What is eye surgery?

Indications and Procedures

Compared to surgery performed on internal organs and any number of outpatient procedures, eye surgery can fill patients with added fears, often concerned with great suffering and the possibility of permanent sight loss. Surgery to an internal organ is usually perceived as happening in a remote location in an unseen portion of the body, and most patients have little idea of the organ’s function. Often, if an internal growth or organ is removed, the body continues to function quite well. Most patients have some knowledge of the eye, unlike most internal organs, and thus are more likely to develop anxiety about even common surgical procedures involving it. Patients know what eyes are and what they are used for and that they are extremely sensitive and painful to touch. A grain of sand or a hair touching the eye is painful, so the thought of contacting the eye with a needle or making an incision in it with a scalpel or laser can be almost unimaginable. Patients with ocular problems requiring surgery fear damage to the eye and know all too well the consequences of removal. In most instances, the general public has little to no knowledge or
understanding of the function and mechanics of eye surgery. Common eye surgeries include, but are not limited to, cataract surgery, corneal transplantation, vision correction, pterygium removal, retinal detachment repair, and tear duct surgery.

A cataract is an opacity on the eye’s lens. A cataract may be minimal in size and low in density, so that light transmission is not appreciably affected, or it may be large and opaque so that light cannot gain entry into the interior eye. When the cataract is pronounced, the interior of the patient’s eye cannot be seen with clarity, and the patient cannot see out clearly. Over time, the lens takes on a yellowish hue and begins to lose transparency. As the lens thus becomes “cloudy,” the patient needs brighter and brighter lights for visual clarity. If the lens becomes completely opaque, then the patient is functionally blind. A cataract is removed when it endangers the health of the eye or interferes with a patient’s ability to function. Conditions such as contrast sensitivity, glare, pupillary constriction, and ambient light may significantly affect a patient’s functionality.

The objective of cataract surgery is to remove the crystalline lens of the eye that has become cloudy. Modern surgical procedures involve removing the lens, either intact or in pieces after shattering it with high-frequency sound. The surgery is usually performed under an operating microscope because magnification is necessary. Many methods are used for cataract surgery, including an extracapsular procedure, an intracapsular procedure, and phacoemulsification. Most surgeons perform cataract surgery in freestanding surgical centers on an outpatient basis.

In extracapsular surgery, an incision is made at the superior limbus and a small opening is made into the anterior chamber. A viscoelastic substance is introduced and then a small, bent needle, or cystotome, is introduced. An incision is made into the anterior capsule in a circular, triangular, or D-shaped fashion. The wound is enlarged to a diameter of 10 to 11 millimeters, allowing removal of the cataractous nucleus.

The most common cataract surgical procedure is phacoemulsification, or small-incision cataract surgery. A stair-stepped incision of between 1.5 and 4.0 millimeters is made in the front of the eye. A cystotome is inserted to cut the anterior capsule of the lens. An emulsifier and aspirator is inserted to remove the collapsed lens. The missing lens is then replaced by an artificial substitute that is folded and inserted through the incision and rotated into place. The wound is sealed with a single suture or no suture at all. This procedure has become favored because it causes less tissue destruction, less wound reaction, and less astigmatism, and patients can resume normal activities immediately after surgery. Vision is then fine-tuned with glasses or contact lenses, if needed.

Another common eye surgery is corneal transplantation.
The cornea is the clear portion in the front part of that eye. When injured, degenerated, or infected, the cornea can become cloudy and vision disrupted. Corneal surgery restores lost vision by replacing a portion of the cornea with a clear window taken from a donor eye. Usually, the donor cornea is taken from a recently deceased person. However, not everyone with corneal disease can be helped by corneal transplantation.

The cornea was one of the first structures of the body to be transplanted. Because the cornea is devoid of blood vessels, it is one of the few tissues in the human body that may be transplanted from one human to another with a high degree of success. The absence of blood vessels in the donor cornea reduces immune system reactions.

Two types of corneal transplants are performed: partial penetration, in which a half thickness of the cornea is transplanted, and penetrating transplantation, which involves the full thickness of the cornea. In partial penetration, the anterior of the eye is not entered; only the outer half or two-thirds of the cornea is transplanted. Union is made by several sutures around the periphery of the donor tissue. Depending on the extent of the disease, the donor tissue may be 6 to 10 millimeters in diameter. In a penetrating transplantation, surgery involves entering the anterior chamber of the eye, inserting the donor cornea, and establishing a tight fit with a continuous suture.

