Causal relationshiops & prediliction to glaucoma

Anterior segment OCT provides more objective angle assessment for anterior chamber glaucoma diagnosis than height Source: Julian P. S. Garcia Jr., M.D

Chinese people of short stature experience angle-closure glaucoma, trachoma, pterygium, cortical cataract, and arterial hypertension with more frequency. Although a recent study found this to be true, there were confounding factors involved. “These associations are due to confounding factors such as age, level of education, and anterior chamber depth, which by themselves are associated with the ocular diseases mentioned,” according to study co-author Liang Xu, M.D., Beijing Institute of Ophthalmology, Beijing Tongren Hospital, Beijing. The findings still hold interesting clinical significance. “The association between short body height and presence of angle-closure glaucoma as found in univariate analysis may have some importance in screening for the disease: subjects with a short body may be more likely to be predisposed to angle-closure glaucoma,” Dr. Xu reported.
Red herring?

Dr. Xu and colleagues analyzed ocular and general parameters in association with body height of 3,251 subjects. “In univariate analysis, short body height was significantly associated with a higher frequency of angle-closure glaucoma, trachoma, and pterygium, a higher degree of cortical cataract, and a higher frequency of arterial hypertension,” Dr. Xu reported. “A multivariate analysis, including all confounding parameters which were significantly associated with body height in univariate analysis (i.e., age, gender, rural versus urban region, level of education) revealed that body height by itself was no longer significantly associated with the presence of any of the diseases tested.” Dr. Xu’s study is one of the first to investigate a potential association between height and ocular diseases. “Based on the findings reported by several studies that body height correlates with anterior chamber depth, and considering that a shallow anterior chamber is one of the main risk factors for angle closure, it was logical to assume a relationship between body height and the presence of angle-closure glaucoma,” Dr. Xu noted. However, “angle-closure glaucoma was primarily related to the shallow anterior chamber depth and not to a short body height,” Dr. Xu acknowledged. The study also found, similarly to previous studies, that ocular dimensions are related to body height. “The association between body height and size of the globe is a trans-ethnic phenomenon,” Dr. Xu reported. For instance, taller subjects likely had longer globes, deeper anterior chambers, thinner lenses, and flatter corneas, according to Dr. Xu’s summary of the Singaporean Tanjong Pagar Study. Similarly, Dr. Xu noted, in the Reykjavik Eye Study, “A significant relationship was found between body height and axial length, vitreous chamber depth, and radius of the corneal curvature.”
Other associations

Body height had stronger associations with other factors in the study, namely, level of education and family income. Taller subjects had higher education and income levels. “It may be that rich parents can feed their children better, resulting in a taller body, and simultaneously they may be better able to afford the costs for a higher education,” Dr. Xu concluded.
In fact, all of these associations may be more closely linked than meets the eye, Dr. Xu suggested. “A recent study suggested that subjects with angle-closure glaucoma have a higher mortality than subjects with open-angle glaucoma or non-glaucomatous subjects,” Dr. Xu noted. “The reason for the higher mortality of subjects with angle-closure glaucoma may have been that these subjects had a smaller body stature due to the association between anterior chamber depth and body height. The lower body height is associated with a lower socioeconomic background, which by itself is associated with lower living conditions and a higher mortality.”
Meanwhile, John D. Sheppard, M.D., professor of ophthalmology, microbiology, and immunology, Eastern Virginia Medical School, Norfolk, Va., found the study results to be “extremely curious.” In the United States, he has often wondered about the body stature of particular patients and whether there could be some link to ocular findings. “I’m often intrigued by the big, burly, male, offensive lineman type,” Dr. Sheppard said. “They often have very thick corneas.” These thick corneas often yield falsely higher pressure readings. “In reality their pressure is fine,” Dr. Sheppard said. “I get a high reading because of their thicker corneas.”
As for this study, Dr. Sheppard said he’d be curious to delve more into the multivariate analysis, which again, revealed no significant linkage between body height and the presence of diseases tested. Although Dr. Xu suggested that an association between short body height and presence of angle-closure glaucoma as found in univariate analysis could have some bearing on screening for the disease, Dr. Sheppard suggested this could also lead to “clutter.” “To have my mind cluttered with peripheral data doesn’t seem to make a lot of sense unless the risk factor [for ocular disease in people with short stature] is huge,” Dr. Sheppard said.

Editors’ note: Dr. Xu reported no financial interests related to this study. Dr. Sheppard has no financial interests related to his comments.

Contact information

Sheppard: 757-622-2200, docshep@hotmail.com
Xu: xlbio@yahoo.cn