Qualitative ultrasound biomicroscopy in glaucoma

Background: UBM is a high?resolution ultrasound technique which allows non?invasive, in vivo imaging of the anterior segment and iridocorneal angle. Purpose: This video is compilation of short video clips and images which gives description on identification of angle closure due to pupillary block, peripheral anterior synechiae, iris bombe, plateau iris, supra ciliary effusion, and malignant glaucoma. It also shows video demonstrating partially and fully patent iridotomy and features of trabeculectomy bleb. Synopsis: This video summarizes importance of UBM application in angle closure glaucoma to understand its pathophysiology by showing the relationship between the peripheral iris, trabecular meshwork and ciliary processes. Highlights: UBM provides two?dimensional, grayscale images of the angle structures and allows identification of non?pupillary block mechanism in angle closure glaucoma, which can be recorded for qualitative and quantitative analyses.

Radial peripapillary capillary network in optic disc anomalies with abnormal tissues on disc surface

Background: Optic disc anomalies with abnormal tissue on the disc surface includes, myelinated nerve fiber, optic disc drusen, and Bergmeister papillae. Imaging the radial peripapillary capillary (RPC) network in optic disc anomalies with optical coherence tomography–angiography (OCTA) can give information on the RPC network in these conditions. Purpose: This video describes the OCTA of optic nerve head and RPC network using the angio disc mode in cases of optic disc anomalies with abnormal tissue on the disc surface. Synopsis: This video presents characteristic features of RPC network in one eye each of myelinated nerve fiber, optic disc drusen, and Bergmeister papillae. Highlights: OCTA in optic disc anomalies with abnormal tissue on the disc surface show a dense RPC microvascular network. OCTA is an effective imaging modality to study vascular plexus/RPC and their alteration in these disc anomalies

Imaging iridotrabecular contact in angle closure

Background: With ultrasound biomicroscopy (UBM), radial scans are taken by using a typical ciliary process, to show the details of the iridocorneal angle, the anterior surface of the ciliary body, and its relation to the posterior iris. Appositional closure represents potentially reversible contact between the peripheral iris and trabecular meshwork. The appositional closure can further be classified according to the configuration of iridotrabecular contact (ITC). UBM can be performed in dark and light conditions, which has been shown to be useful for detecting changes in iridocorneal angle configuration associated with dark and light. Purpose: To image ITC configuration in appositional angle closure and also image iridocorneal angle in dark and bright light room illumination. Synopsis: UBM demonstrates two types of ITC configuration in appositional closure which are, B?type and S?type. It can also demonstrate the presence of sinus of Mapstone in S?type of ITC. Highlights: UBM allows imaging of dynamic changes in the iris and shows that the degree of appositional angle closure is a dynamic process that can change rapidly depending on the lighting conditions.

Quantitative ultrasound biomicroscopy of iridocorneal angle

Background: Ultrasound biomicroscopy (UBM) is a high?resolution ultrasound technique, which allows noninvasive, in vivo imaging of the ocular anterior segment structures. Purpose: This video gives a description of the identification of the iridocorneal angle structures in the cross?sectional view in a radial scan through a typical ciliary process and a guide toward measuring the angle parameters. Synopsis: UBM provides two?dimensional, grayscale images of the iridocorneal angle. The real?time image is displayed on a video monitor and can be recorded for qualitative and quantitative analysis. The angle parameters can be measured by in?built calipers in the machine software and manipulated by the examiner. Highlights: This video demonstrates UBM caliper positions as displayed on the monitor and marked by the examiner for the measurement of various anterior segment parameters of the eye.

Qualitative ultrasound biomicroscopy of the normal anterior segment

Background: Ultrasound biomicroscopy (UBM) is a high?resolution ultrasound technique that allows noninvasive, in vivo imaging of the ocular anterior segment structures. Before interpreting the UBM images of the diseased eyes, it is essential to understand the structures seen in the UBM image of the normal eye. Purpose: This video is a compilation of short video clips that gives description of identification of the anterior segment structures in the axial scan, a cross?sectional view through the anterior chamber angle region of a normal subject in a radial scan, and identification of ciliary processes in the transverse scan. Synopsis: UBM provides two?dimensional, grayscale images of the various anterior segment structures and allows all these structures to be imaged simultaneously, in their normal state, as they occur in the living eye. The real?time image is displayed on a video monitor and can be recorded for qualitative and quantitative analysis. Highlights: The video gives an overview of identification of normal anterior segment structures on UBM.

