Corneal Disease and Its Impact on Cataract Surgery

Abstract

The primary focus of this book chapter is to investigate and discuss the impact of corneal disease and how various types of corneal pathology can affect the surgeons preop, intraop and post op management when considering cataract surgery for a patient. Cataract surgery is known to exacerbate ocular surface diseases like dry eye, HSV, inflammatory conditions like ocular cicatricial pemphigoid, SJS, peripheral ulcerative keratitis, Moorens ulcer and endothelial disease like Fuch’s dystrophy secondary to intraoperative endothelial cell loss. Preoperative treatment including optimization of the corneal surface, antiviral prophylaxis in HSV keratitis, quiescence of inflammation and preoperative diagnostic evaluation of endothelial cell counts may all play a role in postoperative outcomes. Corneal disease may also impact intraoperative considerations in cataract extraction to include the use of scleral tunnels or even Extracapsular Cataract extraction techniques, for example, in patients with Mooren’s ulcer to decrease corneal melt. More commonly corneal disease consequently provides a poor view for the surgeon and unfavorable post op visual acuity for the patient. Consideration of staged keratoplasty and cataract surgery vs. combined “triple procedure” have both been shown as reasonable treatment options. Postoperative considerations include management of endothelial cell loss during surgery and minimizing postoperative eye drops and medicomentosa.

1. Introduction

Cataracts are the world’s leading cause of blindness in patients age 50 and older [1], and consequently, cataract surgery is a common ophthalmological procedure. This chapter focuses on the considerations regarding coexisting corneal disease and how various corneal diseases affect cataract surgery preoperatively, intraoperatively, and postoperatively.

2. Ocular surface disease

2.1 Dry eye disease (DED)

Dry eye is a multifactorial disease of the ocular surface characterized by a loss of homoeostasis of the tear film, and a vicious cycle of inflammation on the ocular surface. Generally, DED is classified as aqueous deficient (e.g., secondary to Sjogrens syndrome) or evaporative (e.g., secondary to Meibomian gland dysfunction). This classification can help direct the ophthalmologists when developing an approach to treatment. DED is a critical entity to manage properly perioperatively as it is ubiquitous among cataract patients, can be worsened by surgical disruption of the tear film and postoperative drops, and can have a profound effect on postoperative visual acuity with consequences of patient satisfaction. Prevalence rates are estimated to range from 5 to 50% and as high as 75% in adults over 40 [2, 3]. Patient symptoms include burning, itching, epiphora, and decreased visual acuity. A basic understanding of the anatomy and physiology that contributes to a healthy ocular surface is helpful to understand when tailoring a treatment plan. The Lacrimal Functional Unit (LFU) is a term used to include the lacrimal glands, ocular surface, eyelids and the motor and sensory nerves that connect and regulate these structures. A healthy LFU is responsible for maintaining a healthy tear film, and for maintaining a healthy transparent corneal surface to project a crisp image onto the retina. The eyelids contribute by protecting the ocular surface; blinking which distributes the tear film across the eye and stimulates the lacrimal gland to pump tears out onto the surface of the eye; and producing secretions that contribute to the tear film. Lagophthalmos can be seen secondary to facial nerve palsies from strokes and diseases like Bell’s Palsy, HSV, VZV, and Lyme disease. The secretions (e.g., meibum) from the eyelid primarily help in reducing evaporative loss of tears [4]. Dysregulation of any of these components can contribute to DED.

2.2 Preoperative evaluation

In regards to dryness, the preoperative examination is a crucial step in identifying eyes that need ocular surface optimization prior to cataract surgery. Dryness can be exacerbated by cataract surgery, so treatment preoperatively can decrease the chance of a severely decompensated ocular surface postoperatively. Dryness can have a significant effect in altering the tear film and cornea with consequential effects on preoperative biometry measurements, namely the inaccuracy and variability of keratometry readings. For example, Epitropolous et al. looked at a cohort of 100 hyperosmolar (a point-of-care marker for dryness) and 50 normal eyes and found that the hyperosmolar group had a statistically significant higher variability of keratometry readings as compared to the normal group. The hyperosmolar group had a higher percentage with 1D or greater difference in measured astigmatism as well as a higher percentage of eyes with an IOL power difference of more than 0.5D [5]. Figures 1 and 2 show an example of how preoperative treatment of dryness can not only improve the ocular surface but also lead to more accurate measurements and IOL selection.

Figure 1.

Preoperative keratometry readings and intraocular lens selection in a patient with 2+ SPK. Note the irregular topography and mires on right and left images, respectively.

Figure 2.

For the same eye in Figure 1, repeat measurements after 6 weeks of treatment with artificial tears, ointment, preservative free dexamethasone twice daily, and punctal plugs demonstrate improved topography and mires as well as a change in the IOL selection.

