Here’s some final reviews for the year. There’s some simple evidence to help your interpretation of glaucoma field testing, an encouragement to expand your use of OCT and a glimpse into the future of glaucoma surgery.
Have a great Summer!
Glaucoma: Which OCT scans and when?
Trend Based Analysis of Ganglion Cell – Inner Plexiform Layer Thickness Changes on Optical Coherence Tomography in Glaucoma Progression
Won JL, Young KK, Ki HP, Jin WJ AAO 2017;124:1383-1391
This 3 year prospective observational study evaluated the thinning rates of Ganglion Cell – Inner Plexiform Layer (GCIPL) using OCT on 65 patients already identified with POAG, mean age 53 years. It aimed to identify the diagnostic significance of the GCIPL thinning rate in glaucoma progression.
Subjects were divided into 2 groups including non-progressors (n=38) and progressors (n=27). The locations of GCIPL thinning rates evaluated included global region, affected hemifields and 6 macular sectors. The GCIPL and RNFL thinning rates were also compared. GCIPL thinning rates were determined by linear regression analysis and comparisons were made between the 2 subject groups.
The GCIPL thinning rate was significantly faster in patients with progressive glaucoma than non-progressive glaucoma. The GCIPL thinning rate was also significantly faster in the temporal GCIPL sectors of the affected hemifield than the unaffected hemifield. There was significant correlation between GCIPL and RNFL thinning rates. The authors identify this study’s limitations regarding inclusion of patients with mild to moderate POAG patients with RNFL defect in one hemifield only, therefore further studies for multi-sited defects and advanced glaucoma are necessary.
This study provides further evidence that routinely assessing the structures beneath the macula aids the diagnosis and monitoring of glaucoma. In fact, one recent presentation concluded it may turn out to be the earliest and best predictor of disease and progression. Start doing it!
Post YAG: Be aware of a possible tear
Rate of Retinal Tear and Detachment After Neodymium: YAG Capsulotomy
Wesolosky JD, Tennant M, Rudnisky CJ JCRS 2017;43:923-928
This database observational study from Alberta, Canada waded through 11 years of patient files of which 67,287 met the relevant criteria for inclusion. Their aim was to document the rate of retinal tear and detachment following Nd:YAG capsulotomy for posterior capsule opacification. The rates of retinal tear and detachment at 5 months following YAG was 0.29% and 0.87% respectively. There was a higher risk for RD than a retinal tear occurring within the first 5 months following Nd:YAG, with a return to a baseline plateau thereafter.
These figures are pretty much in line with the “1/100’ risk we have been giving patients for many years. In some ways, all pseudophakic patients should have a YAG as any PCO degrades the image, particularly in patients with multifocal IOLs. On the other hand there is a risk and if patients have good vision and no symptoms it’s best to leave PCO. It’s also important to warn patients having a YAG of the risk, and symptoms or retinal tears and detachment. Perhaps the most controversial issue is whether patients should have a follow up dilated examination, given the low rate of complications. I would argue they should. It’s good to check the vision has improved and get a better view of the fundus. Last year I found two macula-on detachments at one week review. Vision saved!
What’s new in glaucoma surgery?
Minimally Invasive Glaucoma Surgical Devices: Are They Ready for Prime Time? (Editorial)
Srinivasan S JCRS 2017;43: 867-868
This editorial discusses the importance of robust and long term studies and development of new strategies to combat the global projected prevalence of glaucoma increasing globally by 74% from 2013 to 2040 (ages 40-80 years).
The author describes the timeline of the introduction of surgical filtration techniques from the iridectomy in 1856 by Von Graefe to the trabeculectomy in 1968 by Cairns, together with the development of devices to shunt aqueous using a gold wire in 1876 by de Wecker through to New Zealand’s Molteno developing the initial Molteno tube in 1969.
Recent enthusiasm has been directed towards microinvasive glaucoma surgery (MIGS) which involves the insertion of an alternate drainage device which aims to reduce IOP. Depending on the chosen MIGS device, their drainage mechanisms work via transtrabecular meshwork, suprachoroidal or subjunctival structures. Early indications suggest fewer surgical risks than the traditional drainage techniques. Other advantages include being less invasive to the patient, higher safety profile, rapid patient recovery, and the procedure can be performed during cataract surgery.
