Tracy L. Purcell

Corneal asphericity and spherical aberration after refractive surgery

PURPOSE: To evaluate changes in corneal asphericity (Q) and spherical aberrations after refractive surgery using Scheimpflug imaging. SETTING: University of California, San Diego, Shiley Eye Center, La Jolla, California, USA. DESIGN: Cohort study. METHODS: After wavefront‐guided laser in situ keratomileusis, patients within ±0.50 diopter of plano and with an uncorrected distance visual acuity of at least 20/20 were evaluated. The Q values and corneal spherical aberration Zernike values were obtained using Scheimpflug imaging preoperatively and 1 to 3 months postoperatively. RESULTS: The study enrolled 177 myopic eyes and 32 hyperopic eyes. The mean Q value was −0.28 ± 0.11 (SD) and −0.22 ± 0.15, respectively, preoperatively and +0.35 ± 0.44 and −0.64 ± 0.31, respectively, postoperatively. The asphericity change was highly correlated with preoperative spherical equivalent (r2 = 0.81; P≤.001). The mean corneal spherical aberration was +0.21 ± 0.08 μm in myopic eyes and +0.36 ± 0.11 μm in hyperopic eyes preoperatively and +0.36 ± 0.17 μm and 0.00 ± 0.29 μm, respectively, postoperatively. The corneal spherical aberration changes were correlated with the amount of preoperative refractive error (r2 = 0.34; P<.001). There was a tendency for Q values and spherical aberrations to become more positive after myopic ablation and more negative after hyperopic ablation. CONCLUSIONS: Myopic and hyperopic corrections induced changes in the Q value and spherical aberrations in opposite directions (ie, positive and negative, respectively). The changes depended on the magnitude of the refractive correction. Financial disclosure: No author has a financial or proprietary interest in any material or method mentioned.

Gabapentin for Postoperative Pain After Photorefractive Keratectomy: A Prospective, Randomized, Double-blind, Placebo-controlled Trial

PURPOSE To determine whether treatment with oral gabapentin reduces postoperative pain after photorefractive keratectomy (PRK). METHODS This prospective, randomized, double-blind, placebo-controlled study comprised 40 patients scheduled for bilateral PRK. Exclusion criteria were previous refractive surgery; diseases that could affect epithelial healing; use of antihistamines, nonsteroidal anti-inflammatory drugs, or steroids; and use of mitomycin C during PRK. Patients were divided into two groups: 20 patients received gabapentin capsules (300 mg) and 20 patients received identical placebo capsules. Visual acuity, slit-lamp examination, and a 12-question, 10-point visual numerical scale questionnaire were evaluated at each postoperative follow-up. Main outcome measures were the severity of pain at each follow-up and during the previous 24 hours. Secondary outcome measures were maximum and minimum severity of pain, healing time, uncorrected distance visual acuity, and the rating of other symptoms and potential side effects. RESULTS The gabapentin group had less pain during the first 72 hours (P=.024 to .001). A significant difference in favor of gabapentin was found for the first 48 hours regarding minimum pain severity (P=.005 and .01 for 24 and 48 hours, respectively) and for the first 72 hours for maximum pain severity (P=.014, .007, and .001 for 24, 48, and 72 hours, respectively). No significant differences were observed for side effects, symptoms, or healing time except discomfort in favor of gabapentin during the first 24 hours (P=.043). CONCLUSIONS Gabapentin significantly reduced postoperative pain after PRK compared to placebo, with no increase in reported side effects.

Wavefront-guided laser in situ keratomileusis in the treatment of high myopia by using the CustomVue wavefront platform.

Purpose: To assess the efficacy, predictability, and safety of wavefront-guided laser in situ keratomileusis (LASIK) in the treatment of high myopia by using the Visx S4 CustomVue wavefront platform. Methods: A retrospective analysis of consecutive cases of eyes with high myopia (manifest refraction spherical equivalent ≥ −6.00 D) that underwent non-physician-adjusted wavefront-guided LASIK by using the Visx S4 CustomVue wavefront platform. Forty-three eyes of 29 patients were included. Preoperative best spectacle-corrected visual acuity (BSCVA), manifest refraction, WaveScan refraction, postoperative uncorrected visual acuity (UCVA) and BSCVA, and manifest refraction were determined. The clinical outcomes were evaluated on the basis of standard formats and criteria. Data at 3 months postoperatively are presented. Results: Preoperatively, we found mean sphere was −6.89 ± 1.08 D, mean cylinder was −0.97 ± 0.75 D, and mean spherical equivalent (SE) was −7.38 ± 1.20 D. Postoperatively, mean sphere was 0.02 ± 0.40 D, mean cylinder was −0.40 ± 0.40 D, and mean SE was −0.18 ± 0.43 D. UCVA was 20/15 or better in 27.9% and cumulatively 20/20 or better in 58% of eyes. All eyes treated had at least 20/50 UCVA. Efficacy index was 0.94. Eighty-two percent of eyes were within 0.50 D and 97.6% were within 1.00 D of emmetropia at the 3-month follow-up visit. Ninety-one percent of eyes either maintained or gained 1 line of BSCVA. No eye lost >1 line of BSCVA. The safety index was 1.1. Conclusions: The 3-month follow-up results of our study indicate that wavefront-guided LASIK by using the Visx S4 CustomVue wavefront platform is an effective, predictable, and safe treatment of high myopia.

