There is a simple answer, or alternatively, a more complex answer based on an understanding of retinal anatomy and physiology and let’s face it, the pragmatism of the real world.
Simple answer – straight away (or within 72 hours, because most macular problems will respond beautifully to treatment that is instituted within 72 hours).
Complex answer – it depends on some features
• Is the loss of vision of rapid onset or has it slowly evolved
• The nature of the vision loss – central distortion only (metamorphopsia) with no peripheral vision involvement, or loss of peripheral vision, painless or painful.
• Is it a sudden loss of vision or merely a sudden awareness of a more chronic loss of vision (quite common). (the take home message here being that more people should use the Amsler grid to facilitate earlier detection of unilateral decreased vision)
The basic anatomic feature to remember is that we’re issued with approximately 25,000 cone photoreceptors at our fovea, the majority of which will have to last us our lifespan to enable us to have useful central vision. Unfortunately, submacular fluid inevitably causes a loss of photoreceptor mosaic and our cone photoreceptors are not replaceable.
Obviously the entire set of cone photoreceptors don’t die immediately and the damage that is done to the photoreceptors depends on how rapid the onset, the severity of the condition and the duration of the condition. E.g. macular fluid associated with an aggressive blood vessel growth (SRNVM) or with peripheral loss of vision (i.e. serous macular detachment secondary to rhegmatogenous retinal detachment) will experience a more rapid loss of photoreceptors than a more benign Central Serous Retinopathy. But, ALL these conditions do lead to loss of valuable cone photoreceptors if given enough time.
Also, to further confuse the issue, many patients have a sudden onset of awareness of central vision aberration. It is all too common to see patients that have been developing severe macular pathology in one eye that has been there for up to twelve months but the patient has not noticed this because the vision in the other eye has been sufficient to carry them through.(Let’s encourage use of the Amsler grid as a public eye health strategy)
Here’s the common clinical scenario:
Rapid onset metamorphopsia (over a few days) – metamorphopsia (i.e. straight lines appearing wavy or kinked) of rapid onset should be seen within 24 – 72 hours. Although it would most likely be wet macular degeneration in the older age group, it’s still possible that it could be a retinal detachment developing. Obviously symptoms of significant loss of peripheral vision will favour a retinal detachment (or other more extensive retinal pathology such as branch retinal vein occlusion).
Slow onset Metamorphopsia - If the symptoms had come on slowly, e.g. over a period of many weeks or months, I still think it’s useful to review these patients relatively quickly – i.e. within a fortnight. If these patients could monitor their vision during that fortnight and if the symptoms are getting markedly worse quite quickly, then the appointment could be brought forward 24 – 48 hours.
Other less common scenarios:
Sudden painful loss of vision – review straight away. Ask about Giant cell Arteritis symptoms, trauma, CVA etc. It would be very rare for it to be a macular problem, but I have seen SRNVM present as severe subretinal and suprachoroidal haemorrhage with severe pain due to stretching of the choroidal nerves (or high pressure or both).
Summary – treatment of submacular and/or intraretinal fluid from SRNVM, retinal vein occlusions, diabetic retinopathy, CSCR, retinal detachment within 72 hours will result in excellent recovery of macular cone photoreceptors. Other ILM and vitreous related maculopathies such as Macular Hole, Macular pucker, Vitreo-macular traction, will also respond beautifully to restorative Vitrectomy and epiretinal membrane peel within a time frame of a few weeks.
Please note that you can help the patient not only with the urgency of your referral but also with your selection. The referral can be made rapidly, but please keep in mind that retinal subspecialists who see many second opinion cases, witness the fact that the patient’s visual outcome heavily depends on the correct diagnosis, rapid facilitation of appropriate investigations and rapid movement from clinic assessment to actual treatment. An incorrect diagnosis or a treatment plan that consists of too-little-too-late macular treatment will be more damaging to the patient’s macula than a one day delay to see the retinal subspecialist. Our Vision Eye Institute Retinal subspecialists’ clinics are geared up to rapidly accept add-on patients experiencing metamorphopsia and to get their treatment started straight away.