Slit lamp examination can be used to visualize underlying causes of DED to help direct the surgeon’s treatment approach. Meibomian gland dysfunction (MGD), demodex collarettes, punctal stenosis, entropion, ectropion, lagophthalmos, and floppy eyelids can be identified and targeted to optimize the ocular surface preoperatively. Fluorescein and vital dye stains can be used to visualize superficial punctate keratitis (SPK). In addition to the slit lamp exam, several clinical and diagnostic tests are used for the diagnosis and the management of DED. A tear break-up time of less than 10 seconds is considered abnormal and supports an evaporative component of dry eye disease commonly seen in MGD. Interferometry and infrared meibography may also help with diagnosis and follow-up. The Schirmer 1 and 2 tests investigate tear production. Tear osmolarity, IgE, and MMP 9 are all point-of-care tests that analyze the composition of the tears themselves.

2.3 Treatment

Given the many available treatment options for DED, a tailored approach is best for these patients when optimizing the ocular surface in preparation for cataract surgery. For cases of mild dryness or an unstable tear film, a relatively quick regimen of aggressive preservative free lubrication [6] (e.g., tears, ointment) and corticosteroids (often only short-term, e.g. preservative free dexamethasone), with punctal occlusion if necessary, may be all the eye needs for better preoperative testing. It is good to maintain the dry eye therapy perioperatively as cataract surgery and the required postoperative drops can disrupt the tear film and cause additional dryness.

One of the challenges of managing DED is that it stimulates an inflammatory cascade which triggers a positive feedback loop of inflammatory mediators that increase the osmolarity of tears further exacerbating ocular surface dryness. Several of the treatment options try to break the inflammatory cycle. Weak topical corticosteroids can have a fast impact on the ocular surface. Treatments targeting the inflammatory component of DED may be necessary to break the cycle of inflammation in moderate to severe disease. Cyclosporine A is available in three formulations Restasis, Cequa, and now a generic form is available. In large phase 3 trials, both Restasis and Cequa have proven effective in increasing tear production as measured by Schirmer testing [7, 8], and subsequent studies have shown that cyclosporine may also increase goblet cells [9]. In the context of cataract surgery, one study of 28 eyes showed cyclosporine 0.05% used one month preop to 2 months post op improved visual quality after multifocal IOL implantation [10]. Other treatments that target the inflammatory component of dry eye disease include topical corticosteroid drops (Eyesuvis) and lifitegrast ophthalmic solution (Xiidra), an LFA-1 antagonist thereby inhibiting LFA-1 binding to overexpressed ICAM-1. Autologous serum tears have also been used to treat severe dry eyes.

To address blepharitis and meibomian gland dysfunction, eyelid hygiene including warm compresses and lid sprays or wipes work to increase meibomian gland secretions and remove debris. Oral low-dose doxycycline may also be used to obtain a quick response to treating the lids through its anti-inflammatory and lipid layer stabilization properties. Azithromycin has been found to stimulate the accumulation of intracellular phospholipids and lysozymes which are important in the maturation of meibocytes [11]. Microblepharoexfoliation treatment (e.g. Blephex), thermal lid therapy with gland expression (e.g. Lipiflow, TearCare, iLux), and Intense Pulsed Light (IPL) therapies are procedures that are designed to increase meibomian gland secretions onto the ocular surface; several studies have shown them to be effective treatment options as well [12, 13, 14, 15, 16]. These can potentially help combat lid disease quickly prior to cataract surgery. Moisture chamber goggles, sutured tarsorrhaphies and lid weights can all be utilized to prevent evaporative tear loss from the eye. When appropriate, addressing the lid malposition (e.g., ectropion/entropion) may be necessary to help the ocular surface. If the underlying cause of DED is Neurotrophic Keratitis, cenegermin (Oxervate) is a FDA approved drug that works directly upon corneal epithelial cells and corneal nociceptors as recombinant nerve growth factor [17, 18].

2.4 Intraoperative considerations

As illustrated above, dry eye disease can cause decreased visual acuity for the patient and by the same mechanism can cause decreased clarity through the irregular cornea during cataract surgery. To optimize the surgeons view, a dispersive ophthalmic viscosurgical device can be applied to the cornea to decrease dryness during surgery. If the ocular surface dryness is secondary to neurotrophic keratitis the surgeon should minimize additional nerve damage by avoiding the use of limbal relaxing incisions and multiple paracentesis wounds (e.g., using Malyugin ring instead of iris hooks) when possible. Similarly, limbal relaxing incisions should be avoided. At the end of the case, the surgeon may consider the addition of a bandage contact lens or in more severe cases of ocular surface or tarsorrhaphy may be considered. Dropless cataract surgery (e.g., transzonular or intravitreal injectables, resorbable dexamethasone punctal plugs) may be used to minimize medicamentosa along with avoiding/decreasing postoperative topical NSAIDs.

3. Ocular inflammatory diseases

Severe ocular surface inflammatory conditions such as Peripheral Ulcerative Keratitis (PUK), graft vs. host disease (GVHD), Stevens Johnson Syndrome (SJS), mucous membrane pemphigoid (MMP), and Mooren’s Ulcer may need additional preop/postop care and surgical planning due to disease sequelae (e.g. corneal thinning and scarring, conjunctival and limbal stem cell deficiency) and the potential risk of reactivation of disease (e.g. corneal thinning).

