Monocular Diplopia, Foggy Vision, and Uncomfortable Binocular Vision

Case Presentation

A 72-year-old man is referred for a consultation. The patient underwent a series of surgical procedures elsewhere. First was bilateral cataract surgery a few years ago with a myopic target in the right eye for a monovision result. Second was pterygium surgery in the left eye that resulted in significant astigmatism. Third was the implantation of a piggyback lens to address the astigmatism in the left eye, followed later by an Nd:YAG laser capsulotomy.

The patient reports foggy vision and monocular diplopia in the left eye that do not improve with glasses. On presentation, his UCVA is 6/38 OD, and his BCVA is 6/4.8 OD with a manifest refraction of -2.25 -1.75 x 15 degrees (the target had been -1.50 D). His UCVA is 6/38 OS, and his BCVA is 6/12 OS with a manifest refraction of +0.50 -4.00 x 35 degrees.

An examination of the left eye reveals a ruptured pupillary ruff, mild iris transillumination defects, and paracentral corneal scarring. Corneal topography is irregular (Figure 1), with significant aberrations evident in the cornea and lens complex (Figure 2). Most of the astigmatism, however, is internal. Pachymetry readings are less than 500 um in each eye. The right cornea is fairly regular (Figure 3). A posterior examination of both eyes is unremarkable.

Figure 1. Corneal topography (Pentacam, Oculus Optikgerate) of the left eye.

Figure 2. Aberrometry (Schwind Peramis, Schwind eye-tech-solutions) of the left eye.

Figure 3. AS-OCT corneal mapping of the right (A) and left (B) eyes using the MS-39.

The patient's left eye is dominant. He has alternating exotropia with suppression and no binocular diplopia. Measurements of the scotopic pupils with the MS-39 (CSO) are 2.86 and 4.24 mm in the right and left eyes, respectively, and the left pupil is irregular.

His medical history is significant for a cerebrovascular accident in 2020 and atrial fibrillation.

The patient is a farmer by trade and is licensed to operate heavy vehicles and use a shotgun. His main priority is improved distance vision. His only stated concern regarding his near vision is the ability to place a worm on a hook for fishing, and he is happy to wear spectacles for this task.

How would you proceed?

— Case prepared by Abi Tenen, MBBS (Hons), FRANZCO

Shady T. Awwad, MD

Combining Placido technology with anterior segment OCT (AS-OCT), the MS-39 with pyramidal aberrometry (Figure 2) allows total corneal higher-order aberrations (HOAs) to be subtracted from total ocular HOAs, revealing the intraocular component. Corneal astigmatism (C22) is only -0.53 D, and corneal HOAs are 0.73 D, mainly mild trefoil and horizontal coma. In contrast, the internal optics carry 1.31 D of HOAs and most of the astigmatism (C22 = -2.40 D). The cornea is therefore only mildly irregular, and most of the aberrations are intraocular, likely from a malpositioned, off-axis toric piggyback lens implanted before corneal remodeling and astigmatic regression occurred. The IOL is now likely overpowered and off-axis, inducing HOAs and chafing the iris.

Management would prioritize explantation of the toric piggyback lens to address the dominant internal cylinder, HOAs, and iris chafing in one step. Assuming that the primary IOL is well centered in the capsular bag, the residual error should become mainly spherical and quantifiable by a staged manifest refraction, with the option of intraoperative aberrometry if available. Refractive correction could then be achieved with glasses. If, however, the residual refraction is modest and the patient needs a better quality of vision, customized total corneal wavefront-guided surface ablation - possibly combined with wet phototherapeutic keratectomy to smooth the fine irregularities of the corneal surface - could be performed. A trial with rigid gas permeable (RGP) contact lenses could be conducted first to confirm a benefit.

A pinhole or small-aperture IOL is contraindicated because the corneal HOAs are modest and one of these lenses would reduce incoming light and field of vision in the dominant eye. I would refrain from placing another piggyback lens in the sulcus because of potential complications.

The refractive target would be plano to optimize distance vision in the left eye. Because the patient has alternating exotropia, suppression, and no fusion, he can tolerate a substantial amount of anisometropia. His right eye already provides functional near vision, and he has lived comfortably since his original cataract surgery. Baiting a hook is a large-target near task and should not be appreciably affected by 1.75 D of astigmatism.

D. Brian Kim, MD

Considering the patient's history of alternating exotropia and poor fusion, monovision was probably not the best choice. In addition, the right eye has a myopic refractive error of -2.25 -1.75 x 15 degrees beyond the intended -1.50 D target. These issues, however, are secondary concerns. The monocular diplopia in the left eye must be addressed first.

