They are the most common clinical finding in type I neurofibromatosis adults over 20 years.
Karl Lisch, an Austrian ophthalmologist (1907-1999), first described iris hematomas or Lisch nodules in 1937 and associated with type 1 neurofibromatosis.
Unlike café au lait spots, multiple nodules are specific for peripheral neurofibromatosis (Von Recklinghausen).
They can occur in segmental neurofibromatosis, which is due to a somatic mutation of the neurofibromatosis gene but is generally absent in central neurofibromatosis.
In children, nodules are a more likely finding than neurofibromas.
Neurofibromatosis 1 is the most common autosomal dominant neurocutaneous disorder with complete penetrance, although the expression may not be packed by five years.
Lisch nodules are predominantly visible in children generally after the age of six.
Therefore, it is essential to appreciate that the absence of them before this age does not anticipate the diagnosis.
Lisch nodules are dome-shaped gelatinous masses that develop on the surface of the iris.
Lisch nodules are postulated to arise from mast cells, pigmented cells, and fibroblast-like cells.
Friedrich Daniel von Recklinghausen, a German pathologist, identified Lisch’s nodules as a genetic disease.
Lisch nodules are more common in patients with postpubertal NF1, as evidenced by the finding that only 19% of NF1 patients under five years of age show Lisch nodules, while this rate increases to 92% in adult NF1 patients.
Ninety-three percent of cases are affected bilaterally, and an average of 25 nodules can be counted in each iris. Once developed, they remain stable throughout life.
The nodules are not believed to cause any ophthalmologic complications.
Lisch nodules are melanocytic hamartomas, usually light yellow to light brown, appearing as well-defined dome-shaped elevations projecting from the surface of the iris.
Lisch nodules are up to 2 mm in diameter and reach variable sizes in the iris. The presence of Lisch nodules is the most common clinical sign of NF1.
In 80% of the eyes, Lisch nodules can be found in the lower quadrants of the iris, and this may be related to greater exposure to the sun, one of the factors postulated in the development of these benign swellings.
Lisch nodules are almost always pathognomonic for NF1. However, they can occasionally be seen in other rare conditions, including Watson’s syndrome and type 2 neurofibromatosis.
They can be seen without magnification, but a slit-lamp examination may be necessary to distinguish them from nerves in the iris that present flat or minimally raised, densely pigmented lesions with blurred margins.
The differential diagnosis of Lisch nodules should include iris nominations, iridoid-corneal-endothelial syndrome, Rieger’s anomaly or syndrome, iris nevus, melanoma, and inflammatory conditions such as sarcoidosis, leprosy, tuberculosis, and syphilis.
Differentiating Lisch nodules from iris nums can sometimes be particularly important.
Iris mamillations are generally unilateral, cause heterochromia irides, and are often associated with ocular melanocytosis.
In contrast to Lisch nodules, mamillations of the iris show the same color as the underlying iris, are regularly spaced over the iris, and increase in size as they approach the pupillary margin.
These eyes must be closely examined due to the risk of pigmentary glaucoma resulting from excessive pigment accumulation occluding the iridocorneal angle.
Histopathologically, Lisch nodules are composed of melanocytes and spindle cells, generally concentrated in the superficial layers of the iris stroma.
Spindle cells are more significant than normal iris melanocytes.
Immunohistochemical studies show a positive reaction against vimentin, smooth muscle actin, and neuron-specific enolase.
There is currently no treatment for Lisch’s nodules and no need to treat these small benign lesions that do not interfere with visual function.