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Pre-perimetric open angle glaucoma

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Rebecca Milston*
BOptom(Hons) MOptom GradCertOcTher
Senior staff optometrist

Michael Yapp*
BOptom(Hons) MOptom GradCertOcTher FAAO
Chief staff optometrist

*Centre for Eye Health UNSW

 

CASE REPORT

Mrs A, a 60-year-old Caucasian female, was referred to the Centre for Eye Health for a glaucoma assessment due to large cupping in both eyes. The patient did not have any obvious historical risk profile for glaucoma apart from her age.

Entering visual acuities with habitual correction were 6/7.6 OD and 6/6 OS. Corneal thicknesses were measured at 545 µm OD and 537 µm OS with ultrasound. IOPs were 22 mmHg in each eye at 11 pm. Gonioscopy showed open angles with no evidence of secondary glaucoma.

Stereoscopic optic nerve assessment (Figures 1 and 2) showed moderately large optic disc cupping in average-sized optic discs. There was no evidence of Drance haemorrhages, no significant Beta peripapillary atrophy and no evidence of retinal nerve fibre layer (RNFL) defects with red-free assessment. There was some undermining of the neuroretinal rim (NRR) in each eye with deep cupping, prominent but regular lamina pores but no evidence of focal thinning, pallor or notching in either eye.

110 Yapp - Figure 1A - F 110 Yapp - Figure 1B - F

Figure 1A. Stereo photographic image of the right disc at the initial visit (best viewed with base out prism)

Figure 1B. Stereo photographic image of the right disc at the third visit

110 Yapp - Figure 2A - F 110 Yapp - Figure 2B - F

Figure 2A. Stereo photographic image of the left disc at the initial visit

Figure 2B. Stereo photographic image of the left disc at the third visit

RNFL analysis with the Cirrus OCT (Figure 3) classified all sectors as within or above normal limits compared to a normative database. The TSNIT graphs and quadrant analysis however showed an asymmetry inferiorly (right inferior RNFL reduced).

110 Yapp - Figure 3 - F

Figure 3. Cirrus OCT optic nerve and RNFL analysis at the initial visit

Ganglion cell thicknesses (data not shown) were all within or above normal limits in both eyes with minor asymmetries.

Heidelberg Retina Tomograph 3 (HRT3) (Figure 4) classified the NRR as outside normal limits in both eyes compared to a normative database (superior nasal OD and inferior nasal OS).

110 Yapp - Figure 4 - F

Figure 4. Heidelberg Retina Tomograph 3 Moorfields Regression Analysis of the NRR at the initial visit

Visual field testing (data not shown) showed good reliability indices. There was a minor superior field defect in the pattern deviation plot for the right eye and Glaucoma Hemifield Test (GHT) was classified as outside normal limits. The left field was essentially clear.

Based on this initial set of results, the patient was advised to repeat the visual fields at the referrer’s practice to confirm if the defect in the right eye was repeatable and assuming a clear result, be reviewed with repeat imaging annually.

Mrs A was referred back to the centre 18 months later, at which time there was no change in the historical risk profile and IOPs were 20 mmHg OD and OS. There were no notable funduscopic changes in the NRR or RNFL, no marked changes in the HRT or OCT (three results are needed for instrument-based change analysis) and the visual fields were essentially clear in both eyes. Annual review was recommended.

Mrs A was seen again at the centre 12 months later. Her historical risk profile and IOPs were unchanged from the previous visit.

Comparative stereoscopic nerve evaluation (Figures 1A and 1B) showed a darkening of the inferior nasal RNFL extending from the disc in the right eye. There was also a change in contour of a blood vessel overlying the inferior temporal neural retinal rim correlating with a thinning of the rim in this location. There was no apparent change in rim of the left disc however a Drance haemorrhage was noted supero-nasally.

HRT3 topographical progression analysis (Figure 5) correlated with the disc appearance and showed a thinning of the inferior neural retinal rim in the right eye with no statistically significant changes in the left—a minimum area of 20 megapixels (small squares) is required to represent a significant area of change.

