Ophthalmology/Eye Surgery

Laser surgery and incisional surgery

Although the terms "laser eye surgery" and "refractive surgery" are commonly used as if they were interchangeable, this is not the case. Lasers may be used to treat nonrefractive conditions (e.g. to seal a retinal tear), while radial keratotomy is an example of refractive surgery without the use of a laser.

Cataract surgery

A cataract is an opacification or cloudiness of the eye's crystalline lens due to aging, disease, or trauma that typically prevents light from forming a clear image on the retina. If visual loss is significant, surgical removal of the lens may be warranted, with lost optical power usually replaced with a plastic intraocular lens (IOL). Due to the high prevalence of cataracts, cataract extraction is the most common eye surgery.

Cataract in Human Eye- Magnified view seen on examination with a slit lamp

Cataract surgery is the removal of the lens of the eye that has developed a cataract. The natural lens is then replaced with an artificial intraocular lens. It is one of the safest and most successful procedures in all of medicine.

The two main types of cataract extraction are intracapsular cataract extraction (ICCE) and extracapsular cataract extraction (ECCE).

Extracapsular cataract extraction involves the removal of the lens while the elastic lens capsule is left partially intact to allow implantation of an intraocular lens. There are two main types of extracapsular surgery: conventional ECCE and phacoemulsification. Conventional extracapsular cataract extraction involves manual expression of the lens through an incision made in the cornea or sclera. Although it requires a larger incision and the use of stitches, the conventional method is indicated for patients with very hard cataracts or lower counts of corneal endothelial cells. Phacoemulsification involves the use of a machine with an ultrasonic handpiece with a titanium or steel needle which vibrates at ultrasonic frequency under continuous irrigation to sculpt, chop and emulsify the cataract, thus making it easier to aspirate the fine particles. Irrigation-aspiration can then be performed with a bimanual system to clean out the cortical matter. Thereafter, a foldable Intraocular lens (IOL) made of Silicone or Acrylic materials of appropriate power is implanted using a holder/folder, or a proprietary insertion device provided along with the IOL. It is placed in the posterior chamber in-the-bag after cleaning out the cataract. Because a smaller incision is required, few or no stitches are needed and the patient's recovery time is usually shorter. .

Intracapsular cataract extraction (ICCE) involves the removal of the lens and the surrounding lens capsule in one piece. The lens is then replaced with an artificial plastic lens (an intraocular lens implant) of appropriate power which remains permanently in the eye. The procedure has a relatively high rate of complications due to the large incision required and pressure placed on the vitreous body, thus is rarely performed in countries where operating microscopes and high-technology equipment are readily available. Cryoextraction is a form of ICCE that freezes the lens with a cryogenic substance such as liquid nitrogen. Although it is now used primarily for the removal of subluxated lenses, it was the favored form of cataract extraction from the late 1960s to the early 1980s.

A capsulotomy, rarely known as cystitomy, is a procedure to open a portion of the lens capsule. An anterior capsulotomy refers to the opening of the front portion of the lens capsule, whereas a posterior capsulotomy refers to the opening of the back portion of the lens capsule. In an extracapsular surgery, the surgeon performs an anterior capsulotomy, or capsulorhexis, to create an opening through which the lens nucleus can be removed and the intraocular lens implant inserted. An opacification or clouding of the posterior lens capsule frequently occurs in those who have had an extracapsular cataract extraction procedure, therefore, a laser posterior capsulotomy, or YAG laser capsulotomy, is used to clear the back implant surface . (Whereas a capsulotomy is the creation of an opening in the lens capsule, a capsulectomy is the actual removal of lens capsule tissue.)

Cataract operations are mostly performed under a local anaesthetic and the patient will be allowed to go home the same day. Complications after cataract surgery are uncommon. Many people (up to 50%) can develop a posterior capsular opacification (PCO) after initial cataract surgery, although the incidence is rapidly falling. PCO is a thickening and clouding of the lens capsule (which was left behind when the cataract was removed) and it can be easily corrected using a Nd-Yag laser to make holes in the capsule for the person to see through. Retinal detachment is an uncommon complication of cataract surgery.

