Giãn đồng tử thường xuyên để cho phép kiểm tra của đáy là tốt nhất đạt được bằng cách giảm tropicamide 0,5% hoặc 1% vì hiệu ứng kéo dài chỉ khoảng 3 h. Cyclopentolate 1% (0,5% ở trẻ sơ sinh) có thể kéo dài trong 24 h, nhưng vì hiệu ứng cycloplegic của nó | 196 Common Eye Diseases and their Management Drops That Widen the Pupil The pupils can be dilated either by local blockade of the parasympathetic pathway or by local stimulation of the sympathetic pathway. Parasympathetic Antagonists Routine mydriasis to allow examination of the fundus is best achieved by tropicamide or 1 drops because the effect lasts for only about 3 h. Cyclopentolate 1 in babies can last for 24 h but because of its cycloplegic effect blockade of accommodation is preferable for the examination of children s eyes when refraction is also needed. Dilating the pupil runs the risk of inducing an attack of acute narrow-angle glaucoma in a predisposed individual. Because the vision could remain blurred driving should be avoided within the first 6-8h after mydriasis. Atropine in drop form is a long-acting mydriatic which is used when it is necessary to prevent or break down adhesions between iris and lens in acute iritis posterior synechiae . It is also used in the treatment of amblyopia in children. Its effect lasts for about seven days. Allergic reactions are quite common and occasionally systemic absorption can cause central nervous system symptoms of atropine toxicity. Sympathetic Agonist Phenylephrine 5 or 10 drops is a sympathomimetic amine. It is used with a parasympathetic antagonist when extremely wide pupil dilation is required . for intraocular surgery or for peripheral retinal examination . There are reports of severe acute hypertension after use of 10 drops. Drops That Constrict the Pupil In the past meiotics have been widely used for the treatment of chronic open-angle glaucoma. Pilocarpine is available in 1 2 3 or 4 solutions. Although it is effective in reducing the intra-ocular pressure the side effects of dimming of vision and accommodation spasm can be disabling and mean that this treatment has largely been superceded. Pilocarpine is still used in the treatment of acute glaucoma attacks to constrict the pupil and open up the
