Even though the vast majority of cataract surgeries are successful in the vast majority of patients, some patients have reasons to be unhappy after the procedure. Among these reasons are lumps and bumps on the cornea — that is, the surface irregularities — that can adversely affect cataract surgery outcomes in two primary ways. They can cause problems with biometry, which lead to inappropriate IOL selection, including wrong IOL power and inaccurate astigmatism measurements. Also, they can cause irregular astigmatism, which patients may not notice due to their cataract but will often notice after they have the cataract removed, especially if they have a premium IOL.
Mild corneal surface irregularities are very common, especially as patients age. The tricky part is distinguishing between specific etiologies and deciding exactly how to manage them.
A clear corneal surface is a must for optimal vision. Anything that disrupts the corneal surface can affect not only Snellen visual acuity but also the quality of the vision. Conditions such as dry eye syndrome and lid margin disease can disturb the normal ocular surface by causing punctate keratopathy or, if severe, filaments or frank epithelial defects. However, corneal staining is not required for the corneal surface to be irregular. Epithelial basement membrane dystrophy (EBMD), Salzmann’s nodular degeneration (SND) and pterygium can all affect visual function by disturbing the regularity of the corneal surface.
Here, I share what I have learned about diagnosing and treating these lumps and bumps that cataract surgeons encounter most frequently.
The best way to diagnose these conditions is a careful slit lamp examination. A broad slit beam from a side angle can often identify mild epithelial irregularities due to EBMD (Figure 1). It can also be used to find mildly elevated creamy white nodules of SND (Figure 2). A pterygium is not hard to diagnose on slit lamp examination. The question for all three of these conditions is whether they are visually significant and whether they require treatment prior to cataract surgery. Several diagnostic tests can help provide the answer.
The first test is to place fluorescein dye on the eye and examine the cornea carefully with a cobalt blue light looking for areas of negative staining. Negative staining occurs in places where the fluorescein dye runs off elevations in the cornea and it looks darker than the surrounding areas (Figures 3A and 3B). Negative staining can often highlight even very mild corneal irregularities from EBMD and SND.
My rule of thumb is that if negative staining is present in the center of the cornea, typically in the central approximately 6 mm, it has a high chance of being visually significant. A few minor areas of negative staining in the periphery, on the other hand, are probably not causing any issues with visual function.
The second test is computerized evaluation of the corneal curvature using corneal topography. While we have numerous methods to evaluate the curvature of the cornea, I find those that use Placido disc-type rings to be the best at evaluating corneal surface irregularities. This technology involves circular rings of light shined onto the cornea and imaged by a computer, which then calculates curvature and evaluates regularity.
Most systems will show an image of the rings on the cornea in addition to a color-coded map of power and regularity. In my experience, looking at the rings is the best way to assess very small irregularities in the cornea because the color-coded maps often smooth out small but visually significant irregularities (Figure 4).
Epithelial basement membrane dystrophy
EBMD is a very common condition, especially in older patients. It is often an incidental finding and does not cause significant central negative staining or disruption of the corneal topography rings. In those cases, it can be observed. However, if the EBMD changes cause central negative staining or irregularities in the corneal topography rings, they may well be visually significant. In such cases, EBMD should be treated prior to cataract surgery.
The main treatment is to remove the irregular, lumpy, bumpy epithelium. This is performed with epithelial debridement at the slit lamp or under a minor room operating microscope. Epithelial debridement can also be combined with a diamond burr polishing procedure. These procedures involve placing topical anesthesia, a topical antibiotic and an eyelid speculum.
A sharp blade (eg, #15 blade) or semi sharp blade (eg, Tooke knife) is used to remove a large area (about 6-mm to 8-mm diameter) of central epithelium. It is critical to remove all the irregular reduplicated basement membrane overlying Bowman’s layer, which is usually very smooth. When a diamond burr procedure is performed, a large 5-mm diameter diamond dusted drill is used to smooth out the cornea in a uniform fashion for about five seconds. The diamond burr removes all the irregular basement membrane — and perhaps allows for better adhesion of the new epithelium.
