Nasolacrimal drainage system

Patients should be taught how to administer topical therapy. With a forefinger pulling down the lower eyelid to form a pocket, the patient should place the dropper over the eye, look at the tip of the bottle, and then look up and place a single drop in the eye. To maximize topical activity and minimize systemic absorption, the patient should close the lid for 1 to 3 minutes after instillation and place the index finger over the nasolacrimal drainage system in the inner corner of the eye. 

A modified version of niosomes are the so-called discomes, which vary from the conventional niosomes in size and shape. The larger size of the vesicles (12-60 pm) prevents their drainage into the nasolacrimal drainage system. Furthermore, their disclike shape provides them with a better fit in the cul-de-sac of the eye [26]. 

Approximately 90% of the tears are drained in this manner, with the remainder being lost to evaporation. To facihtate normal drainage of tears, the entire nasolacrimal drainage system must be properly positioned and patent. Blockages anywhere along the way generally result in epiphora and may create an environment that is conducive to infection and inflammation. 

The nasolacrimal drainage system consists of three parts the secretory systan, the distributive system, and the excretory system. The secretory portion is composed of the lacrimal gland that secreted tears and is spread over the ocular surface by the eyelids during blinking. The secretory system is stimulated by blinking and temperature change due to tear evaporation and reflux secre-tors that have an efferent parasympathetic nerve supply and secrete in response to a physical and emotional state, for example, crying. 

The excretory part of the nasolacrimal drainage system consists of the lacrimal puncta the superior, inferior, and conunon canaliculi the lacrimal sac and the nasolacrimal duct. In humans, the two puncta are the openings of the lacrimal canaliculi and are situated on an elevated area known as the lacrimal papilla. It is thought that tears are largely absorbed by the mucous membrane that lines the ducts and the lacrimal sac only a small amount reaches the nasal passage. 

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. 

In patients at risk for systemic side effects from topically administered pharmacologic agents, eyelid closure and manual nasolacrimal occlusion (see Figure 3-6) are reasonable procedures to minimize nasolacrimal drainage of drug and subsequent absorption into the systemic circulation. 

It is always wise to advocate nasolacrimal occlusion by digital compression of the lacrimal drainage system when using phenylephrine eye-drops in patients at risk or in patients in whom higher concentrations are necessary (3). 

The possibility of systemic effects due to nasolacrimal drainage as previously discussed should also be kept in mind. FDA has cataloged all inactive ingredients in approved drug products and provides this information in a searchable database at http // www.accessdata.fda.gov/scripts/cder/iig/index.cfin. The FDA database provides route and dosage form, CAS number, UNII, and maximum potency for each listed inactive ingredient. 

The bioavailability of drugs administered as eye drops is severely limited by physiological constraints such as tear turnover and the blinking reflex. Further, drug loss due to nasolacrimal drainage, conjunctival absorption, and protein binding results again in poor bioavailability and systemic side-effects. ... 

Furthermore, the lacrimal fluid flushes out instilled substances from the surface of the eye, and fluid is then drained by the nasolacrimal duct. Systemic drug absorption may also take place through vessels of the conjimctiva or from the nasal cavity after drainage. Thus, the drug is prevented from reaching the anterior part of the eye, and this results in low bioavailability [10]. 

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],... 

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. 

Sensory systems Eyes The frequency of nasolacrimal duct obstruction has been studied in 384 patients [25. There was lacrimal drainage obstruction, especially upper... 

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