What is a Cataract?
The eye can be thought of as analogous to a camera:
- The cornea, which is the transparent covering on the front of the eye, acts much like a lens cover and a focussing element by bending entering light rays through the central ‘black hole’, the pupil, which combined with the coloured iris, the shutter, acts like the aperture of a camera.
- The lens is the next component in line and acts like the lens in a camera by its ability to focus light onto the retina, which acts very much like the film of the camera.
- The retina contains many light sensitive nerve cells called photoreceptors which transmit the light rays into electrical impulses which are delivered to the brain via the optic nerve where an image is perceived.
A cataract is a clouding or loss of clarity of the natural crystalline lens inside the eye. The crystalline lens is normally a clear structure that focusses light onto the back of the eye (retina). When the lens becomes cloudy, images to the back of the eye are out of focus and dull, leading to impaired vision.
What causes a Cataract?
The majority of cataracts develop as a result of natural age-related changes in the eye. Oxygen-related damage to the protein in the natural lens accumulates throughout life. From about 40 years of age, this causes proteins within the crystalline lens to discolour and gradually the lens loses it’s clarity.
Other factors that cause cataract or accelerate its growth include:
- Excessive exposure to UV and other types of radiation
- Use of certain medications (eg. Corticosteroids)
- Previous blunt/penetrating ocular trauma, surgery or disease
- Systemic disease (eg. diabetes and other metabolic disorders)
- Genetics and congenital disorders
What are the symptoms of Cataract?
Early cataracts may not affect the vision or only affect the vision minimally. In these instances, treatment is not generally required. Many patients may not notice any symptoms of cataract until an eye examination reveals them.
Moderate and advanced cataracts can cause symptoms such as:
- Blurry or hazy vision (often likened to a dirty spectacle lens
- Difficulty driving, reading and recognizing faces
- Need for more light when reading (reduced light transmission)
- Double vision in one eye
- Increasing short-sightedness
- Increased glare sensitivity due to internal scatter of light
- Difficulties with night driving (haloes and glare)
- Reduced contrast sensitivity
- Altered colour perception
- Reduced brightness/intensity of colours
Cataract progression is generally very gradual but symptoms may become apparent quite quickly in some people. Spectacle correction may help improve vision in early cataract but not in moderate and advanced cases.
What are the different types of Cataract?
- Nuclear sclerotic cataract is the most common type of cataract and describes an overall clouding in the central part (the nucleus) of the crystalline lens. They are not commonly associated with increased short-sightedness, altered colour perception and blurry vision.
- Cortical cataracts cause spoke-like opacities to form in the periphery of the crystalline lens. Symptoms frequently include increased glare sensitivity and difficulties with night driving.
- Posterior Subcapsular cataracts cause plaque-like opacity to grow on the back of the crystalline lens. They will cause increased glare sensitivity and blurry vision. This form of cataract is sometimes associated with previous steroid use.
What other complications can arise from Cataract?
In certain people, the growth of a cataract can make them prone to primary angle-closure glaucoma. This is where the drainage channel in the front of the eye (trabecular meshwork) is gradually narrowed by the increasing size of the crystalline lens. Eventually, the drainage channel can become completely blocked, resulting in a rapid increase in the pressure within the eyeball and a painful red eye. Long-sighted patients are more likely to be at risk of angle-closure glaucoma.
Your eye care practitioner will be able to assess if you are at risk of primary angle-closure glaucoma and whether you would benefit from cataract extraction or other treatments to prevent his serious condition.
How are Cataracts detected?
Your eye care practitioner will measure you visual acuity on a letter chart. They will also use a slit lamp microscope to classify and grade the cataract. Dilating drops are sometimes used to enlarge the pupil. This will allow thorough examination of the back of the eye and to exclude the possibility of other eye disease. These drops will blur your vision for 2-3 hours and it is recommended that you do not drive on the day of your eye exam.
Optical Coherence Tomography(OCT)
Optical coherence tomography (OCT) allows non-invasive imaging of the macula in cross-section. It will screen for any macular pathology which could also be reducing vision (eg. age-related macular degeneration). We recommend that an OCT be performed on everyone prior to cataract surgery to ensure that the health of the eye is fully evaluated. Some macular problems may not be able to be detected in an eye examination alone, particularly in the presence of a dense cataract.
How are Cataracts treated?