Visual outcomes after wavefront-guided laser in situ keratomileusis with and without iris registration

PURPOSE: To compare the clinical outcomes of wavefront‐guided laser in situ keratomileusis in eyes in which iris registration was used (IR group) and eyes in which iris registration would not engage (no‐IR group). SETTING: Shiley Eye Center, University of California San Diego, La Jolla, California, USA. METHODS: This retrospective analysis comprised 112 eyes of 64 patients who had wavefront‐guided LASIK using the Visx CustomVue S4 IR platform (Advanced Medical Optics) for myopia or myopic astigmatism. The safety, efficacy, predictability, and need for enhancement at the 3‐month follow‐up were evaluated and compared between the IR group and the no‐IR group. RESULTS: By 3 months postoperatively, all eyes in the IR group and 93% of eyes in the no‐IR group had the same best spectacle‐corrected visual acuity (BSCVA) as preoperatively or had gained 1 to 2 lines of BSCVA. No eye in either group lost more than 1 line of BSCVA (P = 0.12). Ninety‐six percent of eyes in the IR group and 93% in the no‐IR group were within ±0.50 diopter (D) of the postoperative manifest refraction spherical equivalent (P = 0.24), and all eyes were within ±1.00 D of emmetropia. Four eyes in the IR group and 11 in the no‐IR group required retreatment during the follow‐up period (P = 0.1). CONCLUSION: The results in the IR group and the no‐IR group were comparable, with no statistically significant differences in measured outcomes.

Epithelial Healing and Visual Outcomes of Patients Using Omega-3 Oral Nutritional Supplements Before and After Photorefractive Keratectomy: A Pilot Study

Purpose: To investigate the effect of omega-3 oral nutritional supplementation on corneal reepithelialization, visual acuity, and tear stability after photorefractive keratectomy (PRK). Methods: This is a prospective, randomized, single-blinded controlled therapeutic trial using omega-3 oral nutritional supplements (TheraTears Nutrition for Dry Eyes; Advanced Vision Research—Akorn, Ann Arbor, MI) conducted at our center. Eighteen healthy patients with refractive error between −1 and −8 diopters were recruited and had bilateral PRK. The treatment group (n = 9 subjects) received omega-3 2 weeks before surgery through 1 month after PRK. The control group (n = 9 subjects) was not given omega-3. Epithelial defects were photographed on postoperative days 0 to 5. Reepithelialization (area in square millimeters) was assessed by fluorescein staining until healing. Tear breakup time (TBUT) and uncorrected distance visual acuity were measured at 1 week, and 1 and 3 months postoperatively. Results: Epithelial defect in the treatment group eyes healed faster compared with that of the controls (P = 0.04). The treatment group eyes healed at an average rate of 1.19% [SD = 0.002; 95% confidence interval (CI), 1.04%–1.34%] per hour, versus 0.83% (SD = 0.0008; 95% CI, 0.77%–0.89%) for controls (Mann–Whitney rank-sum test, P < 0.001). The treatment group eyes maintained a significantly longer TBUT from week 1 through 3 months (mean = 9.52 seconds, SD = 0.81; 95% CI, 8.93–10.10), compared with the controls (mean = 5.52 seconds, SD = 0.81; 95% CI, 4.93–6.10; P < 0.001), and all reached 20/20 vision versus only 4 in the control group 1 month after surgery (P = 0.03). Conclusions: Omega-3 oral nutritional supplements decreased the average time for epithelial healing, and improved TBUT and visual acuity recovery in PRK. These findings suggested that omega-3 oral nutritional supplementation may be a beneficial adjunct therapy for PRK patients.

Photorefractive keratectomy for the correction of residual refractive error with Intacs intrastromal corneal ring segments in place

PURPOSE: To evaluate the efficacy and safety of photorefractive keratectomy (PRK) for residual refractive errors in patients who had previous insertion of intrastromal corneal ring segments (Intacs, Addition Technology, Inc.) for treatment of low myopia. SETTING: Shiley Eye Center, University of California San Diego, La Jolla, California, USA. METHODS: This retrospective case series comprised patients who had Intacs segment implantation and subsequently developed myopic regression. Eight eyes of 5 patients had PRK over the Intacs in situ for the correction of the residual refractive error. RESULTS: Six (75%) of the 8 eyes had plano refraction with 20/20 or better uncorrected visual acuity (UCVA) 1 month after PRK enhancement. Three months postoperatively, all eyes had plano refraction with 20/20 or better acuity. At the last follow‐up examination (up to 2 years), all eyes had near plano vision (20/10 to 20/25). The corneal surface epithelium in all eyes healed in 3 to 5 days. One patient had subepithelial haze in both eyes, which resolved with epithelial scraping with mitomycin‐C (MMC) application and a phototherapeutic keratectomy enhancement. CONCLUSIONS: This small series showed that PRK can be used to treat residual refractive error after Intacs insertion. The UCVA was 20/25 or better in all cases after PRK enhancement. The incidence of post‐PRK haze in this series of patients was high; topical MMC might be used in future cases to mitigate the problem.

