Lecture: Retinal Nerve Fiber Layer Thickness and Optic Nerve Head Parameters

In order to enhance diagnostic OCT information for pediatric glaucoma, neuro-ophthalmology and retinal disorders, a comparison with population-derived normative data is needed to identify deviations from the normal range. The meta-analysis of studies on normative data of RNFL thickness and optic nerve head parameters and interocular asymmetry and variations in these parameters are emphasized in this lecture. Role of Spectral OCT in establishing diagnosis and following treatment in pediatric glaucoma and pediatric neuro-ophthalmology are also discussed.

Lecturer: Dr. Neelam Pawar


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DR PAWAR: Welcome to Cybersight live webinar. I’m Dr. Neelam Pawar, pediatric ophthalmologist from Aravind Eye Hospital from India. And I will have some poll questions for you, and you can answer them instantly, and I will be very glad to answer any queries and questions at the end of my presentation. So I will be presenting on the retinal nerve fiber layer thickness and optic nerve head parameters by spectral OCT and implications for pediatric ophthalmology. Now, the first poll question is: what is your current position? Pediatric ophthalmologist, comprehensive ophthalmologist, fellow or resident, medical student, ophthalmic technician, or allied health? Great. So most of you are comprehensive ophthalmologists. And in second position is pediatric ophthalmologists. A few are fellows and residents, and great to see that ophthalmic technicians are also there. In the literature, there are various studies on nerve fiber layer thickness and optic nerve head and macula in the pediatric population using spectral domain OCT tomography or time delay OCT tomographs. Yeah. So various authors have evaluated the nerve fiber layer thickness or nerve head parameters in eyes of pediatric children using spectral domain optical coherence tomography or stratus OCT tomography. The limitations with all these studies is that measurement is provided by different commercially available machines and the data from one machine cannot be used interchangeably with other machines. And other variations do exist. We will have just a short look on the analysis of studies of normative data evaluating RNFL thickness, optic nerve head parameters, interocular asymmetry in the pediatric population, and the role of spectral OCT in pediatric glaucoma, pediatric nerve head disorders, and pediatric neuro-ophthalmology. OCT is a non-contact, non-invasive device, which is based on the principle of interferometry, and this imaging technique provides cross sectional images of human retinal morphology in vivo. And the role of OCT in monitoring various ocular diseases in adults has been well established, but in pediatric, researchers are still ongoing in various ocular diseases. It has undergone revolutionary changes, and all these advances in OCT technology has led it to be the most utilized imaging technology in the field of ophthalmology. The literature is flooded with studies on normative value of retinal nerve fiber layer thickness, among different age distributions, ethnicity, and various ocular disease states. And all these studies state that retinal thickness changes with age and ethnicity, and children have slightly higher values of retinal nerve fiber layer thickness, compared to adults. And most of these studies demonstrate that there is a decay of 2 to 2.2 microns in retinal nerve fiber layer thickness per decade. The normative values in children in various ethnic populations — the limitations of existing studies is that there’s a consideration of either only a single age group or a single race. Until now, no machine has had pediatric parameters incorporated in there. OCT has taken a generational leap from first generation OCT to second generation OCT. And from third generation time domain OCT to fourth generation spectral or Fourier domain OCT. If you compare spectral domain and time domain OCT, in time domain OCT, a moving mirror is used, and a wavelength of 810 nanometers. It takes a longer scan acquisition time, and takes few axial scans. And it has a resolution of 8 to 10 microns. Why spectral domain doesn’t have any moving parts and broadband source is used — a spectrometer, and gives a very fast scan compared to time domain OCT. Around 25000 to 100000 axial scans per second, and gives resolution of 3 to 7 microns. And calculates the distance from the inner limiting membrane to the retinal pigment epithelium. Commercially available current spectral domain OCT devices are Cirrus HD OCT, by Carl Zeiss, Spectral by Opko, 3D-OCT by Topcon, RTVue, by Optovue, and Spectralis by Heidelberg. Bioptigen is a handheld OCT. It’s proved a very wonderful instrument in diagnosing optic head neuropathies in children. If you see various studies, they have compared the reproducibility of all spectral domain OCT