Steven M Christiansen

Current options in the management of pellucid marginal degeneration.

PURPOSE To review and evaluate current and future directions in the diagnosis and surgical management of pellucid marginal degeneration (PMD), including penetrating keratoplasty, full-thickness crescentic wedge resection (FTCWR), deep anterior lamellar keratoplasty (DALK), crescentic lamellar wedge resection (CLWR), crescentic lamellar keratoplasty, tuck-in lamellar keratoplasty (TILK), toric phakic intraocular lens (PIOL) implantation, intrastromal corneal ring segment implantation (ICRS), corneal collagen cross-linking (CXL), and combined therapies. This is the first review article looking at the literature specific to PMD. METHODS Review of published studies. RESULTS Reported data for each treatment is presented. Penetrating keratoplasty is the treatment of last resort in PMD and is effective, but with considerable complications. DALK provides visual outcomes similar to penetrating keratoplasty without the risk of immune-mediated graft rejection, but its complexity and relative novelty limit its acceptance. FTCWR has good visual outcomes, but with significant astigmatic drift. CLWR is effective, but lacks long-term results. Crescentic lamellar keratoplasty and TILK are effective, but technically difficult and without long-term results. Toric PIOL implantation is effective, but ectasia progression is a concern. ICRS implantation can delay penetrating keratoplasty and improve contact lens tolerance, but does not treat the underlying process. CXL demonstrates effectiveness without complications, although data are limited and long-term results are needed. Combining treatments such as ICRS, CXL, toric PIOL implantation, and refractive surgery is promising, but additional studies are needed to investigate their efficacy and safety. CONCLUSIONS Although little is understood about the etiology, pathophysiology, epidemiology, and genetics of PMD, new treatments are improving visual outcomes and reducing complications. Corneal collagen cross-linking is especially exciting because it halts disease progression. Combined treatments and improved screening could eliminate the need for surgical management in most cases of PMD.

Corneal biomechanics in iatrogenic ectasia and keratoconus: A review of the literature

The Ocular Response Analyzer (ORA) (Reichert Ophthalmic Instruments, Buffalo, NY) allows direct measurement of corneal biomechanical properties. Since its introduction, many studies have sought to elucidate the clinical applications of corneal hysteresis (CH) and corneal resistance factor (CRF). More recently, detailed corneal deformation signal waveform analysis (WA) has potentially expanded the diagnostic capabilities of the ORA. In this review, the role of CH, CRF, and WA are examined in keratoconus (KC) and iatrogenic ectasia (IE). The PubMed database was searched electronically for peer-reviewed literature in July 2012 and August 2012 without date restrictions. The search strategy included medical subject heading (MeSH) and natural language terms to retrieve references on corneal biomechanics, CH, CRF, corneal deformation signal WA, IE, and KC. The evidence suggests that while CH and CRF are poor screening tools when used alone, increased sensitivity and specificity of KC and IE screening result when these parameters are combined with tomography and topography. Recent advances in WA are promising, but little is currently understood about its biomechanical and clinical relevance. Future studies should seek to refine the screening protocols for KC and IE as well as define the clinical applicability of WA parameters.

Laser in-situ keratomileusis in patients with diabetes mellitus: a review of the literature