Intraocular lens calculation adjustment after laser refractive surgery using Scheimpflug imaging.

Purpose To test a new method of intraocular lens (IOL) calculation after corneal refractive surgery using Scheimpflug imaging (Pentacam HR) and partial coherence interferometry (PCI) (IOLMaster) that does not require historical data; that is, the Schuster/Schanzlin‐Thomas‐Purcell (SToP) IOL calculator. Setting Shiley Eye Center, San Diego, California, and Walter Reed National Military Medical Center, Bethesda, Maryland, USA. Design Retrospective data analysis and validation study. Methods Data were retrospectively collected from patient charts including data from Scheimpflug imaging and refractive history. Target refraction was calculated using PCI and the Holladay 1 and SRK/T formulas. Regression analysis was performed to explain the deviation of the target refraction, taking into account the following influencing factors: ratio of posterior‐to‐anterior corneal radius, axial length (AL), and anterior corneal radius. Results The regression analysis study included 61 eyes (39 patients) that had laser in situ keratomileusis (57 eyes) or photorefractive keratectomy (4 eyes) and subsequent cataract. Two factors were found that explained the deviation of the target refraction using the Holladay 1 formula; that is, the ratio of the corneal radii and the AL and the ratio of corneal radii for the SRK/T formula. A new IOL adjustment calculator was derived and validated at a second center using 14 eyes (10 patients). Conclusions The error in IOL calculation for normal eyes after laser refractive treatment was related to the ratio of posterior‐to‐anterior corneal radius. A formula requiring Scheimpflug data and suggested IOL power only yielded an improved postoperative result for patients with previous corneal laser refractive surgery having cataract surgery. Financial Disclosure No author has a financial or proprietary interest in any material or method mentioned.

Delayed diagnosis of microsporidial stromal keratitis: unusual Wessely ring presentation and partial treatment with medications against Acanthamoeba.

The authors report a case of an immunocompetent 38-year-old male who presented with an indolent keratitis that eluded diagnosis after multiple cultures taken over 9 months. He was started initially on medications against Acanthamoeba, after presenting with a nearly complete corneal ring 2 months after trauma. These medications likely partially treated his condition, thereby making laboratory diagnosis more difficult. He was identified as having Encephalitozoon hellum by PCR. The patient subsequently underwent cornea transplant after a full course of medical treatment and recovered best-corrected visual acuity of 20/20.

Comparison of Bursting Pressure after Scleral Tunnel Incision Sealed with Sutures or an Adherent Ocular Bandage in Human Globes

OBJECTIVE: To evaluate the efficiency of a hydrogel adherent ocular bandage for sealing of scleral tunnel incisions in human eye globes. METHODS: A 4-mm scleral tunnel incision was made in each of 10 globes and bursting pressure was measured using the Seidel test to check for wound leakage. Globes were sealed using either two interrupted 10–0 nylon sutures (n = 5) or an adherent ocular bandage in the form of polyethylene glycol hydrogel (n = 5). Bursting pressure was then measured for a second time. RESULTS: Bursting pressure was significantly higher after wound sealing in both groups. There were no statistically significant differences in bursting pressure between the two groups before or after sealing. CONCLUSIONS: The adherent ocular bandage successfully protected the incision in ex vivo human globes immediately after surgery, with a sealing efficiency comparable to two nylon sutures, suggesting that it is a safe and effective alternative to conventional suturing.

A modified deep anterior lamellar keratoplasty using intacs dissectors.

Purpose: To describe a new technique for deep anterior lamellar keratoplasty in the human eye. Methods: We obtained globes from the San Diego Eye Bank and performed central and peripheral pachymetry measurements at the 8-mm optical zone. We made a radial incision at the edge of the optical zone at 90% depth of central corneal thickness. We enlarged the incision and started lamellar dissection. The curved tunnel was created using dissecting instruments (Addition Technology, Des Plaines, IL), used in Intacs channels. With a sweeping motion, we connected these channels. An 8-mm Barron Radial Vacuum Trephine (Baron Precision Instruments, LLC, Grand Blanc, MI) was placed over the optical zone until the 90% depth of thickness was reached. The cap tissue was detached and viscoelastic was used to separate Descemet membrane and stromal tissue. We photographed the surface for analysis. Results: This technique was easy to perform with little remaining posterior stromal tissue. Residual tissue could easily be dissected, and the vacuum trephine could easily reach the same depth of the pocket. The outer edge of the bed had a clean sharp edge. The stromal bed surface and the inner corneal cap were smooth. Conclusions: We conclude that this modified technique is easy to perform and results in a more regular stromal surface. This technique may reduce the need for penetrating keratoplasty.