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 and 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 and have greater risk for post-operative complications
  • Perform ocular surface assessment
  • Routine medical testing does not measurably increase the safety of the surgery

Biometry and Intraocular Lens Power Calculation

  • To achieve target post-op refraction, the minimal requirements are:
    • Accurate measurement of axial length and central corneal power with
    • Appropriate intraocular lens (IOLs) 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 and cross-contamination
  • Biometry should be done before instillation of dilating drops and 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 within the range of 21-25.5 mm and most corneas are relatively regularly curved and similar between the 2 eyes of each individual
  • Formulas for calculating IOL 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 IOL selection process that should be used are the recent-generation theoretical IOL power calculation formulas eg Hoffer Q, Holladay and SRK/T, Haigis
  • It is recommended that the eventual optimization of lens constants for a specific IOL will be based on an individual ophthalmologist’s actual refractive outcome
  • The ophthalmologist should consider the patient’s desires and needs in selecting an appropriate post-op refractive target

Surgical Procedures

Extracapsular Cataract Extraction (ECCE)

  • Main requirement for ECCE and posterior IOL is zonular integrity
  • Retention of the integrity of the posterior capsule

ECCE by Nuclear Expression

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

ECCE 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 IOL
  • Most common and preferred method of cataract extraction
  • Advantages: Only requires a small incision (results in less suture-induced astigmatism) and may be closed with a single suture or without sutures, quicker surgery, uses topical anesthesia, more predictable refractive results, maintains the normal depth of the anterior chamber and 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 (OVD) is used to protect the corneal endothelium, manipulate tissues and maintain adequate working space for surgery
  • Capsulorrhexis is a continuous curvilinear capsulotomy that facilitates hydrodissection, prevents posterior capsule tears and facilitates the implantation, fixation and centration of the IOL within the capsular bag
  • Hydrodissection reduces the zonular stress during phacoemulsification by mobilizing the nucleus and epinucleus
  • Nuclear disassembly and emulsification
  • Thorough removal of remaining epinucleus and cortex
  • Implantation of foldable IOL with injector and centration of a small-incision IOL within the capsular bag
  • Removal of the OVD 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 with less sophisticated equipment and no operating microscopes and irrigating systems available
  • Seldom done due to several disadvantages and post-op complications: Very large limbal incision (160-180 degrees), delayed healing and visual rehabilitation, iris and vitreous incarceration, significant against-the-rule astigmatism, post-op wound leaks, and significant endothelial cell loss

Femtosecond Laser-assisted Cataract Surgery (FLACS)

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

Manual Small Incision Cataract Surgery (MSICS) or Sutureless Small Incision Cataract Surgery (SICS)

  • Lens is removed manually by dividing mechanically into smaller pieces without performing phacoemulsification, then removed from the eye through a small incision through which a foldable lens can be implanted
  • Less or no sutures are needed as compared to ECCE
  • May be preferred in patients with mature nuclei, weak zonules or increased risk of corneal decompensation
  • Advantages include lesser post-op physical restrictions, decreased post-op inflammation, lesser unwanted astigmatic change and earlier and more long-term stability of the refraction

Intraocular Lenses (IOLs)

  • Posterior chamber IOL implantation in the capsular bag is the method of choice to correct aphakia, unless contraindicated
  • Factors to consider in choosing the IOL to use: IOL material, incision size, optic size, haptics, method of insertion, function options, uveal and capsular biocompatibility, documented evidence of safety and effectiveness
  • Foldable IOL 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 and the design of the IOL intended for capsular bag fixation is or is not appropriate for ciliary sulcus placement

Optical and Refractive Considerations

  • The decreased visual acuity in cataract is brought about by the positive spherical aberration of the lens
    • By replacing the cataract eye with an aspheric IOL, 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 IOL can be used
  • Monovision- and presbyopia-correcting IOL 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 with the image from the in-focus eye
    • Multifocal presbyopia-correcting IOL 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 IOL is designed to change position or shape in the eye with accommodative effort

Complications

Major Complications that are Potentially Sight Threatening

  • Infectious endophthalmitis
    • Rare (1 in 10,000) but most feared complication of cataract surgery
    • Cardinal symptoms are ocular pain, redness, blurry vision and eyelid edema
    • 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
    • Risk factors include older age of patient, posterior capsule rupture, vitreous loss, prolonged surgical time, resident-performed surgery, immunocompromised patient, improper incision construction with wound leakage, and topical anesthetic gel application prior to povidone iodine
    • It has been found that the type and size of incision as a possible factor in the development of endophthalmitis
    • Immediate retina specialist referral is recommended within 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, vitreous loss, younger age, male gender, lattice degeneration, zonular dehiscence, retinal detachment in the other eye, post-operative posterior vitreous detachment
  • IOL dislocation
  • Toxic anterior segment syndrome (TASS)
    • Rare; a sterile, post-op, inflammatory reaction that usually occurs 12-48 hours 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 with preservatives and re-sterilized viscoelastics)
    • Clinical findings include severe anterior chamber cells and flare, fibrinous reaction, hypopyon, and diffuse limbus-to-limbus corneal edema
    • Usually responds to anti-inflammatory treatment however, permanent intraocular damage may occur
  • Cystoid macular edema (CME)
    • Clinically significant cystoid macular edema is not common
    • Has deleterious optical effect on vision with advanced technology IOLs
    • Responds well to topical medical therapy; recalcitrant cases may result to visual acuity permanent impairment
    • Risk factors include: Previous uveitis, posterior capsule rupture with vitreous loss, retained lens material, diabetic retinopathy, venous occlusive disease, epiretinal membrane, prior vitreoretinal surgery, nanophthalmos, retinitis pigmentosa, radiation retinopathy, male gender, older age, history of pseudophakic CME in the other eye
    • Optical coherence tomography (OCT) is used for anatomic diagnosis
    • Topical anti-inflammatory medications are used to prevent and treat established CME
  • Persistent corneal edema
  • Posterior capsule tear or zonular rupture
    • Risk factors include male gender, older age, glaucoma, diabetic retinopathy, brunescent or white cataract, posterior polar cataract, inability to visualize the posterior segment pre-op, pseudoexfoliation, small pupils, axial length >26 mm, use of systemic alpha-1a antagonist, previous trauma, coexisting comorbidities, inability of the patient to lie flat, and resident-performed cataract surgery
    • Intraoperative risk factors include miosis, floppy iris syndrome, loose zonules and need for capsular stain
    • Intraoperative posterior capsule rupture may be treated with anterior vitrectomy
  • Endothelial cell loss 