Previously, polymethylmethacrylate was used as the lens material, since it was discovered by Sir Harold Ridley in UK. He observed that the Royal Airforce pilots sustained eye injuries with splinters of glass from fighter plane windshield (made of PMMA). However, the eyes did not show any foreign body reaction. Thus the material was inert and useful for implantation in the eye. Sir Harold Ridley was the first to design and implant Intraocular lenses, which were further refined by using lathe cutting machines. Advances in technology have brought about the use of silicone and acrylic both of which are soft foldable inert material. This allows the lens to be folded and inserted into the eye through a smaller incision. Polymethyl methacrylate (PMMA) and Acrylic lenses can also be used with small incisions and are a better choice in people who have a history of uveitis, have diabetic retinopathy requiring vitrectomy with replacement by silicone oil or are at high risk of retinal detachment. Acrylic is not always an ideal choice due to its added expense. Latest advances include IOLs with square-edge design, non-glare edge design and yellow dye added to the IOL.

An important factor to be considered in modern cataract surgery is the surgically induced astigmatism (SIA). This is the amount of change induced in the corneal curvature due to the surgical procedure. Since astigmatism has a significant bearing on the final visual acuity, it needs to be evaluated and managed by every cataract surgeon. The technically difficult process of evaluating astigmatism can be made simpler by using downloadable SIA Calculators. A series of such calculators may be downloaded from SIA Calculators

Couching was an early form of cataract surgery in which a small probe was inserted in the eye to push the lens down into the posterior chamber.

History

The earliest references to cataract surgery are found in Sanskrit manuscripts dating from the 5th century BC, which show that Susruta in India developed specialised instruments and performed the earliest eye surgery. In the Western world, bronze instruments that could have been used for cataract surgery, have been found in excavations in Babylonia, Greece and Egypt. The first references to cataract and its treatment in the West are found in 29 AD in De Medicinae, the work of the Latin encyclopedist Aulus Cornelius Celsus.

In 1748, Jacques Daviel started with modern cataract surgery, in which the cataract is actually extracted from the eye. In the 1940s Harold Ridley invented the intraocular lens which made efficient and comfortable visual rehabilitation possible after cataract surgery.

According to surveys of members of the American Society of Cataract and Refractive Surgery, approximately 2.85 million cataracts procedures were performed in the United States during 2004 and 2.79 million in 2005[1].

Glaucoma surgery

Glaucoma is a group of diseases affecting the optic nerve that results in vision loss and is frequently characterized by raised intraocular pressure (IOP). There are many glaucoma surgeries, and variations or combinations of those surgeries, that facilitate the escape of excess aqueous humor from the eye to lower intraocular pressure, and a few that lower IOP by decreasing the production of aqueous.

Procedures that facilitate outflow of aqueous humor

Laser trabeculoplasty

A trabeculoplasty is a modification of the trabecular meshwork. Laser trabeculoplasty (LTP) is the application of a laser beam to burn areas of the trabecular meshwork, located near the base of the iris, to increase fluid outflow. LTP is used in the treatment of various open-angle glaucomas. The two types of laser trabeculoplasty are argon laser trabeculoplasty (ALT) and selective laser trabeculoplasty (SLT). As its name suggests, argon laser trabeculoplasty uses an argon laser to create tiny burns on the trabecular meshwork. Selective laser trabeculoplasty is newer technology that uses a YAG laser to target specific cells within the trabecular meshwork and create less thermal damage than ALT.

Iridotomy

An iridotomy involves making puncture-like openings through the iris without the removal of iris tissue. Performed either with standard surgical instruments or a laser, it is typically used to decrease intraocular pressure in patients with angle-closure glaucoma. A laser peripheral iridotomy (LPI) is the application of a laser beam to selectively burn a hold through the iris near its base. LPI may be performed with either an argon laser or Nd:YAG laser.

Iridectomy

An iridectomy, also known as a corectomy or surgical iridectomy, involves the removal of a portion of iris tissue. A basal iridectomy is the removal of iris tissue from the far periphery, near the iris root; a peripheral iridectomy is the removal of iris tissue at the periphery; and a sector iridectomy is the removal of a wedge-shaped section of iris that extends from the pupil margin to the iris root, leaving a keyhole-shaped pupil.

