The Toric Allocation Pathway (TAP): outcomes of a standardised pathway for toric lens allocation at a tertiary referral hospital

Abstract

Aims

To determine if a standardised Toric Allocation Pathway (TAP) improved visual and refractive outcomes for patients undergoing cataract surgery at a tertiary referral teaching hospital.

Methods

Demographic, visual, and refractive data from all patients who underwent cataract surgery and toric intraocular lens (IOL) insertion with an emmetropic target between January 2015 and December 2019 were retrospectively collected and separated into pre-TAP and TAP groups. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), postoperative spherical equivalent refraction (SER) and postoperative cylinder were compared using multivariate regression analysis and Mann-Whitney U testing.

Results

A total of 118 eyes were divided into pre-TAP (n = 59, 50%) and TAP (n = 59, 50%) groups. Case-mix and surgeon rank was comparable between the two groups (all variables p > 0.05). The TAP group outperformed the pre-TAP group in postoperative mean UDVA (6/7.5 ± 0.13 LogMAR vs. 6/9 ± 0.19 LogMAR, p = 0.049, respectively) and residual cylinder (0.47 ± 0.54D vs. 0.87 ± 0.78D, p < 0.001). As well, the TAP group was more consistent, with significantly smaller standard deviations for all outcomes. Consequently, a higher proportion of patients achieved a SER of ≤ 0.5D from emmetropia in the TAP group (78% vs. 58%, p < 0.001).

Conclusions

The TAP improved the visual and refractive outcomes for patients with regular astigmatism while minimising inappropriate implantation of toric IOLs. It is ideal for large teaching hospitals and provides a framework for developing surgeons in correctly selecting patients who would most benefit from toric IOLs.

Introduction

Untreated astigmatism post cataract surgery poses a significant visual burden and often requires spectacle reliance, leading to considerable patient and societal costs. This can be ameliorated with the use of toric intraocular lenses (IOLs) [1], which have revolutionised modern cataract surgery to provide a high quality of vision and spectacle independence for the 32.5–45.5% of patients with astigmatism ≥ 1.0 dioptres (D) [2]. The resultant improvement to falls risk, quality of life, patient satisfaction, and economic freedom from complex spectacle manufacturing costs are substantial [3].

However, these improvements in vision and quality of life come at a cost and toric IOLs are almost double the price of their spherical counterparts. Rationalizing the use of toric IOLs to maximise patient benefit and minimise the cost to a health system poses a significant health-economics challenge for the surgeon and institution. This is heightened in the context of teaching hospitals where there is a large team involved in the patient journey resulting in significant variability with measurement accuracy, clinical expertise with toric IOL use, surgical skills and overall discontinuity of care between preoperative, operative and postoperative follow up [4]. A systematic process for toric IOL use is beneficial in minimizing these limitations and optimizing the cost-effectiveness of toric IOLs across a range of healthcare settings.

This study aimed to determine if a standardised Toric Allocation Pathway (TAP) improved the visual and refractive outcomes for patients, ultimately leading to better cost-efficiency and health economic outcomes while minimizing the inappropriate use of toric IOLs.

Methods

Ethics approval

Ethics approval was granted by the Western Sydney Local Health District Human Research Ethics Committee (1901-03 QA, approved on 24/01/2019) and the study was conducted with adherence to the tenets of the Declaration of Helsinki.

A retrospective review of all consecutive cataract surgery cases that received a toric IOL between January 2015 and December 2019 was conducted at a public tertiary referral teaching hospital (Westmead Public Hospital, Sydney, Australia) comprising twenty-six staff specialist ophthalmologists, three surgical fellows and a rotating cohort of twenty-four trainees per year.

Inclusion and exclusion criteria

Any patient who had a toric IOL inserted for cataract surgery, with a refractive target of emmetropia, was included in the study.

Exclusion criteria was the presence of any ocular comorbidity besides astigmatism. Patients with any intraoperative or postoperative complication or missing visual and refractive measurements were also excluded from the study.