Purpose A growing number of diabetic patients request laser in situ keratomileusis (LASIK) for elective vision correction each year. While the United States Food and Drug Administration considers diabetes a relative contraindication to LASIK surgery, there are several reports in the literature of LASIK being performed safely in this patient population. The purpose of this review was to examine whether diabetes should still be considered a contraindication to LASIK surgery by reviewing the ocular and systemic complications of diabetes, and examining the existing data on the outcomes of LASIK in diabetic patients. Methods A literature review was conducted through PubMed, Medline, and Ovid to identify any study on LASIK surgery in patients with diabetes mellitus. This search was conducted without date restrictions. The search used the Medical Subject Headings (MeSH®) term LASIK linked by the word “and” to the following MeSH and natural language terms: diabetes, diabetes mellitus, systemic disease, and contraindications. Abstracts for all studies meeting initial search criteria were reviewed for relevance. There were no prospective clinical studies identified. Three retrospective studies were identified. Key sources from these papers were identified, reviewed, and included as appropriate. An additional literature search was conducted to identify any study of ocular surgery on patients with diabetes using the MeSH terms refractive surgery, photorefractive keratectomy, radial keratotomy, cataract surgery, vitrectomy, and iridectomy linked by the word “and” to the following MeSH terms: diabetes, diabetes mellitus, and systemic disease. This search was conducted without date restrictions. Abstracts of studies meeting the initial search criteria were reviewed and articles deemed relevant to the subject were included in this review. Conclusion LASIK may be safe in diabetic patients with tight glycemic control and no ocular or systemic complications.

Laser in situ keratomileusis in patients with collagen vascular disease: a review of the literature

Purpose To evaluate the current United States Food and Drug Administration (FDA) recommendations regarding laser in situ keratomileusis (LASIK) surgery in patients with collagen vascular diseases (CVD) and assess whether these patients make appropriate candidates for laser vision correction, and offer treatment recommendations based on identified clinical data. Methods A literature search was conducted using PubMed, Medline, and Ovid to identify all existing studies of LASIK in patients with collagen vascular diseases. The search was conducted without date limitations. Keywords used for the search included MeSH terms: laser in situ keratomileusis, LASIK, refractive surgery, ocular surgery, and cataract surgery connected by “and” with the following MeSH and natural-language terms: collagen vascular disease, rheumatic disease, systemic disease, rheumatoid arthritis, systemic lupus erythematosus, Sjögren’s syndrome, seronegative spondyloarthropathy, HLA B27, ankylosing spondylitis, reactive arthritis, psoriatic arthritis. The abstracts for all studies meeting initial search criteria were reviewed; relevant studies were included. No prospective studies were found; however, four retrospective case studies were identified that examined LASIK surgery in patients with CVD. Several case reports were also identified in similar fashion. Results The FDA considers CVD a relative contraindication to LASIK surgery, due largely to the ocular complications associated with disease in the CVD spectrum. However, recent studies of LASIK in patients with CVD indicate LASIK may be safe for patients with very well-controlled systemic disease, minimal ocular manifestations, and no clinical signs or history of dry-eye symptoms. Conclusion LASIK surgery may be safe in patients with rheumatoid arthritis or systemic lupus erythematosus and the seronegative spondyloarthropathies if stringent preoperative criteria are met. Evidence suggests patients with Sjögren’s syndrome are not suitable candidates for LASIK.

Astigmatism induced by conventional spherical ablation after PRK and LASIK in myopia with astigmatism < 1.00 D

Background The purpose of this study was to evaluate surgically-induced astigmatism after spherical ablation in photorefractive keratectomy (PRK) and laser-assisted in situ keratomileusis (LASIK) for myopia with astigmatism < 1.00 D. Methods The charts of patients undergoing spherical PRK or LASIK for the correction of myopia with minimal astigmatism of <1.00 D from 2002 to 2012 at the John A Moran Eye Center in Salt Lake City, UT, were retrospectively reviewed. Astigmatism was measured by manifest refraction. The final astigmatic refractive outcome at 6 months postoperatively was compared with the initial refraction by Alpins vector analysis. Results For PRK, average cylinder increased from 0.39 ± 0.25 (0.00–0.75) preoperatively to 0.55 ± 0.48 (0.00–1.75) postoperatively (P = 0.014), compared with an increase in LASIK eyes from 0.40 ± 0.27 (0.00–0.75) preoperatively to 0.52 ± 0.45 (0.00–2.00) postoperatively (P = 0.041). PRK eyes experienced an absolute value change in cylinder of 0.41 ± 0.32 (0.00–1.50) and LASIK eyes experienced a change of 0.41 ± 0.31 (0.00–1.50, P = 0.955). Mean surgically-induced astigmatism was 0.59 ± 0.35 (0.00–1.70) in PRK eyes, with an increase in surgically-induced astigmatism of 0.44 D for each additional 1.00 D of preoperative cylinder; in LASIK eyes, mean surgically-induced astigmatism was 0.55 ± 0.32 (0.00–1.80, P = 0.482), with an increase in surgically-induced astigmatism of 0.29 D for each 1.00 D of preoperative cylinder. Conclusion Spherical ablation can induce substantial astigmatism even in eyes with less than one diopter of preoperative astigmatism in both PRK and LASIK. No significant difference in the magnitude of surgically-induced astigmatism was found between eyes treated with PRK and LASIK, although surgically-induced astigmatism was found to increase with greater levels of preoperative astigmatism in both PRK and LASIK.

