Pravin K. Vaddavalli

Role of Confocal Microscopy in the Diagnosis of Fungal and Acanthamoeba Keratitis

PURPOSE To investigate the role of confocal microscopy as a diagnostic modality in microbial keratitis and to determine inter- and intraobserver variation in the analysis and interpretation of confocal microscopy findings. DESIGN Prospective, double masked, nonrandomized, observational clinical trial. PARTICIPANTS We included 146 consecutive patients with clinically suspected microbial keratitis. METHODS Confocal microscopy and microbiology evaluation of study participants. MAIN OUTCOME MEASURES Sensitivity, specificity, and positive and negative predictive values of confocal microscopy in diagnosing fungal and Acanthamoeba keratitis compared with microbiologic evaluation, as well as the intra- and interobserver variation in interpretation of confocal scans. RESULTS We included 148 cases of infiltrative keratitis. Of the 103 microbiologically proven cases of Acanthamoeba or fungal keratitis, the confocal microscope was able to identify fungal filaments or Acanthamoeba cysts in 91 cases with either fungal or Acanthamoeba keratitis with a sensitivity of 88.3% (95% confidence interval [CI], 82.2-94.5) and a specificity of 91.1% (95% CI, 82.8-99.4). The interobserver agreement in interpreting the scans was good (kappa = 0.6; phi = 0.617). The intraobserver agreement was kappa = 0.795 and phi = 0.807. CONCLUSIONS The confocal microscope seems to be an accurate and reliable diagnostic modality in the etiologic diagnosis of fungal and Acanthamoeba keratitis.

Accuracy of intraocular lens power calculation formulae in children less than two years.

PURPOSE To assess the accuracy of IOL power calculation formulae in children less than 2 years of age. DESIGN Retrospective, comparative study, comprising of 128 eyes of 84 children. METHODS We analyzed records of children less than 2 years with congenital cataract who underwent primary IOL implantation. Data were analyzed for prediction error using the 4 commonly used IOL power calculation formulae. We calculated the absolute prediction error with each of the formulae and the formula that gave least variability was determined. The formula that gave the best prediction error was determined. RESULTS Mean age at surgery was 11.7 ± 6.2 months. Absolute prediction error was found to be 2.27 ± 1.69 diopters (D) with SRK II, 3.23 ± 2.24 D with SRK T, 3.62 ± 2.42 D with Holladay, and 4.61 ± 3.12 D with Hoffer Q. The number of eyes with absolute prediction error within 0.5 D was 27 (21.1%) with SRK II, 8 (6.3%) with SRK T, 12 (9.4%) with Holladay, and 5 (3.9%) with Hoffer Q. Comparison between different formulae showed that the absolute prediction error with SRK II formula was significantly better than with other formulae (P < .001). Prediction error with SRK II formula was not affected by any factor such as age (P = .31), keratometry (P = .32), and axial length (P = .27) of the patient. Axial length influenced the absolute prediction error with Holladay (P = .05) and Hoffer Q formulae (P = .002). Mean keratometry influenced prediction error (P = .03) with SRK T formula. CONCLUSION Although absolute prediction error tends to remain high with all present IOL power calculation formulae, SRK II was the most predictable formula in our series.

Boston ocular surface prosthesis: An Indian experience

Context: Boston ocular surface prosthesis (BOSP) is a scleral contact lens used in the management of patients who are rigid gas permeable (RGP) failures as with corneal ectasias such as keratoconus and in those patients who have ocular surface disease such as Stevens–Johnson syndrome (SJS). Aim: To report utilization of BOSP in a tertiary eye care center in India. Materials and Methods: We retrospectively reviewed charts of 32 patients who received BOSP from July 2008 to May 2009. Indications for fitting these lenses, improvement in visual acuity (VA) before and after lens fitting and relief of symptoms of pain and photophobia were noted. Paired t-test was used for statistical analysis using SPSS version 16.0 for Windows. Results: Thirty-two patients (43 eyes) received these lenses. These consisted of 23 eyes of 17 patients who failed RGP trials for irregular astigmatism and corneal ectasia such as keratoconus and post radial keratotomy and scar and 20 eyes of 15 patients with SJS. Mean age of RGP failures was 27.94 years. Pre- and post-BOSP wear mean LogMAR VA was 1.13 and 0.29, respectively, in RGP failures. The P value was statistically significant (P < 0.001). In patients with SJS, LogMAR VA was 0.84 ± 0.92 before and 0.56 ± 0.89 after lens wear. The P value was statistically significant (P < 0.001). VA improved by >2 lines in 7/20 eyes (35%) with SJS, with improvement in symptoms. Conclusion: BOSP improves VA in patients who have irregular astigmatism as in ectasias and RGP failures and improves vision and symptoms in patients with SJS.

