Overview of corneal topography
Corneal topography is a computer-aided diagnostic tool that creates a three-dimensional map of the curvature of the corneal superficial. The cornea (the front window of the eye) is liable for about 70 per cent of the eye’s focusing power. An eye with normal vision has an evenly rounded cornea, but if the cornea is too flat, too slanted, or unevenly curved, vision is not perfect. The greatest advantage of corneal topography is its ability to detect irregular conditions invisible to most conventional tests.
Corneal topography yields a detailed visual explanation of the shape and power of the cornea. This type of analysis provides your doctor with very fine details about the condition of the corneal surface. These facts are used to diagnose, monitor, and treat various eye conditions. They are also used to fit contact lenses and to plan surgeries, including laser vision correction. For laser vision improvement, the corneal topography map is used in conjunction with other tests to control exactly how much corneal tissue will be removed to correct the vision.
Computerized corneal topography can be helpful in the evaluation of certain diseases and injuries of the cornea, with:
- Diseases of the cornea
- Corneal abrasions
- Corneal deformities
- Irregular astigmatism after corneal transplants
- Postoperative extraction of cataracts with acquired astigmatism.
The corneal topography kit consists of a computer connected to a lighted bowl that contains a pattern of rings. During a diagnostic test, the patient sits in front of the container with the head pressed against a bar while a series of data points are generated. Computer software digitizes these data points to produce an impression of the shape of the cornea, using different colours to identify different elevations. The non-contact test is painless and short.
Why is it done
Corneal topography produces a full visual description of the shape and influence of the cornea. Corneal topography analysis provides your doctor with very fine details about the condition of the corneal surface. These facts are used to diagnose, monitor, and treat numerous eye conditions. They are also used to fit contact lenses and plan surgeries, including laser vision correction. For laser vision correction, the corneal topographic map is used in conjunction with other tests to determine exactly how much corneal tissue will be removed to correct vision and with what ablation pattern.
When it’s done
Colour Maps – You will see a rainbow of colours on each topographic map. These range from warm colours (red, orange, yellow) to neutrals (green) to cool colours (blue, purple).
Side effects of corneal topography
Corneal topography is a painless, non-contact technique, which means that the corneal topography device will not touch your eye during measurement. If your eye is dry, a few moisturizing drops may be applied to the eye to improve the quality of the topographic image.
Corneal topography risk factors
Refractive surgery-induced ectasia is probably the most be afraid of the difficulty of laser-assisted in situ keratomileuses (LASIK) and photorefractive keratectomy (PRK). It presents as a progressive eccentric thinning of the corneal stroma with consequent steepening of the posterior surface of the cornea. The disorder is considered irreversible and can significantly reduce visual acuity if left uncorrected and corrected with glasses. Although the overall prevalence of postoperative ectasia is unknown, several reports show a prevalence rate ranging from 0.02% to 0.6%.
Risk factors for developing postoperative LASIK / PRK ectasia include a personal ectasia or family history of keratoconus (KC), abnormal corneal topography (frusta form of keratoconus), high myopia, walking bed with little residue microns), excessive ablation when walking (> 100 microns), a high percentage of altered tissue (PTA> 0.40). Deep primary keratotomy producing a thick corneal flap and low preoperative corneal thickness (<500 microns).
Even when risk factors for ectasia have been identified after refractive surgery, there have been reports of people who have developed ectasia without any of the proposed risk factors, this specific group of patients has shown a tendency to be younger.