Sources of Medical Error in Refractive Surgery

PURPOSE To evaluate the causes of laser programming errors in refractive surgery and outcomes in these cases. METHODS In this multicenter, retrospective chart review, 22 eyes of 18 patients who had incorrect data entered into the refractive laser computer system at the time of treatment were evaluated. Cases were analyzed to uncover the etiology of these errors, patient follow-up treatments, and final outcomes. The results were used to identify potential methods to avoid similar errors in the future. RESULTS Every patient experienced compromised uncorrected visual acuity requiring additional intervention, and 7 of 22 eyes (32%) lost corrected distance visual acuity (CDVA) of at least one line. Sixteen patients were suitable candidates for additional surgical correction to address these residual visual symptoms and six were not. Thirteen of 22 eyes (59%) received surgical follow-up treatment; nine eyes were treated with contact lenses. After follow-up treatment, six patients (27%) still had a loss of one line or more of CDVA. Three significant sources of error were identified: errors of cylinder conversion, data entry, and patient identification error. CONCLUSION Twenty-seven percent of eyes with laser programming errors ultimately lost one or more lines of CDVA. Patients who underwent surgical revision had better outcomes than those who did not. Many of the mistakes identified were likely avoidable had preventive measures been taken, such as strict adherence to patient verification protocol or rigorous rechecking of treatment parameters.

Comparison of the ratio of keratometric change to refractive change induced by myopic ablation.

PURPOSE To compare the ratio of keratometric change (ΔK) to refractive change (ΔSE) induced by refractive laser ablation. METHODS The charts of 3337 eyes that underwent LASIK or photorefractive keratectomy (PRK) from 2002 to 2011 were retrospectively reviewed, and the ratio ΔK/ΔSE measured at 3 months postoperatively was compared between eyes with low ΔSE (0.00 to 2.99 diopters [D]), moderate ΔSE (3.00 to 5.99 D), and high ΔSE (6.00 to 8.99 D). Eyes were further stratified by LASIK vs PRK; custom vs conventional treatments; microkeratome vs IntraLase (Abbott Medical Optics Inc) femtosecond laser-created flaps; and flat (38.00 to 41.99 D) vs moderate (42.00 to 45.99 D) vs steep (46.00 to 49.99 D) preoperative keratometry, and the ratio ΔK/ΔSE was similarly compared. RESULTS Significant differences were found in the ratio ΔK/ΔSE among eyes with low ΔSE (1.00±0.50 D), moderate ΔSE (0.83±0.19 D), and steep ΔSE (0.80±0.15 D) (P<.001), and between eyes with moderate and high ΔSE in LASIK vs PRK, custom vs conventional treatments, and microkeratome vs IntraLase flaps. Significant differences in the ratio ΔK/ΔSE were also found in eyes with low, moderate, and high ΔSE regardless of preoperative keratometry. The ratio ΔK/ΔSE compared with ΔSE follows a nonlinear pattern and tended to be higher and more variable at lower amounts of correction. CONCLUSIONS The change in simulated keratometry required to achieve 1.00 D of myopic refractive correction decreased as the amount of refractive change increased, was more variable with lower amounts of correction, and followed a nonlinear relationship. Many variables, such as LASIK vs PRK, custom vs conventional, and microkeratome vs IntraLase flaps, affected the ratio of ΔK/ΔSE for moderate and high myopic corrections.