Glaucoma
is an ocular disease affecting roughly 2 percent of the population over forty. The major characteristic of the condition is a sustained increase in intraocular pressure so great that the fibrous scleral coat cannot expand significantly and the eye cannot withstand the increasing pressures against surrounding soft tissue without damage to its structure and vision impairment. The results of this pressure increase include excavation of the optic disc, hardness of the eyeball, reduced vision, the appearance of colored halos around lights, visual field defects, and headaches. Surgical procedures are performed to relieve this pressure. Although many types of surgical procedures are performed to treat glaucoma, they are all basically fistulizing surgeries, attempting to create an opening between the anterior chamber and the subconjunctival space or between the surgically prepared layers of the sclera.

Glaucoma surgery involves a small incision made either directly through the cornea at the upper limbus or under a flap of conjunctival tissue. The iris is grasped with small forceps and pulled out of the eye, and a small portion of the trabecular meshwork is partially removed, allowing the aqueous fluid to filter out of the anterior chamber. The cornea is then sutured and the eye bandaged. The most popular procedure of this type is trabeculectomy. As a whole, glaucoma surgeries are performed less often today because of the success of nonsurgical treatments and management with drug therapies. A major consequence of some glaucoma surgery is the development of cataracts.

A common early stage nonincisive procedure in treating glaucoma is laser trabeculoplasty. This procedure involves lasing the middle to anterior portion of the trabecular meshwork with eighty to one hundred equally spaced burns. The argon laser reopens blocked drainage channels and reduces fluid pressure in the eye. More than 90 percent of patients experience successful outcomes from this treatment. Surgery is performed only if patients continue to lose the visual field.

A pterygium is a fibrovascular membrane that extends from the medial aspect of the bulbar conjunctiva and invades the cornea. It is a progressive growth related to overexposure to ultraviolet (UV) light. In time, it can make its way to the central portion of the cornea and interfere with vision. Pterygia are most common in southern climates, where people have greater exposure to UV light. In northern regions, people who work outdoors, especially in open fields or on open water, are most prone to developing a pterygium growth.

The purpose of removing a pterygium is to excise the membrane before it can interfere with vision. The operation requires incision into the cornea as well as the conjunctiva, then removal of the pterygium tissue or its transplantation to another position to redirect its growth.

In a normal eye, the retina lies against the choroidal layer, from which it receives part of its blood supply and nourishment. The retina is loosely attached to the choroid, but when it becomes separated from the choroid, it flaps and hangs within the eye’s vitreous fluid. Retinal detachment does not allow adequate nutrients to reach the retina and thus causes poor function, and it eventually leads to vision loss. Retinal detachment may be caused by injury, myopia, or previous eye surgeries. Often, a tear or hole permits fluid to collect under the retina, causing the detachment.

Retinal detachment surgery corrects the loose retina by bringing it back to the choroid or by pushing the choroid up to the retina. To bring the retina back into place, scleral punctures are made to drain fluids that lay between the retina and the choroid. When the retina returns to lie against the choroid, either electrocoagulation or cryotherapy with a cold probe against the sclera unites the retina to the choroid. Then the retina and choroid are brought together with a silicone buckling band to exert inward pressure. If the retina is not attached at this point, then air, special gas, or oil is injected into the vitreous fluid to push the retina back against the choroid.

Surgery involving corrective procedures to tear ducts is common, especially in older patients. A blockage in the nasolacrimal passage may result in a condition called epiphora, in which the tear ducts water constantly. Such a blockage of the tear canal may result from some form of obstruction. These obstructions are cleared by a surgical procedure called dacryocystorhinostomy. In this procedure, a large incision of 8 to 10 millimeters is made in the wall of the nose, and a union is created between the mucosal lining of the nose and the lacrimal sac. In this way, the lacrimal sac opens directly into the nose. The operation is usually successful in curing the tearing and infection problems arising from stagnation in the blocked tear duct.

Elective refractive eye surgery
for the purpose of vision correction began in the Soviet Union in the 1970s and gained popularity in the United States in the 1990s with the use of lasers. It is performed for the relief of myopia, hypermyopia, and astigmatism, with the goal of eliminating the need for either eyeglasses or contact lenses. It is also used to correct refractive errors caused by cataract surgery and corneal transplantation.

Two of the most common refractive surgeries are radial
keratotomy (RK) and photorefractive keratectomy (PRK), also known as excimer laser surgery. Myopic patients suffer from a cornea that is either too convex or has an axial length that is too long, causing light to converge at a focal point anterior to the retina. In refractive surgery, corneal reshaping is the important concept. The surgical goal is to flatten the center of the cornea so that light will focus more posteriorly.

RK reshapes the cornea by radial incisions made with a diamond knife. This process weakens the cornea, so normal intraocular pressure pushes the center of the cornea outward, flattening the central cornea. PRK uses a laser to remove the superficial layers of the central cornea, about 50 to 100 microns of tissue, to achieve a similar reshaping of the cornea.

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