Have you noticed a slow decline in your vision? Do colors seem not as bright as they used to be? Has night driving, which was already difficult, become more difficult? Have changes in your contact lenses not helped? You could be developing a cataract. Cataract formation, which is ‘clouding’ of the lens, can cause declining vision and visual disturbances very similar to those from keratoconus.
Thus, a trip to your eye care provider may help to determine if the recent changes in vision are from keratoconus or cataract formation.
If a cataract is found, a new series of questions arise: Can I safely have cataract surgery even though I have keratoconus? Should I have cataract surgery alone or should I have it combined with corneal transplantation? What are the unique challenges that keratoconic patients present to their cataract surgeon?
At the Wills Eye Institute, we recently undertook a study to examine these questions about cataract surgery in patients with keratoconus. This small study, published inEye &Contact Lens in September 2007, examined the visual and topographic outcomes of twelve eyes of nine patients with keratoconus and cataracts. We found that cataract surgery can improve best corrected visual acuity (BCVA) in all severities of keratoconus without significant corneal change. Clear-cornea phacoemulsification with intraocular lens implantation improved the BCVA in all severities of keratoconus, with a mean postoperative visual acuity of 20/32. The mean improvement was 4 lines of vision.
To access the cataract, a small incision is made in the cornea and the lens is emulsified using an ultrasound (phacoemulsificiation). Patients with keratoconus have very thin corneas, which make the wound construction a little different and the view to do the cataract surgery a little worse. However, our study found that these patients all had successful, uneventful cataract surgery. The removal of the lens does not ‘fix’ the corneal irregularity of keratoconus, so patients should expect that they will still need contact lenses to achieve their best vision.
The question of whether to have cataract surgery alone or have it combined with corneal transplantation is very patient dependent. The onset of keratoconus usually occurs in young adulthood, progresses for 10 to 20 years, and then stops progressing. So many patients can achieve good vision in contact lenses (sometimes glasses) with essentially the same parameters for many years. If a patient has had good vision in contacts and then develops a cataract, cataract surgery alone will likely be enough for them. If a patient has never had sufficient vision in contact lenses and has severe keratoconus, then a combined surgery may be better. Of course, corneal transplantation is a much bigger surgery with increased risks and follow-up. So, if cataract surgery alone will restore vision, that is preferred. In our study, patients developed good vision with cataract surgery alone and no patient chose to have corneal transplantation after cataract surgery.
One of the main challenges for the cataract surgeon is picking the right intraocular lens (IOL) to place in the eye after the natural lens is removed. In normal eyes, the corneal shape is measured with a keratometer and the eyeball length is measured with an ultrasound. The numbers obtained are placed into a calculation, and the lens is chosen. Patients with keratoconus have unpredictable corneal measurements, lowering the accuracy of these calculations. We usually measure the cornea with both the keratometer and with topography (corneal map). Apart from assessing the effects of cataract surgery, we looked at which methods of measurement and which formulas for IOL calculation method worked best for patients with keratoconus. We did not see a difference in data obtained from the keratometer and the topographer. Not surprisingly, we found more predictable IOL calculations were possible in patients with mild keratoconus than in those with moderate and severe disease. Although not part of our study, patients with keratoconus should not have multifocal lenses placed. Those lenses are not designed for patients with corneal irregularity.
Interestingly, those with mild keratoconus eyes did very well from a refractive standpoint. In this study, two patients did not need corrective lenses post-op, two patients were able to wear soft toric contact lenses post-op instead of RGP lenses, and one used glasses. While the surgery itself did not ‘fix’ their keratoconus, reducing their nearsightedness with cataract surgery likely made it possible to see well with less significant correction.
Patients with moderate and severe keratoconus used RGP lenses after surgery. Among these patients, five of seven eyes were refitted with the same base curve and diameter that as before surgery. Two such eyes needed a steeper base curve as well as a change in diameter, but neither patient had a good RGP lens fit before surgery.
We also found that the patients in our study were fairly young for cataracts. The mean age was 55 years (range, 38-76 years). It is unclear why patients with keratoconus may have cataracts earlier, but we do know that nearsightedness (myopia) is a risk factor for cataract formation. Most patients with keratoconus do have myopia. Additionally, patients with keratoconus often have allergic disease. When treated with steroids, those with allergic disease can develop cataracts at a young age. A larger study is needed to see if there is truly an association between keratoconus and earlier cataract formation.
If you have signs of cataract formation, it is important to see your eye care provider for examination. Cataract surgery can improve best corrected vision in all severities of keratoconus without significant corneal change.
By Kristen Hammersmith, MD*
General Cataract Information
A cataract is a cloudy or opaque area in the natural lens of the eye. Cataracts generally form very slowly and usually develop as a person gets older and may run in families. Other environmental factors such as smoking or exposure to toxic substances can also accelerate the development of a cataract. Cataracts can cause visual problems such as difficulty seeing at night, seeing halos around lights, and sensitivity to glare.
Simply put, a cataract is a “clouding” of the natural lens in your eye, located inside the eye behind the iris or the colored part of the eye. It works like the lens of a camera. It picks up images, then focuses the lights, colors, and shapes on the retina, which sends the images to your brain. However, if the lens is clouded by a cataract, light is scattered so the lens can no longer focus it properly, causing vision problems.
The lens is made of mostly proteins and water. Clouding of the lens occurs due to changes in the proteins and lens fibers.
The lens is composed of layers like an onion. The outermost is the capsule. The middle layer is the cortex and the innermost layer is the nucleus. A cataract may develop in any of these areas and is described based on its location in the lens:
- A cortical cataract affects the middle layer of the lens. It is identified by its unique wedge or spoke appearance.
- A nuclear cataract is located in the center of the lens. The nucleus tends to darken changing from clear to yellow and sometimes brown.
- A posterior capsular cataract is found in the back outer layer of the lens. This type often develops more rapidly.
BCVA: best corrected visual acuity, or vision with glasses or contact lenses
UCVA: Uncorrected visual acuity, or vision without glasses or contact lenses
Intraocular lens (IOL) is a lens implanted in the eye, replacing the existing crystalline lens because it has been clouded over by a cataract. It usually consists of a small plastic lens with plastic side struts, called haptics, to hold the lens in place in the eye.
Keratometer: a medical instrument that uses corneal reflections to measure the curvature of the cornea to determine how flat or steep the cornea is compared to average or normal.The modern keratometer uses optical sensors and computerized technology to measure comparisons and contrasts of the cornea against a predetermined value.
Phacoemulsification refers to modern cataract surgery in which the eye’s internal lens is emulsified with an ultrasonic handpiece and aspirated from the eye.
Dr. Hammersmith is the director of the cornea service at the Wills Eye Institute and an Instructor at Jefferson Medical College. She joined the Wills faculty following a residency at the Wilmer Eye Institute at Johns Hopkins University, and a fellowship in cornea and external disease at Wills Eye in 2003 .