The effect of preoperative keratometry on visual outcomes after moderate myopic LASIK.

Video abstract Video

Vitreous and Aqueous Penetration of Orally Administered Trimethoprim-Sulfamethoxazole Combination in Humans.

Purpose: To determine the penetration of orally administered trimethoprim (TMP)-sulfamethoxazole (SMX) into the aqueous and vitreous cavity of noninflamed human eyes. Methods: Nine adult patients undergoing cataract surgery and 10 adult patients undergoing pars plana vitrectomy were given 3 doses of oral TMP-SMX every 12 hours before the surgery. Aqueous and blood samples were collected from patients undergoing cataract surgery; vitreous and blood samples were collected from patients undergoing vitrectomy. The levels of TMP and SMX were analyzed using high-performance liquid chromatography and were compared with the mean minimum inhibitory concentrations (MIC90) of potential ocular pathogens. Results: TMP-SMX was present in all samples. Among eyes undergoing cataract surgery, the mean concentrations of TMP in aqueous and blood were 0.341 ± 0.141 &mgr;g/mL (mean ± SD) and 1.501 ± 0.433 &mgr;g/mL and of SMX were 5.259 ± 0.929 &mgr;g/mL and 11.835 ± 2.100 &mgr;g/mL, respectively. Among eyes undergoing vitrectomy, the mean concentrations of TMP in vitreous and blood were 1.864 ± 0.807 &mgr;g/mL and 4.591 ± 2.979 &mgr;g/mL and of SMX were 5.910 ± 2.705 &mgr;g/mL and 39.289 ± 15.469 &mgr;g/mL, respectively. MIC90 levels were achieved against many bacterial pathogens, including methicillin-resistant Staphylococcus aureus. Conclusions: TMP-SMX penetrates both the aqueous and vitreous cavities when given orally. The components reach therapeutic inhibitory concentrations in the ocular cavity against many potential pathogens.

Change in keratometry after myopic laser in situ keratomileusis and photorefractive keratectomy

Purpose To compare the change in keratometry (K), spherical equivalent (SE), and visual acuity after myopic laser in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). Setting Academic tertiary care center. Design Retrospective review. Methods The postoperative K, SE, and uncorrected and corrected distance visual acuities were measured 6 months, 9 months, 1 year, 2 years, 3 years, 4 to 5 years, 6 to 7 years, and 8+ years postoperatively. A difference (&Dgr;) for each variable was calculated from its 6‐month postoperative baseline. The rates of change were grouped based on the magnitude of myopic correction (0.00 to 2.99 diopters [D]; 3.00 to 5.99 D; 6.00 to 8.99 D), type of surgery (LASIK versus PRK), and age (<34 years; 34 to 45 years; >45 years). Results Statistically significant differences were found in the rates of change between low and moderate corrections to high corrections for &Dgr;Kavg (P = .0472 and P = .0091, respectively) and &Dgr;SE (both P < .0001). Statistically significant differences were found in the rate of change in &Dgr;Kavg between all 3 ages groups (P = .0330, P = .0051, and P <.0001) and in &Dgr;SE between ages less than 34 years and 34 to 45 years to ages over 45 years (P = .0158 and P = .0015, respectively). There was no significant difference in the rate of change in &Dgr;Kavg and &Dgr;SE between LASIK and PRK (P = .3599 and P = .9403, respectively). Conclusion There was keratometric and refractive regression for myopic LASIK, with the rate of regression depending on treatment magnitude and age. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.