Terry Kim

Anatomy and physiology of the cornea

&NA; The importance of the cornea to the ocular structure and visual system is often overlooked because of the cornea’s unassuming transparent nature. The cornea lacks the neurobiological sophistication of the retina and the dynamic movement of the lens; yet, without its clarity, the eye would not be able to perform its necessary functions. The complexity of structure and function necessary to maintain such elegant simplicity is the wonder that draws us to one of the most important components of our visual system. Financial Disclosure: Neither author has a financial or proprietary interest in any material or method mentioned.

Trends in the indications for penetrating keratoplasty, 1980-2001.

Purpose: To study the leading indications and changing trends for penetrating keratoplasty (PK) over the past 3 decades. Methods: This is a retrospective review of 696 cases of PK. The indications for PKs performed at the Duke University Eye Center during the years 1980-1981, 1990- 1991, and 2000-2001 were tabulated to determine trends over the past 3 decades. The main outcome measures were indications for PK. Results: During this study, 696 PKs were performed. The leading indications for PK and their respective frequencies during 1980-1981, 1990-1991, and 2000-2001 were failed grafts (10.8%, 19.0%, 27.0%, respectively), pseudophakic bullous keratopathy (PBK)/aphakic bullous keratopathy (ABK) (19.4%, 20.6%, 16.7%, respectively), Fuchs dystrophy (15.6%, 13.0%, 23.8%, respectively), keratoconus (13.4%, 8.2%, 11.8%, respectively), and corneal scar (7.0%, 8.9%, 10.7%, respectively). The number of PKs for failed grafts and Fuchs dystrophy increased over time. Conclusions: In this study, failed graft has gradually become the leading indication for PK, whereas most other studies have reported PBK as the leading indication. Unlike many other studies, Fuchs dystrophy was a common indication for PK.

The effects of intraocular lidocaine on the corneal endothelium

OBJECTIVE The study aimed to evaluate the direct effect of intraocular lidocaine hydrochloride (HCl) 1% on corneal endothelial cell function, ultrastructure, and viability using an in vitro perfusion specular microscope system. DESIGN Paired rabbit and human corneas were isolated and mounted in an in vitro specular microscope for endothelial perfusion evaluation. Corneas were perfused with a control solution (BSS Plus for humans, glutathione bicarbonate Ringers [GBR] for rabbits) for a 1-hour stabilization period. After the stabilization period, one cornea of each matched pair was perfused with preservative-free lidocaine HCl 1% for 15 minutes followed by control solution for an additional 2 to 3 hours. The control cornea continued to receive either GBR or BSS Plus. Corneal thickness measurements were taken every 15 minutes throughout the perfusion period. Corneal swelling and deswelling rates were calculated by linear regression analysis. At the end of the experiment, corneas were fixed for scanning and transmission electron microscopy. In another group of corneas, the endothelial viability was assayed after direct perfusion with lidocaine HCl 1%. RESULTS Lidocaine HCl 1% caused endothelial cell edema, which reversed on removal of lidocaine from perfusion media. Corneal swelling and deswelling rates did not differ significantly between the lidocaine and control groups. Electron microscopy showed the effects of transient endothelial cell edema with an otherwise normal mosaic pattern and ultrastructure for both treatment groups. Endothelial cell viability was maintained after the direct lidocaine exposure and a 2-hour washout. CONCLUSIONS Lidocaine HCl 1% causes a transient endothelial cell edema to the in vitro perfused endothelium of human and rabbit corneas. Proper attention should be given to the type of lidocaine injected intraocularly (i.e., concentration, vehicle, preservatives, pH, osmolarity). Although lidocaine HCl 1% appears to be safe to both human and rabbit endothelium during short-term in vitro exposure, further in vivo and in vitro studies are needed to determine long-term effects of intraocular lidocaine on the corneal endothelium.

Refractive change after descemet stripping automated endothelial keratoplasty surgery and its correlation with graft thickness and diameter.