Fluid filled scleral contact lens in pediatric patients: challenges and outcome.

PURPOSE To study the indications and the challenges while fitting scleral contact lens (ScCL) filled with fluid prior to lens insertion in pediatric patients. METHODS We retrospectively reviewed charts of patients of 16 years or less who received ScCL (PROSE - Prosthetic Replacement of the Ocular Surface Ecosystem, Boston Foundation for Sight, Needham Heights, MA, USA) that were filled with fluid (Normal saline) before lens insertion during July 2006 to April 2010. The main goal of ScCL fitting was to improve vision in patients having keratoconus (KC) and improve the ocular microenvironment in ocular surface disease (OSD). Visual acuity before and after lens wear was noted. RESULTS Fluid-filled ScCL were dispensed to 15 patients (20 eyes). The indications for ScCL fitting were KC (n = 3 eyes), Stevens Johnson syndrome (SJS, n = 13 eyes), radiation keratopathy (n = 1 eye), combined KC and SJS (n = 1 eye) and KC and vernal keratoconjunctivitis (VKC, n = 2 eyes). Mean age of the patients was 12.85 years. The average daily lens wear was 9 h. The vision improved by 2 lines or more in 85% and dropped by 2 lines or more in 45% eyes after 4 h of lens wear due to tear debris collection. None of the patients had any complications. Patients were self sufficient inserting and removing ScCL. Two patients had broken lenses during the follow-up. CONCLUSIONS ScCL are useful for pediatric patients who have OSD, irregular astigmatism or the two coexisting; KC combined with VKC or SJS, helping to maintain the health of the ocular surface and improves vision in these patients.

Intracameral Perfluoropropane Gas in the Treatment of Acute Corneal Hydrops

PURPOSE This study is aimed to evaluate the role of 14% nonexpansile concentration of perfluoropropane (C(3)F(8)) gas in the management of acute hydrops in corneal ectasias. DESIGN Retrospective, nonrandomized, comparative, interventional case series. PARTICIPANTS AND CONTROLS The study group consisted of 62 eyes of 57 patients and the control group included 90 eyes of 82 patients with acute corneal hydrops who presented within 30 days of onset of symptoms. INTERVENTION Patients in the control group underwent a single intracameral injection of 0.1 mL of nonexpansile concentration (14%) of C(3)F(8) gas. Patients in the control group were treated conservatively. Patients in both groups were followed regularly for 12.6±7.7 and 13.4±8.3 months in the study and control groups, respectively, and assessed clinically for complete disappearance of epithelial and stromal edema on slit-lamp biomicroscopy. MAIN OUTCOME MEASURES The primary outcome measure was mean time to resolution of corneal edema, which was calculated both from the date of onset of hydrops and the date of initiation of therapy to the date of resolution in days. RESULTS The overall time to resolution both from the date of onset of symptoms (90.5±55.8 vs 125±68.9 days; P = 0.0005) and from the date of initiation of therapy (78.7±53.2 vs 117.9±68.2 days; P = 0.0001) was significantly lower in the study group compared with the control group. However, on subgroup analysis a significant difference in the resolution time was found only in eyes with keratoconus (P<0.0001). No difference in the resolution time was seen in eyes with pellucid marginal corneal degeneration (PMCD) or keratoglobus. The main complication of this procedure was reversible pupillary block (16%; P<0.0001). There was no difference in the final visual acuity or endothelial cell counts between the 2 groups. CONCLUSIONS Intracameral C(3)F(8) gas in a nonexpansile concentration is a useful modality for faster resolution of corneal edema in patients with acute corneal hydrops and keratoconus, and its role in the treatment of PMCD and keratoglobus needs further evaluation.

