INTRODUCTION
Ocular hypertension (OHT) is defined as the presence of elevated intraocular pressure (IOP) measured more than 21 mm Hg on at least two occasions, in subjects with normal, open anterior chamber angles, no glaucomatous optic nerve changes or retinal nerve fiber layer (RNFL) defects or visual field abnormalities. The elevation of IOP must not be secondary to steroid use, uveitis, neovascularization, etc.
Case 1: No treatment required for ocular hypertension
Mr X, a 42-year-old gentleman, was found to have persistently elevated IOPs on three visits [oculus uterque (OU) 24, 25, 24 mm Hg]. The cup-to-disc (C:D) ratio was 0.3:1 and 0.2:1, with a healthy neuroretinal rim. The visual field did not show any changes suggestive of glaucomatous damage. The central corneal thickness (CCT) was 531 microns and 522 microns for the right and left eyes, respectively. The optical coherence tomography RNFL did not show any RNFL defects and gonioscopy showed wide open angles. The risk of developing glaucoma in one eye, over 5 years was found to be less than 15% as per the OHT risk calculator. Risks and benefits of initiating glaucoma therapy were discussed with Mr X, and he agreed that a continuous yearly follow-up was better for managing his condition.
Some patients do not like the unknown desire therapy, while others are comfortable in being followed. If therapy is commenced and adverse effects are noted or the medications are ineffective, then going back to careful monitoring is indicated.
Case 2: Treatment for ocular hypertension required depending on age
An optometrist referred a 25-year-old African-American male for an applanation IOP. Subject's IOP measured 34 mm Hg OU on the noncontact tonometer at his initial visit with the optometrist. His applanation IOP was 34 mm Hg oculus dexter (OD) and 32 mm Hg oculus sinister (OS) and his C:D ratios measured 0.4 OU. His neuroretinal rim (NRR) was healthy with no nerve fiber layer defects. Automated visual field testing and nerve fiber analysis revealed no glaucomatous defects. Gonioscopy reveals open angles with no pigmentation. His grandfather had been operated for glaucoma.
Considering patient's young age, high IOP, race and a positive family history; he was labeled as a “high-risk” ocular hypertensive (Fig. 1.1); therefore, he was started on glaucoma medication.
Case 3: Treatment for ocular hypertension required depending on central corneal thickness
A healthy 50-year-old Caucasian male presented for a routine exam. His IOP measured 24 mm Hg OU and his C:D ratios measure 0.4:0.45 OU. His NRR is healthy and no nerve fiber layer defects are detected. Automated visual field testing and nerve fiber analysis reveal no glaucomatous defects. Gonioscopy reveals open angles with trace trabecular meshwork pigmentation with no peripheral anterior synechiae. He has no family history of glaucoma.
Fig. 1.1: Patient's risk of converting to primary open-angle glaucoma (POAG) as calculated on http://ohts.wustl.edu/risk.
How to Manage this Patient if His Central Corneal Thickness Measured 480 Microns or 610 Microns?
If the patient has a thick CCT (>600 m) and an IOP of 24 mm Hg, his true IOP is likely lower than the Goldmann tonometer measurement and has a negative family history of glaucoma, so we can monitor him. On the other hand, if the patient has a CCT of 480 microns, consideration of medical therapy may be warranted prophylactically.
Physicians must remember that one CCT measurement may not be satisfactory for long-term patient follow-up. It is suggested to perform at least one repeat measurement at a follow-up appointment to ascertain whether the initial CCT value was accurate, and then to repeat it once every year. A helpful strategy while doing pachymetry is to take five measurements, disregard the first and the last measurements and select the lowest of the remaining three measurements.
Interpretation of CCT measurements varies amongst physicians. Some practitioners alter measurements based on a pachymeter adjustment factor, whereas others classify measurements as thin, average or thick. Currently, no single algorithm for adjusting IOP based on pachymetry measurements is accepted because the relationship between IOP and CCT is believed to be nonlinear.
Case 4: Treatment for ocular hypertension required depending on DV and high peak pressures
Mr A, a 44-year-old Asian-Indian man, was found to have persistently elevated IOPs on three visits (OU 26, 30, 24 mm Hg). His CCT was 560 OD and 555 microns OS. The C:D ratio was 0.3:1 OU, with a healthy neuroretinal rim. He was planned for phasing. The maximum IOP was 37 mm Hg OD and 36 mm Hg OS. The peak IOP was in the morning at 5 AM in both the eyes. The difference between the maximum and minimum IOPs was 13 mm Hg OD and 11 mm Hg OS (Fig. 1.2). In view of significant fluctuation in IOP throughout the day and the fact that the patient was a frequent international traveller and had difficulty visiting the clinic for frequent follow-up, he was started on G Travoprost HS.
A study has demonstrated that portions of the lamina cribrosa move maximally during pressure changes of 35–7 mm Hg, in contrast to minimal movement at pressure changes exceeding 15 mm Hg. Kinking of the axons may occur in small pockets of the lamina cribrosa, which move maximally at small pressure changes while other pockets remain relatively stationary. Another proposed theory is that fluctuations may result in an ischemia reperfusion injury.
