A cataract is most simply defined as an opacification of the lens that leads to measurable decreased visual acuity or some functional disability as perceived by the patient.2
The Many “Flavors” of Cataracts
Nuclear Sclerotic Cataract:A nuclear sclerotic cataract is the most common type of aging cataract. Nuclear sclerosis (NS) typically causes a myopic shift in refractive error due to an increase in the refractive index of the crystalline lens. Elderly patients often report a “second sight” due to their newfound ability to read without spectacles.
Patients present with complaints of decreased contrast and increasing glare, especially while driving at night. Patients may also notice a distortion in color vision, as these cataracts can mimic the perception of looking through a yellow filter.
NS starts in the center of the lens at the embryonic nucleus. As this cataract progresses, the lens becomes more yellow (“brunescence”). A doctor can grade these cataracts based on opalescence, as well as color, in which the physician would use an optic section through the lens in order to grade them.
These cataracts can be graded on a scale of trace to 4+, with trace being only a slight, faint yellowish discoloration and 4+ being a brown coloration to the cataract. Grade 1+ is a pale, pastel yellow, and grade 2+ is a brighter, vivid yellow. Grade 3+ is a very deep, dark yellow discoloration to the lens.
NS is the most common reason for cataract surgery, and cataract surgery would want to be done at the time of 3+ or 4+ with patient complaints, if the other cataract surgery criteria is also met. The longer these cataracts stay in the eye, the higher the chances of complications during their removal surgery due to the increase in the density of the cataract. If left in the eye for an extremely long time, cataracts may become so dense that they become white. White cataracts are often difficult in cataract surgery where they are pressurized. Often, an extra-capsular extraction must be completed if phacoemulsification does not fragment the lens.1
Cortical Cataract:A cortical cataract is a radial, spoke-like opacity that begins near the outer edge of the crystalline lens and progresses towards the center. Cortical cataracts affect the middle layers of the cornea, and the spokes can be either white and hazy in appearance or a darker appearance. The closer the spokes get to the visual axis, the more likely they are to affect visual acuity. These cataracts often induce a hyperopic shift.
This type of cataract is also very common with the aging population and in those with diabetes mellitus. Patients with cortical cataracts often have the complaint of glare, with patients having trouble at night due to glare and contrast issues. Cortical cataracts should be examined with retro illumination, as retro makes the peripheral spokes very visible and clearly demarcates them.
These cataracts are graded trace to 4+. Trace is barely any cortical spokes, and 4+ is when more than 90% of the lens shows spokes. Grade 1+ is when <10% of the lens has a spoke, and Grade 2+ is then 10-50% of the lens displays a spoke. Grade 3+ shows 50-90% of visible spokes. These cataracts are less likely to go to surgery.2
Anterior Subcapsular Cataract:An anterior subcapsular cataract (ASC) is located directly underneath the anterior lens capsule. These cataracts can be easily seen with a cross-sectional beam after dilation. ASCs are common age-related changes in the elderly.2
Posterior Subcapsular Cataract:Posterior subcapsular cataracts (PSC) form directly in front of the posterior lens capsule and often affect near vision more than distance vision. These cataracts are more common in younger individuals and are often associated with systemic or topical steroid use, as well as with X-rays. PSC can progress quickly and are associated with myopic shifts.
The main complaint with these cataracts is trouble with near, especially when reading. Since this cataract is at the nodal point of the eye, it affects near vision the most when the eye focuses at near and the pupil becomes miotic. Even a mild PSC can cause significant and marked reduction in visual acuity, with glare being worse compared to other types of cataracts.
PSC is best examined with retro-illumination, as this allows the opacity to be localized centrally within the posterior lens. Additionally, PSC can be seen in cross-section with dilation. PSC will appear hazy, white, and granular inside the posterior capsule itself. There can also get a bubbly, granular appearance. These cataracts can be graded on a scale of trace to 4+, with trace being barely any visible opacification. Grade 1+ is when <5% of the posterior capsule is obscured, and Grade 2+ is when approximately 30% of the capsule is obscured. Grade 3+ is when 50% of the capsule has opacification, and Grade 4+ is when >50% obscuration is visible.2
Christmas Tree Cataract:Christmas tree cataracts are colorful opacities in the deep cortex and nucleus of the crystalline lens. When viewed, these opacities are red, green, and gold-colored particles or sparkles. The refractive bodies can also be purple, and they often look like “Christmas tinsel,” hence their name. These are not as common as other forms of cataracts, but they are an age-related change as the lens ages over time. Christmas tree cataracts are, however, common in individuals with myotonic dystrophy.1
Infantile or Congenital Cataract:These cataracts are present at birth, with approximately 50% being autosomal dominant inheritance. Diagnosis includes ruling out other forms of leukocoria. These cases are usually bilateral in two-thirds of patients, with unilateral cases usually being sporadic, without systemic associations. They are associated with galactosemia and rubella. Recreational drugs and tetracycline are suspicioned to cause congenital cataracts, but there is no specific or confirmed drug to cause these cataracts.