The decision for toric IOL insertion prior to the TAP was made by the senior operating surgeon responsible for the patient at their perioperative assessment. The operation itself would be performed by either the senior surgeon or allocated to a trainee based on patient and trainee factors with direct senior supervision.

Toric allocation pathway (TAP)

The Toric Allocation Pathway (TAP) was introduced into the Westmead Public Hospital ophthalmology department in January 2017 with departmental and subspecialty consultation (Fig. 1). The TAP requires all the following criteria to be satisfied for a patient to qualify for a toric IOL:

• Astigmatism ≥ 2.0D on IOL Master.

• Anticipated uncorrected distance visual acuity (UDVA) of ≥ 6/9 postoperatively.

• Regular astigmatism on Pentacam (Refractive Map).

• Alignment of the axis of astigmatism between IOL Master and Pentacam measurements within 30 degrees.

• Similarity in the power of astigmatism between IOL Master and Pentacam measurements within 0.5D.

Fig. 1

The toric allocation pathway

If these criteria were not met, a spherical monofocal IOL was inserted at the time of cataract surgery. Discretion of IOL choice and patient suitability was ultimately the decision of the senior surgeon operating or supervising at the time of surgery.

For health economics and cost rationalisation purposes, a minimum corneal astigmatism of two dioptres was proposed for the TAP. For the same reasons, an anticipated UDVA of ≥ 6/9 was chosen to reinforce the goal of spectacle independence for distance vision following toric IOL insertion. To maximise accuracy and improve the presurgical probability of good postoperative UDVA, correlation was sought between Pentacam and IOL Master for both power and axis of corneal astigmatism [5,6,7,8].

Patient pre-and post-operative assessment

A full ophthalmic assessment was conducted on each patient prior to surgery to establish suitability for cataract surgery, using the same equipment and IOL formulas between groups. UDVA and CDVA were assessed using a standard Snellen visual acuity chart and converted to logarithm of the minimal angle of resolution (LogMAR). Ocular biometry was measured using the IOLMaster 500 (Carl Zeiss Meditec) on all patients unless density of the cataract necessitated contact biometry, and the Barrett Toric Calculator used to calculate the toric IOL used. In the pre-TAP group, corneal tomography (Oculus Pentacam)was measured at the surgeon’s discretion, while it was routinely measured in the TAP group.

Postoperatively, all patients were instructed to use chloramphenicol 0.5% and dexamethasone 0.1% eye drops four times a day in the operated eye for four weeks. Patients were reviewed at day one and month one at the hospital. UDVA, CDVA, intraocular pressure and slit lamp anterior segment examination were conducted day one and repeated at one month postoperative, where a dilated fundus examination was also performed. All patients included in this study had a postoperative subjective refraction performed at one month post-surgery.

Operative technique

Cataract surgery was performed on all patients under topical, local anaesthesia (subtenons/peribulbar) or general anaesthesia depending on the surgeon’s preference and patient’s needs. Prior to anaesthesia all patients had orientating limbal markings placed by the senior surgeon or trainee either with a corneal marking device in the anaesthetics bay or with the aid of a slit lamp. Phacoemulsification was carried out on all patients via temporal 2.75 mm clear corneal self-sealing incisions. A single piece, toric monofocal IOL was inserted into the capsular bag in all cases. Lenses used included Alcon Acrysof IQ toric (Alcon Laboratories Inc.), TECNIS toric IOLs (Abbott Medical Optics, Inc.) and Zeiss AT TORBI 709 M/MP (Carl Zeiss, Meditech). All lenses were rotated to the correct orientation, with orientation checked manually at the end of the operation before wounds were hydrated and intracameral antibiotics administered.