Diurnal fluctuations in IOP increase the risk of visual field loss for patients with glaucoma. For patients with significant IOP fluctuation, it is suggested to monitor IOP closely and prescribe medication that best controls IOP with the least amount of fluctuation.
Investigations
Every patient of OHT requires a careful and comprehensive eye examination to rule out early signs of glaucoma or secondary causes of elevated IOP.
Mandatory tests include:
Visual acuity and refraction
Tonometry (applanation): On at least two different occasions, at different times of the day, with IOP more than 21 mm Hg is mandatory for diagnosing OHT.
Gonioscopy: Anatomically normal and open angles are mandatory for diagnosing OHT.
Optic nerve assessment: A dilated assessment of the optic nerve head is essential together with a red free evaluation of the peripapillary RNFL. The optic nerve head (ONH) can be documented using a hand drawn, labeled diagram (special emphasis on C:D ratio, notching, RNFL defects, and/or hemorrhage) and/or a clinical picture. A colored photo and a red-free photo of the ONH are essential for serial follow-up.
Visual field testing: Reliable visual fields provide a baseline for future follow-up.
Central corneal thickness or pachymetry is required to make therapeutic decisions.
In addition, the following tests, if performed help in managing the condition better, in case the facilities exist, and are affordable to the patient.
Stereo optic disc photographs to confirm normal optic nerve parameters and document baseline
Imaging of the optic nerve with RNFL analysis (ocular coherence tomography, Heidelberg retinal tomography or scanning laser polarimetry) provide a statistical comparison with the normative database, thereby providing additional information for subsequent management.
Diurnal variation of IOP curve may provide additional information and influence treatment protocol.
Water drinking test (WDT): A WDT with 10 mL/kg body weight of water over five minutes, may be performed as a surrogate for diurnal variation of IOP to provide a rough idea of IOP peaks and fluctuation.
Follow-up Protocol
Follow-up protocol is to be customized to the individual patient, depending on the risk of developing glaucoma, risk factors present, and whether treatment has been initiated or not. Initially, a follow-up may be scheduled every 3–6 months for IOP checks. Repeat visual field and optic nerve testing may be performed annually or sooner, if changes are suspected.
Commentary
The definitive study that influences management of OHT in the current evidence-based practice of glaucoma is the OHT treatment study. The study is described in brief in the Box 1.1, while Box 1.2 describes the European Glaucoma Prevention Study.
POINTS TO REMEMBER
- Intraocular pressure must be measured two or more times on separate occasions, before labeling a patient as having OHT.
- A gonioscopy must be performed to rule out angle closure, and a slit lamp biomicroscopy, and/or imaging studies of the ONH must be performed to rule out optic nerve damage. A reliable visual field is essential for ruling out field changes.
- A pachymetry is required to give an indication of the eyes ability to withstand higher pressures. There are no validated normograms for IOP correction on the basis of CCT. IOP corrected for corneal thickness, therefore, does not provide a valid basis for initiating or not initiating therapy.
- The threshold for starting treatment for OHT must be lower for patients with increased risk factors (Fig. 1.3). These include:
- African or Hispanic ancestry
- Family history of glaucoma or glaucoma induced blindness
- Younger patients
- Patients with myopiaFig. 1.3: Multivariate hazard ratios for predictors of POAG.(C:D: Cup-to-disc; CCT: Central corneal thickness; DIGS: Diagnostic innovations in glaucoma study; EGPS: European glaucoma prevention study; IOP: Intraocular pressure; OHT: Ocular hypertension; OHTS: Ocular hypertension treatment study; POAG: Primary open-angle glaucoma; PSD: Pattern standard deviation).
- Patients with poor access to repeat glaucoma investigations
- Patients with decreased corneal thickness, high C:D ratio and/or visual fields with high pattern standard deviation.
- It is important to consider the economics of glaucoma therapy as also compliance issues. Quality of life costs of treatment versus no treatment must be weighed for the individual patient.
- The risks and benefits of selective laser trabeculoplasty versus topical glaucoma therapy must be discussed with the patient.
SUGGESTED READING
- European Glaucoma Prevention Study (EGPS) Group; Miglior S, Pfeiffer N, Torri V, Zeyen T, Cunha-Vaz J, et al. Predictive factors for open-angle glaucoma among patients with ocular hypertension in the European Glaucoma Prevention Study. Ophthalmology. 2007;114(1):3–9.
- Gordon MO1, Beiser JA, Brandt JD, Heuer DK, Higginbotham EJ, Johnson CA, et al. The Ocular Hypertension Treatment Study: baseline factors that predict the onset of primary open-angle glaucoma. Arch Ophthalmol. 2002;120(6):714–20.
- Herndon LW, Weizer JS, Stinnett SS. Central corneal thickness as a risk factor for advanced glaucoma damage. Arch Ophthalmol. 2004;122(1):17–21.
- Kass MA, Heuer DK, Higginbotham EJ, Johnson CA, Keltner JL, Miller JP, et al. The Ocular Hypertensive Treatment Study: a randomized trial determines that topical ocular hypotensive medication delays or prevents the onset of primary open-angle glaucoma. Arch Ophthalmol. 2002; 120(6):701–13.