cataract
CATARACT
Cataract is the presence of opacity in the crystalline lens of the eye. It causes painless, progressive blurring of vision.
It is the leading cause of blindness worldwide and the most prevalent ocular disease.
The initiating events that lead to loss of transparency of both the cortical and nuclear lens tissue is the oxidation of the membrane lipids, structural or enzymatic proteins or DNA by peroxidases or free radicals induced by UV light.

Surgical Intervention

Pre-operative Evaluation

  • Perform a thorough ophthalmic evaluation
  • Patient-centered visual function evaluation
  • Educate patient on other treatment options
  • Assess & manage patient’s expectations
  • Keratometry to determine the refractive (astigmatic) error by measuring the radius of the curvature of the anterior surface of the central optical portion of the cornea
  • Lacrimal apparatus irrigation (LAI) checks the patency of the nasolacrimal duct; obstruction may cause infection & have greater risk for post-operative complications
  • Perform ocular surface assessment
  • Routine medical testing does not measurably increase the safety of the surgery

Biometry & Intraocular Lens Power Calculation

  • To achieve target post-op refraction, the minimal requirements are:
    • Accurate measurement of axial length & central corneal power w/
    • Appropriate intraocular lens selection based on a power calculation formula
  • Optical biometry is a noncontact high-resolution method of measuring axial length that uses a specialized light source rather than ultrasound
    • More accurate than contact (applanation) A-scan biometry
    • Low risk for corneal compression & cross-contamination
  • Biometry should be done before instillation of dilating drops & before tonometry is performed
  • Axial length measurement should be done on both eyes even when surgery is planned only for one eye
  • 92% of axial lengths fall w/in the range of 21-25.5 mm & most corneas are relatively regularly curved & similar between the 2 eyes of each individual
  • Formulas for calculating intraocular lens power rely on keratometry to determine the net refractive contribution of the cornea
  • Corneal measurements can be obtained by manual or automated keratometry or through corneal topography
    • Corneal topography is preferred as it averages the corneal curvature values from far more locations to calculate “sim K” values
  • The intraocular lens selection process that should be used are the recent-generation theoretical intraocular lens power calculation formulas eg Hoffer Q, Holladay & SRK/T, Haigis
  • It is recommended that the eventual optimization of lens constants for a specific intraocular lens will be based on an individual ophthalmologist’s actual refractive outcome
  • The ophthalmologist should consider the patient’s desires & needs in selecting an appropriate post-op refractive target

Surgical Procedures

Extracapsular Cataract Extraction (ECCE)

  • Main requirement for extracapsular cataract extraction & posterior intraocular lens is zonular integrity
  • Retention of the integrity of the posterior capsule

Extracapsular  Cataract Extraction by Nuclear Expression

  • After the opening of incision & anterior capsulotomy, the hard nucleus is removed from the capsular bag in one piece through the incision & then the residual cortex is removed by irrigation & aspiration
  • Large incision is required in this procedure & needs several sutures to close the wound

Extracapsular  Cataract Extraction by Phacoemulsification

  • An ultrasonic device emulsifies the hard nucleus that will enable the surgeon to remove the lens material by a suction device, leaving an intact lens capsule to hold the intraocular lens
  • Most common & preferred method of cataract extraction
  • Advantages: Only requires a small incision (results in less induced astigmatism) & may be closed w/ a single suture or w/o sutures, quicker surgery, uses topical anesthesia, more predictable refractive results, maintains the normal depth of the anterior chamber & faster recovery

Intraocular steps usually used in phacoemulsification:

  • An appropriately sized incision is constructed that is tight enough to have a fluidically stable anterior chamber
  • An ophthalmic viscosurgical device is used to protect the corneal endothelium, manipulate tissues & maintain adequate working space for surgery
  • Capsulorrhexis is a continuous curvilinear capsulotomy that facilitates hydrodissection, prevents posterior capsule tears & facilitates the implantation, fixation & centration of the intraocular lens w/in the capsular bag
  • Hydrodissection reduces the zonular stress during phacoemulsification by mobilizing the nucleus & epinucleus
  • Nuclear disassembly & emulsification
  • Thorough removal of remaining epinucleus & cortex
  • Implantation of foldable intraocular lens w/ injector & centration of a small-incision intraocular lens w/in the capsular bag
  • Removal of the ophthalmic viscosurgical device to minimize post-op intraocular pressure elevation
  • Assurance of watertight incision

Intracapsular Cataract Extraction (ICCE)

  • After the opening incision, the lens that is still enclosed in the lens capsule is extracted in one piece
  • Used only in special circumstances (eg severely impaired zonular integrity)
  • Can be performed in remote areas w/ less sophisticated equipment & no operating microscopes & irrigating systems available
  • Seldom done due to several disadvantages & post-op complications: Very large limbal incision (160-180 degrees), delayed healing & visual rehabilitation, iris & vitreous incarceration, significant against-the-rule astigmatism, post-op wound leaks, & significant endothelial cell loss

