Dear Editor,

We read with interest the recent paper by Ataş et al.¹ on bacillary layer detachment (BLD) in acute Vogt-Koyanagi-Harada (VKH) disease. We would like to share our experience in the Department of Ophthalmology of Te Whatu Ora in Auckland, New Zealand. Continuous variables are reported as median (interquartile range [IQR]) and categorical variables as number and percentage. Statistical analysis was performed on STATA (version 15; StataCorp LLC, College Station, TX).

We examined a series of 100 eyes (50 patients) with VKH diagnosed according to the revised diagnostic criteria proposed by the First International Workshop on VKH disease.² The median age was 42.0 years (IQR: 32.6-52.3 years) and 31 were female (62.0%). Median vision at presentation was 20/50 (IQR: 20/30-20/112). An initial optical coherence tomography (OCT) scan was available for 94 eyes. BLD was observed in 27 eyes (28.7%). Mean subretinal fluid height was 299 µm and a significant difference was observed between those with BLD (mean 741 µm) and without BLD (mean 120 µm) (p<0.001).

Patients with BLD also had poorer presenting vision (median 20/100 vs. 20/30, p<0.001). Median time to resolution of BLD was 29 days (IQR: 14-48 days) and the overall mean time to resolution of subretinal fluid (for the entire group) was 25 days (IQR: 16-47.5 days). The median follow-up duration for our cohort was 3.6 years (IQR: 1.6-8.8 years). Final visual acuity was 20/25 (IQR: 20/20-20/40). No significant difference was observed in final visual acuity between patients with and without BLD. Central choroidal thickness (CCT) was only available in 36 eyes. Median CCT was 373 µm (IQR: 306-498 µm). No significant difference was observed in those with and without BLD (p=0.564).

BLD has been described in multiple other ocular pathologies besides VKH, such as posterior scleritis, exudative age-related macular degeneration, ocular toxoplasmosis, and acute posterior multiple placoid pigment epitheliopathy.³ The similarity between all these diseases is the primary involvement of the choroid and retinal pigment epithelium either because of pachychoroid disease, choroidal inflammation, or infiltration.

In BLD there is an intraretinal split at the photoreceptor inner segment myoid level, proximal to the external limiting membrane. It has been hypothesized that acute fluid shifts in the posterior pole force the fluid into the neuroretina via hydrostatic pressure, thus splitting the photoreceptors due to shearing forces.⁴ The adhesion between photoreceptors and RPE cells may be disrupted by the accumulation of subretinal fibrin which increases the likelihood of fluid shift, leading to BLD due to hydrostatic pressure.⁵ The suspended hyperreflective particles in the fluid within BLD, which are not commonly found in subretinal fluid, most likely represent inflammatory products, including fibrin, as well as photoreceptor debris.

Despite BLD being a common tomographic finding in eyes with acute VKH with poorer presenting visual acuity, it appears not to have a negative effect on the final visual outcome. Durmaz Engin and Saatci⁴ reported that BLD is predominantly non-vision threatening and often exhibits spontaneous regression or rapid improvement with treatment. Several studies showed rapid restoration of the outer retinal architecture leading to good visual gain after resolution of fluid.^5,6

Chronicity of the disease, severity of the anterior segment inflammation, and the number of recurrent episodes of inflammation increase the risk of late complications such as choroidal neovascular membrane, glaucoma, or cataract.⁷ Read et al.⁷ found that a greater number of complications, older age at onset, and worse visual acuity at presentation were associated with worse final visual acuity.

In conclusion, our observations support those of Ataş et al.¹ in demonstrating good visual outcome despite the presence of BLD. Further studies will be beneficial to examine other OCT features that are associated with poorer prognosis, increased complications (such as choroidal neovascular membrane), or recurrent disease.

Ethics

Peer-review: Internally peer-reviewed.

Authorship Contributions

Surgical and Medical Practices: N.A., R.N., Concept: R.N., Design: N.A., R.N., Data Collection or Processing: A.T., Analysis or Interpretation: N.A., R.N., Literature Search: N.A., A.T., Writing: N.A., R.N.

Conflict of Interest: No conflict of interest was declared by the authors.

Financial Disclosure: The authors declared that this study received no financial support.