Statistical analysis

All data was analysed using Statistical Package for Social Sciences (IBM). Preoperative astigmatism (cylinder) was expressed as an absolute number and was calculated using the difference between the two keratometry values (K1 and K2) recorded by the IOLMaster. Postoperative subjective refraction was collected on every patient and used to calculate spherical equivalent refraction (SER; sphere power + 0.5 × cylinder power) and post-operative cylinder (cylinder component of subjective refraction expressed as an absolute number).

Patients were separated into either a Pre-TAP or TAP group depending on whether the decision ruling in their toric IOL was from individual clinician judgement or strictly following the pathway. Frequencies in both groups were calculated using SPSS and reported as number (n), mean, and standard deviation (SD). Non-parametric testing was used as tests of normality were strongly positive. Statistical significance was determined using the Mann-Whitney U test and considered significant if p < 0.05. Levene’s test was used to determine if a statistically significant change in SD occurred between groups.

Results

A total of 118 eyes from 105 patients were included in the study, with a mean age of 71.3 years ± 13.1 (range 16–91 years). Fifty-eight patients (49%) were female, fifty-six cases (47%) had the senior surgeon as the operating surgeon and fifty-four (46%) surgeries were conducted on the right eye. The pre-TAP and TAP groups both had 59 eyes (50%) in each cohort. The only preoperative difference between the groups was a higher mean preoperative astigmatism in the TAP group (p = 0.025, Table 1). Only the Pre-TAP group had patients with a preoperative astigmatism of less than 2.00D (n = 12, 10.2% of total cohort).

Table 1 Demographic, visual and refraction data in pre-TAP and TAP groups at pre- and postoperative intervals

As demonstrated in Table 1, the implementation of the TAP resulted in statistically significant improvements to the postoperative UDVA and specifically in postoperative residual cylinder (0.87 ± 0.78D vs. 0.47 ± 0.54D, p < 0.001). There were no differences between senior and trainee outcomes in postoperative UDVA (p = 0.641), postoperative cylinder (p = 0.774) or SER (p = 0.723). Beyond this, the TAP group had a significant reduction in the proportion of outliers for postoperative UDVA, cylinder, and SER (Fig. 2). The clearest example of this was the reduction in standard deviation for SER between the pre-TAP and TAP groups (0.71D vs. 0.42D, p = 0.005), indicating that the refractive outcomes were much more predictable after implementing the pathway.

Fig. 2

Comparison of pre-TAP and TAP outcomes for postoperative uncorrected distance visual acuity (A), postoperative cylinder (B), and spherical equivalent refraction (C)

The TAP group had a substantially higher proportion of patients with an UDVA of 6/9 or better compared to the pre-TAP group (88% vs. 66% respectively, p < 0.001), as well as a higher proportion of patients with an UDVA equal to their CDVA (61% vs. 54% respectively, p < 0.001). Moreover, there was a considerably higher percentage of TAP patients achieving a SER equal or less than 0.5D of emmetropia (78% vs. 58% respectively, p < 0.001) and postoperative cylinder equal or less than 0.5D (71% and 39%, p < 0.001), as demonstrated in Fig. 2.

Discussion

The Toric Allocation Pathway (TAP) is a simple and effective algorithm that demonstrated improved visual and refractive outcomes following implementation in a tertiary referral teaching hospital. For an equivalent group of patients, following the TAP yielded better postoperative UDVA, lower residual astigmatism, and closer target SER. This is amplified by the lack of difference in outcomes between senior and trainee operating surgeons, indicating that the TAP performs equally under a wide skill range and overcomes many of the limitations of teaching hospitals, such as the loss of continuity between a patient’s assessing and operating surgeon in the context of pooled cataract lists. The TAP is an ideal tool for large centres such as major teaching hospitals and provides a framework for developing surgeons in correctly selecting patients who would most benefit from toric IOL insertion.

