What is Salzmann’s Nodular Degeneration?
Salzmann’s nodular degeneration (SND) is a rare, slowly progressive condition of the cornea, the transparent dome of tissue at the very front of the eye. It presents as multiple small round or conical raised opacities on the surface of the cornea, typically about 1-3mm in diameter, and is usually located close to the edge of the cornea or in its midperiphery. SND can be found in either one or both eyes though over 60% of cases are bilateral (in both eyes), and is slowly progressive with time.
Although anyone from adolescence onwards can get SND, Caucasian females in the fifth to ninth decade of life appear to be most susceptible. There is sometimes a preceding history of ocular surface irritation and damage, whether from trauma or disease. These situations include vernal keratoconjunctivitis (an allergic eye disease affecting the cornea), meibomian gland disease (a common dysfunction of the oil glands supplying the tear film), trichiasis (ingrown eyelashes leading to chronic irritation of the ocular surface), post-operatively after cataract surgery or pterygium excision, or epithelial basement membrane dystrophy (a condition affecting the superficial layers of corneal tissue). In addition, LASIK surgery and long-term wear of contact lenses have also been associated with SND; however, due to the high prevalence of individuals with such a history it can be difficult to prove direct causation between SND and LASIK or contact lens wear.
Many cases are also known to be idiopathic, indicating there is no known cause or preceding event of trauma or chronic ocular surface irritation. On occasion, there have also been genetic links reported with SND, suggesting a possible autosomal dominant inheritance, but as of yet no specific gene has been identified. The exact underlying mechanisms of SND are not yet fully understood.
The most commonly reported symptom of Salzmann’s nodular degeneration is the sensation of a foreign object in the eye. As the nodules on the cornea are elevated from the surface, these bumps can be felt by the sensitive underside of the top eyelid with each blink. Patients may also describe the feeling as general eye irritation or a sensation of dryness. As the cornea must remain optically transparent for optimal vision, the opacities resulting from SND, particularly if they arise closer to the center of the cornea, can result in a deterioration of vision. In about 15% of cases, there may be no noticeable symptoms at all.
Clinical diagnosis of Salzmann’s nodular degeneration is best made with an appropriately-trained ophthalmologist. Viewing the cornea under the slit lamp allows the clinician to detect the presence of any raised greyish-white to bluish nodules on the superficial cornea. A history of any of the potential preceding factors as mentioned above can aid with diagnosis but is not essential.
A technique known as corneal topography allows visualization of the irregularities of the corneal surface and any resultant astigmatism from the nodules. After appropriate Salzmann’s nodular degeneration surgery, corneal topography can also be used to assess improvements to the corneal surface.
Other techniques may be employed to gain a better understanding of the state of the cornea, whether for diagnosis, treatment, or further assessment. Ultrasound biomicroscopy, confocal microscopy, and high-resolution optical coherence tomography can be used to obtain a more detailed view of the nodules and surrounding corneal tissue.
Salzmann’s Nodule Treatment
Salzmann’s nodular degeneration treatment is guided by the severity of symptoms. Most cases benefit from conservative management with the use of lubricating eye drops and other dry eye disease therapies, such as warm compresses and lid hygiene, to address the foreign body sensation. However, cases involving central nodules that impair vision or where conservative management is insufficient, surgical intervention may be required.
Salzmann’s Nodule Removal
Superficial keratectomy involves manual removal of the Salzmann’s nodules with forceps or a blade under topical anesthesia and can successfully improve the vision in up to 90% of cases though the nodules may eventually reoccur. If the nodules can be removed without disrupting the layer just beneath the epithelium known as Bowman’s layer, the prognosis is much better. Any irregularities or haze remaining on the cornea after the nodules are removed with superficial keratectomy can be smoothed over with a subsequent procedure known as phototherapeutic keratectomy.
In uncommon cases, the nodules may cause disruption to the deeper layers of the cornea and removal results in significant unevenness of the remaining corneal surface. In these situations, a laser can be applied to the eye to smooth the bumps and ridges. Very severe cases of Salzmann’s nodular degeneration may be treated with a partial corneal graft, though fortunately this is rarely required.