Understanding and Optimizing Ocular Biometry for Cataract Surgery in Dry Eye Disease: A Review

ABSTRACT

Purpose

To understand the impact of dry eye disease (DED) on the components of ocular biometry and ways to optimize the visual outcomes of cataract surgery in eyes with DED.

Methodology

A thorough literature review of the components pertaining to this review was undertaken using the databases, PubMed (from the year 2000), MEDLINE, CENTRAL (including Cochrane Eyes and Vision Trials Register; Cochrane Library: Issue 12 of 12 December 2019), metaRegister of Controlled Trials (mRCT) (www.controlled-trials. com), ClinicalTrials.gov (www.clinicaltrial.gov) and WHO International Clinical Trials Registry Platform (www.who.int/ictrp/search/en). The keywords used for the search included “cataract surgery” or “phacoemulsification” combined with “dry eye”, “dry eye disease”,”biometry”, “keratometry”.

Results

Publications considered for this review included meta-analysis, systematic reviews, case–control and cohort studies, case series, and laboratory-based studies. Published articles reporting tear film alteration in DED, its impact on the quality of vision and optical aberrations, the effect of topical medications on keratometry variations, and reports on optimizing the ocular surface before cataract surgery were included.

Conclusions

DED is a common entity seen in patients presenting to routine cataract clinics and is known to impact the accuracy, reliability, and repeatability of ocular biometry and IOL power calculations in them. This review intends to emphasize the preoperative screening for the presence of DED, initiation of appropriate medical management for optimization of the ocular surface before cataract surgery, and recommendations for performing biometry. The algorithmic approach proposed will help the general ophthalmologists in routine practice to provide quality care and acceptable visual outcomes in patients with pre-existing DED.

KEYWORDS:

• Cataract surgery
• Dry eye disease (DED)
• Ocular biometry

INTRODUCTION

The last couple of decades has seen a significant upsurge in the prevalence of dry eye disease (DED), which is estimated to be about 5–50% around the world.^1–5 As defined by TFOS DEW II, DED is a “multifactorial disease of the ocular surface characterized by loss of homeostasis of the tear film with associated tear film instability, hyperosmolarity, ocular surface inflammation and neurosensory abnormalities playing etiological roles”.⁶ DED is broadly classified as evaporative, aqueous deficient, and mixed forms. While the evaporative type is associated with tear film instability leading to a rapid breakdown of the precorneal tear film, aqueous deficiency is associated with subnormal production of the tear film volume from the lacrimal glands. A mixed form of DED includes a combination of both the aforementioned entities.^6–8 All these variants are associated with a significant impact on the vision, ocular surface milieu, mental health, and quality of life (QOL) of the individuals suffering from it.^9,10 The tear film plays an essential role in lubrication and sustaining the integrity of the ocular surface, ensuring the maintenance of a smooth refractive surface that aids in optimal visual performance.¹¹ Pre-corneal tear film being the first refracting medium of the ocular surface needs to be healthy to obtain precise topography, tonometry, and other biometric measurements of the eye. In DED, the disturbed tear film homeostasis results in ocular surface damage due to the induced tear film hyperosmolarity and chronic ocular surface inflammation. The resultant altered tear film dynamics and ocular surface damage lead to inaccuracies in optical measurements, thereby impacting the outcomes of interventions like cataract surgery that largely depend on these assessments.^12–14

Modern-day cataract surgery delivers excellent surgical outcomes along with rapid postoperative recovery and a lower rate of complications.¹⁵ While the technological advancements in cataract surgery over the past five decades have had a positive impact on the QOL of millions of individuals globally, they have also created a rise in surgeon and patient expectations from these interventions.^16,17 Despite evolving as a successful refractive procedure in the modern era, a commonly performed surgical intervention like cataract surgery becomes quite challenging when performed in the background of other associated ocular co-morbidities like DED.^15,18 The sub-optimal outcomes achieved can be attributed to the associated ocular surface alterations, chronic inflammation, inaccuracies in IOL power calculations, epithelial healing issues, and postoperative worsening of DED itself.^1,19,20

DED has been reported to increase after cataract surgery even in eyes without pre-existing disease, thereby affecting the surgical outcomes and increasing dissatisfaction among patients. Dasgupta and Gupta reported that at 12 weeks post-cataract surgery, all the patients showed abnormalities in tear film break-up time (TBUT), Schirmer I test values, and DED symptomatology questionnaire scores.²¹ Choi et al. reported that even at 3 months following cataract surgery, 27% of patients experienced persistent DED symptoms with clinical evidence of reduced TBUT, increased ocular surface staining with fluorescein, and meibomian gland dropouts.²² In addition to aggravated symptoms, patients with DED are more prone to refractive surprises post-surgery due to the inaccuracies in pre-operative biometry assessments.²³ In this modern era of premium intraocular lenses (IOL) and heightened patient expectations, having a better understanding of the factors influencing biometry and surgical outcomes in patients with DED becomes extremely vital.

