BS(Anatomy) BOptom MA(Research)
PhD Student, University of Notre Dame Australia
Honorary Fellow, Australian Health Research Institute, University of Wollongong
Detection of early glaucoma can be difficult even when the eye pressure is relatively high. Visual symptoms that can accompany early chronic and even acute glaucoma are many and varied but in general, are completely absent.
Patients may say that their vision is blurred or haloed. There are many reasons why this may be the case, one of which could be acutely increased eye pressure and it is important for optometrists to exclude the possibility of high IOP when presented with these symptoms.
Most patients have little or only basic understanding of a glaucoma check and many regard it as simply an eye pressure check. The detection of glaucomatous optic neuropathy in primary care optometry requires a clinician to introduce a multimodal narrative to the patient. Among other benefits, this narrative helps to educate patients that a comprehensive glaucoma assessment requires many diagnostic tests apart from eye pressure. For example, gonioscopy, which gives a dynamic assessment of the angle, and other advanced optical diagnostic instruments such as OCT should be used to achieve optimum information to help confirm the diagnosis.
LL is 63 years old and has a long history of elevated eye pressure. She reports that she often ‘calls into’ various optometry practices, including this one, to have her pressures checked. She also reports that she has had her eyes checked regularly and comprehensively by her ophthalmologist and that to date no sign of glaucoma has been detected.
Her corrected vision is normal and she has had lifelong hyperopia: RE +3.00/-1.25x80 6/6 LE +3.00/-0.75x90 6/6.
Her IOPs at this practice in August 2015 were RE 25 and LE 27 with her cornea slightly thicker than normal at RE 0.573 mm and LE 0.571 mm with non-contact pachymetry. Recently, she has had red and sore eyes but this was diagnosed as presumed viral conjunctivitis. Because her eyes were feeling better, on presenting to our practice she requested an eye pressure recheck. Perkins tonometry showed elevated IOP of RE 34 mmHg, LE 38 mmHg with a large amount of variability in each eye reading due to pressure pulsation. Nonetheless, she had no pulsatile tinnitus, proptosis, hypertension or history suggestive of carotico-cavernous fistula.
Her eyes had intact optic nerves (Figure 1), confirmed with OCT results (Figures 2A and 2B), and she reported that visual field threshold tests had been full in the recent past. Slitlamp and anterior OCT showed an iris that was bowed forward (Figure 3).
Figure 1. Retinal photo, left eye
Figure 2A. Right eye, unchanged for two years
Figure 2B. Left eye, unchanged for two years
Figure 3. 2-D anterior OCT illustrating plateau iris
After explaining, with the aid of the anterior eye OCT, that her angle is where the pressure is drained from her eye, gonioscopy was used to confirm the angle as open but somewhat pigmented if not difficult to assess as it was over the horizon of her plateau-shaped iris. Compression gonioscopy showed no peripheral anterior synechiae and the characteristic sine wave, or double hump, of a plateau iris configuration.
Given her case presentation, it was thought that she might require multiple treatment options to control her IOPs and was referred to an ophthalmologist to evaluate treatment options. Initial therapy was commenced with Xalatan and Simbrinza, with a view to additionally performing bilateral selective laser trabeculectomy.
Eventually, she may require peripheral laser iridoplasty to treat her plateau iris configuration if her angle becomes threatened. Therefore, close monitoring by the optometrist and ophthalmologist is key to optimum management.
This glaucoma case illustrates that applanation tonometry and gonioscopy are key examination techniques to be performed on glaucoma suspects.
Tonometry techniques give a convenient screening result, but if the IOP is varying from moment to moment, with a low of 29 mmHg to a high over 30, it is often only the lower values that are recorded reliably with particular instruments, and thus the eye pressure is easily underestimated.
Placed in a clinical context, a screening, electronic eye pressure over approximately 20 mmHg should always be confirmed with Goldmann tonometry or equivalent non-digital applanation technique; however, all glaucoma suspects should have applanation tonometry performed. Whichever eye pressure technique is used, understanding the limitations and benefits of that technique is important.
Similarly, if anterior eye slitlamp microscopy, Van Herrick examination of angels or an anterior OCT shows any unusual features or does not adequately explain the status of a patient’s IOP, then gonioscopy should be performed. Any patients who have risk factors for glaucoma should have routine gonioscopy performed.
OCT assessment of the anterior angle should be a supplement rather than a replacement for gonioscopy. Additionally, gonioscopy allows a dynamic assessment of the anterior chamber angle.