Heart of America Eye Care Congress 2023
Case Report:
Myopic Shift Following Pars Plana Vitrectomy
Dr. Alex Bennett, O.D.
Vista Eye Care
Thornton, Colorado
Abstract
Pars plana vitrectomies are indicated for a variety of pathological conditions of the eye – other times, it may be indicated for symptomatic relief of visual disturbances. These disturbances, typically due to reduced contrast sensitivity, can range from minor – including floaters and vitreous syneresis, to more concerning, such as rhegmatogenous retinal detachments and macular hole. This case examines various causes of refractive shifts in phakic patients following pars plana vitrectomy, in an attempt to understand the cause of a dramatic myopic shift in an otherwise healthy patient.
Introduction
When patients develop ocular pathology associated with the vitreous or vitreoretinal interface, one treatment option is a pars plana vitrectomy. Removal of the vitreous is completed via entering the pars plana, a “safe zone” for treatment which avoids the structures of the anterior chamber (lens, iris and ciliary body) as well as the posterior chamber, mainly the retina.19 This treatment option, while invasive, may provide the best prognosis for restoring functional vision in many cases20. As with any surgical procedure, there are risks and benefits, as well as unintended side-effects. This case, and associated research, discuss the topic of possible causes of a myopic shift following pars plana vitrectomy in a phakic patient.
Case History
Initial visit (8/19/2022)
A 57 y/o WF presented with chief complaint of blurry vision at all distances, and near blur worse than far. She also notices she has to “get closer” to her computer monitor to see the screen clearly while unaided. Patient reported using over-the-counter (OTC) readers as necessary for near vision enhancement and focus, but was unsure of the power. The patient also reported using Refresh tears in the morning, due to the feelings of dryness and irritation, but these feelings did not persist throughout the day. The patient also reports the use of levothyroxine to regulate her hypothyroidism, and Simvastatin to regulate dyslipidemia.
The patient reports she could not remember when her last full eye exam took place; she believes it might have been in the same clinic around 2019. The patient did have a remarkable history of photorefractive keratectomy (PRK) surgery of both eyes in January 2004, and had been seen in the clinic for a total of 3 visits in 2019. These visits, in February, March and December, were all medically focused visits for new onset flashes and floaters in the left eye only, and are the only previous patient records at the clinic. At each of these visits, her visual acuity was 20/20 unaided at distance in the right (OD), left (OS), and both eyes (OU). A review of clinical notes indicates she was referred to a retinal specialist to ensure an intact retina following her last medical visit in Dec 2019.
The retinal specialist recommended a pars plana vitrectomy be performed in early 2020, but the patient was schedule for knee surgery, and deferred until after the knee was healed. Following an additional delay due to COVID-19 restrictions for elective surgeries in 2020, the patient had a vitrectomy of the left eye performed on Aug 26, 2020. The one-day post-op notes were positive, indicating favorable outcome by the surgeon; notes also mention an “air-fill” but not the specific gas used during the procedure; no silicone oil was used as tamponade. The patient was advised to avoid lying on her back, and to use Tobramycin 0.3% topical ophthalmic drops four times daily (QID) in the left eye only. The next follow-up appointment took place Sept 10, 2020 and records indicate continued positive results – the patient was able to reduce the use of Tobramycin 0.3% solution from four times daily (QID) to once daily (QD) for one week, then was advised to discontinue the use of the medication entirely. The patient was cleared to see another provider, who was more conveniently located near her, for follow-up – this was recommended approximately 6 months later. Records indicate the patient did not present for 6-month follow-up, and the patient reports she did not return for any additional follow-up appointments.
Entering visual acuities on 8/19/2022 were: 20/20- OD, 20/400 OS with pinhole improving vision to 20/60. The patient was 20/60 OU at near unaided, and the patient reports the use of reading glasses for near enhancement, but specs were not present during the exam. Confrontation visual fields were full to finger counting in each eye. Extraocular muscle testing showed a full range of motion without reported pain or diplopia. Pupils were equally 4mm in size, round, and reactive to light with no afferent pupillary defect noted. Non-contact tonometry measured 10 mmHg OD and 13 mmHg OS at 4:27 P.M.
