Sunita Radhakrishnan

Correction of geometric and refractive image distortions in optical coherence tomography applying Fermat’s principle

We describe a methodology for quantitative image correction in OCT which includes procedures for correction of nonlinear axial scanning and non-telecentric scan patterns, as well as a novel approach for refraction correction in layered media based on Fermats principle. The residual spatial error obtained in layered media with a fan-beam hand-held probe was reduced from several hundred micrometers to near the diffraction and coherence-length limits.

The Effect of Phacoemulsification on Intraocular Pressure in Glaucoma Patients: A Report by the American Academy of Ophthalmology

OBJECTIVE To examine effects of phacoemulsification on longer-term intraocular pressure (IOP) in patients with medically treated primary open-angle glaucoma (POAG; including normal-tension glaucoma), pseudoexfoliation glaucoma (PXG), or primary angle-closure glaucoma (PACG), without prior or concurrent incisional glaucoma surgery. METHODS PubMed and Cochrane database searches, last conducted in December 2014, yielded 541 unique citations. Panel members reviewed titles and abstracts and selected 86 for further review. The panel reviewed these articles and identified 32 studies meeting the inclusion criteria, for which the panel methodologist assigned a level of evidence based on standardized grading adopted by the American Academy of Ophthalmology. One, 15, and 16 studies were rated as providing level I, II, and III evidence, respectively. RESULTS All follow-up, IOP, and medication data listed are weighted means. In general, the studies reported on patients using few glaucoma medications (1.5-1.9 before surgery among the different diagnoses). For POAG, 9 studies (total, 461 patients; follow-up, 17 months) showed that phacoemulsification reduced IOP by 13% and glaucoma medications by 12%. For PXG, 5 studies (total, 132 patients; follow-up, 34 months) showed phacoemulsification reduced IOP by 20% and glaucoma medications by 35%. For chronic PACG, 12 studies (total, 495 patients; follow-up, 16 months) showed phacoemulsification reduced IOP by 30% and glaucoma medications by 58%. Patients with acute PACG (4 studies; total, 119 patients; follow-up, 24 months) had a 71% reduction from presenting IOP and rarely required long-term glaucoma medications when phacoemulsification was performed soon after medical reduction of IOP. Trabeculectomy after phacoemulsification was uncommon; the median rate reported within 6 to 24 months of follow-up in patients with controlled POAG, PXG, or PACG was 0% and was 7% in patients with uncontrolled chronic PACG. CONCLUSIONS Phacoemulsification typically results in small, moderate, and marked reductions of IOP and medications for patients with POAG, PXG, and PACG, respectively, and using 1 to 2 medications before surgery. Trabeculectomy within 6 to 24 months after phacoemulsification is rare in such patients. However, reports on its effects in eyes with advanced disease or poor IOP control before surgery are few, particularly for POAG and PXG.

Emerging Clinical Applications of Optical Coherence Tomography

Optical coherence tomography (OCT) is an emerging noninvasive imaging technique that provides microscopic tomographic sectioning of biological samples. By measuring backscattered light as a function of depth, OCT fills a valuable niche in imaging of tissue microstructure, providing subsurface imaging with high spatial resolution (on the order of ten micrometers) in three dimensions and high sensitivity in vivo with no contact needed between the probe and the tissue.

Long-term effect of phacoemulsification on intraocular pressure using phakic fellow eye as control

PURPOSE: To investigate the long‐term effect of phacoemulsification on intraocular pressure (IOP) in patients with ocular hypertension and open‐angle glaucoma. SETTING: Three multispecialty ophthalmology practices and one glaucoma specialty group. DESIGN: Retrospective comparative case series. METHODS: Review of medical records of patients with open‐angle glaucoma or ocular hypertension who had had unilateral phacoemulsification (without other prior or concurrent ophthalmic procedure) with the fellow eye remaining phakic at least 3 years postoperatively. RESULTS: Preoperatively, the IOP in the surgical and fellow eyes in the 29 patients was 15.66 mm Hg ± 3.33 (SD) and 15.64 ± 4.23 mm Hg (P=.98), respectively. Postoperatively, it was 13.56 ± 2.04 mm Hg and 14.92 ± 2.85 mm Hg, respectively, at 4.5 months (P=.06); 14.88 ± 3.20 mm Hg and 15.27 ± 3.19 mm Hg, respectively, at 1 year (P=.67); 14.16 ± 2.61 mm Hg and 14.95 ± 2.79 mm Hg, respectively, at 2 years (P=.37); and 14.68 ± 3.44 mm Hg and 14.68 ± 2.68 mm Hg at 3 years (P=1.00), respectively. There was no significant difference in the mean number of IOP‐lowering medications used in the surgical eyes (1.96 ± 1.40) and fellow eyes (2.08 ± 1.44) postoperatively (P=.77). CONCLUSIONS: In a cohort of ocular hypertensive and glaucoma patients, uncomplicated phacoemulsification had no significant IOP‐lowering effect compared with the phakic fellow eye for up to 3 years postoperatively. There was also no difference between the mean number of postoperative IOP‐lowering medications used in the surgical and fellow eyes. Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned.