In cataract patients with astigmatism, the use of toric IOLs result in better visual and refractive outcomes compared to their spherical IOL comparators [3, 9, 10]. Many patients with higher levels of astigmatism can even achieve distance vision spectacle independence. In our study, 71% of patients in the TAP group achieved a postoperative residual astigmatism (cylinder) equal to or less than 0.5D, which is similar to the amalgamated reports in the literature of 700 per 1000 patients [9, 11,12,13]. In contrast, in the pre-TAP group this figure was 58%. There was also a twofold increase in the proportion of toric IOL recipients achieving 6/6 or better UCVA postoperative after implementing the TAP. Thus, the TAP was very effective in consistently identifying patients who benefited from toric IOL use, and arguably more importantly, limited the inappropriate implantation of toric IOLs, resulting in superior refractive and visual outcomes with reduced variability.

From a health economics perspective, there is increasing evidence for the benefit of toric IOL use in regular astigmatism patients. A review of studies from four European countries found a lifetime saving of €392-897¹⁴ for patients with toric IOLs due to the ongoing cost of spectacles [1]. The cost of reading glasses was doubled in those with residual cylinder due to the increased manufacturing costs [1, 14]. Beyond this, there is an increased risk of falls and a lower quality of life associated with untreated astigmatism, both of which have an impact on the economic decision to fund toric IOLs [3, 15]. With these benefits in mind, perhaps the real debate is what the cylindrical cut off should be for implantation of toric IOLs. We argue that the use of pathways such as the TAP can minimise the inappropriate implantation rate such that from a health economics, patient outcomes and surgical training perspective, the cut-off for toric IOL use can be reduced to as low as 1.00D of cylinder.

The TAP was designed to serve as a working guideline for surgeons and their staff, and rather than being dogmatic, aims to reinforce and enable clinical decision-making. Fundamentally, it provides a framework for thinking about and understanding toric IOL use. The pathway has the flexibility to cater to cases outside the criteria where toric IOLs maybe appropriate, provoking discussion about the suitability and likelihood of success in specific cases. A simple example of this would be in the context of stable keratoconus [10, 16,17,18,19] where a toric IOL would be suitable if there was minimal irregular astigmatism and a clinical history of good vision in spectacles, even though the case would not strictly meet all the criteria in the pathway. Thus, the TAP could act as a starting point for teaching junior trainees on when best to adhere to the pathway and when it would be appropriate to deviate away.

The TAP’s strength lies in its simplicity of use and versatility. All surgeons can easily follow the recommendations, as can appropriately trained ophthalmic nursing and allied health staff to improve clinic flow. Furthermore, the pathway can cater for the resources available in each department and allow modification as availability and advances in biometry equipment, IOL formula, surgical technique and lens technology develops. Like any algorithm, its main limitation is its generalisations, for example setting the surgically induced astigmatism to 0.2D to accommodate a wide spread of trainee skills and the 2.75 mm surgical incision. However, most TAP criteria can be adjusted to accommodate modifications based on department and surgeon preference.

Interestingly, there was a considerable difference in the proportion of patients with a postoperative UDVA of 6/9 or better between the pre-TAP and TAP groups (66% vs 88%, p < 0.001). This may reflect the real-world outcomes of non-standardised assessments of patients for a toric lens prior to the implementation of the TAP. For example, rather than correlating IOL Master and Pentacam measurements as the TAP recommends, only one modality may have been used to determine astigmatism. There may have been an assumption that the astigmatism was regular without confirmation with tomography. Additionally, there may not have been a targeted review of confounders, such as dry eye disease. As a result, toric lenses may have been inappropriately used in patients whose ‘regular astigmatism’ is actually due to artefact, ocular comorbidities, or irregular astigmatism. These patients would not benefit from toric lens insertion and would have poorer outcomes compared to patients allocated appropriately through a standardised pathway (i.e. TAP).

Ultimately, the TAP is a practical algorithm for toric IOL use, which can yield superior visual and refractive outcomes while minimising inappropriate toric IOL implantation. It is ideally suited to large training hospitals and can act as a framework for junior trainees in developing an informed, independent approach to toric IOL selection.