devices, and one of the studies stated that Spectralis has a better reproducibility, as is having an eye tracker mechanism, so it gives better results. But we cannot say which machine is best. And there are disadvantages and advantages of all these machines. OCT is also used in OCT angiography, but in pediatrics, still research studies are going on using these OCTs. The international nomenclature for optical coherence tomography panel has proposed a lexicon for anatomical landmarks in posterior segment using spectral optical coherence tomography, and according to this OCT consensus, besides the existing nuclear layer, which we were knowing earlier, now there is a description of the ellipsoid zone, myoid zone, along with the Sattler’s and Haller’s layer. Knowing the ellipsoid and myoid zone is very important in papilledema, optic neuritis, et cetera. If you see this picture — the child is sitting, the examiner is very comfortable, and with ease, he is taking a scan with the use of a handheld OCT machine. Handheld OCT is therefore an amazing tool in uncooperative children, who are not able to place chin rest in tabletop OCTs. This very nice article by Lee et al. on development of OCT — this paper tells that during the process of development, there is centripetal migration of cone receptors to fovea, and therefore generation of these ellipsoid, myoid zone, and there is elongation of outer nuclear layers. And recognition of these layers is very thinning and any changes in these layers are characteristic of certain retinal disorders. So here comes the poll question 2. Do you have OCT in your hospital or clinic? So let’s see. Yeah. Yeah. Still am waiting for response from audience. Oh, great. It’s good to see that around 66% of the audience is having OCT. If you see reproducibility, sensitivity, and specificity in pediatric patients with OCT, all of the studies, they have shown that there is very well agreement, and there is well agreement on intravisit and intervisit reproducibility of retinal nerve fiber layer thickness and optic nerve head parameters, and even Spectralis has shown a good reproducibility for retinal nerve fiber layer and macular thickness measurements in glaucoma or glaucoma suspect eyes of pediatric subjects. It’s shown by handheld optical coherence tomography in children. But besides being a very wonderful machine, there are various pitfalls with this machine. At extremes of age, the retinal nerve fiber layer scan varies, and the machine doesn’t have data for pediatric age group. So each and every one has to analyze the interpretation according to their own ethnic population. Ethnic variations do exist. And cooperation is a must for having a good scan. There could be various machine-related artifacts. Segmentation error. And different machines could give different values of retinal nerve head parameters in the same patient. Signal to noise ratio is again very important, to look for the quality of scan. And usually in Stratus OCT, a signal ratio of more than 6 is considered as having a good quality scan. Media opacity can also affect the reading. While this is not so common in pediatric patients, but even pediatric patients having any lens opacity or corneal opacity can have some effect in OCT scan. The types of artifacts and errors — there can be some technical errors if the machine is not properly calibrated. There are poor optics. And if the machine is not in optimal temperature and humidity, the machine can give you different results. Scan centration is also important. Because offcenter scans and decentration can give you erroneous measurement of retinal nerve fiber layer thickness. There can be motion and blink artifacts, and usually these blink artifacts are seen as horizontal lines. In the scan. Then there can be software-related segmentation errors. Missing scan areas. And patient head tilt can cause changes in scan. There are various ocular factors that in extremes of refractive error — very high myopia or very high hypermetropia — can have errors. And there is something known as the floor effect, which states that the machine never shows any value of zero, even if there is cross thinning of retinal nerve fiber layer thickness. Now, the poll question third has come. Do you take in account age and ethnicity in considering retinal nerve fiber layer thickness and optic nerve head parameters in the evaluation of various pediatric ocular diseases? Yes or no? Yeah? Yeah. It is a tough question. Because for pediatric parameters, different ethnic populations have their… Yeah, most of you consider age and ethnicity, when you are interpreting your scan result in pediatric patients. So the question is: why normative data is required? There is no age matched data incorporated in any of the OCT machines. So there is no internal standard with which to compare the result with the OCT scan in various pediatric ocular disorders. And definitely adult reference OCT data