The most common type of congenital cataract is lamellar or zonullar, which consists of lens opacification surrounding the embryonic nucleus. Surgical treatment is based on visual significance, such as red reflex and fundus view. If the surgery is too premature in life, the risk of glaucoma significantly rises. Surgeons must weigh the risks of amblyopia and glaucoma since up to two-thirds of patients that undergo congenital cataract surgery develop glaucoma within a decade of the procedure (especially if the surgery is done within the first month of life). Additionally, infants cannot complain about a decrease in visual acuity, and these patients will be aphakic after the surgery. Therefore, they will have to wear extended wear CL where the lens will change and become more myopic as the child grows and develops.1
Cerulean Cataract:Cerulean cataracts are a type of congenital cataract that rarely affects visual acuity. Tiny dot or flake-appearing blue opacities can be seen in this type of cataract.2
Presenile Cataract:Presenile cataracts are associated with premature cataracts in younger individuals, and a thorough case history and symptoms can help distinguish these cataracts from other forms of cataracts. These cataracts are associated with diabetes mellitus, myotonic dystrophy, Wilson’s disease, hypocalcemia, and atopic dermatitis. These conditions can cause an imbalance of Ca2+ and, therefore, cause cataract development.
- Diabetic “snowflake”: With these cataracts, faint “snowflakes” around the edges of the lens in a 30-year-old can be seen. Glucose floats in the blood and is filtered by the aqueous. In diabetic patients, glucose gets into the lens and is converted to sorbitol. This leads to high water content in the lens that changes the focal point to more myopic when the blood levels are higher. Higher glucose levels, in other words, leans to increased lens opacities. Therefore, diabetic cataracts are due to the fact that high glucose/sorbitol swells the lens, causing fluctuating refractive error. Diabetic cataracts are the common type of cataracts seen in adults with systemic diseases (excluding children). NS can also commonly be seen in patients with DM.
- Myotonic dystrophy: Approximately 90% of patients with myotonic dystrophy develop cortical opacities by twenty years of age, of which being visually disabling by forty years of age. Theses opacities go undetected until the patient is in his/her 20’s, generally.
- Atopic dermatitis: Approximately 10% with severe disease develop cataracts at the time of teenage years and up, with most having dense ASC cataracts. The lens will thicken and scale.1
Traumatic Cataract:Traumatic cataracts are associated with a star-shaped or flower-shaped opacification and is known as a rosette cataract. These cataracts are caused by blunt trauma or other ocular injuries, such a being hit in the eye with a paintball or baseball. Traumatic cataracts can be associated with other injuries of the eye, and the physician should examine the anterior lens capsule for iris pigment (known as a Vossius ring). Often, iridodialysis can be seen, where the iris is torn away from the root. There are often issue with zonules being broken. These cataracts are usually and more-likely unilateral, unless trauma occurs to both eyes. Patients are often hit directly in the eye, causing this type of cataract to form. Rosette cataracts develop one month after trauma.
- Electric shock-induced: When electrocution coagulation lens proteins and damages lens epithelium, osmotic changes occur. This type of shock changes the tertiary structure of proteins. Swelling leads to opacification, and the opacification occurs after a while after the shock. This type of cataract is not instantaneous.
- Radiation-induced: Infrared radiation can be seen in glassblowers, in which true anterior capsule exfoliation can be seen. The lens capsule or surface peels off and flakes off of the lens. The lens capsule radiates away.
- Ionizing tumor treatment: With focal tumor treatment to the orbit or eye, PSC changes can occur in months to years. These changes do not happen immediately.1
Toxic Cataract:Anterior subcapsular cataracts can be due to chlorpromazine, amiodarone, miotics, and gold salts. Posterior subcapsular cataracts can de due to corticosteroids.2
Vacuoles:This type of toxic cataract can be throughout the lens but commonly around the posterior cortex. Additionally, these forms of cataracts are rarely symptomatic. A vacuole will look like a clear bubble within the lens, and these cataracts are often clustered together centrally (thus mimicking PSC). These bubbles are not something to worry about and often don’t impact vision since they are not a true opacity. You can also see larger vacuoles, often peripherally.1 These bubbles are not something to worry about and often don’t impact vision since they are not a true opacity.
Secondary Cataract:Chronic anterior uveitis, acute angle closure, high myopia, retinitis pigmentosa, Stickler’s syndrome, and gyrate atrophy are all conditions in which secondary cataracts can develop due to these diseases and conditions.
- Chronic anterior uveitis: These cataracts are due to inflammation and subsequent steroids used to treat it.
- Acute angle closure: Central anterior opacities composed of necrotic lens epithelial cells and degenerated subepithelial cortex are visible, also known as glaucomflecken. Cross section just in front of the capsule at the surface of the lens will show grey discoloration. This atrophy is due to high IOP.
- Retinitis pigmentosa, gyrate atrophy, and Sticker’s syndrome: These conditions are fundus dystrophies where PSC are more common than ASC.
- Pathological myopia: Opacification of the lens often occurs early on in life in patients with high myopia.1
Medicare and insurance coverage of cataract surgery varies by region, but generally three things are needed to be documented for coverage of the procedure. First, there must be an effect on activities of daily vision (ADV). The patient must complain of a decrease in vision, increased glare while driving, decreased contrast sensitivity and issues recognizing faces, or other related issues. Second, the best corrected visual acuity (BCVA) must be 20/50 or, if better than that, two lines worse with glare testing. A brightness acuity test (BAT) can be performed to test glare. Third, the optometric physician must rule out other causes of poor BCVA. A dilated fundus exam must be performed to rule out possible pathology, such as age-related macular degeneration, macular edema, and retinitis pigmentosa.1
Bowling, B., & Kanski, J. J. (2016). Kanski’s clinical ophthalmology: a systematic approach (8th ed.). Edinburgh: Elsevier.
Cheatham, K. M., Cheatham, M. A., Wood, K. B., & KMK Educational Services, LLC. (2007). KMK part one : basic science review guide (12th ed.). Overland Park, Ks: Kmk Educational Services, LLC.