3.1 Preoperative evaluation

Obtaining relevant past medical history can be important, especially with attention to rheumatological conditions such as rheumatoid arthritis, spondyloarthritides, and other inflammatory arthritides/systemic disorders. Slit Lamp examination can reveal evidence of current and prior ocular surface inflammation including corneal scarring/thinning, corneal neovascularization, limbal stem cell failure, symblepharon formation, dry eye, and associated uveitis. Conjunctival injection can be a good surrogate marker of current inflammation level or control. Evaluating for signs of dry eye (as above) and appropriate preoperative management are critical for success postoperatively. If there is conjunctival inflammation or associated uveitis, it is important to have the eye quiet for at least 3 months prior to surgical intervention. If there is significant thinning, a pachymap can be useful to determine the best incision placement. Once the diagnosis has been made, the goal is to control inflammation before cataract surgery; otherwise, the surgery may exacerbate inflammation and can lead to worse outcomes. Potentially, control of these diseases requires systemic immunosuppression with collaboration with a rheumatologist, and patient specific surgical planning is critical (Figure 3) [19, 20, 21, 22].

Figure 3.

Slit lamp photograph of peripheral ulcerative keratitis in a patient with rheumatoid arthritis with slit beam highlighting the thinned area (A) and fluorescein highlighting the epithelial defect (B).

3.2 Intraoperative considerations

Having a surgical plan can be quite helpful in these eyes. Base incisions locations from a pachymap or preoperative slit lamp examination to avoid areas of vascularization and thinning. It may be necessary to consider a scleral tunnel if there is a history of corneal melts or thin limbal inadequate areas to make an incision. A study of 15 eyes with MMP showed that cataract surgery could be done successfully on these eyes but recommended the use of small corneal incisions to reduce the risk of conjunctival inflammation [19]. In contrast, patients with a Mooren’s ulcer may require scleral tunnel wounds or even extracapsular cataract extraction to minimize risk of triggering corneal melt [22]. Trypan blue is often useful when there is corneal scarring/opacity to optimize capsulorrhexis creation when visualization is not ideal. A suture may be necessary to help seal incisions when there is adjacent scarring or thinning. A bandage contact lens can be placed at the end of the case to protect the cornea and facilitate rehabilitation of the ocular surface. A subconjunctival or subtenons injection of corticosteroid can be helpful in controlling postoperative inflammation.

3.3 Postoperative management

These eyes require closer follow-up postoperatively as they are at higher risk for ocular surface decompensation, keratolysis, and chronic/recurrent uveitis. When dryness appears to worsen, consider a decrease in particular drops such as NSAIDS to avoid drop toxicity. NSAIDS may even need to be avoided in patients with an increased risk of keratolysis based on past ocular (history of prior melts) and medical history (e.g. GVHD, rheumatoid arthritis). Aggressive DED management can help prevent worsening disease with sequelae such as erosions and melting. Depending on the degree of irregular astigmatism, a rigid gas permeable lens may be needed for best visual acuity after cataract surgery and should be discussed with the patient preoperatively.

4. Pterygia

A pterygium occurs from elastotic degeneration and leads to fibrovascular growth of the limbal/interpalpebral conjunctiva onto the cornea. Despite its benign nature, pterygia can be progressive with further growth toward the visual axis and increased irregular astigmatism.

4.1 Preoperative evaluation

Slit lamp examination is important to determine how far the pterygium extends over the cornea. Other aspects such as injection, elevation, calcifications, underlying fibrosis/scarring, associated thinning, and healthy conjunctiva elsewhere can be helpful for preoperative planning and to establish medical necessity for excision. Topography can help demonstrate the magnitude of irregular astigmatism (often flattening) and how close to the paracentral/midperipheral cornea this encroaches. Placido disk corneal topography can be particularly useful as one can view the distortion of mires from the pterygium.

There are different approaches to the timing of pterygium excision in the setting of planning cataract surgery. If the pterygium is not affecting the midperipheral cornea or more central (and topography is not greatly affected), cataract surgery may be considered without any pterygium surgery. The pterygium is typically less than 2–3 mm encroachment onto the cornea in this setting. Kim et al. noted that pterygia <2.0 mm rarely induce postoperative changes after removal [23]. The patient should be aware that the pterygium may need to addressed in the future if best correctable vision is not satisfactory and glasses will likely be necessary for best vision. If visually significant or impacting cataract surgery corneal measurements, pterygium surgery can be performed prior to cataract surgery or simultaneously. If prior to cataract surgery, there should be approximately 3 months between surgeries to allow for stabilization and repeat measurements. This strategy likely allows for the best chance of achieving the desired post-refractive goal following cataract surgery. If the surgeries are performed simultaneously, this has the benefit of only one surgery for patients, but there is a decreased chance of hitting a post-refractive target. Steepening of the cornea can occur resulting in myopia [24], so IOL power selection should take this into account. Studies have noted that the longer or greater the pterygium size, the greater the change in keratometry readings [23, 25, 26]. Toric correction should only be considered when there is regular astigmatism after pterygium removal, and it should be avoided in irregular corneas and inconsistent corneal readings. Multifocal IOLs are often a poor choice when there is irregular astigmatism and higher levels of higher order aberrations. If there is associated fibrosis especially centrally or paracentrally, the patient should understand that a hard lens may be necessary postoperatively to achieve the best vision (Figure 4).