110 Yapp - Figure 5 - F

Figure 5. Heidelberg Retina Tomograph 3 topographical change analysis of the right eye at the third visit

Cirrus OCT GPA (Figures 6 and 7) showed an area of possible thinning inferiorly on the deviation map, the RNFL thickness profile and inferior quadrant analysis of the right eye.

110 Yapp - Figure 6 - F

Figure 6. Cirrus OCT Guided Progression Analysis of the right eye at the third visit

110 Yapp - Figure 7 - F

Figure 7. Cirrus OCT Guided Progression Analysis of the left eye at the third visit

The left deviation map showed scattered areas of change with the average RNFL thickness, and the inferior and superior nasal regions in particular showed possible loss.

Progression analysis was not available on visual fields results; however, 24-2 testing (Figures 8 and 9) revealed mostly edge point defects in both eyes with no notable correlating defects reflective of the changes seen on imaging and the discs.

110 Yapp - Figure 8 - F

Figure 8. Humphrey 24-2 SITA-Standard Visual Field Analysis of the right eye at the third visit

110 Yapp - Figure 9 - F

Figure 9. Humphrey 24-2 SITA-Standard Visual Field Analysis of the left eye at the third visit

Based on the changes seen in disc appearance which were supported by HRT and OCT results, particularly in the right eye, this patient was diagnosed with pre-perimetric open angle glaucoma and commenced on Xalatan drops which reduced the IOPs to 15mmHg.

Discussion

NHMRC guidelines note that advanced imaging of the optic nerve head can be valuable in diagnosing glaucoma.1 This case highlights how imaging equipment can act as a supplementary technique for detecting glaucoma conversion or progression. The HRT can provide an objective assessment of the NRR including topographic and parameter based change analysis.

OCT measurements are becoming an integral part of a structural glaucoma assessment and progression analysis, with new methods aimed at detecting the loss of neural tissue constantly being researched and developed.

The optic nerve haemorrhage and imaging results prompted further analysis of the NRR with flicker stereo photographs, with it unlikely that the subtle change in the right eye would have been otherwise detected.

The current gold standard of glaucoma diagnosis is still based on assessment of the optic nerve head and visual fields. In the Ocular Hypertension Treatment Study (OHTS), of the patients who converted to glaucoma, 35.2 per cent were diagnosed from visual field changes, 55.2 per cent from optic nerve changes and the remaining 9.6 per cent were diagnosed based on concurrent changes.2 A variety of visual field changes can occur in glaucoma, with two or three examinations required to confirm the repeatability of a defect. Due to literature on progression analysis being currently available only for white-on-white SAP, it remains the gold standard for measuring progression.3

In this patient, the loss of structure precedes a detectable loss of function. This highlights the need for careful stereoscopic nerve examination, ideally with a comparison to previous stereo images to ensure early glaucoma diagnosis. Changes that can occur in glaucomatous progression of the NRR identified and utilised in the OHTS included:

  • A change in the position of the vessels greater than expected from a shift in the position of the eye
  • The development of a notch
  • The development of an acquired pit
  • Thinning of the NRR
  •  Development of localised or diffuse pallor.

Other changes that should also be carefully considered include:

Drance haemorrhages4

  • Changes in Beta zone atrophy (the inner zone of chorioretinal atrophy around the disc)
  • The development of, deepening or widening of localised wedge RNFL defects
  • Changes in the visibility or shape of the Lamina Cribrosa pores.

 

  1. NHMRC Guidelines for the Screening, Prognosis, Diagnosis, Management and Prevention of Glaucoma (2010). Canberra: Australian Government Publisher. Available online from www.nhmrc.gov.au/guidelines/publications/cp113-cp113b.
  2. Kass M et al. Ocular Hypertension 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: 701-713.
  3. Weinreb RN, Garway-Heath DF, Leung C et al. Progression of glaucoma. Amsterdam: Kugler Publications 2011.
  4. Budenz et al. Detection and prognostic significance of optic disc hemorrhages during the Ocular Hypertension Treatment Study. Ophthalmol 2006; 113: 2137-2143.


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