cannot be used in pediatric diseases. If you see on my right hand side, there’s a printout of Cirrus HD OCT in an adult patient. And if you see various color codings, they are seen in these scan areas. And from this, we have been taught that this color or red flag — there is time to intervene according to that disease. But if you see in my left hand side, and in the middle, in my left hand side, there is a printout from Stratus OCT, and in this middle, there is a printout from Cirrus HD OCT, and there is no color coding in these printouts, and the machine says that normative data is not available for a patient less than 18 years of age. Various machines have different protocols for retinal nerve fiber layer thickness analysis and optic nerve head analysis. And most of these machines use a circle diameter of around 3.4 to 3.6, around the optic nerve head. And calculate retinal nerve fiber layer thickness as a ISNT map, that is inferior, superior, nasal, and temporal. And interprets it as a graph. The Cirrus machine uses an optical protocol, which is a 6×6 millimeter area scan, and which is centered on the optic disc. In the previous Stratus OCT machine for optic nerve head analysis, we have to create a manual line for the optic nerve head parameter, for optic disc area, and… Optic disc area… But in… Cirrus HD OCT machine, this Stratus OCT machine interpreted optic nerve head parameters as vertical integrated area, horizontal integrated rim area, disc area, rim area. While the Cirrus HD machine, the machine has the inbuilt software, so we don’t have to do anything manually. So this is the printout from Cirrus HD OCT and Spectralis machine. If you see in my left hand side, this is the typical printout from a pediatric patient. And as you see, there is RNFL and ONH, optic disc, 200×200. On top of this is RNFL deviation map, while in the middle is the RNFL thickness map, there is the RNFL deviation map, and then there are TSNIT parameters, which compares the parameters of right and left eye. In bottom, there is full clock hour analysis, and then there is (inaudible) analysis. If you see the picture, these are extracted horizontal and vertical tomographs and RNFL tomogram. On the right is a printout from a Spectralis machine. It gives the full clock hour analysis, and six sector analysis. If you see the normative data, RNFL data, in the pediatric population, using Stratus OCT, most of the studies — they show that retinal nerve fiber layer thickness varies in the range of 100 to 115 microns. And only Polish pediatric populations have reported retinal nerve fiber layer thickness to be 122, with a standard deviation of 24.5 microns. And this could be attributed to the older OCT machine, which was OCT 2000. And it was used long back. That’s why all the other machines show values of — in the range between 100 to 115. There were large population studies done by Leung et al., in the six year of age group. They reported retinal nerve fiber layer to be 103, with a standard deviation of 11.4. While a large base population by Samarwickrama et al. of European Caucasians reported a retinal nerve fiber layer thickness to be 101 and 104 at age of 6 and 12, while in East Asian, it was 105.45, and 107.921, in 12 years of age. And these studies showed that East Asians have a higher value of retinal nerve fiber layer compared to the European Caucasian population. And based on these studies, they were having a different result and they were done in different ethnic populations. After 2012, there were certain studies on normative data in the pediatric population, using spectral OCT. And if you see all these studies, most of the studies were done by Cirrus HD OCT, and the values are ranging from 93 to 99 microns wide. The other machines, like Spectralis OCT, calculated a slightly higher retinal nerve fiber layer thickness. And if you see all these studies, they follow the ISNT rule, that the inferior rim was thicker than superior, and temporal was the thinnest layer among all four quadrants. On looking over optic nerve head parameters, most of the studies that reported optic vertical are in the range of 0.4 to 0.6, and most of the studies were having similar rim and disc area. But it was slightly more in East Asian populations, compared to other ethnic populations. There is very nice article by Creavin et al., and they have submitted a protocol for optic nerve head parameters in children up to but not including 18 years of age. This is a very nice meta-analysis. Hopefully it will be published soon, and we will have some interesting results describing the ethnic nerve fiber layer thickness in different populations in this age range. RNFL thickness can vary with age and sex. Some of the studies have shown — most of the studies have shown — that there is no difference between male and female pediatric patients, while some studies have shown — like by Huynh et al., they have reported that RNFL thickness