Figure 4.

Slit lamp photograph of a nasal pterygium. Preoperative topography demonstrates nasal flattening with 1.56 D of astigmatism. Following excision with autograft, postoperative topography demonstrates a more regular surface with 0.39 D of astigmatism.

4.2 Intraoperative considerations

During cataract surgery, trypan blue may help with visualization if there is central or paracentral scarring. If a temporal small pterygium is present and the plan is to leave it be, the main incision should be positioned elsewhere.

4.3 Postoperative management

While recurrence rates are low (<10%) following conventional pterygium surgery with an autograft, there typically is no deviation from standard cataract surgery in regards to postoperative management. One should continue to monitor pterygium recurrence.

5. Corneal opacification

Corneal scarring, Salzmann nodules, dystrophies (e.g. epithelial basement membrane dystrophy [EBMD]), and band keratopathy can present unique challenges in preoperative measurements, significantly compromise the view of the surgeon during cataract surgery, and may even require staged or simultaneous keratoplasty along with cataract extraction.

5.1 Preoperative evaluation

Preoperative evaluation of corneal opacities include slit lamp examination, assessment of BCVA using the Snellen chart, and ultrasound B-scan if view of the fundus is obscured. The broad slit beam can often highlight the extent of the scarring and improve visualization of EBMD and fibrosis associated with nodules. Fluorescein can highlight the pathology, especially when there is negative staining of areas that are not seen with broad beam lighting. When these corneal changes are seen in the central 5–6 mm, they are more likely to be visually significant or alter preoperative topography measurements. Topography can help demonstrate how much irregular astigmatism is present and how close to the central/paracentral cornea these conditions are affecting. Placido disk corneal topography can be particularly useful as one can view the distortion of mires from the involved pathology. When the view of the cataract is obstructed by the corneal opacity, additional diagnostic testing can include anterior segment optical coherence tomography (ASOCT) which can allow the surgeon to assess the depth of corneal scars, and it can also be used to provide information regarding anterior chamber depth and characteristics of the cataract. A recent literature assessment demonstrated that ASOCT can be used to reveal structural details of the anterior capsule, objective measurements about the cataract itself including white and hypermature cataracts and the stability of the posterior capsule [27]. Another study compared anterior segment OCT to UBM in identifying posterior capsule rupture in traumatic cataracts. They discovered that ASOCT was superior to UBM in terms of its sensitivity, specificity, and positive and negative predictive values [28]. Corneal densitometry can be analyzed by a rotating Scheimpflug camera (Pentacam AXL; Oculus, Wetzlar, Germany). This modality can demonstrate the opaque area of the cornea and provide an objective score from 0 to 100 (most transparent to most opaque respectively).

5.2 Treatment

Superficial keratectomy (SK) is a procedure in which the corneal epithelium is removed and can be utilized if the corneal disease/damage is superficial to Bowman’s membrane. EBMD, Salzmann Nodules and band keratopathy are easily addressed with a keratectomy (and EDTA for band keratopathy) when the pathology is obstructing the central 5–6 mm (Figure 5).

Figure 5.

Slit lamp photograph of epithelial basement membrane dystrophy. This was treated with a superficial keratectomy prior to cataract surgery.

Multiple studies have demonstrated that SK is a safe and effective treatment to improve visual acuity, reduce corneal astigmatism, and optimize biometry readings [29]. A study at Duke specifically looked at the biometry readings of patients with EBMD and Salzmann nodular degeneration pre and post SK or PTK which showed that 21 out of 26 eyes treated for EBMD had a change in predicted IOL power and 16 of 24 eyes had a change in the recommended IOL toricity with a mean cylinder power change of 1.2 diopters. About 11 of 13 eyes with Salzmann Nodular degeneration had a change in predicated IOL power and 10 of the 11 toric eligible eyes had a change in the recommended IOL toricity with a mean cylinder power change of 1.5 diopters (Figures 6 and 7) [30].

Figure 6.

Intraoperative still photograph demonstrating a superior Salzmann nodule (dotted outline, a). This is peeled off during a superficial keratectomy (B).

Figure 7.

Topography of an eye with a Salzmann nodule treated with a superficial keratectomy: Preoperative, left (note flattening superiorly) and postoperative, right.

When the corneal opacity is restricted to the anterior 100 uM of the cornea, phototherapeutic keratectomy (PTK) using the 193 nm excimer laser can be considered prior to cataract surgery. The primary indications for PTK include anterior corneal dystrophies, such as lattice, granular, and Reis-Bückler’s dystrophy [31]. Corneal degenerations such as Salzmann’s nodular degeneration and climatic droplet keratopathy, also can be successfully treated with PTK [32]. Some of the complications associated with PTK include induced myopia, hyperopia, irregular astigmatism, haze, recurrence, and corneal thinning [31, 32]. As such subsequent cataract surgery should be delayed at least 6–12 weeks after PTK, once stabilization of the cornea has been established. A new topical medication losartan (used off-label 0.8 mg/mL six times per day) may help with treatment of certain types of corneal fibrosis/scarring in preparation for surgery (Figure 8) [33].

