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.

Pharmacotherapy

  • Consists of pre-operative, intra-operative, & post-operative medications

Pre-operative Agents

  • Used to dilate the pupils, as anti-infective prophylactic agents, & as anesthetics

Pupil Dilatation

  • Mydriatic & cycloplegic agents are used together before extracapsular nuclear expression or phacoemulsification
    • Eg Tropicamide (cycloplegic), Phenylephrine (mydriatic)
  • Non-steroidal anti-inflammatory drugs  are used to prevent pupillary miosis, decrease inflammation due to surgery, decrease intra-operative pain, & prevent post-operative cystoid macular edema
    • Eg Diclofenac, Ketorolac, Nepafenac
    • Diclofenac effectively maintains mydriasis during surgery

Anti-infective Prophylaxis

  • Pre-operatively, the most important source of infection is the patient’s own conjunctival & lid skin flora
  • Common infecting agents are: Staphylococci, diphtheroids, streptococci, gram negative bacilli
  • 4th generation fluoroquinolones are the preferred agents because they penetrate better, have broader spectrum of coverage, & have lower incidence of resistance
  • Moxifloxacin appears to have better tissue penetration than Gatifloxacin, although equally safe
  • Complete conjunctival sterility, through the elimination of natural flora, is not usually possible w/ the use of anti-infective prophylaxis
  • Povidone-iodine (5%), a topical antiseptic, dropped into the conjunctival sac pre-operatively & allowed to stay for at least 2 minutes is one of the most effective way to decrease the bacterial flora
    • Appears to be equally effective as pre-op topical antibiotics
    • The presence of lidocaine gel prior to povidone-iodine instillation appears to diminish its antimicrobial efficacy

Anesthetics

  • The choice of anesthesia to be used, the expected pain, discomfort, consciousness level, visual experiences & complications should be discussed w/ the patient
  • Safety, efficacy & completion of surgery w/ the least pain & lowest risk for the patient should be considered in choosing the type of anesthesia to be used
  • General anesthetics are indicated for patients w/ medical, psychosocial & surgical indications, who are unable to comply w/ instructions or unable to communicate
  • Local or regional is the most preferred mode of anesthesia
    • Most commonly used - topical
    • Other examples - peribulbar or retrobulbar inj, sub-Tenons inj, & intracameral
    • Sharp needle local anesthesia techniques have a higher risk of ocular & systemic complications than topical techniques & should only be used when the anesthetist & ophthalmologist consider it absolutely necessary
    • Disadvantages: Increased surgical difficulty in the absence of akinesia & possible need to augment the anesthesia in the event of intra-operative complications
    • Patient cooperation & ability to follow instructions are essential

Intra-operative Agents

  • Include irrigating solutions & its additives, ophthalmic viscosurgical devices, & intracameral antibiotics
  • Generally, the addition of mydriatics, antibiotics, epinephrine, or lidocaine, is not recommended by the companies that produce irrigating solutions for cataract surgery due to possible effects on the pH, chemical stability, or osmolarity
    • Hence, caution is warranted
  • Use of antibiotics intracamerally is controversial
    • Surgical techniques may play the most critical role in contamination (eg anterior chamber), & that antibiotics administered w/ the irrigating solutions may only minimally contribute to reduce the risk of endophthalmitis
  • Intracameral antibiotics are effective in reducing post-operative endophthalmitis rates
    • Intracameral Cefuroxime was noted to be effective in producing 80% reduction
    • Several studies have indicated that intracameral Moxifloxacin injection may be safe for use for endophthalmitis prophylaxis
  • Choice of miotic agents depends on the desired clinical features
    • Acetylcholine takes <1 minute to act, relatively brief duration of action, miosis for 10 minutes
    • Carbachol has an onset of time of 2 minutes, 2-24 hours duration of action

Post-operative Agents

Antibiotics

  • Treatment duration may vary from 5 days for uncomplicated cases, to weeks for prolonged inflammation
  • Choice of antibiotics depends on the presence of drug resistance, eg Gentamicin vs Moxifloxacin or Gatifloxacin
  • Route of administration may also vary, but topical is the most prevalent
  • Subconjunctival injections deliver high levels to the aqueous humor but have a greater risk of eye perforation, macular infarction, subconjunctival hemorrhage & retinal toxicity
  • Oral or parenteral route may reach substantial levels in the anterior chamber but do not provide any advantages over topical routes; tantamount to increased side effects

Corticosteroids & Non-Steroidal Anti-inflammatory Drugs (NSAIDs)

  • Both appears to be equally efficacious in reducing post-operative noninfectious inflammation
    • No difference in astigmatic decay
  • Topical steroids (eg Prednisolone acetate & Dexamethasone phosphate) are most commonly used
  • Non-steroidal anti-inflammatory drugs may be used in patients w/ contraindications to corticosteroids & w/ herpes simplex infection
  • Non-steroidal anti-inflammatory drugs  are contraindicated in patients w/ compromised ocular surfaces
  • Increased risk of corneal or scleral perforation in the presence of epithelial defect when non-steroidal anti-inflammatory drugs  are used alone, w/o concomitant administration of corticosteroids
  • Pretreatment w/ an non-steroidal anti-inflammatory drugs  reduces post-op inflammation as long as the drug is administered over a period of 3 days
  • Addition of non-steroidal anti-inflammatory drugs  to antibiotic-corticosteroid combination has been reported to reduce the incidence of noninfectious post-op inflammatory conditions
  • Rimexolone has been shown to have less potential to cause increase in intraocular pressure compared to Dexamethasone, Prednisolone, or Betamethasone

Non-Pharmacological Therapy

  • Counsel the patient regarding cataract-related visual symptoms
  • Give reassurance about the cause of visual disability
  • Prescribe new eyeglasses (lenses w/ equal base curves & center thicknesses) where appropriate to improve vision
  • Control illumination to reduce glare problems by incorporating filters into the spectacles
  • By using a filter that blocks light w/ wavelengths shorter than 480 nm, an improved visual acuity & contrast sensitivity may be obtained
  • Modify exposure to risk factors (eg smoking cessation, blood sugar level control)
  • Inform patients that are long-time users of corticosteroids that they have high risk of having cataract & should seek consult to their physician for alternative
  • Avoid exposure to ultraviolet B (UVB) lights by wearing brimmed hats & ultraviolet B (UVB)  blocking sunglasses
  • Maintain body mass index (BMI) at <27.8 as values greater have increased risk of developing cataract
  • Follow up at 4- to 12-month intervals should be done to evaluate ocular health & vision & to determine whether functional disability develops
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