A mydriatic is an agent that induces dilation of the pupil. Drugs such as tropicamide are used in medicine to permit examination of the retina and other deep structures of the eye, and also to reduce painful ciliary muscle spasm (see cycloplegia). Phenylephrine (e.g. Cyclomydril) is used if strong mydriasis is needed for a surgical intervention. One effect of administration of a mydriatic is intolerance to bright light (photophobia). Purposefully-induced mydriasis via mydriatics is also used as a diagnostic test for Horner's syndrome.

Anisocoria is a condition characterized by an unequal size of the eyes' pupils. Affecting 20% of the population, it can be an entirely harmless condition or a symptom of more serious medical problems.

Physiological anisocoria is when human pupils differ in size. It is generally considered to be benign, though it must be distinguished from Congenital Horner's syndrome, pharmacological dilatation or other conditions connected to the sympathetic nervous system.

The prevalence of physiological anisocoria has not been found to be influenced by the sex, age, or iris color of the subject.

Anisocoria is a common condition, defined by a difference of 0.4 mm or more between the sizes of the pupils of the eyes.

Anisocoria has various causes:

- Physiological anisocoria: About 20% of normal people have a slight difference in pupil size which is known as physiological anisocoria. In this condition, the difference between pupils is usually less than 1 mm.

- Horner's syndrome

- Mechanical anisocoria: Occasionally previous trauma, eye surgery, or inflammation (uveitis, angle closure glaucoma) can lead to adhesions between the iris and the lens.

- Adie tonic pupil: Tonic pupil is usually an isolated benign entity, presenting in young women. It may be associated with loss of deep tendon reflex (Adie's syndrome). Tonic pupil is characterized by delayed dilation of iris especially after near stimulus, segmental iris constriction, and sensitivity of pupil to a weak solution of pilocarpine.

- Oculomotor nerve palsy: Ischemia, intracranial aneurysm, demyelinating diseases (e.g., multiple sclerosis), head trauma, and brain tumors are the most common causes of oculomotor nerve palsy in adults. In ischemic lesions of the oculomotor nerve, pupillary function is usually spared whereas in compressive lesions the pupil is involved.

- Pharmacological agents with anticholinergic or sympathomimetic properties will cause anisocoria, particularly if instilled in one eye. Some examples of pharmacological agents which may affect the pupils include pilocarpine, cocaine, tropicamide, MDMA, dextromethorphan, and ergolines. Alkaloids present in plants of the genera "Brugmansia" and "Datura", such as scopolamine, may also induce anisocoria.

- Migraines

Relative afferent pupillary defect (RAPD) or Marcus Gunn pupil is a medical sign observed during the swinging-flashlight test whereupon the patient's pupils constrict less (therefore appearing to dilate) when a bright light is swung from the unaffected eye to the affected eye. The affected eye still senses the light and produces pupillary sphincter constriction to some degree, albeit reduced.

The most common cause of Marcus Gunn pupil is a lesion of the optic nerve (between the retina and the optic chiasm) or severe retinal disease. It is named after Scottish ophthalmologist Robert Marcus Gunn.

A second common cause of Marcus Gunn pupil is a contralateral optic tract lesion, due to the different contributions of the intact nasal and temporal hemifields.

When detected during childhood, without any other symptoms and when other disorders are discarded through clinical tests, it should be considered a developmental or genetic phenomenon.

Asymmetric pupil or dyscoria, potential causes of anisocoria, refer to an abnormal shape of the pupil which can happens due to developmental and intrauterine anomalies.

Miosis is excessive constriction of the pupil. The term is from Ancient Greek , "mūein", "to close the eyes.

The opposite condition, mydriasis, is the dilation of the pupil. Anisocoria is the condition of one pupil being more dilated than the other.

Patients must have early consultation with craniofacial and orthopaedic surgeons, when craniofacial, clubfoot, or hand correction is indicated to improve function or aesthetics. Operative measures should be pursued cautiously, with avoidance of radical measures and careful consideration of the abnormal muscle physiology in Freeman–Sheldon syndrome. Unfortunately, many surgical procedures have suboptimal outcomes, secondary to the myopathy of the syndrome.