Figure 8.

Slit lamp photograph of band keratopathy (A). Intraoperative still photograph demonstrating another patient with band keratopathy. (B) Demonstrates the preoperative appearance and (C) demonstrates appearance following removal with superficial keratectomy and EDTA application.

5.3 Intraoperative considerations

Often, the involved pathology is addressed with a keratectomy. In the setting of corneal opacity, trypan blue is safe and has been widely used for better visualization of the anterior capsule [34]. Pupillary enlargement is a technique that can be used to create an optical window via sphincterotomy or an optical iridectomy when the corneal opacity blocks the central visual axis as an alternative to a corneal transplant procedure [35]. Endoillumination is a technique whereby an endoillumination probe is inserted through a corneal paracentesis (or alternatively a transconjunctival chandelier illumination system) to improve visualization during cataract surgery (Figure 9) [36, 37].

Figure 9.

Intraoperative still photograph demonstrating use of trypan due to poor visualization from corneal scarring/opacity (A) and how this improved ability to perform capsulorrhexis (B).

If the corneal opacification is inhibiting a patients best corrected visual acuity or the surgeons view to safely perform cataract surgery, a keratoplasty may be necessary. Depending on the depth of the corneal opacification, surgical options include a combined surgery referred to as a Triple Procedure, that is, Penetrating Keratoplasty (PKP) or Deep Anterior Lamellar Keratoplasty (DALK) with cataract extraction and IOL implantation) vs. a staged procedure where the keratoplasty is performed first and the cataract surgery is done at a later time (Figure 10).

Figure 10.

Slit lamp photograph of dense large scar with overlying rigid gas permeable lens (A). After worsening cataract, it was determined that a deep anterior lamellar keratoplasty would best allow for cataract extraction (B).

Combined surgery should be considered in patients with health problems that place patients at high risk for undergoing multiple surgeries under anesthesia or for patients whose health/life situation necessitates more rapid visual recovery [38, 39]. In a combined surgery, cataract extraction can be performed via phacoemulsification or via the open sky technique with extracapsular cataract extraction. The main disadvantages in a combined surgery using the open sky technique is that the eye is exposed to the outside environment for a longer time thereby increasing the patient’s risk for endophthalmitis, and possible suprachoroidal/expulsive hemorrhage due to acute hypotony. Additionally, patients’ postoperative refractive errors are generally higher due to inaccuracy of IOL formulas when the measurements are estimated as well as postoperative changes in keratometric values, AC depth, and axial length [38, 39, 40, 41, 42]. Staged surgery is generally more controlled as compared to open sky because it is performed in a closed system [41, 42, 43]. Additionally, a staged surgery is more likely to provide the patient with better postoperative vision because it allows for more accurate IOL power calculation due to more accurate preoperative diagnostic testing. As the cornea is allowed to stabilize and astigmatism minimized with suture removal, surgical adjustments such as placement of the main wound at the steep axis of the cornea and placement of arcuate keratotomy can be performed during cataract surgery. Although potentially controversial, toric IOLs can be considered in certain situations; however, they are often avoided with PK and DALK as a future graft replacement would leave a toric IOL with a mismatched cornea. This may not be as significant a factor with the ability to place an endothelial keratoplasty under a PK/DALK. The disadvantages of a staged procedure include endothelial cell loss, the risks of undergoing anesthesia a second time, and the large delay in visual improvement due to the requisite time after keratoplasty for stabilization of keratometric values and suture removal which may take up to 6–12 months [37, 38, 39]. When cataract surgery is performed staged under a keratoplasty, trypan blue may be necessary if visualization is poor. A scleral tunnel may be necessary to avoid crossing the graft-host-junction with the main incision. Using extra OVD is prudent to minimize endothelial damage as there is faster endothelial cell attrition for a keratoplasty compared to a native cornea. Sutures are often needed as wounds may gape and leak due to the inherent contraction from the keratoplasty.

5.4 Post operative management

The etiology of the corneal opacification must be taken into consideration in the post operative period as it may help guide the surgeons post operative management. If the corneal scar was originally from HSV/VZV, it is important to place patient on prophylactic oral antiviral due to the increased risk of recurrence of epithelial or stromal disease following intraocular surgery. Close monitoring is especially important postoperatively in patients with corneal disease as patients can have recurrence of corneal pathology and repeat opacification of the cornea. If the visual acuity is not satisfactory following cataract ± corneal surgery an RGP lens may be utilized to minimize the decrease in visual acuity secondary to irregular astigmatism often seen in these patients.

6. Endothelial disease

Due to the potential collateral damage to endothelial cells during cataract surgery, careful consideration and patient specific planning is necessary in the setting of coexisting corneal endothelial disease. While low endothelial cell density can be seen in patients with a history of intraocular inflammation, prior corneal transplant, prior glaucoma filtering surgery, or trauma, it is most commonly encountered in patients with a history of Fuch’s corneal dystrophy [44]. Once a cataract becomes visually significant, earlier extraction may be beneficial to minimize damage to endothelial cells, especially if a simultaneous corneal procedure is being avoided.