Filtering procedures: penetrating vs. non-penetrating

Filtering surgeries are the mainstay of surgical treatment to control intraocular pressure. An anterior sclerotomy or sclerostomy is used to gain access to the inner layers of the eye [2] [3] [4] in order to create a drainage channel from the anterior chamber to the external surface of the eye under the conjunctiva, allowing aqueous to seep into a bleb from which it is slowly absorbed. Filtering procedures are typically divided into either penetrating or non-penetrating types depending upon whether an intraoperative entry into the anterior chamber occurs [5] [6].

Penetrating filtering surgeries are further subdivided into guarded filtering procedures, also known as protected, subscleral, or partial thickness filtering procedures (in which the surgeon sutures a scleral flap over the sclerostomy site [7]), and full thickness procedures [8]. Trabeculectomy is a guarded filtering procedure that removes of part of the trabecular meshwork[9]. Full thickness procedures include sclerectomy, posterior lip sclerectomy (in which the surgeon completely excises the sclera on the area of the sclerostomy [10]), trephination, thermal sclerostomy (Scheie procedure), iridenclesis, and sclerostomy (including conventional sclerostomy and enzymatic sclerostomy) [11] [12].

Non-penetrating filtering surgeries do not penetrate or enter the eye's anterior chamber [13] [14]. There are two types of non-penetrating surgeris: Bleb-forming and viscocanalostomy [15]. Bleb forming procedures include ab externo trabeculectomy and deep sclerectomy[16]. Ab externo trabeculectomy (AET) involves cutting from outside the eye inward to reach Schlemm's canal, the trabecular meshwork, and the anterior chamber. Also known as non-penetrating trabeculectomy (NPT), it is an ab externo (from the outside), major ocular procedure in which Schlemm's canal is surgically exposed by making a large and very deep scleral flap. The inner wall of Schlemm's canal is stripped off after surgically exposing the canal [17]. Deep sclerectomy, also known as nonpenetrating deep sclerectomy (PDS) or nonpenetrating trabeculectomy is a filtering surgery where the internal wall of Schlemm's canal is excised, allowing subconjunctival filtration without actually entering the anterior chamber [18]; it is commonly performed with the Aquaflow® collagen wick [19]. Viscocanalostomy is also an ab externo, major ocular procedure in which Schlemm's canal is surgically exposed by making a large and very deep scleral flap. In the VC procedure, Schlemm's canal is cannulated and viscoelastic substance injected (which dilates Schlemm's canal and the aqueous collector channels)[20].

Other surgical procedures

Goniotomy and trabeculotomy are similar simple and directed techniques of microsurgical dissection with mechanical disruption of the trabecular meshwork [21] [22] [23]. Gonotomy procedures include surgical goniotomy and laser goniotomy. A surgical goniotomy involves cutting the fibers of the trabecular meshwork to allow aqueous fluid to flow more freely from the eye [24][25]. Laser goniotomy is also known as goniophotoablation and laser trabecular ablation [26]. In many patients suffering from congenital glaucoma, the cornea is not clear enough to visualize the anterior chamber angle. Although an endoscopic goniotomy, which employs an endoscope to view the anterior chamber angle, may be performed [27], a trabeculotomy which accesses the angle from the exterior surface of the eye, thereby eliminating the need for a clear cornea, is usually preferred in these instances. A specially designed probe is used to tear through the trabecular meshwork to open it and allow fluid flow [28].Video

Tube-shunt surgery or drainage implant surgery involves the placement of a tube to facilitate aqueous outflow from the anterior chamber [29][30]. Trabeculopuncture uses a Q switched Nd:YAG laser to punch small holes in the trabecular meshwork with [31][32] [33]. Goniocurretage is an "ab interno" (from the inside) procedure that used an instrument "to scrape pathologically altered trabecular meshwork off the scleral sulcus" [34][35] [36]. A surgical cyclodialysis is a rarely used procedure that aims to separate the ciliary body from the sclera to form a communication between the suprachoroidal space and the anterior chamber. A cyclogoniotomy is a surgical procedure for producing a cyclodialysis, in which the ciliary body is cut from its attachment at the scleral spur under gonioscopic control.

