his study was undertaken by Leo D. Bores, MD beginning in the Fall of 1997 and consists of 289 eyes with the longest follow-up of 24 months at the time of analysis. The mean IOP post-PNT treatment was consistently at least 3 mm Hg less than pre-treatment mean except at 3, 6, 9 and 12 months wherein it was at least 4 mm Hg less than the initial mean IOP. This is similar to the results found in the GLTRG study of ALT.[1] PNT is compared to ALT in the next section.

In 62%(15 out of 24) of eyes at 12 months the lowering of IOP was 2 mm Hg as compared to the initial or pre-treatment mean IOP. 44%(62 out of 139) at 3 months were 1 mm Hg less than the mean initial IOP.

63% of PNT patients were off medication with IOP’s equal to or less than their initial IOP at 3 months; 50%(12 eyes) were still off medications at 1 year; all but 2 of these with IOP’s 16 mm Hg or less.

35.7% of the pre-treated eyes had IOP’s measured at 15 mm Hg or less; 54.3% of these eyes had measured post-treated IOP’s of 15 mm Hg or less at 9 months. Furthermore, whereas the pre-treatment range of IOP was 8 - 48, at 9 months the range was 8 - 29 in the same group.

If IOP’s below 19 are taken as success (as in some ALT studies) then it should be noted that 74.9% of pre-treatment eyes were 19 mm Hg, whereas 91.3% of eyes post-treatment at 9 months were 19 mm Hg.

It should also be noted that of the post-treatment group 88.4% of patients were on 1 medication or less compared to 67.3% of pre-treatment eyes; 54.9% were off medications altogether compared to 15.9% in the pre-treatment group. This can be more easily seen in the following histogram showing the left kurtosis of the data set:

In many ALT series, a post-treatment IOP of 22 mm Hg is considered a success. In the current series, if we exclude the patients who began with an IOP of 22 mm Hg (35.9%), the PNT success rate was 54% (overall, 89.3% were 22 or less post-PNT). The mean drop in IOP of 5.5 mm Hg compares favorably with ALT in the same pre-treatment IOP range. The greatest drop in IOP was seen in the one case with an initial IOP of 48 whose IOP post-treatment dropped to 25 mm Hg at 1 month — a 23 mm Hg difference. This is comparable to the maximum IOP drop in the series by Lieberman, et al.[2]

The difficulty assessing some of the results of PNT in this series is that no patient was excluded except those with previous filtering surgery (except one case of trabeculectomy failure in whom application of the ring opened the fistula dropping the IOP to 8 mm Hg where it has remained with a small bleb; his data was excluded from this analysis).

Some physicians consider 15 mm Hg to be a ‘magic number’ since statistically patients whose IOP is at 15 mm Hg or less show less progression of visual field defects. Evaluating the current series under those conditions (IOP 16 mm Hg ranging from 16-48) we find the following:

At 9 months post-PNT, 36.7% of a group of 130 eyes showed IOP’s of 15 mm Hg or less; that is: 37% of eyes reached the ‘magic number’. 86.7% were £19 mm Hg post-PNT as compared to 60.9% pre-treatment.

It has been stated that upwards of 40% of patients with an established diagnosis of glaucoma have IOP’s in the normal range (15-22). If we examine a group of eyes in this series whose pre-treatment IOP’s range from 16-22 mm Hg, we find:

The mean pre-treatment IOP in this group of 144 eyes was 18.5 mm Hg; 22.9% had an IOP of 16 mm Hg. At 9 months, the mean IOP was 16.3 mm Hg (with a range from 11-23). In that group 47.6% had IOP’s of 15 mm Hg or less. 52.4% were at 16 mm Hg or less and 4.8% were at 16 mm Hg.

References

1. GLTRG, The Glaucoma Laser Trial (GLT) and glaucoma laser trial follow-up study: 7. Results. Glaucoma Laser Trial Research Group. Am J Ophthalmol, 120(6): p. 718-31; 1995. 
2. Lieberman, M.F., H.D. Hoskins, Jr., and J. Hetherington, Jr., Laser trabeculoplasty and the glaucomas. Ophthalmology, 90(7): p. 790-5; 1983.