When operative measures are to be undertaken, they should be planned for as early in life as is feasible, in consideration of the tendency for fragile health. Early interventions hold the possibility to minimise developmental delays and negate the necessity of relearning basic functions.

Due to the abnormal muscle physiology in Freeman–Sheldon syndrome, therapeutic measures may have unfavourable outcomes. Difficult endotracheal intubations and vein access complicate operative decisions in many DA2A patients, and malignant hyperthermia (MH) may affect individuals with FSS, as well. Cruickshanks et al. (1999) reports uneventful use of non-MH-triggering agents. Reports have been published about spina bifida occulta in anaesthesia management and cervical kyphoscoliosis in intubations.

Tropicamide is used as a mydriastic agent during cataract surgery. Anticholinergics such as atropine, hyoscyamine, and scopolamine antagonize the muscarinic acetylcholine receptors in the eye. By blocking these receptors, the pupils are no longer capable of constriction and dilation results. Such alkaloids present in many plants of the family "Solanaceae" may also induce mydriasis when used

The neurotransmitter norepinephrine regulates many physiological processes in the body and brain. One of them is the autonomic constriction and contraction of certain muscles. The psychoactive drug cocaine potently inhibits the normal reuptake of norepinephrine into presynaptic nerve terminals, resulting in an increased level of extracellular norepinephrine. Amphetamines also potently release and prevent the reuptake of norepinephrine. The released norepinephrine then proceeds to bind to adrenergic receptors, and the biological effects of norepinephrine finally occur. When a solution of cocaine is dropped into the eye, this process takes place and the end result is dilation of the pupil. Cocaine itself is not typically used for this task, however. Any potent norepinephrine reuptake inhibitor or release agent should be capable of such an effect.

Opiates such as morphine and heroin do not cause pupil dilation. Instead they cause miosis (pupil contraction). Mydriasis occasionally occurs during opiate rebound and withdrawal.

Patients and their parents must receive psychotherapy, which should include marriage counselling. Mitigation of lasting psychological problems, including depression secondary to chronic illness and posttraumatic stress disorder (PTSD), can be very successfully addressed with early interventions. This care may come from the family physician, or other attending physician, whoever is more appropriate; specialist care is generally not required. Lewis and Vitulano (2003) note several studies suggesting predisposal for psychopathology in paediatric patients with chronic illness. Esch (2002) advocates preventive psychiatry supports to facilitate balance of positive and negative stressors associated with chronic physical pathology. Patients with FSS should have pre-emptive and ongoing mixed cognitive therapy-psychodynamic psychotherapy for patients with FSS and cognitive-behavioural therapy (CBT), if begun after onset of obvious pathology.

Adler (1995) cautioned the failure of modern medicine to implement the biopsychosocial model, which incorporates all aspects of a patient’s experience in a scientific approach into the clinical picture, often results in chronically-ill patients deferring to non-traditional and alternative forms of therapy, seeking to be understood as a whole, not a part, which may be problematic among patients with FSS.

Furthermore, neuropsychiatry, physiological, and imaging studies have shown PTSD and depression to be physical syndromes, in many respects, as they are psychiatric ones in demonstrating limbic system physiological and anatomy disturbances. Attendant PTSD hyperarousal symptoms, which additionally increase physiological stress, may play a part in leading to frequent MH-like hyperpyrexia and speculate on its influence on underlying myopathology of FSS in other ways. PTSD may also bring about developmental delays or developmental stagnation, especially in paediatric patients.

With psychodynamic psychotherapy, psychopharmacotherapy may need to be considered. Electroconvulsive therapy (ECT) is advised against, in light of abnormal myophysiology, with predisposal to MH.

The Marcus Gunn pupil is a relative afferent pupillary defect indicating a decreased pupillary response to light in the affected eye.

In the swinging flashlight test, a light is alternately shone into the left and right eyes. A normal response would be equal constriction of both pupils, regardless of which eye the light is directed at. This indicates an intact direct and consensual pupillary light reflex. When the test is performed in an eye with an afferent pupillary defect, light directed in the affected eye will cause only mild constriction of both pupils (due to decreased response to light from the afferent defect), while light in the unaffected eye will cause a normal constriction of both pupils (due to an intact efferent path, and an intact consensual pupillary reflex). Thus, light shone in the affected eye will produce less pupillary constriction than light shone in the unaffected eye.

