Interesting Results Of Combining Timoptic and Xalatan

 

I normally use Xalatan first, wait 10 minutes and then use Timoptic XE.

[UPDATE: Here is the bottom line. I found out that simply not waiting 10 minutes between drops (when using Xalatan and Timoptic) results in my IOP being 4.65 mm Hg lower on average. A reader pointed out to me in the comments that I had not made this clear, so I thought I should update this post. I now use the eye drops at the same time with no delay and my IOP is about 5 points lower. Because this is such a difficult thing to believe, when I originally posted this information I took a purely statistical approach. The info below explains my analysis. Basically, the statistics indicate that the effect is not due to chance. In the month following this post, my personal experience confirms that the effect is real.]

Once I used both drops at the same time without waiting. The next two days my IOP was significantly lower than usual. In fact, careful measurement shows that my IOP has never been this low before or since.

I wondered if the way I combined the drops could have produce this superior effect, so I decided to do some tests.

The date when I used Xalatan and timolol together in my right eye was 9/9/2006. I used Timoptic GFS 0.5%. The following day, 9/10/06, I recorded these IOP measurements.

	RIGHT EYE
9/10/06 7:51 AM	12.0
9/10/06 8:36 AM	11.0
9/10/06  I:42 PM	9.3
9/10/06 2:44 PM	10
9/10/06 2:46 PM	10.7
9/10/06 3:46 PM	10.3
9/10/06 6:29 PM	9.0
9/10/06 7:22 PM	10.3
9/10/06 8:35 PM	10.0
9/10/06 9:14 PM	9.7
9/10/06 11:13 PM	9.7

Since that time I have never recorded another IOP value below 10 in my right eye. Below is the histogram for all IOP measurements for my right eye going back to the first day I began treatment. (The 8 values in the 10 mm Hg bin are from the single day above.)

Bin	Frequency
8	0
10	8
12	99
14	249
16	318
18	382
20	312
22	220
24	110
26	55
28	22
30	8
32	4
34	2
36	1
More	0
Count	1790

Last night I again mixed Xalatan and timolol together without waiting my usual 10 minutes between drops. This time I used Timoptol XE 0.25%. Today, I again recorded some IOP values below 10. I recorded a 9.3 and a 9.7. (Each IOP value consists of at least 3 measurements with my Reichert AT555.)

Out of 1790 IOP values (each of which consists of multiple individual measurements), the only time I have recorded values below 10 was when I mixed Xalatan and timolol together without waiting my usual 10 minutes between drops.

For the whole day today, my IOP values averaged 13.0 for my left eye and 12.9 for my right eye, which seems like a meaningful difference from what I normally see when I wait 10 minutes between eye drops.

The above results made me want to do further analysis. As of now I have 88 IOP measurements on my right eye on the two days following the mixing of Xalatan and timolol together without waiting my usual 10 minutes between drops. I pulled a sample of 625 IOP measurements on my right eye following Xalatan and timolol with a 10 minute separation between doses where other conditions were equal to the sample of 88. Even though the variances for the two data sets are not significantly different (P(F<=f) one-tail = 0.108656461), I used the t-Test assuming unequal variances to be conservative.

The results show that there is a highly significant difference (p < 0.01) between "mixing the two medicines together" and "waiting 10 minutes between drops".

t-Test: Two-Sample Assuming Unequal Variances
	Mixed Together	Separated by 10m
Mean	11.95454545	16.6
Variance	10.6645768	8.830128205
Observations	88	625
Hypothesized Mean Difference	0
df	108
t Stat	-12.62852743
P(T<=t) one-tail	2.65478E-23
t Critical one-tail	2.361372079

Keep in mind the fact that the statistics would not differ if these same numbers had come from 15-20 different people instead of just from me. The sample size is sufficient to make these results very meaningful.