What causes this? Is it the pupil opening up wider than the optical
zone of the lens (if I’m using that term correctly)? Does a larger
lens imply a larger OZ? I ask because I got some bigger lenses to
address some annoying edge effects – and I thought that night vision
might improve too – but in fact it seems to be noticeably worse. I get
quite distracting starbursts around lights, and if something is backlit
and dim (like at dusk) the light bleeds into the dark and makes it hard
to see.
Assuming this isn’t edema (it doesn’t match the descriptions I’ve read,
which were more like colored halos) are there any parameters that can
be adjusted to try to address this? Is this likely to be less of a
problem with soft contacts?
–
Do glasses cause the same? RGPs are supposed to give better vision, not
worse!
Charles wrote:
> What causes this?
possibly the edge of the lens is too close to the pupil thereby
creating a flare effect. the len could be made larger or the base
curve steepened to center the lens better to counter this effect.
> Is it the pupil opening up wider than the optical
> zone of the lens (if I’m using that term correctly)? Does a larger
> lens imply a larger OZ?
not necessarily.
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> I ask because I got some bigger lenses to
> address some annoying edge effects – and I thought that night vision
> might improve too – but in fact it seems to be noticeably worse. I get
> quite distracting starbursts around lights, and if something is backlit
> and dim (like at dusk) the light bleeds into the dark and makes it hard
> to see.
> Assuming this isn’t edema (it doesn’t match the descriptions I’ve read,
> which were more like colored halos) are there any parameters that can
> be adjusted to try to address this? Is this likely to be less of a
> problem with soft contacts?
> —
Charles schreef:
> What causes this? Is it the pupil opening up wider than the optical
> zone of the lens (if I’m using that term correctly)? Does a larger
> lens imply a larger OZ?
Not necessarily so and some lens designs have a OZ nearly the same size
as the total diameter of the RGP lens.
However in some older lens designs there is more or less a relation
between the total diameter of the lens and the OZ.
A professional fitter can use a change in this relation do fit the lens
better.
I ask because I got some bigger lenses to
> address some annoying edge effects – and I thought that night vision
> might improve too – but in fact it seems to be noticeably worse.
Maybe your fitter changed the total diameter and kept the OZ the same size.
If this is the case then you also noticed that your lens moves more.
I get
> quite distracting starbursts around lights, and if something is backlit
> and dim (like at dusk) the light bleeds into the dark and makes it hard
> to see.
It is possible that your lens "low rides" due to the more lose
fitting.(more weight of the contactlens due to the greater total diameter)
It is also possible (in higher minus lenses) your lens just ‘high rides’
It’s also possible that your fitter have changed your lens design also.
There are lots of other possibilities to explain BTW.
> Assuming this isn’t edema (it doesn’t match the descriptions I’ve read,
> which were more like colored halos) are there any parameters that can
> be adjusted to try to address this?
Yes, several but you need a fitter (face to face) to observe what is
wrong with the fitting to get the correct contactlenses.
Is this likely to be less of a
> problem with soft contacts?
In general, yes
Jan (normally Dutch spoken)
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