The only way to treat a cataract is to surgically remove it. Currently, the most common type of cataract surgery is known as micro incision phacoemulsification cataract extraction. This procedure is performed under local anaesthetic and 'twilight' sedation.
A small (2-2.5mm) self-sealing incision is made on the side of the cornea, the clear dome on the surface of the eye.
A fine ultrasound (phaco) handpiece is then inserted through this self sealing incision
Vibrations from the tip of the phaco probe will fragment and emulsify the cataract into a pulp.
These fragments of cataract are the carefully removed under microscopic guidance.
Following this, an intra-ocular lens (IOL) implant that has been specifically preselected for your eye, is inserted to replace the crystalline lens. The implant is rolled up in a special lens injector and gently guided into place by your surgeon.
In the majority of cases, the IOL will sit within the natural bag that originally held the crystalline lens (the capsule), and sutures are not usually required to position the IOL.
How is the power of the Intraocular Lens calculated?
Because an IOL replaces the natural crystalline lens, it is possible in most cases to choose the prescription that you will be left with after cataract surgery. To do this, a series of scans are taken at your initial visit. These include measurements of the length of the eye and the curvature of the front of the eye. These values are then inserted into a regression mathematical formula and an IOL power is calculated according to your needs. There is a 90% chance of achieving the desired outcome.
Your Ophthalmologist will discuss with you in detail your postoperative options. Some possibilities include:
- Distance Vision for Both Eyes
No spectacles will be required for distance but you will require correction for intermediate and near vision. This is a particularly common option.
- Blended Monovision
This describes a mix of distance and intermediate/near vision. The dominant eye is corrected for distance and the non-dominant eye is corrected for intermediate vision. The brain generally adapts naturally and quickly to this configuration. Spectacles may still be required for reading (especially in dim light, with small writing and for long periods) and night-driving. Patients are often trialled with a contact lens to ensure they can tolerate the difference between the two eyes.
- Full Monovision
This describes a mix of distance and near vision. The dominant eye is corrected for distance and the non-dominant eye is corrected for near vision. There is a greater difference in the prescription between the two eyes as compared to Blended Monovision, and adapting to this Full Monovision can take longer. Spectacles may still be required for intermediate vision.
Multifocal Intraocular Lenses
These IOLs contain concentric ‘rings’ of distance and near vision. These lenses will give good postoperative distance and near vision, however, spectacles may be required for long periods of intermediate vision (eg. computer). Multifocal IOLs can also cause significant haloes around lights at night time.
What happens if the desired focus is not achieved?
There is a degree of variability in achieving the desired prescription following cataract surgery, between both individuals and eyes. This is because the IOL implant selected for your eye is calculated using a regression equation that is based on results from 35,000 cataract surgeries. It is possible that your particular eye may not conform exactly to this mathematical model.
In the majority of cases, even if the focus is not exactly as predicted it is likely to be very close to the to the expected result and the quality of your vision should still be very good. Wearing glasses for certain activities may be necessary. In cases where the desired postoperative prescription is significantly different from the expected result, your surgeon may discuss with you the possibility of fine-tuning your vision. Treatment options include inserting a secondary (piggy-back) IOL or performing laser refractive surgery.
What can I expect during and after cataract surgery?
Cataract Surgery is performed in a day theatre setting and is considered a "clean" procedure. 99% of cataract operations are uneventful with no complications.
There is little to no awareness of your surroundings during the surgery and there is no pain involved at any time. An anaesthetist ensures that your eye is "numb" via the use of local anaesthetic and will provide sedation for comfort.
You may experience mild grittiness and dry eye symptoms following surgery and this can last for weeks to months. These symptoms are usually managed with lubricating eye drops.
It is common to use artificial tears prior to surgery to ensure post-operative eye comfort.
Vision is expected to good 1 day post-operatively, and will gradually continue to improve over the first week. After 4-6 weeks post-operatively, reading spectacles can be prescribed.
Postoperatively, there are no significant restrictions on lifestyle. In the first week, it is advisable to defer any activities which could introduce foreign matter into the eye (this includes avoiding getting water into the eye when showering) or potentially causing significant blunt trauma. You will be given a clear shield (for use when sleeping) and dark safety glasses to protect the eye.
Moderate Physical Exercise should be avoided for 2 weeks and swimming for 4 weeks.