The annual conference of the Scottish Contact Lens and Ocular Surface Society (SCLOSS) is now established as one of the important dates in the diary for live CET. The ever-expanding event continues to attract eye care clinicians from the UK and many from overseas and this year was noteworthy for having expanded its brief beyond matters of the anterior segment (figure 1).
A packed, indeed at times almost too packed, agenda offered a full range of lectures, discussion seminars and workshops (figures 2 to 5). The popularity of the event is now being discussed by the organisers so that next year the programme will be spread to offer greater access to individual sessions as competition for places at each was very high.
The two workshops I will focus on in these two review features were designed to look at how technology is helping to distinguish disease changes and their course over time from expected physiological changes.
Figure 2
Changes
Many of the instruments currently used to assess retinal health are sensitive enough to reflect quite subtle change in retinal structure and function. As the retina changes with age and between individuals, it is important to be able to distinguish what changes might be expected as opposed to those that reflect underlying disease processes. This was the main theme of a three station workshop where delegates were asked some questions regarding the use of high resolution OCT, macular pigment measurement and the use of OCT combined with visual fields data.
Figure 3
Station 1: High resolution OCT (supported by Heidelberg Engineering UK)
This station had two halves – firstly delegates were taken through the assessment of the retinal layers, the vitreous, and the choroidal vasculature of a patient. Depending on the session (workshops ran four times), the guinea pig was either 26 years old or someone in their seventies.
Figure 4
It was noted firstly how retinal structures thin with age. For example, the thickness plot for the ganglion cell layer showed such a change. Delegates were also reminded how this is portrayed in the data plots. Thickness maps show thicker areas as thicker areas as hot or redder colours and thinner areas as cold or bluer colours. Importantly, accurate tracking techniques mean changes over time are measurable, usually displayed as change or significance maps, and these can be used to decide when changes to structure are outside what one might expect through typical ageing processes.
Figure 5
High resolution assessment, as is possible for example with the OCT2 software in the Spectralis OCT used for this session, offers much greater clarity in vitreous assessment and the gradual deterioration and liquefaction of the vitreous with age is easily seen. Furthermore, newer OCTs offer a better cross-sectional view of the choriocapillaris and this structure is seen to thin with age too. Many clinicians are expecting some normative database to make choroidal assessment part of the health screening process but obviously this is not an easy analysis as there are so many variables affecting vascular structure.
Figure 6
The second half of the station involved ophthalmologist Fahd Quhill showing OCT results from two patients; one having dry AMD and the other a younger patient who had suffered dramatic sight loss due to macular damage from a laser pointer. The profile of macular damage was clearly different (the acute lesion showing para-lesion oedema for example) and Quhill was able to use the session as a reminder of the extreme and avoidable dangers of laser pens (figure 6).
Station 2: Macular pigment measurement (supported by BondEye)
At this station, Dr Ian Murray, a key researcher in macular pigment assessment, took delegates through the use of a macular pigment measurement (using the MPS II, figures 7 and 8) and discussed what influences the levels found. As most are aware, diet is the source of lutein and zeaxanthin and so a key modifiable influence in the levels of the pigments measured.
Figure 7
Heterochromatic flicker photometry is employed by the MPS II to determine the amount of blue light required to achieve isoluminance when looking through your macular pigment (central measurement). The measurement is then repeated without the macular pigment by using peripheral fixation target. The blue light levels are compared and the difference is the absorption by the macular pigment. The clinical data collected has allowed us to remove the peripheral measurement and use age estimate as the eyes’ response with age is known. Age is a significant non-modifiable influence upon pigment levels. The macular pigment is measured by its optical density. Optical density ranges from 1 = 1 log unit of macular pigment optical density (MPOD) through to 0 (zero) where all light passes through.
Figure 8
Station 3: Structure and function – fields and OCT (supported by Zeiss Instruments)
The accurate integration of perimetric (functional) data with structural (OCT) data is useful to see how vision loss might relate to tissue change. The aim of this station (figure 9) was to develop understanding of how changes in OCT structure might be relevant to the patient’s vision by superimposing the perimetric data, representing function, upon the OCT data, representing structure, to see how the two relate and indicate change through either normal processes or disease.
Figure 9
Firstly, delegates were reminded of the appropriate choice of visual fields program. Where disease might be suspected, such as those patients presenting with significant risk factors for primary open angle glaucoma (including being over a certain age), a more sensitive full threshold program should always be considered. The trade-off here, of course, is that some normals may show anomalous results for more sensitive testing and so improvements to specificity are essential (as offered by the SITA algorithms).
Other areas of reliability include fixation stability and delegates were reminded of the importance of not only monitoring the reliability indices but of ensuring the appropriate fixation target is employed, such as using multiple paracentral targets where the patient has a central scotoma.
Figure 10
Zeiss has developed its FORUM software that allows the combination of OCT data and visual fields data in one output (figure 10). This is an invaluable way of confirming whether area structural change, such as disc anatomical variation or retinal thinning, has had any measurable impact on subjective vision. Both structure and function change with age and so unusual change in one outside expected levels is significant.