Adaptive optics optical coherence tomography (AO-OCT)
Pablo Artal in Handbook of Visual Optics, 2017
The time domain (TD) approach was the first technique OCT method to be successfully applied to the eye and subsequently commercialized. The general implementation rapidly scans the reference mirror in an axial direction to generate a single A-scan; this is then repeated along a series of retinal locations to build up the two-dimensional B-scan. When combined with AO this image acquisition geometry has been superseded by transversal scanning (TS); here the beam is rapidly scanned in an en-face geometry to build a single retinal image akin to an SLO frame. The reference mirror position is then adjusted shifting the coherence gate position within the sample and the process repeated hence building a three-dimensional retinal volume. One benefit of this approach is that the scanning geometry is identical to that of an SLO; thus, both an OCT and SLO image can be acquired simultaneously with pixel-to-pixel registration with added benefit of shifting focal plane together with coherence gate resulting in dynamic focus imaging. A limitation of the (TS)-OCT approach is the sensitivity to axial eye motion, which can be overcome by using an active eye tracker (Pircher et al. 2007, 2010, Cucu et al. 2010). Merino et al. demonstrated the first AO-(TS)-OCT-SLO system in 2006 (Merino et al. 2006), but image improvement was somewhat limited due to the AO technology employed.
Panuveitis
Gwyn Samuel Williams, Mark Westcott, Carlos Pavesio, Bushra Thajudeen in Practical Uveitis, 2017
Irrespective of whether the endophthalmitis is endogenous or exogenous this condition needs to be treated as an emergency. All patients need an urgent vitreous tap and injection of antibiotics, called a ‘tap and inject’. Prior to this a B-scan ultrasound is traditionally carried out at this point to see if the retina is detached. While a B-scan can be helpful to assess the posterior segment, if endophthalmitis is suspected do not delay a ‘tap and inject’ while you wait for this investigation if not immediately available. Retinal detachment is rare in endopthalmitis pre-tap. You should, however, arrange for a B-scan of all patients within 24–48 hours post-tap, if not performed beforehand.
Ocular Blood Flow and Metabolism
Neil T. Choplin, Carlo E. Traverso in Atlas of Glaucoma, 2014
Ultrasound technology uses sound waves to locate structures in the body. By timing the delay between sound transmission and echo, ultrasound can measure the depth and location of an anatomic structure. For example, an A-scan ultrasound determines axial length by measuring the time between transmission of a sound wave into the eye and the returning echo from the back of the eye. By sweeping the A-scan in a line through the eye, a map of structural locations through a slice is obtained. This is commonly known as B-scan ultrasound and has been used to produce grayscale images of ophthalmic structures. CDI is based on B-scan technology with an additional processing step.
Ultrasonic ocular dimensions and anthropometry in normal and myopic eyes: a case-control study
Published in Expert Review of Ophthalmology, 2022
Faosat Olayiwola Jinadu, Iskilu Adekunle Jolaoso, Modupe Balogun, Tawaqualit Abimbola Ottun, Ufuoma Oluwaseyi Olumodeji, Ayokunle Moses Olumodeji
There was consistency between ocular biometric measurements obtained by B-mode and A-mode ultrasonography in this study (Table 7). This is in support of the growing belief in the accuracy of B-scan in the assessment of ocular biometry [18,28,29]. Previous studies by Yang et al. [21], Olivier et al. [28], and Abu et al. [29] on myopic eyes with cataracts found no significant difference in ocular axial biometric measurement (AL) using A-mode, B-mode ocular scan and IOL master in individuals with AL > 26 mm. They also suggested that the accuracy and reproducibility of AL measurement using B-mode is better than contact A-mode scanning. Gonzalez et al. [18] in their study on highly myopic eyes further opined that B-scan provides a more accurate AL measurement in calculating intraocular lens power than the A-scan because of its ability to locate the macula which commonly bulges to form staphyloma (and thus an increase in ocular axial length) in highly myopic eyes. The ability is absent in A-scan and as such provides a false shorter AL measurement. These suggest that B-scan is a suitable alternative to the A-scan in the measurement of ocular axial parameters.
Iris Juvenile Xanthogranuloma Presenting with Hypopyon
Published in Ocular Immunology and Inflammation, 2022
Mine Esen Baris, Mukaddes Damla Ciftci, Melis Palamar, Suzan Guven Yilmaz
A 45-day-old infant was referred to our clinic for unilateral hypopyon. The mother indicated noticing a whitish color change in the left eye multiple times that resolved rapidly. However, at the time of consultation, the whiteness was more intense and was retained for almost 2 weeks. The baby was examined under general anesthesia and found to have hypopyon that gave a level of about 2 mm in the left eye. No pathology was observed in the visible areas of the iris. Intraocular pressure (IOP) was 13 mmHg (Tono-Pen®, TP; Reichert, New York, USA) and the fundus examination was completely normal. Anterior and posterior segment examinations of the right eye were normal and IOP was 12 mmHg. B-scan ultrasound examinations of both eyes were within normal limits. Cranial and orbital MRI scans were reported to be normal as well. Complete blood count, along with the erythrocyte sedimentation rate and C-reactive protein levels, was within normal limits. Langerhans cell histiocytosis and granulomatous infections (tuberculosis and syphilis) were investigated. Syphilis was excluded by serological tests and interferon gamma release assay (IGRA) was applied for exclusion of tuberculosis. Examinations of the infant by the pediatrician and the blood tests along with cranial and orbital MRI revealed no pathology; therefore, Langerhans cell histiocytosis was also excluded.
Upper Limit of Retinal Nerve Fibre Layer Thickness in Patients with Pseudopapilloedema
Published in Neuro-Ophthalmology, 2022
Varsha Pramil, Mary Tam, Laurel N. Vuong, Thomas R. Hedges
Recently, various studies have attempted to determine the most useful imaging modality in differentiation of pseudopapilloedema and papilloedema. For example, B-scan ultrasonography has been suggested as one of the best methods for diagnosing patients with pseudopapilloedema and specifically, patients with pseudopapilloedema and buried drusen.13,14 The cost-effectiveness of using B-scan ultrasonography to make a diagnosis before neuroimaging or additional invasive tests in patients suspected to have papilloedema has also been documented.15 Although B-scan ultrasonography has been shown to be useful, it is not available in all clinics and requires a trained technician.13,16 Unlike B-scan ultrasonography, OCT devices are widely available and easy to use. Because it is non-invasive and can be used as an initial test like B-scan ultrasonography, we can also assume that it would be as cost-effective. Additionally, EDI-OCT has been shown to provide unparalleled optic nerve head drusen visualisation and is able to differentiate pseudopapilloedema from papilloedema with high specificity and sensitivity.16–18
Related Knowledge Centers
- Tendon
- Tissue
- Ultrasound
- Skeletal Muscle
- Medical Imaging
- Therapeutic Ultrasound
- Pregnancy
- Obstetric Ultrasonography
- Sound
- Ultrasonic Transducer