Real-time optical coherence tomography of the anterior segment using hand-held and slit-lamp adapted systems

Real-time optical coherence tomography (OCT) was used to visualize and quantify structures in the anterior segment of the eye. Results obtained with hand-held and slit-lamp adapted OCT systems are presented. Preliminary data indicates strong potential for the use of real-time OCT in anterior segment biometry and in non-invasive assessment of normal and pathological anterior segment anatomy.

Blebitis After EX-PRESS Glaucoma Filtration Device Implantation-A Case Series.

Purpose:To present the management and outcomes of blebitis in patients who underwent EX-PRESS Glaucoma Filtration Device (GFD) implantation. Design:Retrospective case series. Participants:The study included 5 patients who developed blebitis following EX-PRESS GFD implantation. Methods:Charts of all patients who underwent EX-PRESS GFD implantation at the Glaucoma Center of San Francisco between 2007 and 2013 were reviewed. Five patients with blebitis were identified and their clinical course was recorded. Main Outcome Measures:Clinical course of blebitis. Results:Of 325 eyes that underwent EX-PRESS GFD implantation, 5 eyes (1.5%) with blebitis were identified. The mean interval between EX-PRESS GFD surgery and blebitis was 2.3±0.8 years. Four of the 5 eyes with blebitis had potential risk factors for bleb-related infection; 1 had chronic blepharitis, 2 had contact lens use, and one had 2 episodes of bleb leak before blebitis. All patients were treated with topical antibiotics; in addition, 3 received oral antibiotics and 1 received intravitreal antibiotics. None of the patients developed endophthalmitis. One patient had recurrent blebitis, which was treated with topical, oral, and intravitreal antibiotics. None of the patients had the device removed. The mean follow-up time after blebitis was 16.8±8.9 months (range, 10 to 32 mo). Conclusions:This case series suggests that blebitis after EX-PRESS GFD implanted under a scleral flap may be treated without removal of the device. Further study is required to determine the optimal method of treating this condition.

Quantitative OCT image correction using Fermat's principle and mapping arrays

Optical coherence tomography (OCT) is a relatively new developed technique to image tissue microstructure in vivo with a resolution of about 10 micrometers . So far, the research has focused on increasing the resolution, increasing the acquisition rate, developing new sample arm scanning techniques, or functional imaging like color Doppler OCT. But one of the main advantages of OCT compared to ultrasound, non-contact imaging, also results in a mayor image distortion: refraction at the air-tissue interface. Also, applied scanning configurations can lead to deformed images. Both errors prevent accurate distance and angle measurements on OCT images, necessary e.g. for Glaucoma diagnosis in the anterior segment of the eye. We describe a methodology for quantitative image correction in OCT which includes procedures for correction of arbitrary spatial warping caused by non-uniform axial reference and lateral sample scan patterns, as well as a novel approach for refraction correction in layered media based on Fermats principle. The de-warping corrections are implemented in real-time by use of pointer (mapping) arrays, while the refraction correction algorithm is more computationally intensive and is performed off-line.