Auto refraction and keratometry readings were noted as:
OD: +0.25 -0.75 x145 Keratometry: 40.50 / 41.25 x175
OS: -6.50 -0.25 x005 Keratometry: 40.50 / 41.00 x171
Manifest refraction:
OD: +0.75 -1.00 x140 VA: 20/20
OS: -7.25 -0.25 x005 VA: 20/30+2
Slit lamp biomicroscopy revealed normal appearance of adnexa, lids, lashes, puncta, and palpebral and bulbar conjunctiva in both eyes. The corneas were intact and clear through all layers in both eyes. The anterior chamber of each eye appeared deep and quiet, demonstrating open angles, graded 4+ using the Von Herrick estimation method; irises were flat and even. The patient was dilated following consent using one drop of Tropicamide 1.0% in both eyes at 4:44 P.M. Upon full dilation, an evaluation of the posterior segment was performed using the slit lamp microscope with 90D lens, and by binocular indirect ophthalmoscope (BIO) with 20D lens. The media of the crystalline lenses was not clear, and judged to be a grade 1 nuclear sclerotic cataract (NSC) OD, and a grade 2+ NSC OS. Assessment of the fundus revealed the optic nerve heads were well perfused with healthy rim tissue and C/D ratios of 0.20H/0.20V in both eyes. A flat and evenly pigmented macula was noted in each eye. The retinas were flat and intact with no pathology noted in either eye, and an appropriate 2/3 A/V ratio noted in each. Widefield fundus images were taken concurrently to photo document the retina.
The two primary treatment concerns were: 1. Determine the mechanism behind the myopic shift, then treat as necessary; and 2. Correct the patient’s blur OS. The possible differential diagnoses for the myopic shift were:
1. Cataract
2. Macular edema
3. Post-refractive ectasia
4. Epiretinal membrane
5. Macular hole/pseudo-hole
The differentials were not able to be ruled in/out at the exam, since there was more imaging and data necessary to properly evaluate the affected eye. A plan was formed to assess the health of the eye, and to treat the blur with a soft contact lens to minimize retinal image disparity due to the anisometropia. The patient stated that she works in a medical building with eye specialists, and may be able to get her imaging completed at work, so no services would need to be billed to insurance. Imaging was deferred until it could be completed and reviewed, or until she returned for an insertion and removal refresher course; the patient was agreeable with the plan.
Follow-up visit (9/1/2022)
The patient presented for an insertion and removal refresher course, to treat the blur in her left eye. The patient reports no perceived change in vision in either eye, although the intermittent blur due to her left eye was now subjectively more noticeable. She currently reports using reading glasses to help with near vision – she reported having multiple strengths that all worked well, from +1.50 to +2.00, depending on the situation and time of day. The patient reported no additional health changes or concerns in the several weeks since her previous encounter.
The patient reports she was unable to have any OCT/retinal imaging completed at work, so imaging was completed upon arrival; her results can be seen in figures 1 and 2.
Figures 1: 5-line raster image of the fovea OD – note the intra-retinal cystoid space and irregularity of the fovea (in image 4), likely due to vitreomacular traction prior to the posterior vitreous detachment; vitreous is imaged at the top of the raster image
Figures 2: 5-line raster image of the fovea OS – note the irregularity of the fovea, likely due to vitreomacular traction prior to the posterior vitreous detachment; the vitreous is not pictured here due to the vitrectomy.
The OCT imaging allowed differentials for the myopic shift to be ruled out. Macular edema, a macular hole, and epiretinal membrane formation, were all eliminated as differential diagnoses in the left eye. It is noteworthy to mention the irregularity of the foveal pits in each eye, due to vitreomacular traction prior to the vitreous detaching. A close examination of the raster scan actually demonstrates a cystic pocket in the inner layers of the right-eye retina - this hole was likely the result of vitreomacular traction, but does not seem visually significant to the patient.
Post-refractive ectasia was also ruled out as a possible source of refractive shift, since both eyes had similar keratometry readings at both visits in August and September of 2022. The readings demonstrate flat corneas, which is expect post-surgical PRK. The astigmatism of each eye appears consistent with refractive values, and are approximately equal in both eyes.
It appears the most likely cause of the refractive shift is phacomorphic in nature. The asymmetrically noted cataract and physiological lens appearance noted during the previous dilated exam seem to be the most likely explanation for the shift. There is also a question of whether any changes to axial length occurred following the vitrectomy, but no axial data was available from before or after, the procedure was completed - and no axial measuring device was available during any visit the patient had with the clinic, so this remains a confounding factor in this case. In the discussion section below, additional data is provided to support the hypothesis of lenticular changes as the probable cause of the myopic shift in this case.
The second item to address was to treat the blur in the left eye. At the follow-up appointment, entering visual acuities were: 20/20- OD, 20/300 OS (pinhole vision of 20/40); 20/60 OU at near unaided. Confrontation visual fields were full to finger counting in each eye. Extraocular muscle testing showed a full range of motion without reported pain or diplopia. Pupils were equally 4mm in size, round, and reactive to light with no afferent pupillary defect noted.