Radial peripapillary capillary network in congenital cavitary optic disk anomalies

Background and Purpose: "Congenital cavitary optic disk anomalies" is a term used to include optic disk pit (ODP), optic disk coloboma, and morning glory disk anomaly (MGDA). Imaging the radial peripapillary capillary (RPC) network in congenital optic disk anomalies with optical coherence tomography?angiography (OCTA) can shed light on its pathogenesis. This video describes the OCTA findings of optic nerve head and RPC network using the angio?disk mode in five cases of congenital cavitary optic disk anomalies. Synopsis: The video presents characteristic RPC network alterations in two eyes of ODP, one eye of optic disk coloboma, and two eyes of noncontractile MGDA. Highlights: OCTA in ODP and coloboma shows absence of RPC microvascular network and a region of capillary dropout. This finding is in contrast to MGDA, where the microvascular network is dense. OCTA is an effective imaging modality to study vascular plexus and RPC and their alteration in congenital disk anomalies, which could provide information about the structural differences among them.

Clinical identification of optic disk vascular alteration in glaucoma

Background: Several characteristic vascular changes can be observed in the glaucomatous eyes, including changes in the vessel configuration and caliber, presence of collateral vessel on disk, and disk hemorrhage. Purpose: This video describes characteristic vascular changes in the optic nerve head, which can be observed on clinical examination in the glaucomatous eyes, and useful teaching points to identify the same. Synopsis: In glaucoma, as the optic cup enlarges, the normal pattern and course of retinal vessels on the optic disk are altered and show characteristic changes. Identification of these changes provides a clue to the presence of cupping. Highlights: In this video, the vascular changes and its identification in the glaucomatous disc are described, which would be useful to the residents.

Hidden blind spot and pseudofixation loss

Background: Correct mapping of the blind spot is important, as it serves as an estimate of fixation reliability. When the blind spot is not seen in the expected location in Humphrey visual field (HVF) printout, the clinician should give a thought to why this might be the case. Purpose: This video describes a series of cases, in which due to different reasons the blind spot could not be seen in the presumed expected location in the grayscale and numeric data of the HVF printout and the possible explanation behind this. Synopsis: When interpreting perimetry results, it is important to know whether the field test is reliable or not. A stimulus presented at the location of physiologic blind spot should not be seen by a patient with a steady fixation in Heijl– Krakau method. Responses will also occur, however, if the patient has a tendency for false?positive responses, or when the blind spot of the properly fixing eye is not in the location where the test stimulus is presented, because of anatomic variation, or if the patient's head is tilted while performing the test. Highlights: Perimetrist should recognize these potential artifact, during the test and relocate the blind spot. In case, such results are seen after finishing the test, it is recommended for the clinician to repeat the test

Sources of errors in measurement of retinal nerve fiber layer thickness using optical coherence tomography

Background: Optical coherence tomography (OCT)–obtained retinal nerve fiber layer (RNFL) thickness measurements allow for qualitative and quantitative assessment of RNFL thinning in glaucoma. Errors in data acquisition or in software analysis may result in artifacts and erroneous RNFL thickness measurements that may lead to an inaccurate clinical interpretation. Purpose: This video describes tips to recognize artifacts in RNFL thickness measurement in various OCT printouts. Synopsis: The video presents a series of OCT of optic nerve head printouts with artifacts and useful teaching points to identify the same and its source of error. Highlights: The technician must confirm the quality and accuracy of the acquired data before the patient returns to the physician with the final printout. Recognition of artifacts and identifying its source of error is critical to interpret the data accurately, avoiding erroneous clinical interpretation.

“Trigger happy” visual field: Ten pointers

Background: While performing the visual field test, some patients press the response button, at random and not in response to seeing a stimulus, resulting in a classical trigger happy visual field. Purpose: This can be identified by 10 pointers as shown in this single field analysis printout of Humphrey visual field (HVF), 24?2, Swedish interactive threshold algorithm (SITA) standard test of the right eye. These points are useful teaching points for the students to recognize. Synopsis: The video describes classical 10 points, which can be identified in an HVF 24?2 printout in a patient with high false?positive (FP) error. Highlights: The FP index is the most useful of the reliability indices. In SITA strategy, the FP rate is based upon the assessment of patient’s reaction time over the entire course of the test, and hence is not calculated until the test is completed. Therefore, it is important for the perimetrist to be alert to recognize the signs early during the test, such as high fixation los s (despite good fixation as seen on screen monitor) and unusually high retinal sensitivity values (up to 50 dB), and reinstruct the patient. If the test is completed, it should be repeated. This is important as the FP rates >15% are associated with compromised test results and are automatically removed from the glaucoma progression analysis.