The piggyback IOL was supposed to neutralize the approximately 1.00 D of corneal against-the-rule astigmatism induced by the pterygium surgery but instead resulted in 4.00 D of oblique cylinder. The case presentation states that most of the astigmatism is internal, but topography also shows a component of irregular corneal astigmatism. Whether the IOLs are toric models is not mentioned.

Signs of trauma with a ruptured pupillary ruff, irregular pupil, and iris transillumination defects raise concern about a surgical complication with a misplaced IOL. Although the history is not clear on this point, monocular diplopia appears to have developed after piggyback IOL surgery. A slit-lamp examination, AS-OCT, and/or ultrasound biomicroscopy might clarify the positions of both lens implants in the left eye. Exploratory surgery would be performed, with iris hooks used to improve visualization and reposition or remove the problematic IOL(s).

Contact lens trials are a useful diagnostic tool. A 3-mm tinted prosthetic contact lens would be trialed to determine whether pupillary reconstruction could address the iris defects. A trial with an RGP contact lens would indicate the degree to which smoothing the cornea could reduce the irregular astigmatism.

The patient desires good uncorrected distance visual acuity (UDVA) and does not mind wearing readers. Because pachymetry readings are lower than 500 um, bilateral PRK would be the least invasive and best choice. LASIK would be less favored. An IOL exchange would be a reasonable approach, but scleral fixation of the lens may be necessary if the capsular bag is unstable. Piggyback IOL options are limited in the United States, where I practice, and would be a less attractive option given his struggles.

Abhay R. Vasavada, MS, FRCS(England)

The dominant left eye has an irregular cornea, a corneal scar, two IOLs in the anterior segment, and an open posterior capsule. The corneal aberrations, particularly coma, appear to be most responsible for his monocular diplopia and blurry vision. In the right eye, myopic astigmatism is hampering his UDVA.

Because the patient's priority is to optimize his UDVA, a contact lens trial with an RGP or semiscleral contact lens would be conducted for his left eye. This would be the most noninvasive approach possible and would indicate how much the quality and quantity of vision in this eye could be improved. Additional surgery on the left eye would be risky and might not solve his problems.

If he wishes to improve the UDVA in his right eye without the use of a contact lens, I would recommend PRK with adjunctive mitomycin C. Despite the borderline corneal pachymetry reading (500-550 um), the risk of ectasia would be lower than in an otherwise healthy eye given the patient's age and the possible natural crosslinking of the corneal collagen fibers.

What I Did: Abi Tenen, MBBS (Hons), FRANZCO

I advised the patient that monovision was not an ideal strategy given his exotropia/suppression and his license to operate heavy vehicles. I therefore recommended reversing the monovision and addressing the refractive surprise in the right eye. Achieving excellent UDVA in the left eye was unlikely, so improving the UDVA in the better-seeing right eye was a reasonable aim. The patient agreed with this plan, and we discussed laser surface ablation for the right eye.

For the left eye, we discussed the options of an IOL exchange and laser vision correction. The latter was chosen for a couple of reasons. First, the corneal irregularity would have made achieving an accurate refractive result with lens surgery alone challenging. Second, the iris had already sustained trauma, and the capsule was open. Customized corneal ablation was therefore the preferred option for the left eye to improve his quality of vision, correct the high astigmatism, and reduce or eliminate his monocular diplopia (Figure 4).

Figure 4. Customized ablation of the left eye using Schwind CAM software and the Schwind Amaris 1050RS (both from Schwind eye-tech-solutions).

A contact lens trial was conducted in both eyes to simulate the desired outcome, and the patient was satisfied with the refractive correction. Bilateral transepithelial PRK was performed, with a customized ablation in the left eye and a 30-second application of mitomycin C in each eye.

Two weeks following surgery, his eyes were comfortable, and the corneas were clear. The monocular diplopia in the left eye had disappeared. His postoperative regimen consisted of steroid and lubricant drops instilled four times per day. His UCVA was 6/9 OD and 6/15 OS. His BCVA was 6/6 OD with -1.00 D spherical equivalent and 6/9 OS with a manifest refraction of -1.00 -0.25 x 125 degrees. His uncorrected near visual acuity was N5 OU.

With both eyes open, his UCVA was 6/7.5 and N5, and the patient reported that his UDVA had been improving daily.

At 8 weeks postoperatively (the patient's most recent visit), his UCVA was 6/6 OD and 6/9 OS. The shadowing had resolved, and he reported feeling comfortable with all visual tasks. He has yet to complete his postoperative course but has begun tapering the medications.