Laser Peripheral Iridotomy in Primary Angle Closure: A Report by the American Academy of Ophthalmology

PURPOSE To examine the efficacy and complications of laser peripheral iridotomy (LPI) in subjects with primary angle closure (PAC). METHODS Literature searches in the PubMed and Cochrane databases were last conducted in August 2017 and yielded 300 unique citations. Of these, 36 met the inclusion criteria and were rated according to the strength of evidence; 6 articles were rated level I, 11 articles were rated level II, and 19 articles were rated level III. RESULTS Reported outcomes were change in angle width, effect on intraocular pressure (IOP) control, disease progression, and complications. Most of the studies (29/36, 81%) included only Asian subjects. Angle width (measured by gonioscopy, ultrasound biomicroscopy, and anterior segment OCT) increased after LPI in all stages of angle closure. Gonioscopically defined persistent angle closure after LPI was reported in 2% to 57% of eyes across the disease spectrum. Baseline factors associated with persistent angle closure included narrower angle and parameters representing nonpupillary block mechanisms of angle closure, such as a thick iris, an anteriorly positioned ciliary body, or a greater lens vault. After LPI, further treatment to control IOP was reported in 0%-8% of PAC suspect (PACS), 42% to 67% of PAC, 21% to 47% of acute PAC (APAC), and 83%-100% of PAC glaucoma (PACG) eyes. Progression to PACG ranged from 0% to 0.3% per year in PACS and 0% to 4% per year in PAC. Complications after LPI included IOP spike (8-17 mmHg increase from baseline in 6%-10%), dysphotopsia (2%-11%), anterior chamber bleeding (30%-41%), and cataract progression (23%-39%). CONCLUSIONS Laser peripheral iridotomy increases angle width in all stages of primary angle closure and has a good safety profile. Most PACS eyes do not receive further intervention, whereas many PAC and APAC eyes, and most PACG eyes, receive further treatment. Progression to PACG is uncommon in PACS and PAC. There are limited data on the comparative efficacy of LPI versus other treatments for the various stages of angle closure; 1 randomized controlled trial each demonstrated superiority of cataract surgery over LPI in APAC and of clear lens extraction over LPI in PACG or PAC with IOP above 30 mmHg.

Noninvasive characterization of anterior segment structures using real-time optical coherence tomography at 1310 nm

Real-time optical coherence tomography (OCT) was used to visualize and quantify structures in the anterior segment of the eye. Current results of ongoing clinical trials are presented. Preliminary data indicates strong potential for the use of real time OCT as a tool for noninvasive characterization of the anterior chamber angle and for anterior segment biometry.

Spectral-Domain OCT: Helping the Clinician Diagnose Glaucoma: A Report by the American Academy of Ophthalmology

PURPOSE To review the current published literature on the use of spectral domain (SD) OCT to help detect changes associated with the diagnosis of glaucoma. METHODS Searches of the peer-reviewed literature were conducted on June 11, 2014, November 7, 2016, August 8, 2017, and April 19, 2018, in the PubMed and Cochrane Library databases and included only articles published since the last glaucoma imaging Ophthalmic Technology Assessment, which included articles up until February 2006. The abstracts of these 708 articles were examined to exclude reviews and non-English articles. After inclusion and exclusion criteria were applied, 74 articles were selected, and the panel methodologist (K.N.-M.) assigned ratings to them according to the level of evidence. Two articles were rated level I, 57 articles were rated level II, and the 15 level III articles were excluded. RESULTS Spectral-domain OCT is capable of detecting damage to the retinal nerve fiber layer (RNFL), macula, and optic nerve in patients with preperimetric and perimetric glaucoma (level I and II evidence). The most commonly studied single parameter was RNFL thickness. Of note, RNFL thickness measurements are not interchangeable between instruments. Various commercially available SD OCT instruments have similar abilities to distinguish patients with known glaucoma from normal subjects. Despite different software protocols, all SD OCT instruments are able to detect the same typical pattern of glaucomatous RNFL loss that affects primarily the inferior, inferior temporal, superior, and superior temporal regions of the optic nerve (level II evidence). Across many SD OCT instruments, macular imaging also can detect a preferential inferior, inferior temporal, and superior temporal thinning in patients with glaucoma compared with controls. Best disc parameters for detecting glaucomatous nerve damage are global rim area, inferior rim area, and vertical cup-to-disc ratio. Studies suggest that newer reference-plane independent optic nerve parameters may have the same or better detection capability when compared with older reference-plane dependent disc parameters (level II evidence). CONCLUSIONS Structural glaucomatous damage can be detected by SD OCT. Optic nerve, RNFL, and macular parameters can help the clinician distinguish the anatomic changes that are associated with patients with glaucoma when compared with normal subjects.