Thus, in this narrative review, we aim to provide an update on existing literature to improve understanding of the preoperative keratometric fluctuation and methods to optimize biometry in patients with DED presenting for cataract surgery. Additionally, we aim to identify the existing lacunae in literature which will act as a base for future research.

METHODOLOGY

A search was undertaken using the databases, PubMed (from the year 2000), MEDLINE, CENTRAL (including Cochrane Eyes and Vision Trials Register; Cochrane Library: Issue 12 of 12 December 2019), metaRegister of Controlled Trials (mRCT) (www.controlled-trials. com), ClinicalTrials.gov (www.clinicaltrial.gov) and WHO International Clinical Trials Registry Platform (www.who.int/ictrp/search/en). The search terms included “cataract surgery or phacoemulsification” combined with “dry eye”, “dry eye disease”, “biometry”, “keratometry”. Published articles in English were preferentially selected. Published data focusing on the potential burden of pre-existing and postoperative DED following cataract surgery, the effect of dry eye on the ocular surface, variations in biometry due to dry eye, and current evidence on the management options to ameliorate refractive surprises after cataract surgery in eyes with DED were reviewed.

TEAR FILM ALTERATIONS IN DED

DED is characterized by subnormal production of tears, rapid breakup of the tear film layer, and accelerated evaporation of tears from the ocular surface.⁶ The increased osmolarity of the tear film along with tear film instability is the core pathophysiologic processes involved in DED. Tear film hyperosmolarity due to any etiology of DED is responsible for increased tear evaporation and low TBUT.⁷ TFOS DEWS II report suggests that dry eye irrespective of the subtype enters a final common pathway in which hyperosmolarity of the tear film and ocular surface inflammation creates a vicious cycle perpetuating DED.¹¹ The inflammatory cascade along with tear hyperosmolarity causes reduced expression of glycocalyx mucins and goblet cell damage.¹¹ Low levels of MUC5AC in the tear film result from the goblet cell loss seen in DED.¹¹ Reduced expression of glycocalyx mucins is the most likely cause for inadequate ocular surface wetting leading to early tear film breakup. All the above changes further perpetuate dry eye disease, affect the ocular surface integrity and thereby impact any optical measurements that need to be performed on these eyes.

OPTICAL ABERRATIONS IN DED AND ASSOCIATED IMPACT ON QUALITY OF VISION

The tear film serves as the first refracting interface of the optical system of the eye, thereby exerting a significant impact on the quality of vision. Conventional measurements like visual acuity testing do not detect all aspects of compromised visual functions.¹² Quantitative objective assessments for detecting the quality of vision like corneal topography and wavefront sensors have made remarkable advances supplementing visual acuity testing in this aspect.

Corneal topographers like the Placido disc-based systems measure the anterior corneal curvature contours by analyzing reflected concentric mires on the air–tear interface.²⁴ The changes in the tear film can thus be detected by this system. The TMS-2 N corneal topography instrument (Tomey Technology, Nagoya, Japan) developed and inculcated a novel software called tear film stability analysis system (TSAS). This software enables the topographer to capture serial topography scans once every second for 10 s. The reverse-engineered Placido ring-based corneal topographic map calculations utilized in this system enable it to detect subtle tear film changes from distortion of mires.²⁵ Various studies in the past have also highlighted that irregular astigmatism is seen more markedly among patients with DED and is caused by the increased fluctuations and irregularities of the tear film.^26–28

Studies have taken into account surface regularity index (SRI) and surface asymmetry index (SAI) to better understand the changes occurring at the level of the cornea in DED.^29–31 As per these studies, both SRI and SAI were found to be higher in DED as compared to normal eyes. In a study by Kojima et al., TSAS software was used to analyze tear film stability, regularity, and asymmetry indices named TSRI and TSAI, which emanated from SRI and SAI respectively.³² This study found out that TSRI and TSAI were significantly more in dry eyes than in normal eyes. Additionally, the insertion of punctal plugs as a therapeutic tool in treating DED significantly reduced both SRI and SAI.³²