Red flags and artifacts in perimetry

Background: As perimetry is a psychophysical test, the thresholds obtained are not only dependent on the functional architecture of the visual system but also on a variety of physical and cognitive factors. Factors such as, Lens rim artifact, improper refraction, miosed pupil and blepharoptosis, can affect luminance thresholds. Additionally, cognitive factors such as patient's attention, motivation, fatigue, and response bias can influence the obtained thresholds. Purpose: The video describes identification of various artifacts in Humphrey visual field printout and it has some useful teaching points to recognize and learn. Synopsis: Visual field test is critical for assessment and to document progression of glaucoma, but is prone to errors and artifacts. Fortunately, the patterns of such artifactual field loss are often characteristic and easily recognizable. Highlights: Several types of errors canlead to inaccurate results. Proper instructions and patient supervision during the test helps to improve the test results. The technician should ensure correct patient’s data entry. Careful examination of the obtained data on the printout is essential to detect any errors that can lead to misinterpretation of visual field, false alarms, and wrong clinical conclusion.

Management of Ahmed glaucoma valve tube exposure after scleral patch graft shrinkage

Background: Ahmed glaucoma valve (AGV) is an useful modality in the management of medically refractory glaucoma. Human donor scleral patch graft (SPG) can be employed to cover the external portion of the tube to prevent its exposure and associated sight?threatening complication. Purpose: To report the management of a case of AGV tube exposure due to SPG shrinkage in the right eye (RE) of a patient. Synopsis: Under peribulbar anesthesia, the conjunctiva is undermined posteriorly, on either side of the exposed tube. The AGV tube is noted to lay firmly against the sclera without any excessive movement. The shrunk and displaced SPG is excised, and a larger, 6 × 8 mm, full?thickness, human donor SPG is placed on the episcleral bed, over the exposed segment of the tube, to ensure its adequate coverage. The SPG is sutured with four interrupted, 10?0 nylon sutures. The SPG is adequately covered with conjunctiva, by conjunctival mobilization and advancement to avoid excessive tension over the tube and closed with interrupted, 8?0 Vicryl suture. Highlights: SPG shrinkage and overlying conjunctival erosion can occur after AGV implantation. This can cause AGV tube exposure, which can be managed by donor SPG to cover the exposed tube

Sources of errors in measurement of retinal nerve fiber layer thickness using optical coherence tomography

Background: Optical coherence tomography (OCT)–obtained retinal nerve fiber layer (RNFL) thickness measurements allow for qualitative and quantitative assessment of RNFL thinning in glaucoma. Errors in data acquisition or in software analysis may result in artifacts and erroneous RNFL thickness measurements that may lead to an inaccurate clinical interpretation. Purpose: This video describes tips to recognize artifacts in RNFL thickness measurement in various OCT printouts. Synopsis: The video presents a series of OCT of optic nerve head printouts with artifacts and useful teaching points to identify the same and its source of error. Highlights: The technician must confirm the quality and accuracy of the acquired data before the patient returns to the physician with the final printout. Recognition of artifacts and identifying its source of error is critical to interpret the data accurately, avoiding erroneous clinical interpretation.

Influence of disc area on retinal nerve fiber layer thickness measurement by spectral domain optical coherence tomography.

Background: To examine the eff ect of optic disc area on peripapillary RNFLT (retinal nerve fi ber layer thickness) measurement at circle diameter of 3.4 mm around optic nerve head using spectral OCT/SLO (Optical coherence tomography/scanning laser ophthalmoscope). Materials and Methods: In this prospective, cross sectional study, one hundred and two eyes of 102 normal subjects underwent RNFLT and disc area measurement using spectral OCT/SLO. Based on disc area, subjects were divided into three groups i.e., <3 mm2 (32 eyes), 3-4 mm2 (36 eyes) and >4 mm2 (34 eyes). The eff ect of disc area on RNFLT parameters was analyzed using linear regression analysis. Results: The mean and quadrant RNFLT did not show signifi cant correlation with disc area in subjects with disc area of <4 mm2, however in eyes with disc area >4 mm2, average RNFLT, superior and temporal quadrant RNFLT showed negative correlation with disc area, which was statistically signifi cant (P = 0.004, P = 0.005 and P = 0.002, respectively) Conclusion: In healthy eyes of disc area <4 mm2, disc size does not appear to aff ect peripapillary RNFLT measurement by spectral OCT/SLO. Average, superior and temporal quadrant RNFLT measurements were inversely proportional to disc area in eyes with disc area >4 mm2. Hence, RNFLT measurement by OCT in eyes with optic disc area of >4 mm2 should be interpreted carefully.

