About Cataracts
Updated: Mar 20
Introduction
A cataract is a clouding of the natural crystalline lens inside the eye, leading to a drop in vision. It is one of the leading causes of vision impairment and blindness worldwide, particularly in older adults.
Cataracts develop gradually and can affect one or both eyes. They occur when proteins in the lens break down and clump together, causing cloudiness. While cataracts can be age-related, they can also result from trauma, certain medications, or medical conditions like diabetes.
Signs and Symptoms
Blurry or cloudy vision:
The most common symptom, especially when looking at objects in bright light or when driving at night. This can come on gradually or more quickly depending on the type of cataracts and the progression. This is a symptom commonly picked up at optical shops - the optician may realise that your vision has dropped since the last visit.
Difficulty seeing at night:
Cataracts often cause glare, halos around lights, and reduced contrast sensitivity, particularly in low-light environments, such as when walking about at night or watching a movie in a cinema.
Fading or yellowing of colors:
The clouded lens reduces contrast and causes colours to look less vibrant, and can cause a yellow or brown tint to vision, and in severe cases affect the ability to distinguish colors.
Frequent changes in prescription glasses or contact lenses:
A cataract’s progression may lead to frequent adjustments in vision correction or spectacles prescription, so if you are changing your glasses more often, it could be a sign of cataracts.
Double vision in one eye:
This can occur in more advanced stages of cataract development or in certain types of cataracts, where there seems to be a lighter or faded copy of objects you are looking at.
Increased sensitivity to light and glare:
Bright lights or sunlight can become irritating, and halos may appear around lights such as a ceiling spot light or around car headlights.
Diagnosis
Cataracts are diagnosed through a comprehensive eye exam, which includes:
Visual acuity test: To assess how well you can see at various distances, to determine the extend of visual impairment.
Slit-lamp examination: A slit of light is used to examine the eye’s structures using a bio-microscope, including the lens, to detect any presence of cataract.
Retinal examination: The back of the eye is often also examined, to determine if there may be any other underlying causes of poor or deteriorating vision.
Tonometry: To measure intraocular pressure, as a developing cataract can 'crowd' the anterior (front) chamber of the eye and reduce the outflow of fluid, causing an increased pressure which leads to glaucoma.
Treatment
Non-Surgical Treatments:
Initially, cataracts can be managed with updated glasses prescriptions or magnifying lenses to help compensate for vision changes.
Anti-glare sunglasses or brighter lighting may also help in managing the symptoms, especially for night driving or reading.
Surgical Treatment:
The only effective treatment for cataracts is surgery, which involves removing the cloudy lens and usually replacing it with an artificial intraocular lens (IOL).
Cataract surgery is one of the most common and successful surgeries worldwide, typically performed under local anesthesia. It is done when cataracts significantly interfere with daily activities like driving, reading, or watching TV.
There are different types of surgical techniques, including phacoemulsification (the most common technique) and extracapsular cataract extraction (for more advanced cataracts).
Phacoemulsification, a modern method of cataracts surgery, uses ultrasonic waves to break up the cloudy lens in the eye, before it can be suctioned out. This is typically done through a small incision less than 3mm.
After the cataract is removed, an intraocular lens (IOL) is typically inserted. Options for IOLs include monofocal (for distance), multifocal, and EDOF or extended depth-of-field lenses (which can help with near and far vision). Read more about IOL lens options here. Or, read about what happens during cataracts-removal surgery.
Post-surgery:
Most patients recover quickly and experience significant improvement in vision. However, some may need corrective lenses (glasses or contact lenses) after surgery, depending on the type of IOL used.
Follow-up appointments are necessary to monitor recovery and ensure there are no complications, such as infection or retinal issues.
Prognosis
Cataract-removal surgery for the treatment of cataracts has a very high success rate, with improvement in vision for most patients. Over 90% of patients report better vision after surgery.
Cataracts tend to develop slowly over time, so vision loss happens gradually, which may not be immediately picked up as a concern.
If left untreated, cataracts can lead to significant vision impairment and blindness, particularly in severe cases. However, surgical intervention offers a permanent solution to this problem, restoring quality of life.
As with most surgeries, cataract-removal surgery also carry risks, such as post-operative complications like infection and retinal detachment, but these are rare.
