Nasolacrimal duct

Use of nasolacrimal occlusion decreases systemic absorption up to 60% and may increase ocular bioavailability of the drug. After instillation of the eye drop, the patient should close the eye and press a finger gently against the nasolacrimal duct (tear duct) for 2 to 3 minutes. 

Nasolacrimal occlusion The closing of the tear duct by application... 

Minimize systemic absorption of ophthalmic drops by compressing lacrimal sac for 3 to 5 minutes after instillation. This retards passage of drops via nasolacrimal duct into areas of potential absorption such as nasal and pharyngeal mucosa. 

At the inner corners of the eyelids, two small punctae or openings exteriorises to the globe and drain the tearfilm to the nasolacrimal duct. These openings are approximately 0.3 mm in diameter and sit on top of an elevated mound—the papilla lacrimalis—that are visible as pale... 

The synchronized movement of the eyelids spreads the precorneal tearfilm across the cornea and pushes it toward the nasolacrimal duct. Precorneal drainage is quite efficient. An aqueous instilled dose leaves the precorneal area within 5 min of instillation in humans. Most of the drug absorbed by transcorneal penetration, without retention modification, is spread across the cornea by the eyelids in the first minutes postdosing. In the precorneal space transcorneal penetration is limited by solution drainage, lacrimation and tear dilution, tear turnover, conjunctival absorption, and the corneal epithelium. Slowing down tear film turnover has well-established benefits to topical ocular drug delivery. 

The tear film leaves the surface of the globe and eyelids, enters the upper and the lower punctum at the medial aspect of the lid margin, and enters the lacrimal sac before drainage to the nasolacrimal duct and the nasal cavity. However, much of the tear film is eliminated by direct evaporation or by absorption at the level of the lacrimal sac. The lacrimal outflow system is based on an active and dynamic pumping mechanism. Blinking cycle leads to changes in the drainage canaliculi that activate a pump mechanism that drains tears even with the head held in an inverted position. When the palpebral blink mechanism is impaired, tears accumulation leads to spillover to the skin of the lids and cheek [4],... 

The most common drug delivery method for treating ocular disorders is topical administration, due to its convenience and safety. However, the anterior segment of the eye also has various protective mechanisms for maintaining visual functions. After instillation of an ophthalmic drug, most of it is rapidly eliminated from the precorneal area due to drainage by the nasolacrimal duct and dilution by the tear turnover (approximately 1 pL/min) [17,18]. In addition, there is a finite limit to the size of the dose that can be applied and tolerated by... 

Examples of product-related advice include discussing with patients the risk of experiencing mild transient burning sensations after drop administration, with possibly a bad taste sensation at the back of the throat following nasolacrimal duct drainage. 

Solutions The reasons behind choosing solutions over other dosage forms are their favorable cost advantage, the simplicity of formulation development and production, and the high acceptance by patients [170], However, there are also a few drawbacks, such as rapid and extensive precorneal loss, high absorption via the conjunctiva and the nasolacrimal duct leading to systemic side effects, as well as the increased installation frequency resulting in low patient compliance. 

The normal volume of the tear layer is 8 to 10 mcl, including the fluid trapped in the folds of the conjunctiva. A total volume of perhaps 30 mcl can be held for a brief time if the eyelids are not squeezed after dosing. When a single drop of medication of 50 mcl (0.05 ml) is applied, the nasolacrimal duct rapidly drains the excess, although some may be blinked out of the eye onto the lid. 

To enhance corneal drug absorption, the tear film concentration can be prolonged by manually blocking the nasolacrimal ducts or by tilting the head back to reduce drainage (see Chapter 3). Another effective technique to increase corneal penetration is to administer a series of ophthalmic solutions at intervals of approximately 10 minutes. It has been determined, however, that when different drug formulations are given as drops in rapid succession, the medications first applied are diluted and do not achieve fiill therapeutic potential. 

Systemic reactions to 2.5% phenylephrine after topical ocular application to an intact eye have rarely been reported in adults. However, an acute rise in systolic blood pressure occurred in a 1-year-old child after the instillation of 0.5 ml of 2.5% phenylephrine during nasolacrimal duct probing. 

