Increase in choroidal thickness seen after CPAP therapy

Terry Wood, MD

Uslu and colleagues have undertaken a study with important ramifications in ophthalmology as well as within medicine more broadly. Obstructive sleep apnea (OSA) is increasingly recognized as an important etiologic factor in the morbidity of several systemic disorders, including cardiac disease, stroke, neurocognitive degeneration and chronic kidney disease, not to mention the occupational hazards associated with daytime somnolence. Epidemiologically, the linkage of OSA with obesity implies that this public health concern will almost certainly increase in prevalence over the coming years.

As the authors point out, a connection between OSA and several ophthalmic disorders has been recognized. These include floppy eyelid syndrome, glaucoma, central serous chorioretinopathy (CSCR), retinal vein occlusion, non-arteritic anterior ischemic optic neuropathy and idiopathic intracranial hypertension.

Serendipitously, OCT was developed and has been refined over a period that roughly parallels an increased understanding of OSA. OCT affords us the opportunity to evaluate not just the retina but the choroid as well in several ophthalmic disorders. We now know, for instance, that choroidal thickness is often diminished in several conditions, such as age-related macular degeneration, myopic degeneration and, indeed, many if not most other degenerative ophthalmic diseases. Similarly, we observe that unusually thick choroids are often seen in the context of CSCR and certain inflammatory and infiltrative choroidopathies.

OCT provides us with strong evidence to support a conclusion implied by histologic studies dating back more than a century. Namely, that the choroid is a structure with significant compliance, exemplified and demonstrated by diurnal variations in thickness in normal individuals.

It is this normal variation in choroidal thickness that forms the primary criticism of Uslu’s study. As the authors point out, their study lacks a control group and proper randomization. It is noteworthy that the magnitude of change in choroidal thickness differed greatly at various points of measure, in some locations not achieving statistical significance. Perhaps most importantly, the magnitude of change in thickness before and after CPAP treatment did not differ greatly from the normal diurnal thickness changes observed in Tan’s study, creating doubt as to whether the observed thickness changes truly represent a treatment effect vs. normal physiologic variation. Coupled with the limitations of manual segmentation and still evolving refinement of OCT resolution, the authors’ case for further investigation with more rigorous controls is indeed with merit.