Cataract surgery in patients with corneal opacities

Phacoemulsification is a standard cataract surgery with excellent outcomes. However, it is not unusual to encounter patients with coexisting corneal opacification and visually debilitating cataracts [1]. Corneal opacity can impede visualization during cataract surgery. There are two surgical options under such circumstances. The first is to perform simultaneous penetrating keratoplasty (PKP), cataract extraction and intraocular lens (IOL) implantation, which provides a shorter visual rehabilitation period [2]. However, the disadvantages include risk of expulsive hemorrhage, inadequate cortical cleaning and inaccuracy in IOL power calculation [3, 4]. The second option is to postpone cataract surgery after PKP to achieve refractive accuracy [5]. The drawbacks include a delay in visual rehabilitation and the risk of endothelial loss [4, 6]. In addition, factors such as graft rejection in high-risk recipients, poor patient compliance, meticulous follow-up and a paucity of good-quality donor corneas mean that immediate keratoplasty is often not possible. Therefore, cataract surgery alone can provide timely visual rehabilitation.

To enhance visibility during cataract surgery in opacified corneas, techniques such as capsule staining or alternative methods have been applied [7, 8]. However, toxicity of the staining dye should be taken into consideration, especially in a currently compromised cornea. Furthermore, uncontrolled dye dispersion through zonules can obscure the capsular anatomy [9]. With regards to modified illumination methods, transcorneal oblique illumination and endoscope-assisted phacoemulsification have been utilized, however, they are time consuming and require skilled clinicians [5, 10].

Variable outcomes have been reported after cataract surgery in eyes with corneal opacities [11, 12], and corneal opacity severity has been one of the major prognostic factors. Optical coherence tomography (OCT) has been used to investigate the histopathology of corneal opacities [13], and the degree of opacity has been reported a useful parameter in preoperative planning [14]. Corneal haze could hinder the light transmission resulting backward and forward scattering. Light-backscattering analysis with OCT seems to be a reliable method of detecting backscatter [15].

However, routine analysis has not been applied to evaluate the efficacy of cataract surgery in opacified corneas [16].

Recently, studies assessing the corneal pathology has included double-pass instrument for intraocular forward scattering [17], Scheimpflug rotating camera for backward scattering and corneal higher-order aberrations. Kamiya et al. suggested no significant correlations between visual performance and backward scattering in band keratopathy, while intraocular forward scattering maybe the only effective objective assessment for corneal pathology regarding visual acuity [18]. Although the correlation between reduced visual acuity and Scheimpflug corneal densitometry is not significant but still provide a quantitative value for backscatter in previous normative cohort study [19]; but in another study, significant level of correlations between visual performance was found in assessing granular corneal dystrophy [17]. Regarding backward scatter, previous study had demonstrated optical coherence tomography can precisely detect depth and visualize different corneal dystrophy in augment of treatment planning [20, 21]. But no quantitative analysis of the corneal opacities with visual performance was performed yet.

Therefore, the primary goal of this study was to report the visual outcomes and complications in patients undergoing cataract surgery in eyes with coexisting corneal opacities. The second aim was to evaluate whether anterior segment OCT can be used as an alternative objective modality to predict visual prognosis. To our knowledge, this is the first report to evaluate and compare non-transparent cornea with densitometry and new OCT grading methods.

Medical records of patients with cataracts and corneal opacities who underwent phacoemulsification and IOL implantation were reviewed. Inclusion criteria were a best-corrected visual acuity (BCVA) less than 20/40 and corneal opacification involving the visual axis and advanced cataracts. Only eyes with partially visible anterior capsules and pupillary margins were enrolled. The exclusion criteria were use of ancillary techniques or those who received simultaneous keratoplasty. No patients had previously ocular surgeries except for one who had PKP before cataract surgery.

The presence of corneal opacities can be challenging for surgeons during cataract surgery and combined corneal transplantation may be preferred. However, patients may hesitate to receive PKP for only mild-to-moderate nebulae. For one-eyed patients whose corneal opacities are accompanied by deep stromal vascularization, it may not be appropriate to perform corneal transplantation due to high-risk of graft rejection [8]. Therefore, cataract surgery may be an alternative in these patients [12].

Panda et al. reported that phacoemulsification with IOL implantation with 0.06% trypan blue improved BCVA from less than 40/200 to 20/60 [12]. A similar study reported that 64.7% of patients improved visual acuity, and that 47.1% of those with advanced cataracts achieved 20/100 or better [11]. In this study, 78% improved BCVA, with 60.8% achieving better than 20/100 postoperatively. Although final visual acuity was suboptimal, the patients had improvements of at least two lines except for one eye with worse BCVA. Cataract surgery alone can also be an interim procedure for patients awaiting donor corneas. Two cases suffered from corneal lacerations and traumatic cataracts had improved vision after cataract surgery with a final BCVA of 20/22 after corneal transplantation (Fig. 3).

Corneal haze impedes visibility even with adequate fundus glow. Various techniques were used to improve visualization through opaque corneas during surgery [24]. To optimize visualization, attempts were made to adjust light setting and the following maneuvers resulted in high success rate. First, avoid the corneal opaque area and look for a transparent window to initiate continuous curvilinear capsulorhexis. Visualization during phacoemulsification in eyes with corneal opacity superimposed with mature cataracts can be extremely difficult and technically demanding, therefore we suggest that this procedure be reserved for experienced surgeons. Second, obtain favorable contrast in the surgical field by adjusting the illumination to low or medium intensity, as coaxial lighting of most operating microscopes may interfere with the surgical field due to backscatter and reflection of light from the cornea [25]. Finally, perform “continuous” capsulorhexis with a constant tethered force under the opaque area. Non-continuous capsulorhexis is likely to cause radial tearing and intraoperative complications are even harder to manage in eyes with poor corneal clarity. Therefore, patients must be aware of alternative surgical options and secondary surgeries during preoperative consultation.

