Prevalence of complications in eyes with nanophthalmos or microphthalmos: protocol for a systematic review and meta-analysis

INTRODUCTION: Microphthalmos and nanophthalmos are uncommon ocular conditions, whereby affected eyes have smaller dimensions compared to the normal population. Microphthalmos and nanophthalmos present several challenges to ophthalmologists; they have spontaneous and post-operative sequelae such as high hyperopia, angle-closure glaucoma, uveal effusion syndrome, and retinal detachment. This systematic review and meta-analysis intends to assess the prevalence of both the spontaneous complications associated with nanophthalmos and microphthalmos, as well as the post-surgical complications associated with nanophthalmos or microphthalmos. METHODS AND ANALYSIS: Articles will be searched for, on four online databases: PubMed, EMBASE, Scopus, and Web of Science. Two independent reviewers will identify the studies according to prespecified inclusion and exclusion criteria. All studies included with participants diagnosed with microphthalmos or nanophthalmos in one or both eyes, will be included if they have (i) more than 4 cases and (ii) defined microphthalmos/nanophthalmos as an axial length of < 21 mm or a high lens/eye volume ratio. Nanophthalmos may have an additional diagnostic criterion of posterior wall thickness greater than 1.7 mm. The prevalence of the following complications will be assessed: high hyperopia (spherical equivalent >3D), angle closure glaucoma, uveal effusion syndrome, retinal detachment, and chorioretinal folds. Studies that will be excluded are those that have not adequately defined the criteria for the diagnosis of nanophthalmos or microphthalmos, those studies that have less than five cases, studies with criteria not defined above, and deemed unsuitable, and studies in languages other than English with no published translation. Relevant data will be extracted and assessed for the risk of bias in each article using a modified Joanna Briggs Institute (JBI) assessment tool. The data will then be pooled to determine the prevalence of complications among patients with microphthalmos and nanophthalmos. If the data allows, subgroup analysis will be carried out according to axial length as well as subtype of microphthalmos/nanophthalmos (simple, complex, relative anterior, and posterior). DISCUSSION: Although nanophthalmos is an uncommon condition that affects the eye, its management and complications can be sight-threatening. Thus, it is important to counsel patients and their families correctly (in the case of children) upon diagnosis and prior to any surgical intervention. This can only be done if the overall prevalence of complications is known. REGISTRATION: PROSPERO CRD42021227847