Corneal Thickness in Keratoconus: Comparing Optical, Ultrasound, and Optical Coherence Tomography Pachymetry

PURPOSE To compare the central and peripheral pachymetry measurements determined using Orbscan IIz (Bausch & Lomb, Rochester, NY), Visante optical coherence tomography (OCT; Carl Zeiss Meditec, Dublin, CA), and RTVue OCT (Oculus Technologies, Wynwood, WA) with ultrasound pachymetry in eyes with established keratoconus and to evaluate the agreement between them. DESIGN Evaluation of diagnostic technologies. PARTICIPANTS One hundred six eyes of 67 consecutive patients with a clinical diagnosis of keratoconus ranging in age from 12 to 40 years. METHODS Central corneal thickness (CCT) was determined by all the 4 techniques. Peripheral corneal thicknesses were determined using Orbscan IIz, Visante OCT, and RTVue at 8 points (superior, inferior, temporal, nasal, superior-temporal, inferior-temporal, superior-nasal, and inferior-nasal) all in the 5.0- to 7.0-mm arcuate zone. MAIN OUTCOME MEASURES Central and peripheral keratoconus thickness. RESULTS Ultrasound pachymetry determined significantly higher CCT values than Orbscan IIz (P<0.001), Visante (P<0.001), and RTVue (P = 0.037), with a mean ± standard deviation difference of 14±3 μm, 13±2 μm, and 5±3 μm, respectively. The mean CCT difference was minimal (1±3 μm; P = 0.69) between the Orbscan IIz and Visante. A strong correlation was found (r>0.80) between all the CCT measurement techniques. Orbscan IIz significantly overestimated the peripheral thickness compared with the rest, and the mean differences ranged between 21 and 60 μm. Mean peripheral thickness differences between RTVue and Visante OCT always remained less than 20 μm. Weak correlations and larger limits of agreement were found between the techniques in thinner and peripheral zones. CONCLUSIONS Orbscan IIz, Visante, RTVue, and ultrasound pachymetry show high correlation, although Orbscan IIz and Visante significantly underestimated CCT measurements compared with ultrasound pachymetry in keratoconus. Orbscan IIz significantly overestimated peripheral corneal thickness compared with RTVue and Visante.

Anterior segment optical coherence tomography features of acute corneal hydrops.

Purpose: To describe the clinical significance of in vivo corneal findings in eyes with acute corneal hydrops. Methods: Medical records and anterior segment optical coherence tomography (ASOCT) images of 24 patients with keratoconus and unilateral acute corneal hydrops were reviewed. Clinical findings and position, integrity, and orientation of the Descemet membrane (DM) on ASOCT were noted. Size of the DM break, depth of the DM detachment, and corneal thickness were measured by ASOCT and correlated with the duration of corneal edema, assessed clinically. Outcomes of intracameral perfluoropropane (C3F8) gas in 13 eyes and histopathological findings after penetrating keratoplasty in 2 eyes were also correlated with serial ASOCT findings. Results: Duration of corneal edema was 9.3 ± 4.4 weeks. On ASOCT, DM showed 3 patterns: detachment with break and rolled ends (n = 13), detachment with break and flat ends (n = 10), and detachment with no break (n = 1). Initial corneal thickness was 1.3 ± 0.25 mm, size of the DM break was 1.1 ± 0.8 mm, and depth of the DM detachment was 0.9 ± 0.6 mm. On multiple regression analysis, duration of corneal edema showed significant positive association with the depth of DM detachment (P = 0.0002) and size of DM break (P = 0.002) and negative association with intracameral C3F8 (P < 0.0001). Correlation of ASOCT with histopathological findings revealed 2 stages of resolution of hydrops: reattachment of DM and endothelial migration. Conclusions: Eyes with deeper DM detachments and larger DM breaks required more time for resolution of corneal edema despite intracameral C3F8. This association needs to be validated by a prospective study.

Evaluation of central corneal thickness measurement with RTVue spectral domain optical coherence tomography in normal subjects.