Other Post-operative Complications (early, intermediate, and late)

  • Ocular hypertension
  • Wound leak with shallow, flat, or well-formed anterior chamber
  • Iris prolapse or vitreous in the wound
  • IOL dislocation, decentration/pupillary capture
  • Corneal decompensation
  • Anterior uveitis
  • Anterior ischemic optic neuropathy
  • Posterior capsular opacity
  • Malignant glaucoma
  • Endophthalmitis
  • Ptosis
  • Diplopia
  • Hyphema
  • Choroidal detachment
  • Epithelial downgrowth
  • Pseudophakic CME
  • Prolonged inflammation

Incision Complications

  • Incision that is not watertight may lead to post-op wound leak, hypotony and endophthalmitis
  • There is an increased risk of wound burn and lesser ability to cool the ultrasonic phacoemulsification if the incision is too small, while too big incision can cause destabilization of the anterior chamber and 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 and it is dependent on the location and 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 IFIS in patients taking Tamsulosin
  • Intracameral epinephrine, viscomydriasis and 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 with phacoemulsification tip
    • Sphincterotomies
    • Excessive stretching or manipulation with expansion devices and instruments

Corneal Complications

  • Descemet’s membrane tears or detachment is the result of improper instrument entry into the anterior chamber
  • By repositioning and tamponading the flap of the Descemet’s membrane with an air bubble, large tears can be repaired
  • Prolonged elevated IOP and phacoemulsification time (ultrasonic energy) can result to further endothelial decompensation and corneal edema

Retained Lens Fragments

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

Intraocular Pressure (IOP)

  • Transient elevation of IOP is a recognized tendency during the early post-op period
  • It causes pain and some eye may be more susceptible to vascular occlusion or optic nerve damage
  • If there is an excess amount of OVD remains in the eye at the close of surgery, there is an increased likelihood of having elevated IOP and thorough OVD removal should be attempted
  • Although unclear, it appears that topical aqueous suppressants and intracameral Carbachol are beneficial in immediate post-op elevated IOP prophylaxis
  • Topical corticosteroids use increases the risk of elevated IOP 
    • Although cataract surgery has been found to reduce IOP, at least transiently, in patients with angle closure or without glaucoma

Intraocular Lens (IOLs) Complications

  • IOLs dislocation occurs when the IOL 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 IOL may dislocate causing the capsule to be partially torn or the zonules broken
  • Patient usually presents with sudden vision loss and/or diplopia
  • Inferior direction of displacement of the posterior chamber IOL known as “sunset syndrome” is the most common direction of displacement
  • Limiting physical activity that would aggravate the dislocation of the IOLs is advised to patients prior to prompt referral to the ophthalmologist
  • Positive dysphotopsia includes ghost images, starbursts and arcs, rings or flashes of light and 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 OVD in the bag, improper haptic or optic placement, capsulorrhexis diameter and inversion of the IOL are factors that can affect the effective lens position

Posterior Capsular Opacification

  • Often occurs after ECCE; causes gradual decrease in visual function
    • Newer sharp-edge IOLs have been shown to decrease incidence
    • Visual deterioration is more significant with multifocal IOLs
  • 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 and restore visual function and to improve contrast sensitivity

Second Eye Surgery

  • Cataract surgery for both eyes is an appropriate treatment for patients with 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
  • Indications for second-eye surgery are the same as the first eye surgery
  • Factors that would determine the interval between the first-eye surgery and the second-eye surgery:
    • Patient’s visual needs and preferences
    • Visual acuity and function of the second eye
    • Medical and 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 IOL power for the second eye
  • Delayed sequential bilateral cataract surgery (DSBCS) is preferred over immediate sequential bilateral surgery (ISBCS) for patients with bilateral senile cataracts
    • ISBCS may be performed in the following circumstances:
      • General anesthesia is needed in the presence of bilateral visually significant cataract
      • When travel for surgery and follow-up care is significantly difficult for the patient
      • Patient’s health does not allow for >1 surgical encounter
    • Disadvantages of ISBCS include the possibility of bilateral infection, reduced possibility of optimization of post-op refractive error and reduced possibility for modification of regimens based on any complications in the 1st eye
  • There should be enough interval time to diagnose and treat any early complications of the first-eye surgery before the patient and the ophthalmologist be satisfied with the recovery and 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 and vomiting are controlled
  • Absent or minimal pain
  • Follow-up appointment has been scheduled
  • Post-surgical care has been reviewed with the patient and caretaker and written post-op instructions have been provided
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