The utility of wavefront analysis for aberrometry has been growing worldwide. Wavefront sensing has been utilized in the detection and quantification of irregular astigmatism as higher-order aberrations. Subjective visual outcomes in patients with DED were correlated with progression index for corneal higher-order aberrations (HOA).³³ One study highlighted that optical quality degraded in patients with DED and was associated with visual impairment during driving.³⁴ Total ocular HOAs are usually found to be stable between blinks in normal eyes, but one study reported that HOAs can fluctuate dynamically after blinking even in clinically normal subjects.³⁵ Short TBUT DED is a terminology that has been gaining importance in recent years, which is reserved for subjects with symptoms of DED with a reduced tear film break-up time (TBUT) without ocular surface damage or aqueous tear deficiency.³⁶ In eyes with short TBUT, HOAs have been found to increase with time after blinking and in the 10 seconds inter-blink interval as noted on TSAS systems.³⁶ Subjects with aqueous deficiency DED have higher total ocular HOAs and these were even more marked in subjects having superficial punctate keratopathy (SPK) due to DED.³⁷ Kaido et al. confirmed these findings and reported that optical degradation in the central zone of corneas with DED may affect the visual quality.³⁸ This also applies to short TBUT dry eyes where patients often complain of severe dry eye symptoms and visual disturbances despite having a good visual acuity on regular assessment.³⁹ The impact of dry eye on HOA and visual quality has been demonstrated in Figure 1. By utilizing functional visual acuity and sequential wavefront analysis, clinicians can now understand the importance of treating short TBUT dry eye in a better way.^40,41 In a study by Koh et al., it was found that ocular forward light scattering and corneal backward light scattering were significantly greater in DED subjects as compared to normal eyes. SPKs as commonly found in DED might be responsible for causing backward light scattering from the anterior surface of the cornea.⁴² The above-cited studies on quantitative and qualitative analysis with corneal topography and wavefront sensing highlight that instability of tear film and ocular surface damage significantly degrade the quality of vision in patients with DED, despite their distant visual acuity being recorded as reasonable Figure 2.

Figure 1. Impact of optical aberrations on the image quality in DED. The image shows the image quality in normal subjects with a stable pre-corneal tear film resulting in a sharp image(a). Image b shows the scatter of light in eyes with dry eye disease (DED) resulting in higher-order aberrations (HOAs) and blurred images.

Figure 2. Algorithm for appropriate management of DED patients presenting in cataract clinics. The algorithm highlights a systematic approach in screening, evaluating, and optimizing dry eye disease (DED) in patients presenting for cataract surgery. It also discusses the recommendations for obtaining reliable ocular biometry in eyes with DED to improve the postoperative outcomes after cataract surgery.

VARIABILITY OF KERATOMETRY IN DED

According to the Royal College of Ophthalmologists cataract surgery guidelines, the outcomes of biometry can be considered excellent when at least 85% of the eyes attain target refraction within 0.5–1.0 diopter.⁴³ Accurate IOL power calculation is vital in providing satisfactory visual outcomes in patients undergoing cataract surgery and keratometry serves as a key component in this endeavor. The measurement and magnitude of anterior corneal astigmatism is an important factor in determining the need for toric IOL. A Manual keratometer, IOLMaster (Carl Zeiss Meditec AG), and Lenstar (Haag-Streit USA) are a few of the many instruments used widely for the calculation of keratometry preoperatively.

Keratometers rely on a good reflection of mires from the precorneal tear film, and the tear film instability can affect the reliability and sensitivity of keratometry measurements. This is due to the hampered quality of corneal reflections caused by the unstable tear film in eyes with DED.⁴⁴ The tear film instability is responsible for the dynamic changes of the anterior refractive surface of the cornea and affects the methods of ocular biometry that rely on the reflected light from the anterior corneal surface. Furthermore, the prevalence of dry eye is known to increase with age, and hence tear film instability is a common concern in the patients presenting with cataracts who often belong to the geriatric age group. In clinical practice, patients with DED have high short-term and long-term keratometry fluctuations and the ocular biometry needs to be repeated multiple times.¹³ A study by Epitropoulos et al. showed that subjects with tear film hyperosmolarity had poor repeatability of keratometry values and IOL power calculation as compared to subjects with normal tear film osmolarity.¹³ Thus, preoperative measurement of tear film osmolarity can identify patients who have higher chances of refractive surprises after cataract surgery.¹³ Table 1 illustrates the impact of dry eyes on ocular biometry parameters.