A Marcus Gunn pupil is distinguished from a total CN II lesion, in which the affected eye perceives "no" light. In that case, shining the light in the affected eye produces no effect.

Anisocoria is absent. A Marcus Gunn pupil is seen, among other conditions, in optic neuritis. It is also common in retrobulbar optic neuritis due to multiple sclerosis but only for 3–4 weeks, until the visual acuity begins to improve in 1–2 weeks and may return to normal.

In mechanical anisocoria, this is the result of damage to the iris dilator muscle, which may be caused by trauma, angle-closure glaucoma, surgery such as cataract removal, or uveitis (inflammation of the eye). Slit lamp examination is often used as a diagnostic aid: damage to the dilator muscle is indicated by anisocoria when light intensity is lowered.Anisocoria refers to a common eye condition in which the two pupils differ in size.

Because HFM is a rare disorder, there are no studies that define its optimal treatment. Correction of the systemic folate deficiency, with the normalization of folate blood levels, is easily achieved with high doses of oral folates or much smaller doses of parenteral folate. This will rapidly correct the anemia, immune deficiency and GI signs. The challenge is to achieve adequate treatment of the neurological component of HFM. It is essential that the folate dose is sufficiently high to achieve CSF folate levels as close as possible to the normal range for the age of the child. This requires close monitoring of the CSF folate level. The physiological folate is 5-methyltetrahydrofolate but the oral formulation available is insufficient for treatment of this disorder and a parenteral form is not available. The optimal folate at this time is 5-formyltetrahydrofolate which, after administration, is converted to 5-methyltetrahydrofolate. The racemic mixture of 5-formyltetrahydrofolate (leucovorin) is generally available; the active S-isomer, levoleucovorin, may be obtained as well. Parenteral administration is the optimal treatment if that is possible. Folic acid should not be used for the treatment of HFM. Folic acid is not a physiological folate. It binds tightly to, and may impede, FRα-mediated endocytosis which plays an important role in the transport of folates across the choroid plexus into the CSF (see above). For a further consideration of treatment see GeneReviews.

A blind spot, scotoma, is an obscuration of the visual field. A particular blind spot known as the "physiological blind spot", "blind point", or "punctum caecum" in medical literature, is the place in the visual field that corresponds to the lack of light-detecting photoreceptor cells on the optic disc of the retina where the optic nerve passes through the optic disc. Because there are no cells to detect light on the optic disc, the corresponding part of the field of vision is invisible. Some process in our brains interpolates the blind spot based on surrounding detail and information from the other eye, so we do not normally perceive the blind spot.

Although all vertebrates have this blind spot, cephalopod eyes, which are only superficially similar, do not. In them, the optic nerve approaches the receptors from behind, so it does not create a break in the retina.

The first documented observation of the phenomenon was in the 1660s by Edme Mariotte in France. At the time it was generally thought that the point at which the optic nerve entered the eye should actually be the most sensitive portion of the retina; however, Mariotte's discovery disproved this theory.

The blind spot is located about 12–15° temporally and 1.5° below the horizontal and is roughly 7.5° high and 5.5° wide.

Research needs to be performed on the efficacy of the various pharmaceuticals for treating illusory palinopsia. It is unclear if the symptoms' natural history and treatment are influenced by the cause. It is also not clear if there is treatment efficacy overlap for illusory palinopsia and the other co-existing diffuse persistent illusory phenomenon such as visual snow, oscillopsia, dysmetropsia, and halos.

Future advancements in fMRI could potentially further our understanding of hallucinatory palinopsia and visual memory. Increased accuracy in fMRI might also allow for the observation of subtle metabolic or perfusional changes in illusory palinopsia, without the use of ionizing radiation present in CT scans and radioactive isotopes. Studying the psychophysics of light and motion perception could advance our understanding of illusory palinopsia, and vice versa. For example, incorporating patients with visual trailing into motion perception studies could advance our understanding of the mechanisms of visual stability and motion suppression during eye movements (e.g. saccadic suppression).

