Fundus check: Should I dilate pupils or not?
Glaucoma risk due to ophthalmic drops which cause pupil dilation is rare.
Fundoscopy is used primarily for diabetic retinopathy (DR) detection. Fundoscopy’s sensitivity through pupil dilation for DR detection is two times higher, in relation to detection through non dilated pupils. However, researches have revealed that only one out of 250 doctors frequently dilate their patients’ pupils. A usual reason of non pupil dilation is the concern about the risk of narrow angle glaucoma.
How big is the risk?
Recent researches show that this risk is extremely low. In a study that took place in Rotterdam in 6.750 people, the use of mydriatic eye drops caused narrow angle glaucoma only in 2 patients (0,03%). In Australia the “Blue Mountains Eye Study” in 3.654 subjects also found no cases of narrow angle glaucoma due to pupil mydriasis.
A scientific review showed that in 600.000 subjects who received mydriatic eye drops, 33 (0,006%) had narrow angle glaucoma, giving an estimated risk of about 1 in 20.000 patients.
Even in high-risk groups, the risk of narrowangle glaucoma due to mydriatic eye drops is found to be very low. In 13 studies which included more than 1.000 patients with chronic open-angle glaucoma, no one showed acute glaucoma after mydriasis. In the Rotterdam study 1 in 149 people (0,7%) showed acute glaucoma due to mydriasis , as revealed in the slit lamp examination. The authors recommend that in primary care, patients should look for immediate treatment, if they have acute glaucoma symptoms.
There are few published data on Asian populations, where the risk of narrow angle glaucoma is believed to be higher. In a study of 1.232 Chinese subjects, where no one showed acute glaucoma after mydriasis, the assessment of risk for Chinese Asians is less than 1 in 1.000. In another study in 2.400 Singapore Malaysians, only one subject showed acute glaucoma, attributing the risk of 1 in 2.400 for Malaysian Asians.
There are pathophysiological reasons why it is unlikely that mydriasis leads to acute glaucoma. The pupil obstruction, the mechanism of acute narrow angle, is considered to happen when the pupil is in a state of half-dilation than in full dilation stage. In fact, the pupil is in half-dilation stage in dimly lighted environments, which means that staying in a dark room sets in greater risk of acute glaucoma, compared with instilling mydriatic eye drops.
Pupil dilation is very important in extensive fundoscopy and the risk of acute narrow angle glaucoma using mydriatic drops is close to zero. Tropicamide 0,5% is a safe substance to use in primary care. However, in all cases the patients should always be advised to look for medical care if they develop acute glaucoma symptoms (red eye, eyeball pain, blurred vision, nausea and vomiting), even if both the patient and the doctor are certain that this possibility is extremely low.