Table 1. Inaccuracies of biometry in DED and impact of treatment.

Study	Effect on biometry in DED	p-Value
Epitropoulos et al.^Citation13	Keratometry difference of >0.5 D in the tear film hyperosmolar group than in the normal group	0.02
Liu et al.^Citation29	The SRI, SAI and magnitude of astigmatism were significantly higher in patients with DED as compared to normal subjects	0.02
	A significantly greater percentage of irregular patterns on topographic maps were noted in DED	<0.005
Kim et al.^Citation23	Mean absolute error in refraction at 1 month after cataract surgery was significantly lower in the pretreatment group as compared to the non-treatment group Significantly lower refractive surprises were noted after cataract surgery in the pretreatment group	0.008 0.024

A study by Roggla et al. focused on the influence of instillation of artificial tears on keratometry measurements before cataract surgery.⁴⁵ This study observed significant changes in keratometry values after instilling both low- and high-viscosity lubricating eye drops lasting for a duration of 5 min. These fluctuations were noted to be higher among patients with dry eyes with lower reproducibility and reliability. Therefore, they concluded that biometry measurements should be taken either before or 5 min after instillation of lubricating eye drops in patients with DED with the former being more preferred.⁴⁵ Numerous eyedrops have been reported to impact optical biometry and Table 2 illustrates the impact of various such eyedrops on keratometry measurements.

Table 2. Effect of different topical medications on keratometry and optical aberrations in DED.

Topical medications	Effect on keratometry and optical aberrations	p-Value
Cyclosporine (0.09%)^Citation46	Significant predictive accuracy of corneal power measurement following treatment Mean improvement in HOA by 0.28 ± 0.27 µm	<0.03 <0.0001
Lifitegrast^Citation47	Accuracy of anterior keratometry measurements in predicting postoperative spherical equivalent refractive error improved	<0.04
	Improvement in HOA by 0.16 ± 0.33 µm	<0.001
Rebamipide^Citation48	Reduction in the variability of astigmatisms after treatment with rebamipide (0.13 ± 0.06)	<0.001
Low-viscosity artificial tears^Citation45	Significant variability of >0.5 D was observed in 27.8% up to 5 min.	<0.001
High-viscosity artificial tears^Citation45	Significant variability of >0.5 D was observed in 34.3% of cases up to 5 min.	<0.001

A study by Aysun Sanal Dogan et al. studied the repeatability of Scheimpflug-based Sirius corneal topography system in normal versus mild-to-moderate dry eyes. It was concluded that the anterior segment topographers (dual Schiempflug imaging plus Placido disc-based system) like Sirius had excellent repeatability of anterior segment parameters including Sim K values in both healthy as well as dry eye candidates.⁴⁹ This might give us some hope for a more reliable calculation of IOL power in mild-to-moderate dry eye patients.

NEED FOR PREOPERATIVE OPTIMIZATION OF THE OCULAR SURFACE IN DED

The ocular surface disease is highly prevalent in patients presenting for cataract surgery as measured by objective tests for DED.¹ Cataract surgery has been implicated in causing or worsening DED.^8,50–52 According to a few studies, 50% of patients presenting to cataract clinics with meibomian gland dysfunction were asymptomatic and 77% of patients with DED had positive corneal staining.^19,20 A compromised ocular surface affects the preoperative planning including keratometry and topography measurements, IOL power calculations, and toric IOL axis and magnitude. Cataract surgeons should be cognizant of the fact that intraoperative factors like antiseptic procedures, dilating drops and solutions, anesthesia type and duration, surgical technique (small incision cataract surgery/phacoemulsification), length of the incision, phacoemulsification technique, surgical time and duration of intraoperative exposure to light can cause or worsen dry eye postoperatively, especially among those vulnerable or with subclinical disease.⁵³ Also, DED might affect visual recovery after surgery, leading to refractive surprises and affecting the postoperative outcomes. Hence, ophthalmic practitioners must recognize, diagnose and manage DED optimally before planning cataract surgery. As visual outcomes would be better if ocular surface dysfunction is treated before surgery, it is worth considering preoperative screening for DED and tear film instability, especially in those patients where premium IOLs are being planned.¹