Purpose: To determine (1) repeatability of central corneal thickness (CCT) measurements by spectral domain optical coherence tomography (RTVue; Optovue, Inc, Fremont, CA) and (2) agreement between CCT measurements by RTVue and those by ultrasonic pachymetry, Orbscan, and anterior segment optical coherence tomography (ASOCT). Methods: In a prospective observational study, 2 cohorts of normal subjects were recruited. In the first cohort (51 subjects), 5 measurements of CCT were obtained by RTVue during the same visit to determine the repeatability. In the second cohort (65 subjects), CCT measurements were obtained by RTVue, ultrasonic pachymetry, Orbscan, and ASOCT during the same visit to determine the agreement among these instruments. Repeatability was assessed by intraclass correlation coefficient (ICC), within-subject standard deviation, coefficient of repeatability, and within-subject coefficient of variation. Agreement was assessed by ICC and Bland and Altman plots. Results: Repeatability of CCT measurements by RTVue as assessed by ICC, within-subject standard deviation, coefficient of repeatability, and within-subject coefficient of variation was 0.99 (0.99-0.99), 2.2 (1.9-2.5), 4.2 μm (3.6-4.8), and 0.4% (0.3-0.5), respectively. The average CCT by RTVue (529 μm) was comparable to that by ultrasonic pachymetry (539 μm; P = 0.15), Orbscan (536 μm; P = 0.54), and ASOCT (526 μm; P = 0.77). The 95% limits of agreement on Bland and Altman plots ranged from 20 μm (between RTVue and ASOCT) to 33 μm (between RTVue and Orbscan). Conclusions: CCT measurements by RTVue have an excellent repeatability. Although CCT measurements by RTVue are comparable to that by ultrasonic pachymetry, Orbscan, and ASOCT, the difference between instruments can be significant depending on the clinical situation considered.

Role of confocal microscopy in deep fungal keratitis.

Purpose: The purpose of this study was to assess the role of in vivo confocal microscopy in cases of fungal keratitis presenting with a deep stromal infiltrate. Design: Retrospective, noncomparative case series. Methods: We reviewed the medical, microbiologic, and histopathologic data of 6 patients, whose clinical presentation was characterized by deep stromal or multifocal endothelial lesions. These patients were subjected to in vivo confocal microscopy on the day of presentation. All the patients underwent therapeutic penetrating keratoplasty. The excised corneal buttons were bisected and subjected to microbiologic and histopathologic examinations. Results: Microbiologic and/or histopathologic examination proved that the keratitis in all the 6 patients was caused by filamentous fungi. Five corneal buttons were positive for the fungus on histopathologic examination. Four specimens grew out fungus on microbiologic examination. In 5 (83%) cases, confocal microscopy revealed double-walled, septate, linear branching structures resembling fungal filaments. Conclusions: In vivo confocal microscopy can be a useful diagnostic tool in patients presenting with deep stromal lesions.

Microbial keratitis after LASIK.

PURPOSE To report cases of microbial keratitis after LASIK from a tropical climatic zone. METHODS This retrospective case series included 17 eyes of 15 patients managed at our center from January 1999 to December 2007. All patients had a detailed clinical evaluation followed by corneal scrapings. The material obtained on scraping was subjected to detailed microbiology evaluation. Initial medical treatment was based on microbiology results and included irrigation of the interface with appropriate antimicrobial solutions. The flap was amputated in patients who developed flap necrosis. N-butyl cyanoacrylate tissue adhesive was applied for gross thinning and penetrating keratoplasty (PK) was performed for advanced cases of keratitis. RESULTS Mean patient age was 25.8 years (range: 18 to 44 years). Two patients had undergone unilateral surgery. Thirteen patients presented with infection in 1 eye and 2 patients had bilateral infection. The microorganisms isolated were filamentous fungi (4 eyes), Nocardia asteroides (5 eyes), atypical mycobacteria (4 eyes), Acanthamoeba (2 eyes), Corynebacterium (1 eye), and Staphylococcus epidermidis (1 eye). The infection resolved with medical treatment in 6 eyes, medical treatment and flap amputation in 4 eyes, and PK in 4 eyes. Two patients were lost to follow-up. Five eyes of 4 patients referred to us within 10 days of symptom onset resolved on medical treatment with final visual acuity ranging from 20/20 to 20/80. CONCLUSIONS In a tropical region, it is important to consider uncommon organisms such as fungi, Nocardia, and Acanthamoeba as possible etiological agents in keratitis after LASIK. A detailed microbiology work-up will help in definitive diagnosis and appropriate treatment.