Secondary cataracts (a condition known as posterior capsular opacification) can sometimes occur after cataract surgery, but this can be treated with a quick, non-invasive laser procedure.
Conclusion
Cataracts are a common cause of vision impairment, primarily affecting older adults (senile cataracts). While they can be managed in the early stages with corrective lenses and lifestyle adjustments, the only definitive treatment is surgery.
Cataract surgery is safe and effective, offering most patients significant improvements in vision. Although cataracts can lead to blindness if untreated, early diagnosis and surgical intervention can prevent these severe outcomes. Regular eye exams are key to detecting cataracts early, especially in populations at risk, such as the elderly or those with conditions like diabetes.
Further bedtime reading (of if you are an optometrist):
Biometry - required!
For phacoemulsification (cataracts-removal surgery) with intraocular lens (IOL) implantation, accurate ocular biometry is essential to calculate the correct IOL power and optimize refractive outcomes.
Biometry is the measurement of physical characteristics, and in this case we do it for the eye, and here are the important biometry data we obtain through scans:
Axial Length (AL)
Distance from corneal epithelium to retinal pigment epithelium. This is measured by devices such as the Zeiss IOLMaster or the Haag-Streit Eyestar 900 (or the Lenstar). In some patients where this is not possible, some practitioners will use A-scan ultrasound, which can include the immersion or contact methods.
In the immersion method, the patient lays supine and a cylindrical device is placed on the eyem, which is then filled with saline and a probe is placed inside the solution and readings taken.
In the contact method, the patient can be seated as per normally and a probe is gently used to touch the front surface of the cornea (after the instillation of numbing eye drops, of course!), where readings are then taken.
Why this is important:
The biometry readings is the most critical determinant of IOL power, and every 1 mm error equates to about 2.5 to 3.0 diopters of refractive error, or "250 to 300 degrees of power.
Keratometry (K Readings)
This measures the corneal curvature (the anterior surface of the eye), and is given in either radius or in diopters (D). There are two "K"s - the K1 which is the flatter meridian and the K2 which is the steeper meridian. These readings are at two axis that are 90 degrees away from each other, and also provides us the axis of the corneal astigmatism.
Why this is important:
Besides being required for IOL power calculation, the K-readings also determines need for toric IOL as well as whether certain types of IOLs are suitable, especially for very steep or very flat corneas. A flatter-than-usual cornea may indicate that LASIK has previously been done.
Anterior Chamber Depth (ACD)
ACD is the distance from corneal epithelium/endothelium to anterior lens capsule which helps to predict effective lens position (ELP). This is important - just like moving your glasses further away or pushing it up against your nose and closer to your eyes will give a different resultant 'power'.
Lens Thickness (LT)
LT is used in modern IOL formulas such as the Barrett and Holladay 2. Different formulas have been developed to calculate the prescription of the IOL that is to be inserted into the patient's eye - which can differ from each other, with some formulas preferred for certain more 'extreme' prescriptions, etc.
White-to-White (WTW) Diameter
WTW is the horizontal corneal diameter, essentially from the white on the left to the white on the right side of the cornea. This is used in some IOL-calculation formulas and may be used in choosing the size of the IOL.
Central Corneal Thickness (CCT)
The CCT reading is not directly used in the IOL power calculation, but is taken into consideration in terms of eye pressure readings (pre and post operatively), and in some cases can be used to assess the swelling of the cornea after the surgery is performed.
Corneal Topography / Tomography (When Needed)
Sometimes, topography can be used to detect irregular astigmatism, which can then affect the patient's resultant satisfaction of vision. An irregular cornea can cause light to scatter differently, and can interfere with vision post surgery depending on what IOL was used.
IOL Power Calculation Formula Selection
While this differs from surgeon to surgeon (and indeed surgeons may use more than one formula to compare the differences), typically based on axial length:
For short eyes (<22 mm): Haigis, Hoffer Q, and Holladay 2 formulas
For long eyes (>24.5 mm): Barrett Universal II, Haigis (with optimized constants), Olsen, and SRK/T formulas
Summary
The minimum core parameters / critical data needed:
Axial length
Keratometry
Anterior chamber depth
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