Quantitative evaluation of changes in anterior segment biometry by peripheral laser iridotomy using newly developed scanning peripheral anterior chamber depth analyser

Abstract

Aim: Using the newly developed scanning peripheral anterior chamber depth analyser (SPAC), the effects of peripheral laser iridotomy (PLI) on peripheral anterior chamber depth (PACD) were determined quantitatively as was the association between PACD and chronic elevation of intraocular pressure (IOP) after PLI.

Methods: 16 eyes of 15 patients with acute primary angle closure glaucoma (PACG) attack, 14 eyes of 14 patients with narrow angle and PACG attack in their fellow eyes, and 13 eyes of seven patients with chronic angle closure glaucoma (CACG) were enrolled. The SPAC scanned the anterior ocular segment from the optical axis to the limbus and took 21 consecutive slit lamp images at 0.4 mm intervals. A computer installed program automatically evaluated the PACD and the averaged values of three measurements were employed for analysis.

Results: PLI significantly increased PACD and changed the iris contour from convex to flat or concave in all the enrolled eyes. The extent of the PLI induced PACD increase was enhanced with increasing distance from the optical axis. Comparing PACDs after PLI, eyes that received prophylactic PLI showed the greatest extent of PLI induced PACD increase, followed by eyes with CACG and eyes with PACG attack. The PACD of eyes with PACG attack was almost the same as that of the fellow eyes of PACG attack before prophylactic PLI. Eyes with PACG attack showed poorer IOP control after PLI than eyes with narrow angle and CACG with PLI.

Conclusions: PLI significantly increases PACD and the small PLI induced opening of PACD may contribute to chronic IOP elevation after PLI.

Figures

Figure 1

Schematic illustration of SPAC system. The major components of this system are one slit lamp system, ⅓ inch black and white charge coupled device (CCD) camera, and one computer system including a monitor and a printer. A slit ray is illuminated from the temporal side at an angle of 60 degrees and a slit lamp is moved laterally (as indicated by an arrow) on the track by a distance of 8 mm in 0.5 second, thereby taking 21 consecutive images at 0.4 mm intervals. The slit lamp images are transferred to the computer system. Biometric analysis is instantly performed and calculated values and images are displayed on the monitor. PC  =  personal computer.

Figure 2

Representative SPAC images. Representative SPAC images of a female having narrow angle. (A) Twenty one consecutive images (right panel), eye monitoring window (lower left panel), and values (upper left panel) are displayed. (B) Sample image for determining PACD and corneal thickness. A slit lamp image (first row) and a histogram of the number of white pixels calculated from the slit lamp image (second row). Two major peaks indicate cornea (left) and iris (right). Determined margins of the cornea and the iris (third row). Margins are superimposed on the slit lamp image (fourth row). (C) An installed program creates a plot of PACD profile. The X axis is the distance from the optical axis and the Y axis is PACD in mm. (D) Drawing of the anterior ocular segment. Bold lines indicate boundaries of corneal epithelium, corneal endothelium, and iris surface.

Figure 3

Representative images of PLI induced PACD changes. A 67 year old female patient whose left eye had a PACG attack and right eye showed narrow angle. Prophylactic PLI was performed on her right eye. The anterior chamber was narrow and iris contour was convex before the prophylactic PLI (A). The anterior chamber was widened and iris contour became flat after PLI (B).

Figure 4

Prophylactic PLI induced PACD changes. Prophylactic PLI significantly increased PACD at all measured points. The p value of PLI induced PACD change at a distance of 6 mm from the optical axis is 0.03, whereas those at other investigated points are less than 0.01. Paired t test was employed. PLI  =  peripheral laser iridotomy, n = 15 eyes, bar = SD.

Figure 5

Amount of PLI (peripheral laser iridotomy) induced PACD change. There were no significant differences among the investigated points (the repeated ANOVA). n = 15 eyes, bar = SD.

Figure 6

Percentage change of PACD induced by PLI (peripheral laser iridotomy), n = 15 eyes, bar = SD.

Figure 7

Comparison of PACD between attacked eyes and fellow eyes. PLI significantly increased PACD at all measured points. The p value of PLI (peripheral laser iridotomy) induced PACD change at all investigated points is less than 0.01 (paired t test). The paired t test was employed. Fifteen attacked eyes and 14 PLI eyes were enrolled. Bar = SD.