What tests are done before Cataract Surgery?
I am an Ophthalmologist in Melbourne who believes careful tests performed prior to cataract surgery are the key to successful surgery. Precision eye measurements performed in the weeks before cataract surgery are as important as the meticulous surgical techniques I use in cataract surgery, here in Melbourne.
Below is an outline of these essential tests:
Fig 1. Pre-operative biometry of the eye before cataract surgery
Biometry carefully measures the length, width and depth of the eye, and the curvature of the cornea (front window) of the eye, to determine the correct power for the intraocular lens (IOL). In modern cataract surgery the eye’s natural lens is removed and an artificial IOL inserted in its place, restoring vision. Like spectacles that can be ground to a tailored focusing power, the IOL has many power options, and hence it is crucial to choose the correct focusing power for the eye, based on accurate biometry tests.
Some eyes require a special toric IOL that corrects astigmatism. Astigmatism is not a disease; it occurs when the eye’s focusing power differs in different directions, for instance is greater horizontally, and lesser vertically. Only through use of the modern biometry can we determine an eye’s suitability for a toric IOL, and the best power toric correction to use. This technique has recently been enhanced by Computer Assisted Cataract Surgery, here in Melbourne. Computer Assisted Cataract Surgery involves eye-recognition software that guides the Ophthalmologist through the operating microscope to get best lens orientation to fully correct the astigmatism.
Figure 2. Astigmatism. The focussing power of the eye differs for vertical and horizontal light. A toric shaped lens corrects for this.
Figure 3. Surgical printout of Biometry formula for correct lens power insertion and orientation of IOL
I am proud to be part of an elite group of Ophthalmologists in Melbourne, Eye Surgery Associates, which uses only the best biometry and surgical equipment for excellent results. We take great care to keep up with the latest scientific evidence as to the most accurate formulae to calculate lens power, and educate our staff well to know how to take the best possible measurements. For instance, our staff know that if the eye is not well lubricated the biometry readings will be effected – they know to measure the eye’s hydration and if too dry to repeat the biometry after lubrication with moisturising eye drops.
1. Corneal topography
Biometry does not provide all the crucial information about the cornea. Corneal topography helps measure the 3-dimensional structure of the cornea, providing extra information to biometry. Corneal topography can identify irregular thinning of the cornea, such as in keratoconus or other corneal degenerations. Although rare, it is important to identify these corneal diseases before cataract surgery, as they can affect the final vision after the surgery. Corneal topography helps identify when irregularity is so great that a toric lens might not be suitable. Corneal topography also helps identify patients with tear film abnormalities due to dry eye; an irregular topography map implies inaccuracy of biometry that needs repeating.
2. Macular and optic nerve OCT scan
The macula is the central portion of the retina, where light from the front of the eye is focused for clear vision. An OCT scan of the macula can identify sight threatening macular diseases, including macular holes or epiretinal membranes, and other subtle diseases that can be undetectable through clinical exam alone. These conditions might limit the final visual outcome, and some of them can be successfully treated prior to cataract surgery or at the same time as cataract surgery.
Figure 4. OCT scan
Additionally an OCT scan of the optic nerve can be performed. The optic nerve provides all the visual input from the eye to the brain. Optic nerve OCT is an important test to detect common optic nerve diseases, such as glaucoma. As a glaucoma specialist I take great care and interest in diagnosing and treating glaucoma.
Glaucoma can result in irreversible visual loss if untreated, but if detected early can be treated and the vision saved; the OCT is a very useful test to determine if any glaucoma is present. This has become more important recently for people being assessed for cataract surgery, as minimally invasive glaucoma stents can be inserted at the time of surgery. Some of these stents have an excellent safety profile with proven good outcomes, but are only available at the time of cataract surgery. Hence it is important to identify any glaucoma prior to, and not following cataract surgery, when the opportunity may be missed.