Semilunar sign on the cornea revealing sign of scleritis
September 02, 2022
4 minute read
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Scleritis is inflammation of the sclera and is primarily autoimmune. Corneal thinning, astigmatism, and peripheral ulcerative keratitis are common corneal changes after scleritis.
Scleritis can be anterior or posterior. Anterior scleritis is classified as diffuse or nodular, depending on the clinical presentation. In 1976, Watson and colleagues described approximately 29% anterior scleritis causing corneal changes primarily involving the anterior and stromal layers of the cornea. In 1974, Holt Wilson and Watson reported four cases of non-syphilitic deep nummular keratitis with vasculature involving the corneal endothelium in the scleritis. We report a new semilunar sign observed in the cornea, which may be a telltale sign of anterior non-infectious scleral inflammation.
The lunate sign is visible on the posterior cornea (Figure 1) and is often associated with anterior or concurrent scleritis. Clinical features include the presence of posterior corneal opacity, a concave semilunar opacity pattern under diffuse direct illumination, absence of blood vessels, and a normal anterior cornea.
Evaluation of the semi-lunar sign
Serial documentation by digital slit lamp photography (10x magnification), spectral domain OCT (Figure 2), specular count analysis (Figure 3), and confocal microscopy are the modalities that can be used to assess sign progression. semilunar. High-resolution anterior segment OCT using the Spectral Domain Platform (1 µm to 5 µm axial resolution) can be used to measure the extent of posterior corneal opacity, Descemet’s status, and the corneal thickness.
Differentiate from interstitial keratitis
One must differentiate the lunate sign from the interstitial keratitis seen in conditions such as syphilis, post-viral keratitis, or tuberculosis. The lunate sign is often adjacent to the location of the scleritis, unlike interstitial keratitis, which can occur anywhere on the cornea. The absence of blood vessels or phantom vessels also differentiates it from classic interstitial keratitis. The typical concave or semilunar pattern is mostly followed in scleritis-induced semilunar sign whereas no specific pattern is observed in interstitial keratitis.
Clinical model and demographics
A good history and physical examination are the initial clinical evaluation in patients with scleritis. The identification of systemic signs such as joint pathologies, skin problems and integumentary disorders to detect autoimmune diseases is crucial. A recent study by us showed that in 76 eyes of 72 patients with anterior scleritis evaluated in an outpatient setting, 11 patients (15.3%) had a lunate sign. They were nine women (81.8%) and two men (18.1%) with a mean age of 40.5 ± 11.8 years (22 to 56 years). Anterior scleritis was noted in all 15 eyes in the active (n = 3) (Figure 4) or inactive (n = 12) state. Four out of 11 patients (36.3%) had a bilateral presentation. The referring symptoms were pain (n = 3, 27.2%) and blurred vision (n = 4, 36.3%). No corneal edema or Descemet’s fold was noted. The pupil was not completely covered by any of the eyes. There was a clear zone of 0.2 to 0.5 mm noted between the opacity and the limbus in 11 eyes. No clear areas were seen in four eyes. Full-thickness corneal involvement was not observed in either eye.
The study showed an average area of endothelial opacity and standard deviation of 7.7 mm2 and 5.2mm2, respectively. The overall area involved ranged from 2 mm2 at 17 millimeters2. The percentage of corneal endothelial surface involved represented 5.8% of the total endothelium. The central endothelial cell density ranged from 1,652 cells/mm2 at 2924 cells/mm2 (mean 2540.8 ± 351.7 cells/mm2). There was a statistical difference in endothelial cell density between the uninvolved central cornea and the involved peripheral cornea (P = .05). The mean OCT thickness of endothelial opacity was 212.5 ± 129.3 µm. The corneal epithelium remained intact. There was no statistically significant correlation between posterior corneal opacity thickness and best corrected visual acuity. However, in three eyes whose opacity partially crossed the pupil, the BCVA was reduced.
All patients with a lunate sign will require appropriate laboratory evaluation. Blood tests include complete blood count, differential count, hemoglobin and erythrocyte sedimentation rate, C-reactive protein, rheumatoid arthritis factor, venereal disease research lab, antinuclear antibodies, cytoplasmic antineutrophil P and C antibodies and the Mantoux test. A conjunctival swab should be obtained from eyes with active scleral disease for Gram and Ziehl-Neelsen staining to exclude an infectious etiology. In our previous study, although Mantoux was positive in 54.5% of eyes, Mantoux sensitivity showed no significant correlation with posterior corneal opacity.
Autoimmunity and the semilunar sign
A probable reason for the formation of the lunate sign could be the embryological association (the corneal endothelium and the prominent part of the sclera are derived from the neural crest cells). Besides the embryological element, there are a few common factors, such as close anatomical proximity, closely related collagen structures, and immunological response. Frequent corneal pathologies consecutive to anterior scleritis have been noted as sequelae of a common immune response in both corneal and scleral tissue in noninfectious anterior scleritis. Thus, noninfectious scleritis is commonly associated with the semilunar sign. Unlike common autoimmune conditions, corneal endothelial opacity does not decrease with steroid treatment.
The lunate sign in scleritis should raise awareness of a dormant condition that may affect endothelial function. Therefore, due care should be taken by anterior segment surgeons when operating on eyes with a lunate sign (Figure 5). Steps such as proper planning of the surgical incision, use of limited ultrasound power, and viscoelastic-guided endothelial protection can prevent endothelial loss. Treatment of scleritis can reduce the extent of corneal involvement. Patient follow-up and prompt intervention are required in eyes with a lunate sign.
- Holt Wilson AD, et al. Trans Ophthalmol Soc UK. 1974;94:52-57.
- Kumar DA, et al. Indian J Ophthalmol. 2022;doi:10.4103/ijo.IJO_2073_21.
- Kuroda Y, et al. Br J Ophthalmol. 2017; doi:10.1136/bjophthalmol-2016-308561.
- Watson PG, et al. Br J Ophthalmol. 1976; doi:10.1136/bjo.60.3.163.
- Watson PG, et al. Exp Eye Res. 2004;doi:10.1016/s0014-4835(03)00212-4.
- For more information:
- Amar Agarwal, MS, FRCS, FRCOphth, director of Dr. Agarwal’s Eye Hospital and Eye Research Centre, is the author of several books published by SLACK Books, sister company of publisher Healio eye surgery news, including Phaco Nightmares: Conquering Cataract Catastrophes, Bimanual Phaco: Mastering the Phakonit/MICS Technique, Dry Eye: A Practical Guide to Ocular Surface Disorders and Stem Cell Surgery and Presbyopia: A Surgical Manual. He can be contacted at 19 Cathedral Road, Chennai 600 086, India; email: [email protected]; Website: www.dragarwal.com.