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Cataracts, a clouding of the eye’s natural lens, is caused by proteins in the eye becoming deformed which prevent the lens sending clear images to the retina. Cataract surgery restores vision by removing the opacified natural lens and replacing it with a new clear artificial intraocular lens (IOL).
Keratoconus is a disease of the cornea that can occur in young people and causes a progressive worsening of vision. The cornea’s function is to bend and focus light onto the retina at the back of the eye. In Keratoconus, the cornea becomes very thin, irregular and cone shaped and can no longer focus the light, causing blurred vision.
People who have Keratoconus can still develop a cataract; the damage is in a different part of the eye. However, the good news is that the cataract can be treated.
Having cataract surgery when you have Keratoconus offers some challenges. Cataract surgery in eyes with Keratoconus requires additional considerations; such as wound healing - where to place the incision entering the eye, choosing the right formula to calculate the power of the intraocular lens to use, and the choice of intraocular lens to implant.
Wound healing
As the cornea is very steep and thin the wound healing may not be the same as in a cornea of a person who does not have Keratoconus. In some cases, the surgeon may plan to enter the eye through an incision in the sclera (scleral tunnel technique) rather than making an incision through the thin cornea. Sometimes a small stitch is required to close the cornea wound for cataract surgery.
Lens power calculation
Lens power calculation formulas are based on ideal eyes. The traditional formulas used to calculate the new lens power are inaccurate. Keratoconus brings challenges as the steep corneas and high astigmatism provide unpredictable corneal measurements, lowering the accuracy of the calculations. The cornea is usually measured with a 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) and with topography (a corneal map). If the standard IOL formulas to determine the lens strength are used, this will often result in hyperopia. Your ophthalmologist will use equipment to measure the cornea and then adjust the formula to get the best result after the cataract surgery. This will require formulating for a mild myopia (short sightedness).
Choosing the Intraocular lens
Another challenge is choosing the right intraocular lens to place in the eye after the natural lens is removed. Multifocal lenses are not recommended as those lenses are not designed for patients with corneal irregularity. Monofocal or Toric lenses may be used. If you have mild Keratoconus and have previously seen pretty well in glasses then a topic IOL may be considered. If however your Keratoconus is more advanced and you rely on contact lenses then the best option would be a monofocal IOL.
Treatment options for people with Keratoconus and cataracts
If someone has a visually significant cataract, the surgeon may recommend to perform the cataract surgery first to improve vision. Then glasses, soft contacts or a scleral lens may be used to further improve the vision, depending on the level of Keratoconus.
If corneal cross-linking is part of the treatment plan in a person with an advanced cataract, the cataract surgery is normally done first and then the cross-linking. Cross-linking is an effective treatment for patients with Keratoconus, but the improvement in the corneal shape is slow, developing over months to years rather than weeks. If the person is young, the ophthalmologist may want to do the crosslinking first, let it stablise and then do the cataract.
Your surgeon will discuss and design a treatment plan of action that works for your individual case.
If you have Keratoconus and now have cataracts contact Bowen Eye Clinic on 0800 69 2020 for an assessment and discussion on how your vision can be improved.