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Principles and Methods of Ocular Pharmacokinetic Evaluation
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
Once in the anterior chamber, the drug must traverse this 3 mm deep, liquid-filled space through which the fluid is passing at 1% of the total volume per minute. Since the volume is about 250 μl, the flow rate is roughly 2 to 2.5 μl/min. This fluid is formed at the ciliary processes and passes into the anterior chamber through the pupil. If the pupil is relatively small, i.e., 3 to 4 mm, then the velocity of the fluid passing between the anterior lens surface and the posterior face of the iris is fairly high. If it has overcome these impediments to diffusion, then the compound must pass either through or around the lens, and into the gel-like vitreous in order to reach the posterior pole of the eye. The characteristics of the vitreous humor, however, change with age, causing the vitreous to become more liquid.2 Thus, the penetration characteristics of this bulk compartment also may change with aging of the eye.
Head and Neck
Published in Bobby Krishnachetty, Abdul Syed, Harriet Scott, Applied Anatomy for the FRCA, 2020
Bobby Krishnachetty, Abdul Syed, Harriet Scott
It is produced by the ciliary processes of the ciliary body and is secreted into the posterior chamber. It then flows between the iris and lens and into the anterior chamber through the pupil. Most exits the anterior chamber via the trabecular meshwork at the iridocorneal angle into the canal of Schlemm. The canal of Schlemm is a scleral venous sinus which drains into the anterior ciliary veins (then into the superior ophthalmic vein and the cavernous sinus), with some exitting via the uveoscleral route being absorbed through the ciliary muscle into the sclera (Figure 1.7).
The Special Sense Organs and Their Disorders
Published in Walter F. Stanaszek, Mary J. Stanaszek, Robert J. Holt, Steven Strauss, Understanding Medical Terms, 2020
Walter F. Stanaszek, Mary J. Stanaszek, Robert J. Holt, Steven Strauss
The hollow eyeball is divided into three cavities: the anterior chamber located between the iris and cornea; the vitreous chamber, the space behind the lens that contains the vitreous humor; and the posterior chamber between the iris, lens, and vitreous chamber. The other chambers of the eye are filled with aqueous humor, which is secreted by the ciliary processes and reabsorbed into the venous system through the canal of Schlemm (Figure 13.3).
Repeatability and reproducibility of anterior lens zonule length measurement using ArcScan insight 100 very high-frequency ultrasound
Published in Expert Review of Medical Devices, 2023
Zehui Zhu, Han Zou, Hongzhe Li, Xueer Wu, Yiyi Wang, Zhangliang Li, Yune Zhao
The scanning was performed in the horizontal direction (transverse diameter passing through the corneal apex from 9 to 3 o’clock) with a tissue penetration depth of 15 mm (Figure 2). Figure 2 demonstrates that the settings are located on the left-hand side of the software interface. In this particular case, we have selected the ‘capsule’ scan type, center fixation light, manual range, and manual centering. To measure the length of the zonule, the critical point was to ensure that the two endpoints of the zonule at the anterior capsule and the ciliary process were clearly imaged. In a preliminary study, we found that the zonule near the ciliary process was difficult to image clearly in many cases when centered at the corneal apex under automated procedures. Thus, the examiners manually adjusted the scanning frame to be centered on the nasal iris when obtaining images of the nasal zonule (centered on the temporal iris when obtaining images of the temporal zonule) and moved the probe to reach the echo signal of the anterior capsule (Figure 3). In this way, the lens zonules can be captured in all five images, and these images can then be combined into a single picture for improved clarity and visualization. Two examiners (ZZH and ZH) learned and mastered the scanning methods in the preliminary study.
Treatment of Nanophthalmos Cataracts: Surgery and Complications
Published in Seminars in Ophthalmology, 2022
Mei-Ying He, Jing-Ru Feng, Lu Zhang
Transscleral cyclodiode laser treatment is quick and remarkably effective for those who are not responsive to lasers and drugs, and who have poor visual function. This method safely reduces aqueous humor generation and correctly directs aqueous humor flow by shrinking the ciliary processes.59 Simultaneously, research has revealed that cyclodiode can be used as the primary treatment for refractory glaucoma with good vision.60 Anterior vitrectomy combined with hyaloido-capsulo-iridectomy is also a good treatment.61 Faisal et al.62believe that the ocular axis of the nanophthalmos is short, and the place 3.5 mm away from the corneal limbus may not be the flat part, but the retina. Thus, vitrectomy via anterior chamber approach and establishment of posterior and anterior chamber connecting holes through iris incision is a safer method.62,63
Endoscopy-assisted pars plana lensectomy for brunescent cataracts in eyes with microcornea with microphthalmos
Published in Seminars in Ophthalmology, 2022
Deepika C Parameswarappa, Vivek Pravin Dave, Mudit Tyagi, Rajeev R Pappuru
The surgery was performed under local anesthesia. The steps, in brief, included sterile draping of the eye, and subsequently, three vitrectomy ports were made at a distance of 2.5 mm from the limbus as reported in previous studies with respect to short pars plana length in cases of microcornea and microphthalmos5–7(Figure 1b). Also, pars plana structures were visualized through transillumination from outside the sclera to avoid injury to the ciliary body and zonules.8 A 20 G endoscopy probe E4 Laser and Endoscopy System (EndoOptiks, Inc., Little Silver, NJ, USA) with light and video dual function was then introduced through the supero-nasal quadrant. With the aid of a camera connected, the infusion cannula was visualized with the endoscope. Subsequently, the ciliary processes and the retina were examined