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Central nervous system
Published in A Stewart Whitley, Jan Dodgeon, Angela Meadows, Jane Cullingworth, Ken Holmes, Marcus Jackson, Graham Hoadley, Randeep Kumar Kulshrestha, Clark’s Procedures in Diagnostic Imaging: A System-Based Approach, 2020
A Stewart Whitley, Jan Dodgeon, Angela Meadows, Jane Cullingworth, Ken Holmes, Marcus Jackson, Graham Hoadley, Randeep Kumar Kulshrestha
The lacrimal system comprises the lacrimal gland, which secretes tears, the lacrimal sac and the ducts through which the tears pass into the nasal cavity (Figs 11.59a–c). The lacrimal gland lies anteriorly in the upper outer quadrant of the orbit and communicates with the lacrimal sac via the lacrimal canaliculi. Tears wash over the surface of the eye and drain through the lacrimal canaliculi into the lacrimal sac through two openings, the puncta lacrimalia, which are situated on the medial aspects of the upper and lower eyelids. The lacrimal sac drains into the nasolacrimal duct, which runs vertically through the lateral nasal wall on the medial aspect of the maxillary antrum. The nasolacrimal duct opens into the nasal cavity below the inferior nasal conchus.
Designing for Head and Neck Anatomy
Published in Karen L. LaBat, Karen S. Ryan, Human Body, 2019
The lacrimal apparatus, the drainage system for tears produced to lubricate and clean the surface of the eye, is also vulnerable to compression by nose pads and eyewear. Tears collect at the medial corner of the eye, drain into the lacrimal sac, then the nasolacrimal duct (both seen on Figure 3.3, left side) and finally empty into the lower lateral portion of the nose. Compression of these anatomical features may be signaled by tears overflowing the eyes, without crying.
The tear turnover and tear clearance tests – a review
Published in Expert Review of Medical Devices, 2018
Izabela K. Garaszczuk, Robert Montes Mico, D. Robert Iskander, Alejandro Cerviño Expósito
Few different models have been used to analyze the tear flow data based on this imaging technique [49]. Linear compartmental model assumes that the tears are flowing with the same pace through all the different compartments of the nasolacrimal drainage system. Later on, it has been shown that variable tear flow is a normal feature of the drainage facility and does not follow a linear model [48,49]. A compartmental model was proposed incorporating data from separate components – conjunctival sac, lacrimal sac, the nasolacrimal duct, and nasal cavity [49]. This model has been used to qualitatively assess tear flow. A mean tear turnover of 0.45 µl/min was estimated based on the assumption that the slow component of clearance from the conjunctival sac represents the net fractional turnover of that compartment and taking a compartmental volume of 7 µl. Based on an alternative four-compartmental model calculations, the tear flow was estimated at 1 up to 8 µl [49]. Craig and Tomlinson were able to measure values of reflex and basal turnover as 3.33 ± 1.95 and 0.56 ± 0.32 µl/min, respectively, using a single compartment model for decay of the radioactive tracer on the conjunctival surface [84].