Friday, October 13, 2006

Section 7-D: Using Glaucoma Medications

Once a decision is made to initiate glaucoma treatment, often one glaucoma medication is tried in one eye only to see if there is an effect. If there is a documented effect in the treated eye, then the medication is added to the fellow eye if necessary. By doing this “one-eye trial”, the untreated eye is used as a control and serves as a basis for comparison to see if the treated eye actually had any effect from the medication. The reason for the one-eye trial is that there is a diurnal fluctuation of IOP throughout the day. The fluctuation of IOP can be significant in the glaucoma patient; however, the IOPs tend to fluctuate together between fellow eyes. The one-eye medication trial takes advantage of this fact and uses the untreated eye as the control for the treated eye. If there is no effect, this is documented and another medication tried. If there is an effect but the IOP still needs to be lower, another medication may be added in a similar fashion.

Practice with instilling eyedrops improves the success of administering them correctly (Figure 7-4). The eye can normally hold 7 - 9 µl, and the average drop from an eye dropper or dropper tip is 39 µl. If half of the eye drop fails to stay in the eye, there is still enough retained in the eye to be absorbed. If multiple eye drops are being applied to the same eye, it is best to wait at 15-30 minutes between eye drops to enhance drug absorption. Another way to improve absorption (and to decrease the systemic side effect) is to occlude the tear drainage from the eye by nasolacrimal occlusion (Figure 7-5). This is performed by pressing on the tear ducts near the inner lower corner of the eyes. Eyelid closure for several minutes after eye drop instillation has also been noted to be helpful.

Instilling eye drops

Nasolacrimal or punctal occlusion

Figure 7-4. One glaucoma drop is placed on the eye while retracting the lower eyelid.

Figure 7-5. Simple eyelid closure or occlusion of the tear drainage system (punctual occlusion) helps improve ocular absorption while minimizing systemic absorption.

If maximum glaucoma medications fail to sufficiently lower the IOP, then further treatment is indicated with either laser or surgery. The surgical treatment options are based on the stage of glaucoma and anatomic characteristics of each individual.


References

Allingham RR, et al., editors. Shields’ Textbook of Glaucoma, ed. 5. Philadelphia: Lippincott Williams & Wilkins, 2005. pp. 457-508.

Alward WLM. Glaucoma. St. Louis: Mosby, 2000. pp. 186-205.

Bartlett, JD, editor. “Agents for Glaucoma.” IN Ophthalmic Drug Facts. St. Louis: Facts and Comparisons, 2003. pp. 181-252.

Bartlett JD. Jaanus SD, Fiscella RG, Sharir M, “Ocular Hypotensive Drugs.” IN Bartlett JD, Jaanus SD, eds. Clinical Ocular Pharmacology, ed. 4. Boston: Butterworth-Heinemann, 2001. pp. 167-218.

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