There is no current cure for superficial siderosis, only treatments to help alleviate the current symptoms and to help prevent the development of further symptoms. If a source of bleeding can be identified (sources are frequently not found), then surgical correction of the bleeding source can be performed; this has proved to be effective in halting the development of further symptoms in some cases and has no effect on symptoms that have already presented.

Patients with superficial siderosis are often treated with deferiprone, a lipid-soluble iron chelator, as this medication has been demonstrated to chelate iron in the central nervous system.

While on this drug you will need a frequent blood test (weekly) to keep an eye on the blood levels as this drug is known to lower certain blood levels such as the neutrophils and WBC (white blood count) and etc. While it is ok if these levels go low in the average person, if they go low while taking Deferiprone Ferriprox it can cause life threatening infections that can result in death.

Alleviation of the most common symptom, hearing loss, has been varyingly successful through the use of cochlear implants. Most people do not notice a large improvement after successful implantation, which is most likely due to damage to the vestibulocochlear nerve (cranial nerve VIII) and not the cochlea itself. Some people fare far better, with a return to near normal hearing, but there is little ability to detect how well a person will respond to this treatment at this time.

Light entering the eye strikes three different photoreceptors in the retina: the familiar rods and cones used in image forming and the more newly discovered photosensitive ganglion cells. The ganglion cells give information about ambient light levels, and react sluggishly compared to the rods and cones. Signals from photosensitive ganglion cells have multiple functions including acute suppression of the hormone melatonin, entrainment of the body's circadian rhythms and regulation of the size of the pupil.

The retinal photoceptors convert light stimuli into electric impulses. Nerves involved in the resizing of the pupil connect to the pretectal nucleus of the high midbrain, bypassing the lateral geniculate nucleus and the primary visual cortex. From the pretectal nucleus neurons send axons to neurons of the Edinger-Westphal nucleus whose visceromotor axons run along both the left and right oculomotor nerves. Visceromotor nerve axons (which constitute a portion of cranial nerve III, along with the somatomotor portion derived from the Edinger-Westphal nucleus) synapse on ciliary ganglion neurons, whose parasympathetic axons innervate the iris sphincter muscle, producing miosis. This occurs because sympathetic activity from the ciliary ganglion is "lost" thus parasympathetics are not inhibited.

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Horner's syndrome is a combination of symptoms that arises when a group of nerves known as the sympathetic trunk is damaged. The signs and symptoms occur on the same side as the lesion of the sympathetic trunk. It is characterized by miosis (a constricted pupil), partial ptosis (a weak, droopy eyelid), apparent anhidrosis (decreased sweating), with or without enophthalmos (inset eyeball).

The nerves of the sympathetic trunk arise from the spinal cord in the chest, and from there ascend to the neck and face. The nerves are part of the sympathetic nervous system, a division of the autonomic (or involuntary) nervous system. Once the syndrome has been recognized, medical imaging and response to particular eye drops may be required to identify the location of the problem and the underlying cause.

A number of pharmaceuticals may be used in an attempt to bring the polydipsia under control, including:

- Atypical antipsychotics, such as clozapine, olanzapine and risperidone

- Demeclocycline, a tetracycline antibiotic, which is effective due to the side effect of inducing nephrogenic diabetes insipidus. Demeclocycline is used for cases of psychogenic polydipsia, including those with nocturnal enuresis (bed-wetting). Its mechanism of action involves direct inhibition of vasopressin at the DCTs, thus reducing urine concentration.

There are a number of emerging pharmaceutical treatments for psychogenic polydipsia, although these need further investigation:

- ACE Inhibitors, such as enalapril

- Clonidine, an alpha-2 adrenergic agonist

- Irbesartan, an angiotensin II receptor antagonist

- Propranolol, a sympatholytic beta blocker

- Vasopressin receptor antagonists, such as conivaptan

- Acetazolamide, a carbonic anhydrase inhibitor

Lithium was previously used for treatment of PPD as a direct competitive ADH agonist, but is now generally avoided due to its toxic effects on the thyroid and kidneys.