Dacryocystitis occnrs when the lacrimal drainage system is blocked and bacteria from the tears infect the lacrimal sac. Bacterial etiology includes staphylococci. Streptococcus pneumoniae, and H. influenzae in children, all of which are susceptible to oral amoxicillin/ clavulanate. More serious infections require intravenous administration of ampicillin/sulbactam. This bacterial infection needs to be treated before nasolacrimal duct irrigation, probing, or surgery is performed. 

Figure 23-30 (AJ Recurrent sebaceous gland carcinoma of the right upper eyelid with ill-defined borders. (B) Postoperative right orbital exenteration and nasolacrimal duct resection of the patient in A. (Courtesy Dr. Nick Holdeman, University of Houston, College of Optometry.)...

The lacrimal sac is normally collapsed when the eyelids are open. As the eyelids close, tears are squeezed into the sac, aided by the negative pressure within the sac (see Figure 24-5). A valve-like structure at the opening to the lacrimal sac helps to retain tears within the sac and prevent their backflow into the canaliculus. The nasolacrimal duct (NED) is continuous with the lacrimal sac inferiorly. The NLD extends 15 to 20 mm caudally... 

Figure 24-12 Hydrostatic massage technique for congenital nasolacrimal duct obstruction.The puncta are held gendy closed with one finger while the area over the lacrimal drainage apparams is gendy massaged downward.

Clinical manifestations of bacterial ophthalmia neonatorum are nonspecific and similar to those caused by other pathogens discussed previously. Infants experience the acute onset of hyperemia, chemosis, eyelid edema, and purulent or mucopurulent exudate 5 to 21 days postpartum. Practitioners should take care to rule out nasolacrimal duct obstruction, a finduig that is relatively common in newborns and that can be associated with a secondary bacterial infection. 

Fig. 1 (A) Cross-sectional structure of the human nose. NV = nasal vestibule AT = atrium NP = nasopharynx IT = interior turbinate and orifice of the nasolacrimal duct MT = middle turbinate and orifices of frontal sinus, anterior ethmoidal sinuses, and maxillary sinus ST = superior turbinate and orifices of posterior ethmoidal sinuses hatched area, olfactory region. (B) Four major cell types in the nasal epithelium (a) non-ciliated columnar cell with microvilli (b) goblet cell with mucous granules and Golgi apparatus (c) basal cell and (d) ciliated columnar cell with many mitochondria in the apical part. (Reprinted from Ref. with permission from Elsevier.)...

In a double-blind, controlled study of a possible causal relation between 1 % silver nitrate solution and 1 % tetra-cychne solution in prophylaxis of ophthalmia neonatorum there was no statistically significant difference in the incidence of nasolacrimal duct obstruction between the two groups at either 2 weeks or 2 months of age (28). 

Hick JF, Block DJ, Dstrup DM. A controlled study of silver nitrate prophylaxis and the incidence of nasolacrimal duct obstruction. J Pediatr Ophthalmol Strabismus 198522(3) 92-3. 

Figure 9.32 Diagrams of parts of the eye of importance in medication the superior and inferior punctae are the drainage ports for solutions and tear fluids, and medicaments can drain via the canaliculi into the nasolacrimal duct and then to the nasal cavity, from whose surfaces absorption can occur.

Chronic toxicity studies on fenthion are available in the rat, dog, and monkey. The dog and monkey studies did not reveal any systemic signs of toxicity due to prolonged exposure to fenthion with the exception of cholinesterase inhibition. In the rat study, however, pathology was noted in the epididymis, the nasolacrimal duct, and in ocular tissue. Fenthion is not considered to be a carcinogen. While one test of carcinogenicity in mice indicated that fenthion may be a carcinogen in male mice, further studies in mice and rats did not support this. 

Routes of absorption that lead to the removal of drag from the precorneal area, and do not result in direct ocular uptake, are referred to as nonproductive. These noncomeal pathways, which are in parallel with comeal absorption and include conjunctival uptake and drainage via the nasolacrimal duct, lead to systemic absorption by way of conjunctival blood vessels in the former case and removal through the nasal mucosa and gastrointestinal tract in the latter. As discussed, drag can penetrate the conjunctiva, and, via the sclera, enter the eye however, blood vessels within the conjunctiva can also lead to systemic absorption. 

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