I went to several glaucoma lectures at The AAO meeting in New Orleans recently. There is a lot happening as folk try to get their head around the indications for all the new devices, and whether they actually work. One presenter outlined that patients that respond to pilocarpine seem to have the best results. Another demonstrated an ab interno trabeculotomy, pointing out that we know the procedure is effective for paediatric glaucoma and that 5.0 nylon costs about 5% of the new MIGS devices. Refreshing in an American setting! The bottom line is that it will take years to ascertain if these new procedures achieve lasting IOP reduction. Watch this space.
Can I trust this visual field?
Evidence-Based Criteria for Assessment of Visual Field Reliability
Yohannan J, Wang J, Brown J, Chauhan BC, Boland MV, Friedman DS, Ramulu PY AAO 2017;124:1612-1620
This retrospective study examined 909 subjects to determine the impact of False Positives (FP), False Negatives (FN), Fixation Losses (FL) and Test Duration (TD) on Visual Field (VF) reliability. The patient inclusion criteria were those aged over 18 years, with any glaucoma related diagnosis including glaucoma suspect and having performed ≥ 5 Visual Field tests.
The commonly accepted standard for an unreliable examination for the Humphrey Field Analyser (HFA) is determined if the patient reaches one or more of the following: 33% False Positives (FP) or False Negatives (FN), and 20% for Fixation Losses (FL). Studies have found limitations in using only these 3 indices. Further studies have developed a different method to define a quantitative VF reliability whereby the predicted mean deviation (MD) and observed MD were calculated. Using this data the authors calculated the difference between these 2 variables, giving the change to the mean deviation (ΔMD), and defined VF reliability on the quantitative measure of ΔMD. They then assessed the impact FP, PN and FL had on the ΔMD.
The study concluded that patients with established glaucoma, FL have little impact on reliability, but FP, and to a lesser extent FN and TD, significantly impact the reliability. The impact of FP and FN varies with disease severity and over the range of catch trials. The authors recommend that quantitative measures (ie ΔMD) should be incorporated into the VF machine output so clinicians can take this indice into account when assessing their patients’ VF reliability.
In a sense, visual fields are the most important index of all in the detection and monitoring of glaucoma. Neither we, nor the patients, want field loss to occur or worsen. As we all know, getting good fields, and interpreting them is very difficult. Ideally, all patients should be carefully supervised. This is time consuming (and expensive) but pays dividends. There is good evidence that fields should be done every 6 months in patients suspected of having, or diagnosed with glaucoma, but this is difficult to achieve. I find it very useful to discuss with patients the type of errors they make. Be kind. It’s not easy but simply saying, “Some people tend to look around to make sure they see everything, others like you tend to only push the button when you are absolutely sure you see a light – it’s OK to get it wrong”, can make a big difference to the test quality.
New indications for OCT
The Use of Optical Coherence Tomography in Neuro-Ophthalmology
Chan NCY, Chan CKM Current Opinion – Ophthalmology 2017;28:552-557
Advances in tissue penetration and analysis algorithms now allow clinicians to diagnose, monitor, manage and predict prognosis in neuro-ophthalmic diseases in adults and, even more importantly, children.
There is well established value in assessment of periperipheral Retinal Nerve Fibre Layer (pRNFL) in patients with disc swelling. Now macular Ganglion Cell Complex (mGCC) analysis has been found to supercede the value of optic nerve head imaging. For example, patients with Leber’s hereditary optic neuropathy demonstrate mGCC damage as early as 6 weeks before visual loss.
Detection of true versus pseudo-papilloedema has been improved in analysis of peripapillary total retinal thickness (PTRT) which has a high sensitivity for detecting mild papilloedema and elevated cranial pressure (ICP). Also, enhanced depth imaging has been found to have a higher detection rate of ONH drusen than ultrasound; particularly useful in paediatrics.
pRNFL, mGCC and pRNFL thickness (pRNFLT) analysis can also quantify the amount of papilloedema, rate of progression, treatment efficacy and drug side effects before visual field changes are detected in patients with idiopathic intracranial hypertension, multiple sclerosis, Vigibactrin-induced retinopathy, compressive optic neuropathy and nonarteritic anterior ischaemic optic neuropathy.
Some years ago I bought my OCT to look for subtle cystoid after cataract surgery. It seemed an expensive toy but now is an essential part of everyday practice. Expect this to expand as we see it used more and more in neuro-ophthalmology.