OPTIMIZATION OF THE OCULAR SURFACE BEFORE CATARACT SURGERY IN EYES WITH DED

The secondary level of prevention in DED aims at early and effective management of DED for reducing ocular morbidity.⁵⁴ Proper optimization of the ocular surface before performing surgery usually has good visual outcomes with a low rate of complications intraoperatively.⁵⁵ Artificial tears remain the first-line therapy in the medical management of DED, but it may have to be supplemented with other forms of treatment, based on the underlying mechanisms of dry eye. In the case of MGD, eyelid hygiene, warm compresses, and lid massage is the mainstay of therapy. Additionally, an option of using a short course of topical or systemic antibiotics, fatty acid intake, androgen use, intense pulsed light therapy, or thermal pulsation therapy may be tried. In cases where ocular surface inflammation is evident, a short-term regimen of non-preserved low potency steroids, cyclosporine A and lifitegrast have consistently produced encouraging outcomes^56,57 and may be proposed as a supplementary treatment in moderate-to-severe cases.^58,59 However, it should be borne in mind that usage of artificial tears or any topical ophthalmic medication just before keratometry should be discouraged due to its impact on astigmatism measurements in dry eyes.⁴⁵ The use of Rebamipide for mucin deficient DED and lipid-based formulations for EDE have been found to have a promising effect on the improvement of the ocular surface and the tear film.^18,21 Rebamipide is effective in improving the higher-order aberrations and discrepancies in astigmatism power and axis as compared to artificial tears thereby enhancing the accuracy of intraocular lens power calculations in patients with dry eyes.⁴⁸

Certain preoperative considerations like avoiding epitheliotoxic non-steroidal anti-inflammatory agents (NSAIDs), avoiding any benzalkonium chloride (BAK/BKC) containing eye drops, treatment with artificial tears and treatment of pre-existing meibomian gland dysfunction before surgery will help in improving postoperative outcomes.⁶⁰

Preoperative ocular surface irregularity leads to variability in keratometry and improper selection of intraocular lens leading to refractive surprises. Therefore, improving the ocular surface in dry eye patients will lead to greater accuracy in lens power selection.^47,61,62 A study conducted by Hovesian et al. assessed the effect of 0.09% cyclosporine on regularisation of the ocular surface and the predictive accuracy of preoperative keratometry measurements in patients with dry eye presenting for cataract surgery. The study concluded that patients who were prescribed 0.09% cyclosporine preoperatively showed significantly improved accuracy in prediction error of spherical equivalent outcome following surgery.⁴⁶ Dissatisfaction among patients implanted with multifocal IOL has commonly been linked to HOA. The study by Hovesian et al.,⁴⁶ also found out that pretreatment with 0.09% cyclosporine results in significant improvement of root mean square HOA. A similar patient population was recruited by the same group and DED was treated with lifitegrast.⁴⁷ In both the studies it was evident that there was a significant improvement in predictive spherical equivalent power for IOL implants, and pretreatment with pharmacological agents approved for DED significantly improved clinical signs of severity in DED. Both the studies help us to reiterate the fact that adequate treatment of DED plays a vital role before performing ocular biometry to achieve optimal visual outcomes.

SUMMARY

DED is associated with variability in keratometry and poor repeatability of IOL power calculations, often resulting in refractive surprise and dissatisfaction among patients after cataract surgery. DED is implicated in the deterioration of optical quality in the form of dynamic fluctuations over the anterior corneal surface, variable keratometry magnitude and axis of astigmatism, induction of HOA due to tear film instability, and ocular surface inflammation.

Objective as well as subjective testing of dry eye in the form of dry eye questionnaires, Schirmer’s testing, TBUT analysis and tear film osmolarity before cataract surgery in a vulnerable subgroup of patients is recommended. This will help us in diagnosing and treating pre-existing dry eyes adequately before cataract surgery that can help attain more optimal and satisfactory visual outcomes. Adequate control of DED before cataract surgery with medications like artificial tears, topical cyclosporine, lifitegrast, warm compresses and lid massage would certainly help in reducing preoperative biometric fluctuations and postoperative aggravation of dry eye symptomatology. Instillation of topical medications just before biometry should be discouraged and it is recommended to repeat the biometry multiple times till minimal fluctuations are seen to have more reliable results. Future studies aimed to understand the various factors that impact the ocular biometry and modifications that can help us arrive at more reliable IOL power calculations in eyes with DED can help achieve optimal results.

Abbreviations

TBUT: tear film break-up time, LG: lacrimal gland, OSDI: Ocular Surface Disease Index

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Additional information

Funding

The author(s) reported there is no funding associated with the work featured in this article.