Straylight after Cataract Surgery with Implantation of a Clareon or a Vivinex Monofocal Intraocular Lens

It is a common experience to be blinded by a sun that sits low in the sky or by
headlights of upcoming cars at night. This is called disability glare and is
due to light that scatters in the eye. It causes a veil of light over the
retina and thereby reduces the contrast of the retinal image. This (retinal)
straylight may also cause perception of halos and may induce spatial
disorientation.

The amount of straylight varies per eye and increases with age. In the young
normal eye, a third of straylight is due to light scattered in the cornea, a
third due to scattering of light in the crystalline lens, and the remaining
third due to transmittance of light through the iris and sclera and scattering
of light at the retina.

Cataract is an opacification of the crystalline lens. It is a leading cause of
visual disability in the world. When cataract develops, straylight strongly
increases because of an increase in small particles in the lens. With cataract
surgery, the opacified lens is removed and replaced by a clear artificial
intraocular lens (IOL). This leads to a decrease in straylight after surgery
and subsequent improvement of visual disturbances.

Nonetheless, IOLs induce scattering of light to some extent as well. Typically,
however, they induce less straylight than the crystalline lens of a 20-year
old. Nonetheless, different types of IOLs induce a different amount of
straylight. For example, it has been shown that hydrophobic IOLs induce more
scattering of light than hydrophilic ones. In addition, glistenings (i.e.,
small fluid-filled vacuoles) may develop in hydrophobic lenses and also raise
straylight.

The amount of straylight in a pseudophakic eye, i.e. an eye that has underwent
cataract surgery with implantation of an artificial IOL, is described by the
pseudophakic straylight norm. This is a function that provides normal values
for straylight in the pseudophakic eye as a function of age. Interestingly,
although straylight levels of an IOL itself are thus lower than that of a
20-year old phakic lens, straylight levels of the eye after cataract surgery do
not fall below that of a 20-year old (phakic) eye. For example, the straylight
value in a 20-year old pseudophakic eye (log[s], 0.98) is 1.3x higher than that
in a 20-year old phakic eye (log[s], 0.87). Therefore, other factors than the
IOL itself may increase straylight after cataract surgery.

Of note, it is not known how the level of straylight changes in the immediate
postoperative period and when it can be deemed stable. To date, studies on
straylight after cataract surgery (with implantation of other types of IOLs
than currently under investigation) have typically measured straylight at
either 1 or 3 months after surgery.

The Clareon (www.alcon.com) and the Vivinex (www.hoyasurgicaloptics.com) IOLs
are two routinely used hydrophobic IOLs with similar optical properties that
have been shown to be optically very clear.10 These lenses are thus expected to
have a very low amount of straylight by themselves. However, the amount of
straylight in eyes with implantation of either of these IOLs has not yet been
evaluated. In addition, these lenses are made of different proprietary
hydrophobic acrylic materials. This is illustrated, for example, by a
difference in hydrophobicity [De Giacinto, 2019]. Such differences might affect
factors such as adhesion of the IOL to the lens capsule or adhesion to the IOL
of lens epithelial cells that remain after cataract surgery. This, in turn,
might affect postoperative straylight and a reason why straylight levels of the
eye after cataract surgery do not fall below that of a 20-year old eye.

We currently intent to study the clarity characteristics of the Clareon IOL and
the Vivinex XY1 IOL by assessing how it translates to straylight in actual
patients, compare these straylight values to the pseudophakic straylight norm,
determine when straylight can be deemed stable in these eyes after cataract
surgery, and investigate which parameters may affect straylight after cataract
surgery.

Knowledge on the amount of straylight in eyes with implantation of a Clareon
IOL or a Vivinex XY1 IOL will provide us clinical knowledge whether these
lenses also provide clear optics in the eye. In addition, knowing the average
straylight value of these IOLs, as well as its standard deviation, will make it
possible to calculate how many patients would be necessary to include in a
study for comparing these IOLs to each other. Furthermore, knowledge of when
straylight values after cataract surgery can be deemed stable will improve
information given to patients about when they can expect to have optically
clear vision after surgery. In addition, for future studies, it is important to
know when measurements of straylight can be reliably measured after surgery. In
addition, exploring which parts of the eye might be responsible for any
differences in straylight after cataract surgery, may allow for new
developments to minimize straylight in the eye after cataract surgery.

Primary Objective: To determine when straylight stabilizes in eyes after
cataract surgery, determine the amount of straylight in eyes implanted with a
Clareon monofocal IOL and a Vivinex XY1 monofocal IOL, and compare these
straylight values to those in the normal pseudophakic eye (i.e., the
pseudophakic straylight norm).

Secondary Objectives: To assess the relative contributions of the cornea, the
(pseudo)phakic lens, the posterior capsule, and any vitreous opacities to the
total amount of ocular straylight in the eye, to determine the
uncorrected-distance visual acuity (UDVA) and the best-corrected distance
visual acuity (CDVA), to determine the refractive outcome by means of spherical
equivalent refractive error (SEQ) and defocus equivalent refractive error
(DEQ), to investigate the lens position by means of anterior chamber depth, and
to evaluate the presence (and severity) of any opacities in the ocular
structures in the slit lamp photographs.

The study design will be prospective, observational, comparative, single-arm,
and single center.

With cataract surgery, the patient*s opacified lens is removed and replaced
with a clear artificial IOL. The intervention in the present study consists of
implanting a different, albeit very comparable, intraocular lens in one eye
compared to the other eye. More specifically, patients will receive a Clareon
monofocal IOL (www.alcon.com) in one eye and a Vivinex XY1 monofocal IOL
(www.hoyasurgicaloptics.com) in the other.

Although we feel that the risk for patients will be negligible, a potential
risk might be that patients will have two different, albeit very comparable,
IOLs in their eyes. If they were to compare their eyes to each other by
alternatively covering one eye and the other, they might notice a difference in
clarity or color between their eyes. However, the color and the clarity of the
two IOLs are highly comparable. It also has to be noted that in normal phakic
and pseudophakic subjects, the amount of straylight differs between the two
eyes within the same subject to some extent (albeit less than between
individuals). In addition, based on our clinical experience, we do not think
people will be able to notice a difference in color between their eyes. In
routine clinical practice, different types of IOLs are frequently implanted in
both eyes of patients. A reason for this may be that the patient is operated on
the second eye in a different hospital than for the first eye. Another reason
may be that the hospital where the patient is operated started to use a
different type of IOL after the patient*s first eye cataract surgery. It may
also be that a certain power of an IOL that is needed to achieve a set
refractive target is not available in the model used in the other eye.
Furthermore, it may be that a toric IOL is implanted in one eye of a patient
and a non-toric IOL in the fellow eye. In all these cases, two different IOL
models are implanted in the eyes. In practice, patients do not report a
difference in clarity or visual function between the two eyes in all these
cases. What*s more, there are several published reports on implantation of IOLs
with very different colors or with different optical properties in the two eyes
of patients without any noticeable discomfort to them.