Diagnostic suspicion of optic disc hinges on presence of corroborating findings
Attentive evaluation of the optic disc in clinical practice provides invaluable information for identifying glaucoma, but no single feature provides diagnostic certainty, said Francisco Goñi MD at the ESCRS/EGS Glaucoma Day meeting in Paris, France.
“When a sign of glaucoma is detected, search carefully for other signs and place the information in the context of the complete examination,” advised Dr Goñi, a glaucoma specialist practising in Barcelona, Spain.
In his talk, Dr Goñi discussed the approach to optic disc examination and signs that raise suspicion of glaucoma. Through a series of clinical examples, he showed that individual signs can lack specificity for glaucoma and thus the need to look for corroborating evidence.
To assess the optic disc, Dr Goñi recommended performing the examination through a dilated pupil and prior to knowing information about IOP or the findings from OCT imaging, which could bias the subjective judgment of the optic disc. He also emphasised the importance of comparing the optic disc appearance between eyes by moving the slit-lamp from one eye to the other.
Systematic evaluation of the optic disc focuses on size, cupping and the neuroretinal rim. Dr Goñi said that when considering the cup-to-disc ratio (CDR), however, clinicians must remember that disc size matters.
“We cannot classify patients in terms of glaucoma based only on the CDR. It must be put into the context of cup size because a large disc usually has large cupping and a small disc usually has small cupping,” he explained.
IS or ISNT?
Care is also needed in evaluating neuroretinal rim thickness, recognising that the “ISNT” rule, stating that normal disc rim thickness of inferior the region is ≥ superior ≥ nasal ≥ temporal is not obeyed in 50% of normal eyes and also does not apply to non-standard optic discs. In eyes with a CDR >0.57, clinicians may consider the IS rule (inferior≥superior) that is more specific than the ISNT rule.
Dr Goñi observed that positional changes of vessels at the optic disc that occur due to narrowing of the neuroretinal tissue are important to observe when looking for glaucoma progression but they are not typical as an early sign. Retinal nerve fiber layer defects and disc haemorrhages may also be signs of glaucoma but they are not specific and so need to be considered in the context of whether there are additional glaucoma signs. Beta zone paripapillary atrophy can also be a clue to glaucoma, but is not a definite sign.
Francisco Goñi: firstname.lastname@example.org