Download Quality of vision, the precorneal tear film and cataract surgery

EDITORIAL
Quality of vision, the precorneal tear film and
cataract surgery
Dry eye disease (DED) is the most frequent ophthalmic condition. Its prevalence
increases with age, female gender, low omega 3 intake, and after ocular surgery (mainly
refractive and cataract surgery). For this reason, at present and in the future, DED will
constitute a true epidemic in our clinics.
The inclusion of visual disturbance into the definition of DED provides new evidence
that DED is indeed associated with dynamic visual changes. Patients with DED have
problems reading, watching TV and driving because the frequency of blinking decreases
in these situations. When testing for visual disturbances in a DED patient the standard
static methods for visual testing are not useful, because patients can blink when the
image become blurred1. Thus we need instruments to assess vision dynamically when
blinking is impaired. Previous studies suggest that reduced optical quality of the eye is the
primary cause of blurry vision associated with DED and tear-film disruption. A marked
interference in vision in patients has been reported as well as a significant improvement
in visual acuity and threshold readings in static perimetry after artificial tear instillation.
DED may affect the optical quality of the retinal image as a result of several different
factors. Tear film changes in DED may lead to irregularities of the corneal surface and
irregular tear film distribution over the corneal epithelium. This implies that dry eyes have
greater optical aberrations than normal eyes. In addition, the dynamics of the tear film
differ between normal subjects and patients with dry eye.
Different optical-based methods have been proposed for testing the quality of the tear
film. Some studies characterize the tear-film meniscus to estimate tear-film quality by
applying optical coherence tomography techniques. Other studies analyze the use of the
Hartmann-Shack wavefront sensor to diagnose DED by analyzing the changes in the
aberration maps. We have used OQAS system to obtain double-pass retinal images as an
indirect indicator of the relative quality of the tear film in DED patients. Our results suggest
that the addition of lubricating eye drops reduces ocular scattering as a measure of optical
quality in patients with mild to moderate DED for at least 60 minutes after instillation2.
Several studies have explored the therapeutic effect of artificial tears or punctal occlusion
on different aspects of optical quality. An analysis system has been used to evaluate tear
stability with dynamic videokeratoscopic images of the tear film captured continuously
every second for 10 seconds, employing topographical surface regularity and asymmetry
indices. This revealed significant degradation of the kinetic tear stability in DED patients
with worsening of the indices over time. An improvement of surface regularity and
asymmetry indices in DED patients who underwent punctum plug occlusion has been
demonstrated. Montes-Micó et al. have reported a significant improvement in high order
aberrations (HOAs) after instilling lubricating eye drops in DED patients. The reduction
of HOAs was maintained 10 minutes after artificial tear instillation3.
Refractive surgeons have learned that corneal refractive surgery induces DED. DED
is one of the most common causes of dissatisfaction after LASIK. Refractive surgery
associated-DED is related with previous DED, female gender and the ablation depth.
Thus, refractive surgeons study the ocular surface before surgery, inform patients and treat
DED.
Nevertheless, the majority of cataract surgeons are not aware that cataract surgery
induces DED. Usually after cataract surgery patients complain about visual fluctuation.
This may be caused by DED unless other etiologies such as post-operative corneal oedema,
© 2010 SECOIR
Sociedad Española de Cirugía Ocular Implanto-Refractiva
ISSN: 2171-4703
115
116
EDITORIAL
residual astigmatism or refractive error, and cystoid macular oedema are proven. There are
various factors that could contribute to the appearance of DED after cataract surgery.
Inflammation of the ocular surface can occur after surgery and drugs, the latter producing
toxic changes in the cornea and conjunctiva due to the existence of preservatives, particularly
benzalkonium chloride. A corneal incision, notwithstanding its small size, can cause certain
corneal irregularities, favouring rupture of the tear film. Moreover, an alteration in central
corneal sensitivity has been found in patients who have undergone cataract surgery. This
is secondary to the corneal nerve section, which may potentially disrupt the neural loop,
reducing tear secretion by the lacrimal gland.
We have recently shown that the addition of lubricant eyedrops to standard treatment
generates fewer visual disturbances after phacoemulsification, thanks to lubricant treatment4.
This is of utmost importance when dealing with multifocal intraocular lens implants.
Woodward et al. evaluated patients dissatisfied with visual outcomes after multifocal IOL
implantation due to blurred vision and photic phenomena, finding that both of these
issues can be related to DED1. Nowadays, in the phacorefractive age, cataract surgeons
must interest themselves in further improving the outcomes of cataract surgery. This can be
done by decreasing symptoms such as burning or foreign body sensation and by improving
the quality of vision after surgery (associated to ocular dryness), as patients are demanding
20/20 long and short distance vision when paying for premium IOLs. By aggressively
treating the ocular surface after surgery (in particular but not only in patients with previous
problems), we provide better patient comfort and visual acuity. We must inform patients
about the possibility of ocular dryness symptoms and visual fluctuation after surgery in
order to avoid patient complaints about cataract surgery. Recently, an ‘ocular surface stress
test’ has been reported to identify high-risk patients for developing dry eye signs and
symptoms after phacoemulsification. We recommend lubricant treatment at least during
the first month after phacoemulsification in all the patients undergoing cataract surgery.
In another study, cyclosporin A 0.05% twice a day for one month preoperatively and
one month postoperatively, resulted in an improvement in symptoms but not in TBUT
(cyclosporine usually takes two months to become effective)6.
In conclusion, refractive and cataract surgery induces DED, which in turn decreases
visual acuity. As such, patients must be informed. The addition of lubricant eyedrops after
surgery should be implemented in order to comply with the patient´s visual expectations.
REFERENCES
1.
2.
3.
4.
5.
6.
Goto E, Yagi Y, Matsumoto Y, Tsubota K. Impaired functional visual acuity of dry eye patients. Am J
Ophthalmol 2002; 133: 181–186.
Diaz-Valle D, Arriola-Villalobos P, García-Vidal SE, Sánchez-Pulgarín M, Borrego Sanz L, GegúndezFernández JA, Benitez-Del-Castillo JM. Effect of lubricating eyedrops on ocular light scattering as a
measure of vision quality in patients with dry eye. J Cataract Refract Surg. 2012;38:1192-7
Montes-Mico R. Role of the tear film in the optical quality of the human eye. J Cataract Refract Surg
2007; 33: 1631–1635.
Sánchez MA, Arriola-Villalobos P, Torralbo-Jiménez P, et al. The effect of preservative-free HP-Guar on
dry eye after phacoemulsification: a flow cytometric study. Eye. 2010;24:1331-7.
Woodward MA, Randleman JB, Stulting RD. Dissatisfaction after multifocal intraocular lens
implantation. J Cataract Refract Surg. 2009;35:992-7.
Roberts CW, Elie ER. Dry eye symptoms following cataract surgery. Insight 2007; 32: 14–21.
José M. Benítez del Castillo
Catedrático de Oftalmología Universidad Complutense de Madrid Hospital Clínico San Carlos
JOURNAL OF EMMETROPIA - VOL 3, JULY-SEPTEMBER