6.1 Preoperative evaluation

Slit lamp examination of the cataract maturity is important as denser cataracts predictably require more ultrasonic energy and lead to more endothelial cell loss. The status of the cornea should be evaluated at slit lamp specifically looking for guttata, edema, and fibrosis from longstanding stromal edema which can all diminish a patient’s best corrected vision and may also impair the surgeons view into the anterior chamber during cataract surgery. Any preoperative clinical signs of corneal edema warrant consideration of addressing the endothelial function at the time of cataract surgery (Figure 11).

Figure 11.

Slit lamp photograph with slit beam (A) demonstrating guttata and corneal edema with anterior haze and microcystic edema in an eye with Fuchs corneal dystrophy. This is highlighted with sclerotic scatter lighting technique to demonstrate the microcystic edema and bullae (B).

While pachymetry and specular microscopy classically were used to determine risk of corneal decompensation following cataract surgery, these may be poor measures of prognosis. Unless there was a baseline pachymetry taken years ago, pachymetry is not often useful as it may not correlate well with edema. Tomography may be a more useful tool in evaluating early Fuchs prior to cataract surgery. Sun et al. created tomography criteria that can be helpful to evaluate Fuchs eyes to determine subclinical edema. These include loss of parallel isopachs, displacement of the thinnest point of the cornea, and focal posterior corneal surface depression [45]. Another study from this group also evaluated the risk for progression of Fuchs and/or needing surgical intervention following uncomplicated cataract surgery using the same criteria. Risk was 0% when no criteria/patterns were present, 50% when any 1 or 2 of the criteria/patterns were present, and 75% when all 3 were present [46]. Given the possibility for needing a surgical intervention, it can be prudent to aim myopic for the post-refractive goal as endothelial keratoplasty will often cause a hyperopic shift. To account for this, aiming for −0.50 to −0.75, −1.00, and − 1.00 to 1.25 sphere for DMEK, nano-thin DSEK, and ultrathin DSEK, respectively. Avoid placing a hydrophilic intraocular lens given the possibility of calcification with these following the gas/air with an endothelial keratoplasty (Figure 12).

Figure 12.

Preoperative tomography in an eye with Fuchs demonstrates loss of parallel oval/circular isopachs, displacement of the thinnest point of the cornea (white arrow), and focal posterior corneal surface depression (red arrow).

6.2 Intraoperative considerations

Factors that increase the risk of endothelial cell loss during cataract surgery include longer phacoemulsification time such as that required with denser cataracts and shorter axial length [47]. Care should be taken to refill the anterior chamber to coat the endothelium with dispersive viscoelastic between cataract quadrants/segments in these situations. Systemic illnesses may also increase the risk of endothelial cell loss during cataract surgery. One study investigated endothelial cell loss in diabetic patients undergoing cataract surgery as compared to non-diabetics and showed a significant increase in endothelial cell loss 3 months postoperatively in the diabetic study group [48]. Surgical treatment options for patients with cataract and coexisting endothelial disease include cataract surgery alone or combined surgeries (with either a simultaneous triple procedure or staged). Combined options include DMEK with phacoemulsification and IOL placement, DSAEK with phacoemulsification and IOL placement, DSO with phacoemulsification and IOL placement. Factors that may determine a simultaneous compared to stage procedure include degree of cornea vs. lens pathology, post-refractive goals (may be more accurate with corneal surgery and repeat measurements prior to cataract surgery), and patient preference (1 surgery versus 2 surgeries). Torics may be considered for mild Fuchs with a clear regular corneal cylinder on topography of more than 2 diopters. It may be better to stage toric IOL given the hypotony and anterior chamber shallowing during endothelial keratoplasty (especially DMEK) which could potentially rotate the IOL.

Trypan blue can be useful to see through dense guttata especially in corneal haze or bullae are associated. If edema is severe, one may perform a keratectomy to improve the view. If performing cataract surgery alone, phacoemulsification at iris plane (more posterior) may decrease endothelial damage, while phacoemulsification near the cornea in combined surgery is fine as the endothelium will be replaced and damage to the posterior capsule can be minimized. Additionally, a smaller capsulorrhexis may be better for combined cases to keep the IOL in the capsular bag during anterior chamber shallowing; similarly, using only cohesive viscoelastic in combined cases can allow for less chance of having retained viscoelastic in the graft interface.

6.3 Postoperative management

Postoperatively, patients with Fuchs should be counseled that there may be delayed deturgescence of their corneas following cataract surgery. This may even take several weeks to a couple months, and topical sodium chloride can be helpful. If the edema fails to clear, one can then consider endothelial surgery. In the setting of Fuchs post-cataract surgery, it can be prudent to avoid a large YAG treatment to minimize vitreous prolapse into the anterior chamber with future endothelial keratoplasty (especially DMEK).