Purpose: The purpose of this study was to evaluate the refractive change after Descemet stripping automated endothelial keratoplasty (DSAEK) surgery and its correlation with graft thickness and diameter. Methods: We retrospectively analyzed the refractive outcomes of 45 cases of DSAEK surgery that were performed at Duke University Eye Center between August 2005 and December 2006. We divided our study groups into DSAEK triple cases and pseudophakic DSAEK cases. We measured manifest refraction preoperatively and postoperatively in each group and compared the difference between the preoperative and the postoperative spherical equivalent. We evaluated the correlation of the refractive change with graft thickness and diameter. Results: Forty-five DSAEK cases in 44 patients (27 women and 17 men) were evaluated and analyzed. Mean age of the patients at surgery was 67.6 years (15-81 years, SD 10.7 years). Forty cases were treated for Fuchs endothelial dystrophy and 5 for pseudophakic bullous keratopathy/bullous keratopathy. Seventeen cases were DSAEK triple cases and 28 pseudophakic DSAEK cases. In the DSAEK triple group, the mean change in refraction at an average of 4 months postoperatively was +1.15 D (range −0.02 to 2.87, SD 1.15). In the pseudophakic DSAEK group, the mean change in refraction at an average of 5 months postoperatively was +0.71 D (range −1.75 to 3.0, SD 1.11). The overall refractive change was +0.88 D (range −1.75 to 3.0, SD 1.02). Correlation of refractive change with graft diameter was modest (r = 0.29, P = 0.05), and a small correlation was found with respect to graft thickness (r = −0.16, P = 0.31). Conclusions: Our study of DSAEK grafts demonstrated a hyperopic refractive shift after DSAEK surgery. This observation should be taken into consideration when deciding on the appropriate intraocular lens power in DSAEK triple surgery and may also aid in anticipating refractive outcomes after pseudophakic DSAEK surgery. Further studies to follow these refractive changes over a longer follow-up period and to investigate the mechanism of this refractive change after DSAEK surgery are warranted.

Corneal wound architecture and integrity after phacoemulsification: Evaluation of coaxial, microincision coaxial, and microincision bimanual techniques

PURPOSE: To compare the effects of microincision bimanual phacoemulsification, standard coaxial phacoemulsification, and microincision coaxial phacoemulsification on clear corneal incision architecture and wound integrity. SETTING: Department of Ophthalmology, Duke University, Durham, North Carolina, USA. METHODS: A prospective study of 15 human cadaver eyes (3 groups of 5 eyes) ranging 1 to 4 days postmortem had simulated phacoemulsification by bimanual phacoemulsification (1.2 mm incision), standard coaxial phacoemulsification (2.75 mm), or microincision coaxial phacoemulsification (2.2 mm). All phacoemulsification settings were kept constant across each group. After phacoemulsification, intraocular pressure (IOP) was cyclically raised and lowered from 0 to 125 mm Hg. Two eyes in each group had India ink placed above the wound, and the IOP was varied as above. Entry of India ink into the wound or aqueous leakage from the wound was recorded. The same 2 corneas in each group were removed for histopathologic review of India ink penetration. Scanning electron microscopy was used to evaluate wound architecture in 1 eye in each group. RESULTS: Spontaneous wound leakage was evident in all 5 eyes having bimanual phacoemulsification, in 1 eye (20%) having standard coaxial phacoemulsification, and no eye having microincision coaxial phacoemulsification. India ink penetration was grossly evident in 2 of 2 eyes having bimanual phacoemulsification, 1 of 2 eyes having standard coaxial phacoemulsification, and neither of the 2 eyes having microincision coaxial phacoemulsification. Scanning electron microscopy showed increased endothelial cell loss and greater compromise to Descemets membrane with bimanual phacoemulsification than with standard coaxial phacoemulsification or microincision coaxial phacoemulsification. CONCLUSION: Results in this experimental setting suggest microincision coaxial phacoemulsification and standard coaxial phacoemulsification induce less wound stress and alteration of wound morphology leading to wound leakage than microincision bimanual phacoemulsification.

Inhibition of experimental corneal neovascularization by using subconjunctival injection of bevacizumab (Avastin).

Purpose: To evaluate the effect of subconjunctival bevacizumab (Avastin) administration on corneal neovascularization (NV) in rabbits. Methods: NV was induced by placing a suture at the corneal periphery of the right eye of 20 rabbits. Immediately after suturing and again 1 week later, rabbits were divided into 2 groups and administered a subconjunctival injection of normal saline (control) or bevacizumab (Avastin; 5 mg/0.2 mL), respectively. On day 14, digital photographs of the cornea were taken and analyzed to determine the area of the cornea covered by NV. In addition, immunohistochemical analysis was used to determine CD31 and vascular endothelial growth factor (VEGF) expression in corneal tissue. Results: Analysis of digital photographs showed that there was less corneal NV in bevacizumab-treated eyes than in controls (P < 0.001, Mann-Whitney U test). In addition, there was less staining for VEGF and CD31 in corneas from bevacizumab-treated eyes than in control eyes. Subconjunctival bevacizumab injections were not associated with any complications during observation. Conclusions: Subconjunctival bevacizumab administration decreased suture-induced corneal neovascularization in rabbits.

A photopolymerized sealant for corneal lacerations.