Quantification of retinal nerve fiber layer thickness using spectral domain optical coherence tomography in normal Indian population.

The purpose of this study was to measure peripapillary retinal nerve fiber layer thickness (RNFLT) using spectral domain optical coherence tomography (SD-OCT) in normal Indian eyes, for which, 210 normal volunteers were recruited. One eye of each subject underwent RNFL scanning at 3.4 mm circle diameter around optic nerve using SD OCT. The data were analyzed to determine RNFLT in the sample population and its variation with age and gender. The average peripapillary RNFLT was 114.03 ± 9.59 μm. There was no effect of gender on RNFLT parameters. Age had significant negative correlation with average (P = 0.005), superior (P = 0.04), temporal (P = 0.049), and nasal quadrants (P = 0.01) RNFLT. Inferior quadrant RNFLT also had a negative correlation with age, but it was not statistically significant (P = 0.15).

Ability of spectral domain optical coherence tomography peripapillary retinal nerve fiber layer thickness measurements to identify early glaucoma.

Purpose: To evaluate the ability of spectral domain optical coherence tomography (OCT) peripapillary retinal nerve fiber layer thickness (RNFLT) parameters to distinguish normal eyes from those with early glaucoma in Asian Indian eyes. Design: Observational cross-sectional study. Materials and Methods: One hundred and seventy eight eyes (83 glaucoma patients and 95 age matched healthy subjects) of subjects more than 40 years of age were included in the study. All subjects underwent RNFLT measurement with spectral OCT/ scanning laser ophthalmoscope (SLO) after dilatation. Sensitivity, specificity and area under the receiving operating characteristic curve (AROC) were calculated for various OCT peripapillary RNFL parameters. Results: The mean RNFLT in healthy subjects and patients with early glaucoma were 105.7 ± 5.1 μm and 90.7 ± 7.5 μm, respectively. The largest AROC was found for 12 o’clock- hour (0.98), average (0.96) and superior quadrant RNFLT (0.9). When target specificity was set at ≥ 90% and ≥ 80%, the parameters with highest sensitivity were 12 o’clock -hour (91.6%), average RNFLT (85.3%) and 12 o’ clock- hour (96.8 %), average RNFLT (94.7%) respectively. Conclusion: Our study showed good ability of spectral OCT/ SLO to differentiate normal eyes from patients with early glaucoma and hence it may serve as an useful adjunct for early diagnosis of glaucoma.

Optic disc topography in normal Indian eyes using spectral domain optical coherence tomography.

Purpose: The aim was to study optic nerve head (ONH) parameters in normal Indian eyes using spectral domain optical coherence tomography (OCT)/scanning laser ophthamoscope (SLO). Materials and Methods: One hundred and fifty-seven eyes of 157 normal subjects of various age groups underwent ONH imaging with spectral OCT/SLO and the parameters obtained were correlated with disc size. The effect of age, gender, and refractive error on various ONH parameters were also studied. Results: The mean optic disc area was 3.36 ± 0.64 mm2 (range, 2.13–5.08 mm2), mean rim area was 2.49 ± 0.58 mm2 (range, 1.20–3.62 mm2), and mean cup area was 1.10 ± 0.75 mm2 (range, 0–3.07 mm2). The disc area showed significant positive correlation with the rim area, cup area, horizontal cup disc ratio, vertical cup disc ratio, cup disc area ratio, mean cup depth, and maximum cup depth (P < 0.001). Neither gender nor refractive error showed any significant difference in various ONH parameters. ONH parameters did not show significant change with age except for rim area which declined with the advancing age (r = –0.25, P < 0.001). Conclusions: The quantitative measurement of ONH topography obtained with this study provides a normative database for an Indian population with spectral OCT/SLO. As optic disc area influences ONH topography, disc size should to be considered when evaluating optic disc for progressive optic neuropathies such as glaucoma.