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.

Physical Examination

Ocular Evaluation

  • Ocular examination involves assessment of any other diseases that might contribute to the symptoms or limit the potential for good vision following cataract surgery
  • Determine visual acuity under low & high illumination
    • Gives objective evaluation of the impact of cataract
    • Excellent method for testing distance refractive error in healthy eyes
  • Check refraction to rule out refractive shift as a cause for the decreased vision
  • Perform dilated examination of the lens, macula, peripheral retina, optic nerve & vitreous
  • Examine the ocular surface to see if there is a presence of dry eye as it is increasingly being recognized as a complication of post-cataract surgery
  • Measure for intraocular pressure (IOP)
  • Assess ocular motility & binocularity

Biomicroscopy w/ pupillary dilation

  • Used to evaluate the 3 clinical zones of the lens, & the classification & quantification of the cataract

Dilated fundoscopy

  • Obstruction of the red-orange reflex is noted
  • Used to evaluate the presence of ocular conditions that may complicate cataract (eg glaucoma & retinal problems)

External examination of lids, lashes & lacrimal apparatus

  • Used to rule out any external ocular infections (eg blepharitis) & blocked nasolacrimal duct

Screening

Supplemental Tests

  • Used to identify the cause & the level of severity of the patient’s visual symptoms, & functional disability as well as the extent to which comorbidities may be contributing to these symptoms

Glare testing

  • Determines the degree of visual impairments by swinging a light source in the patient’s visual field
  • Presence of severe visual disability in brightly lit conditions (eg ambient daylight) is typical of cataracts
  • To see if the patient’s symptoms of functional disability is far worse than suggested by visual acuity measurements

Contrast sensitivity

  • Measures visual function by testing the ability of the eyes to detect subtle variations in shading by using figures that vary in contrast, luminance & spatial frequency
  • Uses linear sine-wave gratings

Wavefront aberrometry

  • Measures the optical quality in terms of spatial distortion

B-scan ultrasonography

  • Used when a dense cataract precludes adequate visualization of the posterior segment or to confirm the presence of posterior staphyloma
  • Establishes that the retina is attached; may be used to identify any intraocular masses

Electrophysiologic testing

  • The electrical response to visual stimuli presented is measured & potential retinal function in nonverbal patients is indicated

Assessment

Assessment & Grading of Cataracts

  • Done through the use of direct ophthalmoscopy w/ retroillumination, lens opacification classification system II (LOCS-II) slit-lamp grading system
  • Most commonly done in cataract research, in studies to define causation, & in clinical trials of anticataract drugs
  • Surgical removal of the cataract remains the only effective treatment available to restore or maintain vision
  • Visual acuity, visual impairment & potential for functional benefits should be the primary considerations

Indications for Cataract Surgery

  • Visual function does not meet the patient’s needs & for which cataract surgery can provide reasonable likelihood in obtaining improved vision is the primary indication for surgery
  • Presence of clinically significant anisometropia
  • The opacity of the lens affects the optimal diagnosis or management of posterior segment conditions
  • The lens causes inflammation or secondary glaucoma
  • The lens induces angle closure or angle-closure glaucoma

Contraindications for Cataract Surgery

  • The refractive correction is tolerable & provides the patient’s vision needs & desires
  • Surgery is not expected to provide improvement in visual function & no other indications for lens removal exist
  • The patient has coexisting ocular or medical conditions that may cause the patient not to safely undergo the surgery
  • Appropriate post-op care cannot be arranged
  • The patient or patient’s surrogate decision maker is unable to give informed consent for nonemergent surgery

Classification

Cortical cataract

  • Liquefaction of the lens fibers is due to electrolyte imbalance that leads to over hydration of the lens
  • Glare is the usual complaint & vision is not much degraded
  • Slit lamp: Shows white spoke-like opacities in the outer layers of the lens w/ formation of vacuoles, clefts, wedges or lamellar separations

Nuclear cataract

  • Caused by deamidation of the lens proteins by oxidation, proteolysis & glycation
  • Progression is slow & affects distance vision more than near vision
  • Slit lamp: Reveals an opaque nucleus, manifested as a yellow-brown hazy structure at the center of the lens that interferes w/ visual function
  • The lens becomes brown & opaque in advanced cases

Posterior subcapsular cataract (PSC)

  • It is found to be associated w/ trauma & systemic & topical steroid use
  • The usual symptoms are glare & poor vision w/ bright lighting
  • Progress quickly & near vision is more affected
  • Slit lamp: Reveals “frost like” haze just anterior to the posterior lens capsule which is the back surface of the lens
  • Commonly affects young patients

Immature cataract

  • The retina is still visible & transmits a red reflex
  • Vision is only mildly decreased

Mature cataract

  • There is absence of red reflex
  • Parts of the cortex becomes white & opaque usually in a heterogenous pattern
  • Vision is at 20/40 level or usually worse

Hypermature cataract

  • The nucleus of the lens is mobile w/in the capsule & the cortex of the lens is liquefied
  • Increased risk of phacolytic glaucoma
  • Increased difficulty of surgery
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