Auto refraction and keratometry readings were repeated to ensure consistent results:
8/19/2022
OD: +0.25 -0.75 x145 Keratometry: 40.50 / 41.25 x175
OS: -6.50 -0.25 x005 Keratometry: 40.50 / 41.00 x171
Manifest refraction:
OD: +0.75 -1.00 x140 VA: 20/20
OS: -7.25 -0.25 x005 VA: 20/30+2
9/1/2022
OD: Plano -0.50 x144 Keratometry: 40.50 / 41.25 x175
OS: -6.75 -0.25 x007 Keratometry: 40.50 / 40.75 x004
Manifest refraction:
OD: +0.75 -1.00 x140 VA: 20/20
OS: -7.25 DS VA: 20/25-2
Due to the high degree of anisometropia, the most reasonable form of vision correction was a soft contact lens. The patient had previously worn soft contact lenses, and was curious about the types of lenses being used. After a discussion and review of current modalities, a daily disposable soft lens was decided to be the most appropriate form of correction, due to its all-day hydration and comfort in arid environments – as well as being the most hygienic form of vision correction.
The patient was initially fitted with her first lens:
OS only: Acuvue Oasys 1-day lens (Senofilcon A), Pwr: -6.50, BC: 8.5, Dia: 14.3mm, VA: 20/25-
The patient did not like any over refraction using a loose lens with power of +/-0.50; she reported the best vision from the -6.50D lens.
The patient was satisfied with the overall comfort and vision of the contact lens. She reported more comfort with the use of reading glasses when using the contact lens – she spent a short time reviewing her telephone, a reading card, and other literature while in-office, and appeared genuinely satisfied with the resulting binocularity. Due to the high degree of anisometropia, it was explained that glasses would not be a reasonable alternative, and that the patient would have to wear contact lenses as the best means of functional correction. The patient was amicable to this solution, and the contact lenses were finalized for dispense; the patient was asked to return to clinic in 1 year for follow-up and to renew her contact lens prescription.
Discussion
Vitreous opacities, specifically “floaters,” are a frequently reported visual complaint, affecting 76% of the general population.1 These complaints appear to be primarily caused by a reduced contrast sensitivity function (CSF), up to 33% compared to control subjects.2 Thankfully, vision was reported as subjectively normalized following vitrectomy.2 A meta-analysis and multiple reviews of clinical literature demonstrate that the procedure is effective at restoring visual function by treating the symptoms of opaque floaters in patients in the majority of cases -although the procedure is not entirely without risks or unintended side-effects.3-5 The procedure has also been demonstrated to improve not only quality of vision, but also quality of life in some patients.6
The myriad of literature on the subject of pars plana vitrectomy are divided among the indications for the procedure, including: vitreous hemes, vitreomacular traction due to syneresis, and rhegmatogenous retinal detachment, to name a few; see table 1 for a more comprehensive list.7
Table 1: Non-inclusive list of indications for a pars plana vitrectomy7
· Macular hole
· Epiretinal membrane
· Vitreomacular traction
· Vitreous hemorrhage
· Tractional retinal detachment
· Rhegmatogenous retinal detachment
· Refractory macular edema
· Vitreous biopsy
· Endophthalmitis
· Dislocated intraocular lens
· Retained lens material
· Intraocular foreign bodies
There are many articles discussing the implications of vitrectomy in each case, typically focused on those specific case outcomes. These articles also tend to be divided amongst phakic and non-phakic patients, and each treatment option is dependent on a number of independent factors including: overall health of the patient, objective assessment by the practitioner, and how emergently the treatment procedure needs to occur. Research on the subject of vitrectomies performed due to visually symptomatic floaters in phakic patients appears to be a topic less frequently examined, perhaps due to phakic patients requiring vitrectomy for symptomatic floaters is not as likely as needing a vitrectomy for other cases.
A comprehensive resource on the topic of refractive shifts in phakic patients following vitrectomy was compiled by Tseng et al. in the Taiwanese Journal of Ophthalmology in 2012. The authors discussed how phakic patients tended to experience an average refractive shift of -1.60D with a 95% confidence interval of -2.35 to -0.85, p <0.001, paired t-test, following vitrectomy.9 While there are outliers in the data that demonstrate -6.00D of refractive shift, the sample size of the entire study is inadequate to make proper inferences. 37 of 172 participants were phakic patient’s post-vitrectomy in this study, and only 9 of 172 received vitrectomies for “miscellaneous” labelled disease types, meaning it is not definitive how many suffered from floaters. The data did not indicate if any of the 9 “miscellaneous” disease types were phakic or pseudophakic, which further confounds the data.