7. Keratoconus

Keratoconus is a corneal ectatic disease resulting in irregular astigmatism often characterized by inferior steepening of the cornea, irregularities in the corneal stroma and breaks in Bowman’s layer. Risk factors for keratoconus include patients’ with connective tissue disease, Down syndrome, and patient’s with atopic disease or habitual eye rubbing [49]. The onset of keratoconus is generally in adolescence and tends to stabilize by 30–40 years of age [50, 51]. Treatment options include hard contact lenses, intrastromal corneal ring segments, corneal cross linking, and DALK or PKP in later stages of the disease. Patients with keratoconus tend to develop cataracts at a younger age [52] and successful surgical treatment of cataracts in patients with keratoconus requires additional considerations in the preoperative and intraoperative period (Figure 13).

Figure 13.

Slit lamp photograph of an eye with keratoconus demonstrating Munson’s sign with V-shaped indentation of the lower eyelid with downgaze (A). Slit beam highlights the apical thinning with ectasia and anterior scarring (B).

7.1 Preoperative evaluation

Most notably in the preoperative period, one of the challenges in keratoconus is obtaining reliable IOL power measurements due to unreliable keratometric values and potentially different anatomy (increased axial length and anterior chamber depth leading to more posterior effective lens position) [53]. As keratoconus is a progressive disease, stability of disease should ideally be demonstrated before cataract surgery should be attempted. The Global Consensus on Keratoconus and Ectatic Diseases describes progression as a change in two or more of the following parameters – steepening of the anterior or posterior corneal surface, or thinning and/or an increase in the rate of corneal thickness change from the periphery to the thinnest point [54]. Contact lenses can distort the cornea and as such need to be discontinued prior to preoperative measurements. Soft contacts should be discontinued for at least 1 week [55] and rigid gas permeable (RGP) lenses should be discontinued for 1–2 weeks for every decade of use [56]. Patients with progressive disease may be candidates for corneal crosslinking (CXL) which has been shown to help strengthen the cornea by forming new bonds between the collagen fibers in the cornea [57]. As there can be a flattening effect from crosslinking, one should observe for at least 6 months and repeat measurements to document stability prior to cataract surgery. Aiming with a myopic post-refractive goal would be prudent since additional flattening may occur later after the CXL. Additionally, intrastromal corneal ring segment (ICRS) placement has been shown to flatten the cornea. For patients with severe ectatic disease not amenable to contact lenses or with scarring, DALK or PKP can also be effective treatments [58, 59]. Depending on patient goals and surgeon preference, the patient’s cataract surgery may have to wait until sutures are removed (starting 3–6 months following surgery) or astigmatism is minimized with selective suture removal. Again, stability of corneal measurements should be documented prior to cataract surgery.

Preoperatively cone location and centration should be evaluated. Patients with central cones tend to be more myopic whereas peripheral cones can actually result in mild hyperopia. Cylinder is affected by both cone location and shape as well [60]. Disease staging helps guide preoperative planning and can be done using the Amsler-Krumeich classification or the newer ABCD classification which has the advantage of staging early and subclinical disease by assessing anterior and posterior radii of curvature from a 3-mm optical zone at the thinnest point of the cornea, minimal corneal thickness, and best spectacle distance visual acuity [61]. One study emphasized the importance of accurately staging keratoconus by showing that using measured K values for IOL selection results in better outcomes in mild to moderate disease while standard K values (43.25) produce better results in severe keratoconus (K > 55) [62].

There are several devices available to measure biometry and keratometry. Routine methods using Placido disk based corneal topography devices assess only the anterior surface of the cornea whereas an elevation-based Scheimpflug imaging device will calculate total corneal refractive power by assessing anterior and posterior corneal curvatures [63]. The ratio between anterior and posterior corneal curvature is altered in keratoconus [64] thereby making the Placido disk based corneal topography devices less accurate and may lead to a higher chance of residual hyperopia, especially for advanced Keratoconus [63]. Currently available keratometry and biometry measuring devices include the Pentacam HR and AXL (Oculus GmbH, Wetzlar, Germany), IOL Master 700 (Carl Zeiss Meditec AG, Jena, Germany), Lenstar LS 900 (Haag-Streit AG, Koeniz, Switzerland), Sirius (Costruzione Strumenti Oftalmici, Florence, Italy), and Galilei G6 (Ziemer, Biel, Switzerland). Multiple studies have been conducted comparing these various devices in patients with keratoconus [65, 66, 67, 68, 69, 70, 71, 72, 73]. After reviewing the available data comparing these devices, Moshirfar et al. published a paper ultimately recommending obtaining Pentacam measurements, comparing them across more than one device and selecting the measurements that result in the highest calculated IOL power. Doing so reduces the risk of hyperopic surprise postoperatively [56].

As alluded to above, formula selection in patients with keratoconus is challenging as traditional formulas were developed based on a normal eye. Many studies comparing outcomes using different formulas have been done and demonstrate that the best formula may depend on the stage of the patient’s disease. The largest case series of cataract surgery in keratoconus looked at a total of 147 eyes and compared the precision of IOL formulas which are used routinely in normal eyes, (Haigis, Barrett Universal 2, Holladay 1 and 2, Hoffer Q , SRK/T, and Kane) compared to IOL formulas which are made exclusively for Keratoconus patients (Kane Keratoconus formula and Holladay 2 with Keratoconus Adjustment). The authors concluded that the Kane Keratoconus formula performed best in all stages of keratoconus followed by SRK/T. Furthermore, the authors suggested target refractions specific to each Krumeich stage. In stage 1 Keratoconus patients, there should be between no adjustment to −1.0 for the target refraction, for stage 2 a myopic target of −0.75 to −1.5 should be aimed for, and for stage 3 a myopic target of −2.0 to −3.0 [74].

