When optical coherence tomography (OCT) first became available, it was obvious that it was an impressive technology; however, I was not sure why it would be needed in my practice, as I felt it was a tool for retina specialists. As an anterior segment surgeon, I assumed I could already visualize most of the significant pathology that was relevant to making decisions about patient care, and, if there was something I was unsure about, I could refer the patient to a retina specialist.
Once I had this technology available in my practice, however, it became clear that my previous notions about macular pathology were misguided. Whereas I once believed that most of the macular pathology that affected patient outcomes was readily visible to a careful examiner at the slit lamp, it soon became evident that there are many things occurring at the level of the macula that are observable or quantifiable only with high-definition OCT imaging.
OCT is an essential technology to the anterior segment surgeon’s practice that, once available, will be used every day to make crucial decisions about patient care. This article explores the categories of patients for whom OCT is particularly useful and the pathologic processes of the macula that can be visualized only with this modality.
COMMON CATEGORIES OF USE
There are five common categories of patients for whom OCT is particularly indispensable. First is the patient who presents for cataract surgery in whom the use of a presbyopia-correcting IOL is considered. Second is a patient referred for a second opinion who has had cataract surgery elsewhere, often with premium IOL implantation, and is unhappy with the outcome for whatever reason. Third is a patient in whom I have recently performed surgery and who now presents with decreased vision of uncertain etiology. Fourth is the patient referred for a complicated anterior segment surgical problem in whom we are considering surgery and need to know the status of the macula. Often these patients have factors that preclude detailed examination of the macula, such as a dislocated IOL, cloudy cornea, or pupil that does not dilate well; in these cases, OCT allows me to see what I otherwise could not. Finally, there is the patient with known macular disease—be it age-related macular degeneration (AMD), epiretinal membrane (ERM), diabetic retinopathy, or a retinal vein occlusion— for whom we need the information provided by OCT to follow changes in the macula that may affect vision and require intervention.
In all of these situations, the ability to image the macula is an indispensible tool that affects the decisions I make on a daily basis. A good example of this would be a patient referred with an anterior chamber lens and a cloudy cornea, in whom I cannot clearly visualize the macula. If OCT shows that the macula is normal, I may perform Descemet-stripping automated endothelial keratoplasty (DSAEK) alone, but if there is cystoid macular edema (CME) I will most likely do an IOL exchange prior to or in concert with DSAEK.
SEEING THROUGH COMPROMISED MEDIA
Newer technologies such as eye tracking and image summation with noise suppression allow current machines to build amazingly clear OCT images of the macula when the view at the slit lamp is so compromised that you can barely see anything. The following case provides a good example of this ability.
Case No. 1. A 62-year-old nurse presented with trauma in her left eye that occurred more than 50 years prior. She was aphakic and had a corneal scar. Her iris was adherent to the cornea, and there was a membrane of scar tissue and residual lens material completely blocking any view of the retina. She was interested in surgical rehabilitation of this eye, but, beyond doing a B-scan, there was no way to assess the posterior segment because there was no view whatsoever (Figure 1).
To determine what was going on in the back of the eye, I created a small opening in the membrane with an Nd:YAG laser. Although the opening was not large enough to see through, I was able to obtain excellent OCT images of her optic nerve and retina, which were essentially normal (Figure 2). Based on this information, I made an informed decision to proceed with a corneal transplant, sutured posterior chamber IOL, and pupil reconstruction. These were done successfully (Figure 3).
The patient recovered some useful vision in this eye, which was fortunate, as 2 weeks after this surgery was performed she presented with an unrelated central retinal vein occlusion in her fellow eye.
DETAILED VIEWS WITH SD-OCT
In addition to being able to see through compromised media, spectral-domain OCT (SD-OCT) can capture details in the macula that no other technology can obtain. There are many macular disorders in which the macula may look relatively normal at the slit lamp but significant pathology is present. Conversely, the macula may look abnormal, but OCT demonstrates relatively normal macular architecture. In particular, I have found that the following entities are best understood or quantified with the information provided by OCT imaging (and, for the most part, poorly appreciated otherwise):
- Vitreomacular interface abnormalities;
- Lamellar or full thickness macular holes;
- Macular thinning or atrophic changes;
- Photoreceptor abnormalities (ie, inner segment/ outer segment [IS/OS] junction abnormalities);
- Age-related choroidal atrophy (ARCA);
- CME; and
- Central serous retinopathy.
Many of the aforementioned conditions can significantly affect vision even if the exam at the slit lamp is unremarkable. One may easily miss a fine ERM or have little understanding of how one visualized on examination affects the architecture of the macula and, thus, the patient’s vision. However, these changes become much clearer with SD-OCT, as illustrated in the following case examples.
Case No. 2. A woman presented with 20/25 vision in her right eye (Figure 4A) and 20/40 in her left (Figure 4B). She had a history of laser iridotomy for narrow angles, moderate nuclear sclerosis, and cortical cataracts and was interested in cataract surgery with multifocal IOL implantation. She had mild ERMs in both eyes on exam.
Although the scanning laser ophthalmoscope (SLO) images showed the ERM as more impressive in the patient’s right eye than in her left and the ERM in her left eye appeared mild at the slit lamp, on OCT we could see marked changes in the macular architecture of the patient’s left eye that would likely be associated with a more complicated postoperative course, including macular edema and less-than-perfect vision. I advised against using a multifocal IOL, and we decided to delay her cataract surgery, as some of the visual problems she was attributing to cataract were likely related to the ERM in her left eye.
