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Versatility with precision

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Françoise Rateau
BSc BScOptom FACO FACBO FCOVD
Paul Croucher
BSc BScOptom FACO FACBO FCOVD
Howell Croucher Rateau and Associates, Heathmont VIC

Product
Spectralis OCT

Supplier
Heidelberg

 

We have had our Heidelberg Spectralis OCT for more than a year and while understanding how to incorporate it into our patient examinations took some effort, it is now indispensable in our clinical care.

Some OCTs are more highly-automated and easier to use initially, but automation often results in less versatility.

The Spectralis OCT has two lasers. One acquires the B-scans to give us the image we all know as the OCT image, which is guided by a confocal scanning laser ophthalmoscope. This provides a live retinal image used for the eye-tracking function. The Spectralis follows the retina through micro saccades, torsional movements and drifts, and continues to scan. Many machines stop scanning when they lose registration. The Spectralis will also stop scanning, but only during a blink, and then the scan continues.

There are times when the operator may require a scan of either a larger area, with significant pathology, or a smaller area, for greater detail. The Spectralis allows adjustment of the scan size and position and can increase the amount of averaging in any given OCT scan, which improves image quality in the presence of cataract.

Conversely, patients with poor fixation, such as the elderly or children, may require a quicker scan with less averaging. We were even able to diagnose juvenile retinoschisis in a four-year-old boy by looking at a single live B-scan and make an appropriate referral. It was not possible to take a retinal photo or get an adequate ophthalmoscopic view with this child.

One of the hallmarks of glaucoma is asymmetry, between eyes and between superior and inferior hemi-retinas of the same eye. Heidelberg Posterior Pole Asymmetry Analysis enables early detection of ganglion cell changes in the paramacular region and it can map progression over time.

The numerical values provide objective data in patients who have unreliable field test results. It is reported that more than 50 per cent of all ganglion cells are at the macula. Because of the high density of ganglion cells in this area, we know that visual field testing does not find a loss here until glaucoma is advanced.

 

EQ 158 Figure 1 - online.jpg

Combined report showing marked retinal thickness asymmetry together with RNFL and ONH minimum rim width both outside normal age limits. Note the white line showing fovea to disc alignment.

 

EQ 158 Figure 2 - online.jpg

Thickness Map report set for ganglion cell layer segmentation exhibits apparent thinning OS and marked inter-eye asymmetry

 

The Spectralis glaucoma package allows for early detection of ganglion cell loss by comparing the relative thickness of superior and inferior hemi-retinas. A big advantage of the Spectralis OCT is the ‘Glaucoma Premium package’ with the ability to objectively identify the optic nerve margin based on Bruch’s membrane opening and measure the optic nerve rim from this anatomic landmark.

This allows more certainty when assessing unusual discs such as high myopes, tilted discs or in the presence of peripapillary atrophy. The Spectralis Fovea to Disc alignment ensures that retinal nerve fibre layer and optic nerve head scans are always correctly oriented even when the patient’s head is tilted.

At our practice, our OCT measures of glaucoma are:

•  ONH rim width analysis compared to normal population data

•  RNFL thickness compared to the normal population and between eyes

•  Post pole retinal thickness asymmetry, between eyes and between hemifields.

Progression over time will be very interesting for us over the next 12 months. We are led to believe that there is little age-related attrition of ganglion cells and that if it does exist, it is likely to result in generalised rather than localised thinning.

The Spectralis is upgradeable. It has modules for anterior eye across the whole anterior chamber, autofluorescence, multicolour and wide-field OCT and cSLO (similar to but not as wide as the Optos unit). An OCT angiography module will be available soon. We look forward to investigating some of these options.



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