7.2 Intraoperative considerations

A potentially controversial topic is the use of toric IOLs in patients with keratoconus. Their use has been investigated in patients with stable mild to moderate keratoconus. In these patients, toric lenses have shown significant improvement in postoperative uncorrected and best corrected visual acuity without causing significant corneal higher order aberrations [75, 76]. Toric IOLs should not be considered in patients with progressive disease, difficult refraction, or if there is a high difference between preoperative RGP lens corrected visual acuity and spectacle corrected visual acuity [77]. Aspheric IOLs should not be placed in patients with keratoconus as these IOLs are designed to eliminate the positive spherical aberration added by traditional IOLs. Due to the hyperprolate nature of keratoconus eyes, they would experience more negative spherical aberration [78] and worsen the hyperopic refractive shift. If the surgeon believes the patient will need a keratoplasty in the future after cataract surgery has been performed, the presence of a low power IOL will likely worsen hyperopia due to the subsequent loss of corneal power after the transplant. It may be better to perform the keratoplasty and later perform the cataract surgery after a period of stabilization and selective suture removal.

The irregular astigmatism secondary to corneal warpage in keratoconus can lead to intraoperative image distortion making cataract surgery more challenging for the surgeon. Use of RGP lenses intraoperatively can be quite helpful to reduce distortion and improve depth perception [79, 80]. Trypan blue can be helpful for visualization through an ectatic cornea often with scarring.

Incision sites can result in changes to K values and the cataract surgery itself might increase the probability of disease progression [81]. A pachymap can be helpful to guide incision sites to avoid the thinnest areas (avoid the cone/apex) [82]. These incisions should be made near the limbus to avoid surgically induced astigmatism and violation of the thinned, ectactic cornea [83]. Alternatively, a small scleral tunnel can be made if universally thin. Multiple studies have shown that clear corneal incisions are safe and may not necessarily need suturing [75, 84, 85, 86]; however, corneal sutures are generally considered more reliable and provide an opportunity for correction of astigmatism and subsequently of best uncorrected visual acuity in some patients [83].

7.3 Postoperative management

Many keratoconus patients will have residual refractive error, particularly those with severe disease. As mentioned previously, IOL calculations can be challenging in keratoconus patients and unsurprisingly postoperative refractive error is common. Spectacles can be used in patients with mild residual error [87] although they cannot correct for irregular astigmatism commonly seen in keratoconus. Soft contact lenses and soft toric lenses can be used in patient’s with low refractive error, regular astigmatism or mild irregular astigmatism as the soft contact lens covers the anterior corneal abnormalities [88]. In patients with a more significant refractive error, RGP, piggyback, hybrid, or scleral contact lenses can be tried [87, 88, 89, 90]. Surgical options include IOL exchange, but it should be noted that IOL exchange may have a higher risk of complications [91] and that if attempted, it is advised to perform the lens exchange within 3–6 months after initial IOL implantation due to fibrosis around the IOL [92]. Surgical placement of a secondary IOL is also an option and both anterior chamber iris claw lens and piggyback lenses implanted in the sulcus have been accomplished with satisfactory results [93, 94, 95, 96, 97, 98].

8. Conclusion

With the prevalence of ocular surface and corneal conditions, ophthalmologists will commonly encounter cataract surgery in the setting of coexisting corneal disease. This chapter has investigated some of these challenges and the available literature specific to ocular surface disease, corneal opacification, endothelial disease, and keratoconus for a cataract surgeon to consider including preoperative assessment, treatment and diagnostic testing, intraoperative pearls and techniques, and postoperative management to facilitate good surgical outcomes for our patients.

Conflict of interest

Brian Bird has no conflict of interest to declare.

Albert Y. Cheung, MD reports consulting for Sight Sciences, Tarsus, Moya ocular, BrightStar Therapeutics.

John D Sheppard reports consulting for Allergan, AbbVie, Alcon, Aldeyra Therapeutics, Bausch & Lomb, BioTissue, ClarisBio, Dompe, EyeDetec, Eye Point, EyeGate, Fortress Bio, NovaBay, Novartis, Noveome, LayerBio, Mallinckrodt, Mati, Ocular Therapeutix, Kala, RPS, Tarsier, Tearlab, Johnson & Johnson, Fidia, Clarios, Visus, Topivert, Noveome, Oyster Point, Santen, Sun Pharmaceutical Industries, Eyevance, ScienceBased Health, and Quidel; and ownership interest in ClarisBio, Noveome, EyeDetec, EyeRx Pharma, Oyster Point, RPS, TearLab, EyeGate, Strathspey Crowne, Mati, and CVP Partners.