Purpose. To determine whether a novel photocrosslinkable polymer synthesized from hyaluronic acid would seal experimental full-thickness corneal lacerations in a rabbit model. Methods. A solution of hyaluronic acid was modified with methacrylate groups (HA-MA), precipitated, dried, reconstituted in an aqueous solution, and sterilized before use. The viscous polymer solution was applied to 38 of 43 experimental corneal lacerations in rabbits and subsequently irradiated with a low-intensity argon laser beam to produce a clear flexible polysaccharide hydrogel patch. The ability of this sealant to repair corneal lacerations was evaluated in four types of full-thickness, 3-mm corneal wounds (linear, linear + epithelium removed, stellate, and stellate + epithelium removed). Slit-lamp examinations, measurements of intraocular pressure, Seidel tests, and histologic studies were performed at selected intervals to evaluate the wound and determine the rate of healing. Results. Corneal perforations were completely sealed and the anterior chambers had reformed by 6 hours in HA-MA–treated eyes. There was no evidence of leakage at this or later times in 37 of the 38 eyes. Intraocular pressure had risen to near-normal levels by day 7 in all four groups, and the sealant was still present in most eyes at day 7. In contrast, the anterior chambers did not re-form in control eyes (five) with untreated perforations because of aqueous leakage through the wounds. Minimal inflammation was observed clinically or in histologic sections of treated corneas. There was extensive proliferation of stromal cells and formation of new extracellular matrix at the wound edges, which became tightly adherent between days 4 and 7. Conclusion. Our novel photocrosslinkable methacrylated hyaluronan polymer sealed 97% (37/38) of the experimental corneal lacerations. HA-MA may prove useful for sealing corneal lacerations in patients and for other sutureless ophthalmic surgical procedures.

DONOR FACTORS ASSOCIATED WITH EPITHELIAL DEFECTS AFTER PENETRATING KERATOPLASTY

The records of 39 patients undergoing 40 consecutive penetrating keratoplasties were reviewed to identify donor factors that might correlate with the presence of an epithelial defect on the first postoperative day. Of the 40 transplanted corneas, 13 (32.5%) had no epithelial defect, 18 (45%) had some epithelial defect, and nine (22.5%) had a total epithelial defect 1 day postoperatively. The status of the epithelium was correlated with several donor factors. The only factor that had a statistically significant association with the degree of epithelial defect was the time interval from preservation to surgery (p = .001). Based on a logistic regression model, the probability of having an epithelial defect 1 day after penetrating keratoplasty increased with respect to longer storage times. These results may aid the surgeon in the selection of donor tissue, particularly when performing penetrating keratoplasty on patients with ocular surface disorders.

The corneal epithelium after optisol-GS storage.

The objective of this study was to evaluate the epithelium of human corneas stored in Optisol-GS (Chiron Intraoptics, Irvine, CA) for extended periods (2-34 days). Human corneas stored in Optisol-GS (n = 64) were obtained from the Georgia Eye Bank. Corneal epithelial viability was assessed by using the Calcein-AM (Molecular Probes, Inc., Eugene, OR) ethidium homodimer stain, a fluorescent assay used to distinguish live from dead cells. Scanning and transmission electron microscopy was used to evaluate epithelial ultrastructure. The results showed that corneas stored up to 6 days in Optisol-GS had minimal damage of the epithelium. Calcein-AM ethidium homodimer staining showed 20-25% epithelial damage. Corneas stored 7-10 days had a further increase in epithelial damage (30-35%). Corneas stored for 11-15 days had marked increases in epithelial damage (40-50%), and corneas stored 16-34 days showed significant epithelial damage (60-70%). The data show that corneas stored in Optisol-GS are able to maintain the epithelium up to 6 days. A gradual decrease in epithelial viability and loss of epithelial cells occurs in corneas stored 6-10 days. Corneas stored for > 10 days have a marked loss of epithelial cells with extensive epithelial damage.

Refractive Surgery in Children: Treatment Options, Outcomes, and Controversies

PURPOSE To summarize the evolution of the treatment of pediatric refractive errors, with an emphasis on recent advancements in the use of refractive surgery to treat children. DESIGN Literature review. METHODS We searched MEDLINE (1950 through October 2007), the Cochrane library (December through October 2007), and the Cumulative Index for Nursing and Allied Health Literature (December 1982 through October 2007) for English language articles using the following search strategy with MeSH terms and key words: pediatric refractive errors and amblyopia, anisometropia, hyperopia, myopia, laser in situ keratomileusis (LASIK), photorefractive keratectomy (PRK), laser epithelial keratomileusis (LASEK), excimer laser, refractive intraocular lens (IOL). We also searched the bibliographies of all identified articles. RESULTS No multicenter, long-term, controlled trial has been published on the use of refractive surgery in children. The current literature shows that LASIK, PRK, and LASEK show promising results in children with refractive amblyopia over the intermediate follow-up period. Corneal haze and myopic regression are the main complications, especially in very high myopia (> 12 diopters). In such patients with extremely high myopia, small studies have reported phakic IOLs or clear lens extraction with or without IOL implantation to be a useful alternative. CONCLUSIONS Refractive surgery is appropriate in children with severe anisometropia or bilateral high ametropia that is resistant to conventional therapy. More information is needed before pediatric refractive surgery can be widely adopted by the ophthalmic community. This could be achieved with a large, prospective, multicenter, randomized, controlled clinical trial.