What Is a Cataract?
A cataract is a clouding of the eye's natural crystalline lens. It is the leading cause of reversible blindness worldwide and is most commonly age-related, though other causes exist. The lens sits behind the iris and normally remains clear, focusing light onto the retina. When proteins within the lens denature and aggregate, transparency is lost and visual quality degrades.
Types of Cataracts
Cataracts are classified by their location within the lens:
| Type | Location | Symptoms | Common Cause |
|---|---|---|---|
| Nuclear sclerotic | Central nucleus | Gradual blur, myopic shift, worse distance vision | Aging (most common) |
| Cortical | Lens cortex (spokes) | Glare, halos, contrast loss | Aging, UV exposure, diabetes |
| Posterior subcapsular (PSC) | Posterior capsule | Worse in bright light or reading; glare | Steroids, diabetes, radiation, trauma |
| Anterior subcapsular | Anterior capsule | Variable blur | Trauma, atopic disease |
| Congenital | Variable | Leukocoria, poor fixation in infant | Genetic, intrauterine infection, metabolic |
💡 Clinical Tip: Posterior subcapsular cataracts (PSC) cause disproportionate visual symptoms early in the disease because they are located directly in the visual axis. Patients with PSC often report that bright sunlight or oncoming headlights are particularly bothersome -- the small pupil in bright light magnifies the central PSC's effect.
Symptoms and Visual Changes
Common cataract symptoms include:
- Gradual blurring of vision (distance or near)
- Glare and halos around lights, especially at night
- Difficulty with bright light (photophobia)
- Colors appearing faded or yellowed
- Myopic shift (index myopia) -- nuclear cataracts can increase refractive power, temporarily improving near vision ("second sight of the aged")
- Monocular diplopia (double image in one eye)
Risk Factors
- Increasing age (primary risk factor)
- UV-B radiation exposure
- Diabetes mellitus
- Systemic or topical corticosteroid use (causes PSC)
- Smoking and alcohol use
- Prior ocular trauma or surgery
- Family history / genetic factors
Diagnosis
Cataracts are diagnosed by slit lamp examination after pupil dilation. The physician evaluates lens clarity, density, and the type of opacity. Dilated retinal examination is also performed to ensure there is no concurrent posterior segment pathology (such as AMD or diabetic retinopathy) that might limit post-surgical visual recovery.
🔑 Key Point: When patients present with reduced vision, a potential acuity meter (PAM) or other potential acuity test may be used to estimate post-surgical visual potential through a clear area of the lens. This helps set appropriate patient expectations.
Surgical Management
The only effective treatment for cataracts is surgical removal. Modern cataract surgery is phacoemulsification (phaco), performed under topical or local anesthesia:
- A small incision (2-3 mm) is made at the limbus
- The anterior capsule is opened (capsulorhexis)
- Ultrasound energy emulsifies and aspirates the lens nucleus and cortex
- The posterior capsule is left intact as a scaffold
- An intraocular lens (IOL) is inserted into the capsular bag
IOL Types
After lens removal, an IOL restores focusing ability. IOL types include:
- Monofocal IOL -- corrects for one distance (usually far); patient may need reading glasses
- Multifocal IOL -- corrects multiple distances; may cause halos/glare
- Toric IOL -- corrects astigmatism in addition to sphere
- Extended depth of focus (EDOF) -- intermediate range with fewer halos than multifocals
Posterior Capsule Opacification (PCO)
Weeks to months after cataract surgery, residual lens epithelial cells can migrate and cause the posterior capsule to become cloudy -- called posterior capsule opacification (PCO) or "secondary cataract." This is treated with a YAG laser posterior capsulotomy, a quick, painless outpatient procedure that restores clarity by opening the clouded capsule.
⚠️ Common Mistake: PCO is not a recurrence of the cataract -- the natural lens has been removed. It is clouding of the capsule that was left behind. Patients often think their cataract came back, and it is important to explain this distinction clearly.
The CPOA's Role in Cataract Care
- Obtaining best-corrected visual acuity pre- and post-operatively
- Performing pre-op measurements: keratometry, A-scan biometry, axial length, IOL power calculation
- Reviewing surgical consent and post-op instructions with patients
- Instilling pre-operative dilating drops and anesthetic drops
- Assisting with surgical preparation (sterile draping, instrument setup)
- Post-op: checking visual acuity, IOP, and anterior segment for complications
- Educating patients about post-op drop schedules and activity restrictions
Key Takeaways
- Cataracts are lens clouding; nuclear sclerotic is most common; PSC causes early, severe glare symptoms
- Steroids are a major cause of PSC cataracts
- Nuclear cataracts can cause a myopic shift ("second sight")
- Phacoemulsification is the standard surgical technique; an IOL is implanted into the capsular bag
- PCO ("secondary cataract") is treated with YAG laser capsulotomy, not repeat surgery
- The CPOA assists with pre-op biometry, surgical prep, and post-op monitoring