Lens vault independently associated with angle closure, study shows

An increased lens vault can raise risk of angle closure, physician says.

Tin Aung

Eyes with angle closure had significantly thicker lenses and greater lens vault, defined as the distance between the anterior pole of the crystalline lens and the horizontal line joining the scleral spurs, a study found.

“Lens vault performed much better than all the other lens parameters such as lens thickness and lens position in terms of distinguishing angle-closure from open-angle subjects,” Tin Aung, MBBS, MMed(Ophth), FRCS(Ed), FRCOphth, FAMS, PhD(Lond), OSN Asia-Pacific Edition Board Member, said in an email interview.

“Lens vault quantifies the degree of the lens that is located anterior to the anterior chamber angles,” Dr. Aung said. “In addition, the presence of an increased lens vault increases the risk of having angle closure by 48 times compared to a smaller vault, and this was independent of lens thickness and lens position.”

Study results were published in Ophthalmology.

Measurement methods

The prospective study included 102 patients with angle closure; 53 patients had primary angle-closure glaucoma. A control group comprised 176 patients with open angles and no signs of glaucoma.

Patients underwent gonioscopy, anterior segment optical coherence tomography, slit lamp examination, Goldmann applanation tonometry and evaluation of logMAR visual acuity.

Anterior segment OCT was used to assess lens vault; gonioscopy was used to identify angle closure.

“Lens parameters cannot be evaluated by gonioscopy, whereas lens vault alone is measured from AS-OCT images,” Dr. Aung said. “Lens thickness can be measured by A-scan, while lens position and relative lens position are calculated from anterior chamber depth, lens thickness and axial length.”

Lens vault, other parameters

Angle closure patients had a mean lens vault of 901 µm, lens thickness of 4.20 mm, anterior chamber depth of 2.66 mm, axial length of 22.86 mm and a 0.18 ratio of lens thickness to axial length.

Controls had a mean vault of 316 ìm, lens thickness of 3.90 mm, anterior chamber depth of 2.95 mm, axial length of 23.92 mm and a 0.16 ratio of lens thickness to axial length.

Data adjusted for age, gender, anterior chamber depth, lens thickness and relative lens position showed lens vault to be associated most significantly with angle closure, the authors said.

Results showed insignificant between-group differences in lens position and relative lens position. Previous studies have yielded inconsistent findings on the relationship between lens position, relative lens position and angle closure, Dr. Aung said.

“While some studies report a more anteriorly placed lens in eyes with angle closure, others have found no such association,” Dr. Aung said. “A possible reason could be that they are calculated from two parameters, namely [anterior chamber depth] and [lens thickness], which seem to be interdependent and compensate for each other.”

The vault of a phakic IOL such as the Visian ICL (STAAR Surgical) differs spatially and mechanically from that of the crystalline lens, Dr. Aung said. – by Matt Hasson

Reference:

• Nongpiur ME, He M, Amerasinghe N, Friedman DS, Tay WT, Baskaran M, et al. Lens vault, thickness, and position in Chinese subjects with angle closure. Ophthalmology. 2011;118(3):474-479.

• Tin Aung, MBBS, N/MEd (Ophth), FRCS (Ed), FRCOphth, FAMS, PhD (Lond), can be reached at Singapore National Eye Centre, 11 Third Hospital Avenue, Singapore 168751; +65-63-228-313; fax: +65-62-263-395; email: tin11@pacific.net.sg.
• Disclosure: Dr. Aung receives financial support from Carl Zeiss Meditec.