Femtosecond-assisted Phacoemulsification

  • Adjunctive procedure that is used to construct corneal incisions to correct corneal astigmatism, perform anterior capsulotomy & fragment the nucleus
  • Has been shown to result in better wound architecture, rounder/more central capsulorrhexis & better centered intraocular lens

Intraocular Lenses (IOLs)

  • Posterior chamber intraocular lens implantation in the capsular bag is the method of choice to correct aphakia, unless contraindicated
  • Factors to consider in choosing the intraocular lens to use: Intraocular lens material, incision size, optic size, haptics, method of insertion, function options, documented evidence of safety & effectiveness
  • Foldable intraocular lens is the most common choice following phacoemulsification; it can easily be implanted through small incisions
  • If there is an absence of a normal capsular bag, the ophthalmologist should determine if the power & the design of the intraocular lens intended for capsular bag fixation is or is not appropriate for ciliary sulcus placement

Optical & Refractive Considerations

  • The decreased visual acuity in cataract is brought about by the positive spherical aberration of the lens
    • By replacing the cataract eye w/ an aspheric intraocular lens, it attempts to return the eye to a normal neutral spherical aberration state
  • To reduce eyeglass dependence after cataract surgery due to corneal astigmatism, toric intraocular lens can be used
  • Monovision- & presbyopia-correcting intraocular lens implants are used in an attempt to improve quality of life by reducing eyeglass dependence after cataract surgery
    • The success of monovision depends on interocular blur suppression where blurred image from one eye does not interfere w/ the image from the in-focus eye
    • Multifocal presbyopia-correcting intraocular lens achieve their effect by dividing incoming light into two or more focal points that is found to be effective at improving near vision
    • Accommodative presbyopia-correcting intraocular lens is designed to change position or shape in the eye w/ accommodative effort

Complications

Major complications that are potentially sight threatening

  • Infectious endophthalmitis
    • Rare (1 in 10,000) but most feared complication of cataract surgery
    • Staphylococcus epidermidis is the most common pathogen that usually invades the anterior chamber at the time of surgery; gram-positive bacteria is the most common group of pathogen
    • It has been found that the type & size of incision as a possible factor in the development of endophthalmitis
    • Immediate retina specialist referral is recommended w/in 24 hours of presence of suspicion of endophthalmitis
  • Intra-operative suprachoroidal hemorrhage
  • Retinal detachment
    • An ocular emergency; patient should be referred to a vitreoretinal subspecialist
    • Postsurgical risk factors include axial length >23 mm, posterior capsular tear, younger age, male gender, lattice degeneration, zonular dehiscence, retinal detachment in the other eye, post-operative posterior vitreous detachment
  •  Intraocular lens dislocation
  • Toxic anterior segment syndrome (TASS)
    • Rare; a sterile, post-op, inflammatory reaction that usually occurs 12-48 hr post-op that can mimic infectious endophthalmitis
    • Most probable cause is the introduction into the anterior chamber of pro-inflammatory substances (eg antiseptics, topical medicine especially those w/ preservatives & re-sterilized viscoelastics)
  • Cystoid macular edema (CME)
    • Clinically significant cystoid macular edema is not common
    • Has deleterious optical effect on vision w/ advanced technology intraocular lens
    • Responds well to medical therapy; recalcitrant cases may result to visual acuity permanent impairment
    • Risk factors include: Previous uveitis, posterior capsule rupture w/ vitreous loss, retained lens material, diabetic retinopathy, epiretinal membrane, prior vitreoretinal surgery, nanophthalmos, retinitis pigmentosa, history of pseudophakic cystoid macular edema in the other eye
    • Optical coherence tomography (OCT) is used for anatomic diagnosis
    • Topical anti-inflammatory medications are used to prevent & treat established cystoid macular edema
  • Persistent corneal edema
  • Endothelial cell loss 

Other post-operative complications (early, intermediate, & late)

  • Ocular hypertension
  • Wound leak w/ shallow, flat, or well-formed anterior chamber
  • Iris prolapse or vitreous in the wound
  • Intraocular lens dislocation, decentration/pupillary capture
  • Corneal decompensation
  • Anterior uveitis
  • Anterior ischemic optic neuropathy
  • Posterior capsular opacity
  • Posterior capsular tear or zonular rupture
  • Malignant glaucoma
  • Endophthalmitis
  • Ptosis
  • Diplopia
  • Hyphema
  • Choroidal detachment
  • Epithelial downgrowth
  • Pseudophakiccystoid macular edema
  • Prolonged inflammation

Incision complications

  • Incision that is not watertight may lead to post-op wound leak, hypotony & endophthalmitis
  • There is an increased risk of wound burn & decrease of the ability to cool the ultrasonic phacoemulsification if the incision is too small, while too big incision can cause destabilization of the anterior chamber & fluid leakage from the wound
  • Sutures or adhesive for proper closure should be applied on not self-sealing incision
  • Sutures can induce post-op astigmatism & it is dependent on the location & tension