Tseng et al. did provide some interesting hypotheses about the mechanisms behind the refractive changes: 1. silicone oil changing the refractive properties of the globe; 2. changes in corneal curvature resulting in a change to refractive power; 3. changes in anterior chamber depth; and 4. axial length change.9
In the case presented, the patient did not receive silicone oil as a tamponade, so this cannot be used to explain the patient’s shift. While post-op keratometry is useful data, it is not as comprehensive as a corneal topographer; there is also no pre-op data for comparison, and the records could be variable given the patient’s history of PRK. Tseng’s team had to rule out changes in anterior chamber depth as a myopic development mechanism during its own research, since it was formerly disproved by Byrne, et al. who were studying refractive shifts in pseudophakic patients; his cohort of 87 demonstrated a refractive shift of +1.00/-2.00D in a Caucasian population.11 This data is at least useable in a comparative sense, because the cohort was Caucasian – this more closely matches the patient’s demographic, being a white woman. Byrne et al. were not able to identify a particular mechanism for the refractive changes, only noting that further investigation of pre- and post-operative corneal topographies, as well as pre- and post-operative axial length measurements, may provide further insight. Similar to not having keratometry readings, there were no pre- or post-operative axial length measurements available for comparison.
A search of Cochran research database yielded only 16 results for searches of “vitrectomy,” with fewer results for “vitrectomy” including modifiers such as “floaters,” “phakic,” and “pars plana.” Of the resulting search, the most useful systematic review included surgery for post-vitrectomy cataract, detailing the need for additional Randomized Clinical Trials to determine whether phakic patients should have cataract surgery performed at the time of a pars plana vitrectomy.8 A meta-analysis of over 51 studies found that the incidence of cataract formation after vitrectomy ranges from 6-100%, and obviously further investigation is necessary, which could help to determine the exact etiology in the case presented.8
Large refractive shifts in phakic patients following vitrectomy when compared to the fellow eye were demonstrated in research by Iwase et al.12 There is a noted difference with this research: the cohort examined suffered from repairs due to rhegmatogenous retinal tears, and epiretinal membrane peels. While the indications for vitrectomy are due to different pathologies, this data cannot be ignored – especially when the results demonstrate such a dramatic shift; the raw data can be reviewed in table 2, but appears much more impressive in figure 3.
Table 2: Data from Iwase et al,12 reproduced with permission, demonstrating large myopic shifts following vitrectomy in phakic patients. Of note: the pathology indicated for vitrectomy in this table was due to rhegmatogenous retinal detachment and epiretinal membrane, not for visually significant floaters, as presented in this case. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4985298/#R23
Figure 3: Graph from Iwase et al,12 reproduced with permission, demonstrating large myopic shifts following vitrectomy in phakic patients. Of note: the pathology indicated for vitrectomy in this graph was due to rhegmatogenous retinal detachment and epiretinal membrane, not for visually significant floaters, as presented in this case. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4985298/#R23
Iwase et al. theorized that an elevated air/gas pressure of the globe following vitrectomy may lead to oxidative stress on the lens, and subsequent changes in the lens structural proteins, resulting in opacification.12 Studies indicate that patients undergoing vitrectomy surgery where a portion of the vitreous posterior to the lens is left intact, have not demonstrated any premature cataract development.16-17
A long-term study on patient satisfaction following vitrectomy was conducted by Schulz-Key et al. This research found that 60% of phakic patients receiving vitrectomies underwent cataract surgery during follow-up, at an average of 15 months.18 As mentioned previously, it was noted that patients requiring complete vitrectomies tend to require cataract surgery sooner than those who only received partial vitrectomies.18 The patient in the case was noted to have a complete vitrectomy of the left eye, and demonstrates asymmetrical opacities of the crystalline lenses, noted as NSC grade 2 OS, compared with NSC grade 1 OD.
Samarawickrama et al. reviewed data from the more than 3500 participant records from the Blue Mountain Eye Study, and discussed how nuclear sclerotic cataracts typically result in a myopic shift – which, as described, may be a contributing factor in this case; although the exact mechanism was indeterminate. As previously noted in the research of Sculz-Key et al, that there is evidence demonstrating the increase prevalence for cataract surgery following vitrectomy in phakic patients.14-15, 18
Conclusion
In the absence of any pathology, the genesis of the refractive shift was the removal of native vitreous tissue, and substitution with a filtered air mixture. The presumed hypothesis for the myopic shift in this case is attributed primarily to phacomorphic changes of the lens, although corneal and axial changes to the globe may have been contributing factors; the degree to which each component contributed is not fully understood. While the underlying cause remains a mystery, the patient is now being monitored for additional changes in vision, but is once again enjoying clear and stable binocular vision.
References
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