Next, a bandage soft contact lens (BSCL) is placed. The patient is prescribed topical antibiotics until the epithelium heals, usually four to five days, at which point the BSCL is removed. Ice packs are used frequently during the first few days along with pain medications as needed. This procedure is more than 90% successful in obtaining a smoother corneal surface (Figure 5). Rare complications include delayed epithelial healing, infection, corneal scarring, decreased vision and, of course, recurrent EBMD.
Salzmann’s nodular degeneration
SND involves single or multiple slightly or severely elevated creamy white corneal opacities. Usually these are located in the peripheral cornea, although they can involve the central cornea (Figures 6A and 6B, page 22). Even when peripheral, outside the central 6-mm zone, they can affect the central corneal topography and thereby the vision. While negative staining can be seen, many eyes with SND have significant irregular astigmatism noted on corneal topography.
The etiology of SND is unknown, but it is much more common in women than men.1
The goal of treatment is very similar to EBMD — remove the lesions to create a smooth corneal surface. However, Bowman’s layer and anterior stroma may be involved in eyes with SND, significantly increasing the chance of an irregular stromal bed after removal of the SND. Additionally, SND tends to recur much more frequently and severely than EBMD.
One way to smooth the cornea after removal of the nodules is with excimer laser phototherapeutic keratectomy (PTK). Some physicians also use topical mitomycin C (MMC) to decrease the chance of recurrence of the SND. The PTK with MMC procedure begins very similarly to the epithelial debridement procedure, with topical anesthesia, topical antibiotics and placement of an eyelid speculum. The nodules are removed manually with a sharp or semi-sharp blade, ideally down to a reasonably smooth Bowman’s membrane. If Bowman’s is fairly smooth, large PTK ablation spots can be used to smooth it a bit further. If Bowman’s is not smooth after the manual SND removal, multiple small, medium and large excimer laser spots need to be used to remove the irregularities and achieve as smooth a base as possible. Afterward, MMC on an 8-mm sponge is placed on the cornea for about 60 seconds and irrigated with 30 mL of cold saline. Then, a BSCL is placed and topical antibiotics and pain medications are used as in epithelial debridement surgery, and follow-up is similar to that for EBMD. PTK with MMC is about 90% successful in obtaining a smoother corneal surface (Figure 7, page 22).
Complications include delayed epithelial healing, infection, corneal scarring, decreased vision and, of course, recurrent SND. Occasionally SND can recur quickly, within three to six months, and be even worse than the original disease. It recurs mildly over five to 10 years, sometimes requiring a repeat treatment.
Many people have small pterygia that do not seem to affect visual function. In general, the larger the pterygium, the greater chance it has of affecting vision. As a general rule, extension approximately 2 mm or greater onto the cornea has a higher chance of affecting vision. Corneal topography is very helpful in determining how visually significant a pterygium is.
When the topography rings are irregular within the central 6 mm or there is significant irregular astigmatism on the color-coded maps, the pterygium should be treated prior to cataract surgery. The surgical management of pterygium is beyond the scope of this discussion. Having said that, pterygium excision with a conjunctival autograft is generally considered the treatment of choice. If a conjunctival autograft is problematic, such as in patients after trabeculectomy or tube shunt surgery, an amniotic membrane graft can also be very successful.
While the corneal epithelial defect after these procedures for EBMD, SND and pterygia usually heals within a week, the corneal curvature may not be stable for many weeks. Most surgeons wait at least six weeks before checking corneal curvature measurements and often repeat them a few weeks later to make sure they have stabilized before proceeding with final biometry measurements and cataract surgery.
For the best results after cataract surgery, the cornea needs to be as healthy and smooth and regular as possible. Evaluating the central cornea for negative fluorescein staining as well as the corneal topography rings and the color-coded maps for irregularities can help diagnose corneal problems before cataract surgery when they can be well managed — as opposed to after cataract surgery when they may be much more problematic.
Corneal lumps and bumps are often readily treatable with excellent outcomes, allowing for more successful cataract surgery. OM
- Maharana PK, Sharma N, Das S, Agarwal T, Sen S, Prakash G, Vajpayee RB. Salzmann’s Nodular Degeneration. Ocul Surf. 2016;14:20-30.