Procedures that decrease production of aqueous humor

Certain cells within the eye's ciliary body produce aqueous humor. A ciliary destructive or cyclodestructive procedure is one that aims to destroy those cells in order to reduce intraocular pressure [37]. Cyclocryotherapy, or cyclocryopexy, uses a freezing probe [38]. Cyclophotocoagulation, also known as transscleral cyclophotocoagulation, ciliary body ablation,[39], cyclophotoablation [40], and cyclophototherapy [41], uses a laser. Cyclodiathermy uses heat generated from a high frequency alternating electric current passed through the tissue, while cycloelectrolysis uses the chemical action caused by a low frequency direct current.

Refractive surgery

• Refractive surgery aims to correct errors of refraction in the eye, reducing or eliminating the need for corrective lenses
  • Keratomilleusis is method of reshaping the cornea surface to change its optical power. A disc of cornea is shaved off, quickly frozen, lathe-ground, then returned to its original power.
  • Automated lamellar keratoplasty (ALK)
  • Laser assisted in-situ keratomileusis (LASIK)
    • IntraLASIK
  • Laser assisted sub-epithelial keratomileusis (LASEK), aka Epi-LASIK
  • Photorefractive keratectomy (PRK)
  • Laser thermal keratoplasty (LTK)
  • Conductive keratoplasty (CK) uses radio frequency waves to shrink corneal collagen. It is used to treat mild to moderate hyperopia.
  • Limbal relaxing incisions (LRI)
  • Astigmatic keratotomy (AK), aka Arcuate keratotomy or Transverse keratotomy
  • Radial keratotomy (RK)
  • Hexagonal keratotomy (HK)
  • Epikeratophakia is the removal of the corneal epithelium and replacement with a lathe cut corneal button.
  • Intracorneal rings (ICRs), or corneal ring segments (Intacs) [43]
  • Implantable contact lenses
• Presbyopia reversal
  • Anterior ciliary sclerotomy (ACS)
    • Laser reversal of presbyopia (LRP)
  • Scleral expansion bands

Corneal surgery

• Corneal surgery includes most of the refractive surgeries as well as the following:
  • Corneal transplant surgery, is used to remove a cloudy/diseased cornea and replace it with a clear donor cornea.
    • Penetrating keratoplasty (PK)
  • Phototherapeutic keratectomy (PTK)
  • Pterygium excession

Vitreo-retinal surgery

Vitrectomy.

• Vitreo-retinal surgery includes the following
  • Vitrectomy [44]
    • Anterior vitrectomy is the removal of the front portio of vitreous tissue. It is used for preventing or treating vitreous loss during cataract or corneal surgery, or to remove misplaced vitreous in conditions such as aphakia pupillary block glaucoma.
    • Pars plana vitrectomy (PPV), or trans pars plana vitrectomy (TPPV), is a procedure to remove vitreous opacities and membranes through a pars plana incision. It is frequently combined with other intraocular procedures for the treatment of giant retinal tears, tractional retinal detachments, and posterior vitreous detachments [45].
  • Pan retinal photocoagulation (PRP) is a type of photocoagulation therapy used in the treatment of diabetic retinopathy.
  • Retinal detachment repair
    • Ignipuncture is an obsolete procedure that involves cauterization of the retina with a very hot pointed instrument.
    • A scleral buckle is used in the repair of a retinal detachment to indent or "buckle" the sclera inward, usually by sewing a piece of preserved sclera or silicone rubber to its surface.
    • Laser photocoagulation, or photocoagulation therapy, is the use of a laser to seal a retinal tear.
    • Pneumatic retinopexy
    • Retinal cryopexy, or retinal cryotherapy, is a procedure that uses intense cold to induce a chorioretinal scar and to destroy retinal or choroidal tissue.
  • Macular hole repair
  • Partial lamellar sclerouvectomy
    • Partial lamellar sclerocyclochoroidectomy
    • Partial lamellar sclerochoroidectomy
  • Posterior sclerotomy is an opening made into the vitreous through the sclera, as for detached retina or the removal of a foreign body [46].

• Radial optic neurotomy macular translocation surgery through 360 degree retinotomy through scleral imbrication technique

Eye muscle surgery

With approximately 1.2 million procedures each year, extraocular muscle surgery is the third most common eye surgery in the United States [47].

