Corneal Astigmatism Clinical Trial
Official title:
Prospective Evaluation of Limbal Relaxing Incision (LRI) in Conjunction With Phacoemulsification Surgery for Astigmatic Correction in Chinese Eyes
The main purpose of this study is to evaluate the use of limbal relaxing incision (LRI) for astigmatic correction. LRI is a procedure where a pair of incisions is made in the peripheral part of the cornea so as to alter its shape and improve the focusing power of the eye.
An important aim in cataract surgery has always been a good postoperative visual outcome.
Efforts have been made to achieve this, with the introduction of intraocular lens in the
1980s and small incision cataract surgery in the 1990s. In the recent years, 'refractive'
cataract surgery has taken the form of corneal astigmatic correction. Patients with
pre-existing astigmatism of more than 1.5D may benefit from surgical correction during
cataract surgery, in the hope of improving uncorrected visual acuity as well as lesser image
distortion from corneal aberrations.
The limbal relaxing incisional technique involves placement of incisions corresponding to
the steep meridian, thereby resulting in corneal flattening and reduction of astigmatic
power. It is increasingly popular due to its advantages. LRI is simple to perform, very safe
procedure in experienced hands, effective for astigmatic reduction of up to 4D, has rapid
visual rehabilitation and is associated with very few visual complications due to the
peripheral location of the incisions. Possible complications include globe weakening,
corneal perforation, worsening of astigmatism, incorrect incisional placement and corneal
hypoesthesia.
LRI technique and the practical nomograms has been described and made feasible by both James
P Gills and Louis D Nichamin. Based on preoperatively measured astigmatic power and axis,
these two nomograms recommend a systematic approach to the amount of surgical correction
required.
The reason for the Nichamin nomogram being more frequently applied, can be attributed to a
few inherent features. It accounts for the age of the patient as a surgical variability and
recommends the use of paired arcuate limbal incisions measured in degrees of arc. Paired
incisions enable symmetric corneal flattening at the steep meridian, whilst arcuate
incisions are more physiological, thereby resulting in accurate astigmatic correction that
is independent of corneal diameter. Nichamin has also implemented a modified Nichamin age
and pachymetry-adjusted nomogram (otherwise known as 'NAPA' nomogram). It accounts for the
patient's peripheral corneal thickness and adjusts the incisional depth accordingly to
achieve 90% of corneal thickness.
Many studies have shown that LRI is an effective option for astigmatic correction in
Caucasian eyes. Whether these results can be further extrapolated to apply to Chinese eyes
are still largely uncertain. To date, there has not been a formal study conducted to
evaluate this hypothesis. Moreover, there has been some anecdotal evidence suggesting less
favorable postoperative outcome of LRI in Chinese eyes. The main objective of our study is
thus to assess the utility and effectiveness of LRI in Chinese eyes.
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Allocation: Non-Randomized, Endpoint Classification: Efficacy Study, Intervention Model: Single Group Assignment, Masking: Open Label, Primary Purpose: Treatment
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