Differential time-course tear film quantitative changes following limbal relaxing incisions

Microscopic damage to the ocular surface during cataract surgery is a widely established theory of postoperative dry eye syndrome resulting in ocular discomfort and dissatisfaction [1].

Corneal astigmatism of variable degree; ranging between 1and 3 diopters; has been found to be coexistent in up to 29% of patients who are complaining of lenticular opacities and probably would undergo cataract surgery [2‐4].

Phacoemulsification; the modern cataract surgery; with intraocular lens implantation has been considered the gold standard treatment of cataract. The standard cataract procedure was simply targeting to correct spherical equivalent refractive error without considering a coexisting corneal astigmatism. Cataract surgery could be an aggravating factor of a pre-existing corneal astigmatism for the incisional nature of the procedure or a precipitating factor for a de novo surgical-induced astigmatism of a variable degree. Postoperative patient’s satisfaction after cataract surgery is basically related to achieving optimal postoperative distant visual acuity without the need to be spectacle or being contact lens-dependent. Despite recent improvements in surgical techniques, biometric measuring tools, and IOL power calculation formula; uncorrected corneal astigmatism still could be a source of postoperative residual refractive error [5‐8]. Patients are usually reluctant to use spectacles or contact lenses for correcting postoperative astigmatism; having their own limitations and complications [3]. With eminence of the modern refractive cataract surgery techniques; limbal relaxing incisions, astigmatic keratotomy, bioptics and toric IOL implantation; both spherical and astigmatic refractive errors were targeted to be corrected simultaneously [2, 9, 10].Being incisional procedures; both phacoemulsification and limbal relaxing incisions, could precipitate postoperative ocular surface changes in the form of decreased tear production, appearance of dry eye and ocular discomfort syndromes; all of which might interfere with the patient’s daily life quality. We have earlier studied the ocular surface changes following simultaneous cataract surgery and LRIs; the current study investigated differential changes that depend on the orientation at which the LRIs were performed [11]. It has been previously reported in literature that corneal nerves enter the cornea predominantly at the horizontal meridian (3 and 9 o’clock positions) [12, 13]; however; other authors reported that nerve fiber bundles in the sub-basal plexus across the central and mid-peripheral cornea run first in the horizontal direction, then after bifurcation, they do travel in the vertical (6 and 12 o’clock hours) direction and after a second bifurcation again they run in the horizontal direction [14]. according to that we postulated that there may be differential changes after performing LRIs in different orientations regarding the ocular surface quality profile. The aim of this study is to longitudinally assess the pre-corneal tear film changes in eyes undergoing simultaneous phacoemulsification and LRI procedures and to investigate whether these changes may vary according to the orientation of LRIs.

Dry eye symptoms which are commonly encountered after all types of corneal refractive procedures could disturb patients’ optimal visual function and hence performing their daily life activities; such morbidities increase proportionately with the severity of symptoms [15]. It was hypothesized that the most important factor in the pathophysiology of corneal refractive surgery-induced dry eye syndrome is the transection of corneal nerves that occurs during all these incisional procedures [16].

Park et al. have studied changes in ocular surface parameters, meibomian gland function and tear inflammatory mediators following phacoemulsification; they reported worsened ocular dryness symptoms but with gradual recovery of TBUT and corneal sensitivity threshold at 1 and 2 months postoperatively. One of the 2 study groups they included had evident dry eye before surgery which was one of the exclusion criteria for the current study [17].

Oh et al. found no difference between the mean preoperative and postoperative Schirmer’s test values following phacoemulsification; however, the TBUT values were significantly decreased at 1 day postoperatively but recovered to the preoperative level after 1 month. Interestingly; they found a reduction in the mean goblet cell density which was correlated with operative time and had not recovered at 3 months postoperatively [18].

Liu et al. also reported initial significant reduction of TBUT and increased Schirmer’s test values at 1 and 2 days postoperatively with later recovery to the preoperative values [19].

To the best of our knowledge we could not find previously published reports in literature studied the ocular surface quality profile after scleral tunnel or small-incision cataract surgery. We postulate that it would not have that much effect on ocular surface profile comparable to phacoemulsification surgery which may be explained by location of the main incision being through the sclera and corneal stroma rather than incising through the limbus or clear cornea which provide the entry ports for the nerve endings.

Even with considering the latest technology of femtosecond laser-assisted cataract surgery (FLACS); a study conducted by Ju et al. reported that dry eye still could develop immediately after that procedure with a peak severity on day 7 postoperatively, most signs could return to basic preoperative levels within 3 months after surgery. They measured the tear film stability using OCULUS Keratograph which was not used in the current study [20].

In a similar way; ocular surface changes after corneal laser-assisted refractive procedures have been found to be due to cutting of corneal nerves during refractive surgeries that subsequently result in suppression of the aqueous component secretion from the lacrimal gland, mucin expression on the corneal epithelial surface, and frequent blinking, previously mentioned cascade occurs because these homeostasis-maintaining mechanisms are driven by a neuronal feedback loop that is mediated by corneal sensitivity [13, 21].

Introducing the confocal microscopy technology has helped better understanding of the dry eye pathophysiology after such incisional surgeries like LRIs as it has been proved that regeneration of the intrastromal corneal nerves usually occur within 3 to 6 months which occurs in concurrence with the recovery of corneal sensitivity and restoration of the ocular surface basic preoperative levels [22].

In a previous study, we reported reduced quality of the ocular surface profile in terms of reduced tear film BUT and tear volume production after simultaneous cataract surgery with LRIs without largely affecting the corneal sensation; however, we did not consider for selective changes according to different location of the LRIs [11].

Limitations of the current study are the relatively small sample size, the uncontrolled non-randomized design, the relatively short follow-up time and the lack of a control group that consist of patients undergoing cataract surgery without LRIs. The aforementioned limitations raised the need for future longitudinal controlled cohort studies with larger sample size and a longer follow-up time is highly recommended.

In conclusion, the current study indicated that simultaneous LRIs with cataract surgery could result in dry eye symptoms and reduced tear film stability which probably would be transient during the early postoperative period and then recover to around the basic preoperative levels soon; those changes differ; however slightly; according to the LRIs orientation. Adequate preoperative assessment of the ocular surface quality parameters should be considered to optimize the postoperative outcome so not to compromise the patient’s life style.