Iris complications

  • Intraoperative floppy iris syndrome (IFIS) or a poorly constructed incision may result to iris prolapse
  • There is a high risk of having intraoperative floppy iris syndrome in patients taking Tamsulosin
  • Intracameral epinephrine, viscomydriasis & pupil expansion devices, either alone or in combination, are used to manage intraoperative floppy iris syndrome
  • Other surgical iris trauma causes are:
    • Toxic anterior segment syndrome 
    • Iris aspiration or agitation w/ phacoemulsification tip
    • Sphincterotomies
    • Excessive stretching or manipulation w/ expansion devices & instruments

Corneal complications

  • Descemet’s membrane tears or detachment is the result of improper instrument entry into the anterior chamber
  • By repositioning & tamponading the flap of the Descemet’s membrane w/ an air bubble, a small tear can be repaired
  • Prolonged elevated intraocular pressure  & phacoemulsification time (ultrasonic energy) can result to further endothelial decompensation & corneal edema

Retained lens fragments

  • An anterior vitrectomy w/ stable placement of an appropriately sized & designed intraocular lens is recommended if there is vitreous loss w/ posteriorly dislocated lens fragments
  • Injected Triamcinolone is reported to aid in visualization of residual vitreous

Intraocular pressure

  • Transient elevation of intraocular pressure  is a recognized tendency during the early post-op period
  • It causes pain & some eye may be more susceptible to vascular occlusion or optic nerve damage
  • If there is an excess amount of ophthalmic viscosurgical device  remains in the eye at the close of surgery, there is an increased likelihood of having elevated intraocular pressure & thorough ophthalmic viscosurgical device removal should be attempted
  • Although unclear, it appears that topical aqueous suppressants & intracameral Carbachol are beneficial in immediate post-op elevated intraocular pressure  prophylaxis
  • Topical corticosteroids use increases the risk of elevated intraocular pressure 
    • Although cataract surgery has been found to reduce intraocular pressure , at least transiently, in patients w/ angle closure or w/o glaucoma

Intraocular lens complications

  • Intraocular lens dislocation occurs when the intraocular lens moves from its posterior position due to lost of most of its tissue support
  • Due to excessive trauma in removing the cataract, the posterior chamber intraocular lens may dislocate causing the capsule to be partially torn or the zonules broken
  • The patient usually presents w/ sudden vision loss &/or diplopia
  • Inferior direction of displacement of the posterior chamber intraocular lens known as “sunset syndrome” is the most common direction of displacement
  • Limiting physical activity that would aggravate the dislocation of the intraocular lens is advised to patients prior to prompt referral to the ophthalmologist
  • Positive dysphotopsia includes ghost images, starbursts & arcs, rings or flashes of light & negative dysphotopsia manifests as dark crescent or curved shadow that can appear similar to a scotoma in the peripheral temporal field of vision
  • Retained ophthalmic viscosurgical device in the bag, improper haptic or optic placement, capsulorrhexis diameter & inversion of the intraocular lens are factors that can affect the effective lens position

Posterior capsular opacification

  • Often occurs after extracapsular cataract extraction; causes gradual decrease in visual function
    • Newer sharp-edge intraocular lens have been shown to decrease incidence
    • Visual deterioration is more significant w/ multifocal intraocular lens
  • Most common cause is the proliferation of lens epithelial cells that remain in the capsular bag following surgery
  • More prevalent among younger patients
  • Neodymium: Yttrium-aluminum-garnet laser (Nd:YAG) laser capsulotomy is done to clear the visual pathway & restore visual function & to improve contrast sensitivity

Second Eye Surgery

  • Cataract surgery for both eyes is an appropriate treatment for patients w/ bilateral cataract-induced visual impairment
  • Studies have shown that the outcomes of patients who had surgery on both eyes had greater improvement in functional status than the ones who underwent only one eye surgery
  • The indications for second-eye surgery are the same as the first eye surgery
  • Factors that would determine the interval between the first-eye surgery & the second-eye surgery:
    • Patient’s visual needs & preferences
    • Visual acuity & function of the second eye
    • Medical & refractive stability of the first eye
    • Degree of anisometropia
  •  Refractive error of the first eye should be determined before the second-eye surgery in order to select the appropriate intraocular lens power for the second eye
  • There should be enough interval time to diagnose & treat any early complications of the first-eye surgery before the patient & the ophthalmologist be satisfied w/ the recovery & outcome of the first-eye surgery, before the second-eye surgery be performed

Criteria for discharge after ambulatory surgery:

  • Stable vital signs
  • Available escort if necessary
  • Restored pre-operative mental state
  • Nausea & vomiting are controlled
  • Absent or minimal pain
  • Follow-up appointment has been scheduled
  • Post-surgical care has been reviewed w/ the patient & caretaker & written post-op instructions have been provided
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