Case No. 3. A 52-year-old patient presented with a moderate 20/40 cataract in his dominant right eye. He previously had a retinal detachment extending to the temporal edge of the macula that was recently repaired with a buckle by a retinal surgeon. The patient was interested in an accommodating IOL.
Although the macular abnormalities on slit-lamp exam and SLO appeared rather impressive (Figure 5), OCT showed that the anatomy was well preserved. We implanted a Crystalens (Bausch + Lomb) in the patient, and he did extremely well, with 20/20 distance and J2 near UCVA.
VITREOMACULAR INTERFACE ABNORMALITIES
Vitreomacular interface abnormalities are pathologic entities visualized and understood almost exclusively via SD-OCT imaging. Consider the following case example.
Case No. 4. A patient came in for a second opinion, as she was unhappy with her visual result after cataract surgery performed elsewhere. Her previous ophthalmologist felt that her retinal examination was normal. When I looked at her macula, it showed some mild changes one might easily attribute to early AMD or miss completely. As shown on her OCT (Figure 6), she had severe vitreomacular traction syndrome that was undetected on clinical exam. She was referred to a vitreoretinal surgeon for surgical treatment.
In the case of vitreomacular traction, the posterior hyaloid may spontaneously separate and, in the process, pull a plug of tissue out with it, leading to either a lamellar or full-thickness hole. These can have a variable affect on visual function, leading to distortion or microscotomas. OCT is the only way to diagnose and quantify this problem, as illustrated in the following cases.
Case No. 5. A patient who underwent recent bilateral Crystalens implantation presented with less-than-perfect visual outcomes in both eyes (Figure 7). Each eye had a recent detachment of the posterior hyaloid with a subsequent small plug of tissue pulled out, and these had a subtle but definite effect on quality of vision, particularly her near vision. Over the course of a few years, macular remodeling was observed, and the OCT images in both eyes essentially normalized. Her vision improved with those changes.
Case No. 6. In another patient who presented with a recent decrease in vision, a plug of retina similarly pulled out as the hyaloid detached, but in this case a full-thickness macular hole resulted (Figure 8). This patient was referred for vitreoretinal surgery.
ARCA is another condition that is essentially an OCT diagnosis. I have seen a handful of patients who were dissatisfied with their multifocal or accommodating IOL surgery outcomes and who turned out to have this diagnosis. First described by Richard Spaide, MD, in 2009,1 ARCA is a condition that may be associated with a slight decrease in vision, in which the choroid is unusually thin, about 25% normal thickness. Although high myopes may present with thin choroids, patients with ARCA by definition are not myopic. I now consider a very thin choroid on OCT a relative contraindication to the use of a multifocal IOL in a prospective cataract patient (Figure 9).
Postoperative CME is a process that most anterior segment surgeons are well aware of and do what they can to avoid. The recognition and management of postoperative CME is greatly simplified and expedited through the use of OCT. Although CME can be visualized on slit-lamp exam, it can be exactly quantified only with SD-OCT. Therefore, SD-OCT is the ideal tool to assess a patient’s response to CME treatment.
Figure 10 shows a patient before and after treatment of postoperative CME. Note that in the posttreatment image there is a slight irregularity in the IS/OS junction (now sometimes referred to as the ellipsoidal zone2) which might signify a subtle decrease in visual function. On OCT, the IS/OS junction line signifies photoreceptor structural integrity, which may be correlated with visual function.
A great deal of information can be obtained from looking at the IS/OS junction line integrity on OCT and correlating it with visual problems. An example of a patient with a lamellar macular hole and a central microscotoma associated with a defect in the IS/OS junction line (Figure 11) can be compared with a less symptomatic patient with a lamellar defect and relatively normal IS/OS junction line (Figure 12).
Patients with AMD are encountered frequently in every anterior segment surgical practice, and SD-OCT can be extremely useful in discovering and visualizing subretinal fluid as a result of neovascularization in these eyes. For example, a one-eyed patient presented with subtle visual symptoms and a well-defined subretinal net with fluid on OCT (Figure 13). This patient responded well to treatment, and a timely diagnosis afforded by OCT undoubtedly played a role in his excellent outcome. As many anterior segment surgeons do not perform fluorescein angiography, the ability to recognize subretinal fluid in patients with AMD using SD-OCT may yield a diagnosis that might otherwise have been missed unless the surgeon referred that patient to a retina specialist.
We have entered an age in which the anterior segment surgeon must be able to factor what can easily be learned about the macula using SD-OCT technology into the equation of what is offered to every patient. There are many pathologic processes of the macula that can be either visualized or quantified only with SD-OCT, and having the information provided by this tool unlocks what was in the recent past a black box of unknowns.
Steven G. Safran, MD, is in private practice in Lawrenceville, New Jersey. Dr. Safran states that he has no financial interest in the products or companies mentioned. He may be reached at tel: +1 609 896 3931; e-mail: email@example.com.
- Spaide RF. Age-related choroidal atrophy. Am J Ophthalmol. 2009;147(5):801-810.
- Spaide RF, Curcio CA. Anatomical correlates to the bands seen in the outer retina by optical coherence tomography: literature review and model. Retina. 2011; 31(8):1609-1619.