 30 to 91 &mgr;m. A marked thickening of the epithelial basement membrane was noted in 58% of corneas. Centrally, anterior limiting lamina (ALL) was thinned or lost over 60% of the area examined, whereas peripheral cornea was also affected but to a lesser extent. Histopathologically, posterior cornea remained undisturbed by the disease. Anteriorly in the stroma, an increased number of cells and tissue debris were encountered, and some of these cells were clearly not keratocytes. Conclusions. It is concluded that Kc pathology, at least initially, has a distinct anterior focus involving the epithelium, ALL, and anterior stroma. The epithelium had lost its cellular uniformity and was compromised by the loss or damage to the ALL. The activity of the hitherto unreported recruited stromal cells may be to break down and remove ALL and anterior stromal lamellae, leading to the overall thinning that accompanies this disease.

Epithelial plugs in radial keratotomy: the origin of incisional keratitis?

Purpose. Incisions in radial keratotomy (RK) patients were examined histopathologically to explore the cause of delayed infections occurring following this procedure. Methods. Four corneas from two successful RK patients were obtained postmortem and 1 cornea from an unsuccessful RK was collected following lamellar keratoplasty. The tissue was prepared for light and transmission electron microscopy. Results All incisions examined contained an epithelial plug. The average depth of the plugs for left and right corneas in the 2 successful cases were 142.58 &mgr;m (range: 36.46–183.04 &mgr;m) and 58.44 &mgr;m (range: 29.27–115.66 &mgr;m), whereas the unsuccessful case these measurements were 121.06 &mgr;m (range: 70.03–172.01 &mgr;m). In the successful cases, the plugs were on average 4.2 cells deep (range: 2–5) in one case and for the other the plugs were 8.78 cells deep (range: 1.5–11.5) and 2.72 cells wide (range: 2–4). In the unsuccessful case the plugs were on average 6.89 cells deep (range: 5–11) and 8.56 cells wide (range: 4–13). The average epithelial thickness, measured 200 &mgr;m on either side away from the plug, was 47.11 &mgr;m and 55.09 &mgr;m for the successful cases, and 27.52 &mgr;m for the unsuccessful case. Degenerate cells were often observed within the plug and along the overlying surface. Lamellae cut during surgery remained severed in all corneas observed. The stroma adjacent to the incision contained an elevated number of stromal cells (8%–78%). Conclusions. Healing did not include repair of anterior limiting lamina or stromal lamellae, which all remained severed in all incisions observed. Epithelial plugs were invariably present in all incisions regardless of clinical outcome, thus, increasing the distance a basal cell travels to reach the epithelial surface by 2 to 4 times. Since the epithelial cell has a limited life, it is hypothesized that cells originating in the plug may die before reaching the surface, thus, leading to intermittent loss of surface integrity. The loss of the epithelial barrier allows invasion of microorganisms and the delayed onset of keratitis. The larger the plug the greater the possibility of surface defects and resultant infection.

Lamellar changes in the keratoconic cornea

The purpose of this study was to identify ultrastructural changes associated with ectasia and to determine the association between lamellar count and corneal thinning.

Recurrence or Re-emergence of Keratoconus – What is the Evidence Telling Us? Literature Review and Two Case Reports

Keratoconus may recur following penetrating or lamellar keratoplasty, but latency is considerably longer in the former. Since keratoplasty involves only partial excision of the cornea, and recent research strongly indicates the presence of the pathology in the peripheral host cornea, the reappearance of the pathology after a latency period is most likely due to migration of the disease from host to donor cornea. This notion is further corroborated by the shorter latency period in partial thickness keratoplasty, where more of the diseased host cornea remains in place. Other proposed causes for the recurrence of keratoconus, such as eye rubbing and contact lens wear, were reportedly not associated with a significant number of cases, and, therefore, are not the primary factor. Based on existing literature, it is concluded that, in post-keratoplasty keratoconus, the etiology stems from re-emergence of the disease rather than recurrence. Keratoconus patients in need of keratoplasty should be counseled on the possibility of the disease re-emerging.