It is important to note that the majority of psychotropic drugs (and a good many of other classes) can cause dry mouth as a side effect, but this is not to be confused with true polydipsia in which a dangerous drop in serum sodium will be seen.

Signs that are found in patients on the affected side of the face include

- partial ptosis

- upside-down ptosis (slight elevation of the lower lid)

- anhidrosis

- miosis

- pseudoenophthalmos (the impression that the eye is sunken, caused by a narrow palpebral aperture)

- pupillary dilation lag

- loss of ciliospinal reflex

- bloodshot conjunctiva, depending on the site of lesion.

- unilateral straight hair (in congenital Horner's syndrome); the hair on the affected side may be straight in some cases.

- heterochromia iridum (in congenital Horner's syndrome)

Interruption of sympathetic pathways leads to several implications. It inactivates the dilator muscle and thereby produces miosis. It inactivates the superior tarsal muscle which produces ptosis. It inactivates the orbitalis muscle which produces the effect of enophthalmos. It also reduces sweat secretion in the face.

Sometimes there is flushing on the affected side of the face due to dilation of blood vessels under the skin. The pupil's light reflex is maintained as this is controlled via the parasympathetic nervous system.

In children, Horner's syndrome sometimes leads to heterochromia, a difference in eye color between the two eyes. This happens because a lack of sympathetic stimulation in childhood interferes with melanin pigmentation of the melanocytes in the superficial stroma of the iris.

In veterinary medicine, signs can include partial closure of the third eyelid, or nictitating membrane.

Palinopsia (Greek: "palin" for "again" and "opsia" for "seeing") is the persistent recurrence of a visual image after the stimulus has been removed. Palinopsia is not a diagnosis, it is a diverse group of pathological visual symptoms with a wide variety of causes. Visual perseveration is synonymous with palinopsia.

In 2014, Gersztenkorn and Lee comprehensively reviewed all cases of palinopsia in the literature and subdivided it into two clinically relevant groups: illusory palinopsia and hallucinatory palinopsia. Hallucinatory palinopsia, usually due to seizures or posterior cortical lesions, describes afterimages that are formed, long-lasting, and high resolution. Illusory palinopsia, usually due to migraines, head trauma, prescription drugs, or hallucinogen persisting perception disorder (HPPD), describes afterimages that are affected by ambient light and motion and are unformed, indistinct, or low resolution.

The "treat empirically" route also has its difficulties, which have all come under wide debate and study. Recommendations are varied but seem to find some common ground around the notion that treatment should be individualized to the specific circumstances under which a patient has developed BLS since these circumstances affect the complex microbial make up of the affected bowel.

Tetracyclines have been the mainstay of treatment for BLS, but recent studies have concluded Rifaximin to be very effective in the treatment of BLS. One study by Di Stefano et al., however, concluded Metronidazole to be more effective than Rifaximin in the treatment of BLS.

Surgical management is reserved for fixing anatomical causes of bowel obstruction that interfere with normal function once they are amenable to such intervention. These conditions include:

- Strictures

- Fistulae

- Diverticula

Surgical methods range from the complete removal of the foreskin to more minor operations to relieve foreskin tightness:

- Dorsal slit (superincision) is a single incision along the upper length of the foreskin from the tip to the corona, exposing the glans without removing any tissue.

- Ventral slit (subincision) is an incision along the lower length of the foreskin from the tip of the frenulum to the base of the glans, removing the frenulum in the process. Often used when frenulum breve occurs alongside the phimosis.

- Preputioplasty, in which a limited dorsal slit with transverse closure is made along the constricting band of skin, can be an effective alternative to circumcision. It has the advantage of only limited pain and a short time of healing relative to circumcision, and avoids cosmetic effects.

- Circumcision is sometimes performed for phimosis, and is effective, but this was becoming less common as of 2012.

While circumcision prevents phimosis, studies of the incidence of healthy infants circumcised for each prevented case of phimosis are inconsistent.

The treatment of hyperplasia would consist upon "which"; in the case of benign prostate hyperplasia the combination of alpha-1-receptor blockers and 5-alpha-reductase inhibitors are effective.