• Eye muscle surgeries typically correct strabismus and include the following [48]:
  • Loosening / weakening procedures
    • Recession involves moving the insertion of a muscle posteriorly towards its origin.
    • Myectomy
    • Myotomy
    • Tenectomy
    • Tenotomy
  • Tightening / strengthening procedures
    • Resection
    • Tucking
    • Advancement is the movement of an eye muscle from its original place of attachment on the eyeball to a more forward position.
  • Transposition / repositioning procedures
  • Adjustable suture surgery is a method of reattaching an extraocular muscle by means of a stitch that can be shortened or lengthened within the first post-operative day, to obtain better ocular alignment [49].

Oculoplastic surgery

• Oculoplastic surgery, or oculoplastics, is the subspecialty of ophthalmology that deals with the reconstruction of the eye and associated structures.
  • Browplasty [50]
  • Eyelid surgery [51]
    • Blepharoplasty is plastic surgery of the eyelids to remove excessive skin or subcutaneous fat.
      • Asian blepharoplasty
    • Ectropion repair
    • Entropion repair
    • Canthal resection
    • Canthoplasty
    • Canthopexy
    • Canthotomy, lateral canthotomy
    • Epicanthoplasty
  • Surgery involving the lacrimal apparatus:
    • Canaliculodacryocystostomy is a surgical correction for a congenitally blocked tear duct in which the closed segment is excised and the open end is joined to the lacrimal sac.
    • Canaliculotomy involves slitting of the lacrimal punctum and canaliculus for the relief of epiphora
    • Dacryostectomy
    • Dacryocystohinostomy
  • Eye removal
    • Enucleation is the removal of the eye leaving the eye muscles and remaining orbital contents intact.
    • Evisceration is the removal of the eye's contents, leaving the scleral shell intact. Usually performed to reduce pain in a blind eye.
    • Exenteration is the removal of the entire orbital contents, including the eye, extraocular muscles, fat, and connective tissues; usually for malignant orbital tumors.
  • Dacryocystorhinostomy (DCR)[52]

Other

• A ciliarotomy is a surgical division of the ciliary zone in the treatment of glaucoma.
• A ciliectomy is 1) the surgical removal of part of the ciliary body, or 2) the surgical removal of part of a margin of an eyelid containing the roots of the eyelashes.
• A ciliotomy is a surgical section of the ciliary nerves.
• A corectomedialysis, or coretomedialysis, is an excision of a small portion of the iris at its junction with the ciliary body to form a artificial pupil.
• A corectomy is any surgical cutting operation on the iris at the pupil.
• A corelysis is a surgical detachment of adhesions of the iris to the capsule of the crystalline lens or cornea.
• A coremorphosis is the surgical formation of an artificial pupil.
• A coreplasty, or coreoplasty, is plastic surgery of the iris, usually for the formation of an artificial pupil.
• A coreoplasy, or laser pupillomydriasis, is any procedure that changes the size or shape of the pupil.
• A cyclectomy is an excision of portion of the ciliary body.
• A cyclotomy, or cyclicotomy, is a surgical incision of the ciliary body, usually for the relief of glaucoma.
• A cycloanemization is a surgical obliteration of the long ciliary arteries in the treatment of glaucoma.
• An iridectomesodialsys is the formation of an artificial pupil by detaching and excising a portion of the iris at its periphery.
• An iridodialysis, sometimes known as a coredialysis, is a localized separation or tearing away of the iris from its attachment to the ciliary body.
• An iridencleisis, or corenclisis, is a surgical procedure for glaucoma in which a portion of the iris is incised and incarcerated in a limbal incision. (Subdivided into basal iridencleisis and total iridencleisis.)
• An iridesis is a surgical procedure in which a portion of the iris is brought through and incarcerated in a corneal incision in order to reposition the pupil.[53]
• An iridocorneosclerectomy is the surgical removal of a portion of the iris, the cornea, and the sclera.
• An iridocyclectomy is the surgical removal of the iris and the ciliary body.
• An iridocystectomy is the surgical removal of a portion of the iris to form an artificial pupil.
• An iridosclerectomy is the surgical removal of a portion of the sclera and a portion of the iris in the region of the limbus for the treatment of glaucoma.
• An iridosclerotomy is the surgical puncture of the sclera and the margin of the iris for the treatment of glaucoma.
• A trepanotrabeculectomy is used in the treatment of chronic open and chronic closed angle glaucoma.