BLOG: Thorough assessment of complex cornea needed before cataract surgery
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The first three installments of our blog on the complex cornea provided an overview of considerations in these patients when they present for cataract surgery.
Here in the fourth installment, we take a deeper dive into the key aspects of our diagnostic approach for three broad categories of irregular corneas: dry eye, “lumps and bumps” and ectasia.
Dry eye
It has been established that many patients with dry eye and resulting tear film abnormalities present for cataract surgery without having been previously diagnosed with ocular surface disease of any kind. Also, it is well known that symptomatology alone is not enough to make a diagnosis due to the lack of correlation between symptoms and signs. Although patient questionnaires are helpful, they can miss dry eye. Studies by Trattler and Gupta, among others, highlight that as many as 80% of patients who are examined during the preoperative cataract evaluation have signs of dry eye but are undiagnosed or asymptomatic, illustrating how crucial the diagnostic portion of the workup is.
Topography
We cannot overstate the importance of topography in evaluating all types of patients with complex corneas. For example, by looking at the Placido ring images of the Atlas corneal topography system (Zeiss) or Galilei topographer (Ziemer), we can pick up irregularities in the cornea. Instead of being crisp and circular, the rings will be smudged in certain locations of irregular astigmatism. It is important to note that patients with dry eye disease (DED) will not have stable topography. The magnitude of astigmatism in a patient with dry eye can vary between two measurements even if they are 1 day apart. Further, if there is disagreement in measurements among devices, whether it is topography, biometry or keratometry, this is a red flag that there is irregularity, and the cause must be determined.
Slit lamp exam
Of course, the slit lamp examination is always key as well. We like to keep in mind the mnemonic from the ASCRS Cornea Clinical Committee’s algorithm: LLPP, or look, lift, push and pull. We are sure to pull on the lid to look for laxity and other abnormalities and push the meibomian glands to evaluate the quality, quantity and rapidity of the meibum’s flow. This gives us insight into the lipid layer of the tear film.
Staining
Staining the ocular surface will help diagnose rapid tear breakup time and find signs of punctate keratitis. Once a patient has fluorescein staining on the cornea, it is no longer a mild case of DED but moderate to severe, as signified by the loss of epithelial cells. Micro-erosions are indicative of chronic moderate to severe DED.
Lumps and bumps
Irregular topography, mires that are not circular and crisp, the presence of staining, plus the slit lamp exam will also point toward things such as epithelial basement membrane dystrophy (EBMD) that can mimic DED. In a busy clinic, without looking at topography it can be easy to miss EBMD on the slit lamp exam, which can significantly affect the quality of calculations.
Topography is essential for finding “hot blue spots” or areas of sectorial flattening that might be indicative of a bump on the cornea whether it be Salzmann or pterygium, for example. Areas of elevation can cause hyperopia, and in these cases, the slit lamp exam helps differentiate the cause of irregular astigmatism secondary to cornea pathology. If the pathology is under the upper lid, superiorly, it can be easy to miss at the slit lamp. The topography clues the ophthalmologist to lift that lid and look for irregular pathology.
Lumps and bumps must be identified and treated before proceeding with surgery.
Keratoconus, post-refractive surgery, corneal scars
It is not unusual to diagnose keratoconus when evaluating topography for the first time at the cataract workup. These patients are used to their mild amount of irregular astigmatism, and clinically their findings aren’t visible at the slit lamp, and therefore it can go undiagnosed.
Patients can even forget they have had refractive surgery. Although RK and LASIK with a flap are obvious at the slit lamp, PRK is not, further underscoring the need for corneal topography in all preoperative cataract patients.
If patients have corneal scars from previous trauma or infection, whether central or peripheral, it will create irregular astigmatism that can be seen on topography. Outside of performing a corneal transplant, there is little that can be done for these patients preoperatively.
Conclusion
Topography plays a critical role in the preoperative workup of all cataract patients in order to identify complex corneas. In the next installment, we will discuss preparation for surgery, IOL calculations and intraoperative considerations for these patients.
- References:
- Gupta PK, et al. J Cataract Refract Surg. 2018;doi:10.1016/j.jcrs.2018.06.026.
- Trattler WB, et al. Clin Ophthalmol. 2017;doi:10.2147/OPTH.S120159.
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