Ocular surface diseases such as OCP and viral keratitis can be exacerbated by uneventful cataract surgery and limit surgical outcomes. Preoperative recognition and effective management can prevent devastating complications [26]. The safety and efficacy of cataract surgery has been reported in patients with OCP; however, reactivation of OCP is possible and results in poor outcomes [27]. In a previous study, postoperative visual acuity was worse in eight of 15 eyes by about 2 years due to progressive cicatricial disease [28]. Similar to their findings, case 6 with OCP had a temporary visual improvement in early postoperative period, but visual acuity deteriorated 2 years later because of missed follow-up and uncontrolled disease. In contrast, Puranik et al. argued that surgeries were not associated with exacerbations of inflammation, and that stable visual outcomes could be anticipated in spite of ongoing disease [29]. However, we strongly recommend adequate preoperative immunosuppression therapy and the use of small corneal incisions in cases with OCP scheduled for cataract surgery in order to ensure better outcomes.

The onset of new and recurrent herpetic simplex virus (HSV) keratitis has been reported after uncomplicated cataract surgery [24]. Triggers for HSV keratitis such as surgical trauma and use of steroids have been proposed. Barequet et al. reported that new HSV keratitis may develop after uneventful surgery within 1–5 months under corticosteroid treatment [30]. In this series, three eyes with preexisting herpetic keratitis had signs of reactivation with a mean inactive period of 14.8 weeks. All patients were under topical steroids for at least 4 weeks, and the mean flare-up time of HSV keratitis was 10 months. All eyes were treated with oral acyclovir or topical acyclovir ointment, and the lesions resolved over a mean period of 4 weeks. Unfortunately, two eyes developed further recurrence, and the final visual outcomes were not favorable due to exacerbation of HSV keratitis. Although herpetic eye disease study suggested that prophylactic oral antivirals for 1 year could be effective in preventing half of ocular and non-ocular cases of recurrence in patients with previous HSV keratitis (Herpetic Eye Disease Study Group 1998), no guidelines for antiviral prophylaxis currently exist for cataract surgery [26]. To prevent HSV exacerbations compromising well-tolerated cataract surgery, we suggest that oral antiviral prophylaxis in cases of suspected reactivation of HSV keratitis.

Recently, OCT has been shown a valuable tool to detect and analyze corneal opacities in different clinical situations [13, 31]. Accumulating evidence has demonstrated that cross-sectional images of the cornea in anterior segment OCT correlate well with the morphology in light microscopy [13]. Wirbelauer and Pham (2004) reported the quantitative assessment of calcified corneal lesions using anterior segment OCT. They found that reflectivity in OCT could be used to represent the severity of opacities, and concluded that OCT was helpful in quantifying the corneal opacity and in guiding the treatment plan. However, the parameters in their study included only depth of the calcified lesions and thickness of the corneas [16]. Normative corneal densitometry in healthy subjects using Oculus Pentacam system and its relation with refractive parameter were published before [32]. Effect of backscatters from corneal pathology on visual performance had also been proven by Kamiya et al. [17, 18]. However, no quantitative analysis using ASOCT and its relations with corneal densitometry and visual outcome has been so far elucidated.

Current study took into consideration the area and density of the corneal opacity involving the pupillary axis, and found that the more severe the opacity index according to the reflectivity signal, the less likely BCVA improvements would be achieved after surgery (Fig. 2d). The similar interfering effect of backward scattering has also been studied but no definite association was proved with corneal densitometry [17, 18]. This is might due to the similar conditions that we found in our study, Pentacam performed poorly to analyzed corneal opacity in moderate-to-high density, location closed to pupil center and pathology concentrated at superficial cornea. Also, the circle or annuli area Pentacam system analyzed is not useful if the opacity area is irregular in shape. In contrasts, one can delineate along contour of opacity area and quantified with the depth detected by ASOCT.

Confounding parameters such as the thickness of the cornea, irregularities of the corneal surface and refractive index in the opacified area were controlled for by comparing preoperative and postoperative visual acuity in the same individual. Because of the simplicity and reproducibility of OCT measurements, surgeons may adopt our proposed grading system as a useful guide to predict visual outcomes in patients who are not candidates or hesitate for combined PKP and cataract surgery.

Although anterior segment OCT allows for non-invasive and objective analysis of corneal structural abnormalities and has good predictability for postoperative BCVA, some limitations still exist. For example, simply averaging vertical and horizontal cross-sectional lines is inadequate to represent the size and shape of corneal opacities due to their non-homogenous properties. Severity of cataract also contributes to the improvement of visual acuity. Above two factors may be reason why we did not find an association between corneal opacity severity and improvements in UCVA. Furthermore, corneal surface irregularities and tearing that may contribute to visual disturbance were not addressed. Finally, due to the retrospective nature, the effects of underlying posterior segment pathologies on visual outcomes were not excluded. Therefore, future prospective studies with well-designed anterior segment OCT software and strict criteria to exclude the confounding factors are warranted to investigate the effects of corneal opacity on visual outcomes after cataract surgery.

In conclusion, phacoemulsification is not an alternative to PKP, however it is a safe and feasible method for patients who are poor candidates for transplantation, especially for those with vision in only one eye and who are unable to comply with follow-up protocols after keratoplasty. Moreover, phacoemulsification can also serve as an interim procedure to allow patients to become ambulatory while they are waiting for PKP, especially in developing countries with a lack of good quality donor corneas.