is slightly higher in boys after adjusting for age and height. While Zhu et al. reported average RNFL thickness in temporal quadrants were significantly thicker in girls. Refraction is also inconsistent in results. Huynh reported a positive correlation of average RNFL thickness with refractive error in children. And most studies have shown that the value can vary with axial length, but the studies show that the pediatric database — we are having only within a range of low to moderate myopia. None of the studies have incorporated very high myopia in evaluation of normative data. Huynh et al. also showed that there was thinner retinal nerve fiber layer thickness with longer axial length in a population-based study of 6-year-old children. Then what is the intraocular asymmetry? And when it should be considered as pathologic? There are few studies on radial asymmetry in the pediatric population by optical coherence tomography. And this concept is based on the fact that no two human organs are identical. So just like that, retinal nerve fiber layer thickness of the right eye cannot be exactly seen as that of left eye. And there can be some pathologic variation. So what are these pathologic variations and when should the pathologic variation or pathologic entity should be considered? So these studies have given some parameters in various ethnic populations. So there are only four studies in the pediatric population about interocular asymmetry. Al-Haddad et al. and Altemir et al. reported that retinal nerve fiber layer thickness was thicker in the right eye in temporal and nasal quadrant, while the left eye showed thicker retinal nerve fiber layer thickness in the superior quadrant. Qian et al. showed thicker retinal nerve fiber layer in the left eye. Huyn et al. reported that superior and inferior quadrant were more in right eye. All these studies showed that there can be some variation in retinal nerve fiber layer thickness, even in healthy eye, even in healthy pediatric patients, in the two eyes. But all of these studies are very consistent that the optic nerve head parameters are quite symmetrical. And this suggests that if there is asymmetry — and usually all of these studies have reported that asymmetry of 0.25 should be considered as a sign of pathology. Huyn et al., though they did their study in large population, they found it to be more in East Asian population, and left eye had more disc area, and neural rim area was more, compared to right eye. They also presented a poster in AAO Chicago, about interocular symmetry in Indian population, and we found a thicker temporal quadrant in right eye and thicker superior quadrant of left eye in Indian pediatric population. So with all these studies, we can conclude that different machines in pediatric patients, they can give different results. Ethnic variation can exist. And gender variation — there can be some gender variation. There can be some variation, according to axial length and refraction, and some asymmetry does exist in healthy pediatric patients. So what is your routine choice of spectral OCT? Cirrus, Spectralis, Optivue, Rtvue, Topcon, Spectral OCT/SLO, or any other machine? The choice of machine — it depends on the ophthalmological… On the country… I’m waiting for the poll result. Yeah. Good. It’s good to see that most of them — because most of my presentation is focusing on Cirrus HD OCT. So I have poll result that most of you are using Cirrus HD OCT and Spectralis also, a very large number are using. And quite a few people are using Optivue machine. So does amblyopia affect retinal nerve fiber layer thickness and optic nerve head parameters? Various studies have shown different results. Some have shown that there is no difference in retinal nerve fiber layer between an amblyopic eye and fellow eyes. But some have shown that there are some differences in retinal nerve fiber layer thickness. Li J et al. in their meta-analysis of 28 trials found that in most of the studies, RNFL was thicker in amblyopic eye compared to fellow eye. But then also there could be variation in anisometropic and mixed type of amblyopias. Going through the previous slides on normative data — let’s have a look on implications in pediatric ophthalmology. OCT has already become a diagnostic and monitoring tool in pediatric optic nerve head glaucoma. And pediatric optic nerve head pathology. Like pediatric optic neuritis, papilledema, optic nerve atrophy, and optic nerve hypoplasia. But reading of the OCT scan in pediatric patients is a complex art, because one has to compare these results, and you cannot take any studies or any interpretation with just comparing to adult OCT. And therefore, if there is any normative data, it would definitely facilitate the pediatric OCT imaging interpretation. OCT in glaucoma, in primary congenital glaucoma and juvenile open-angle glaucoma — OCT usually investigates retinal nerve fiber layer thickness, to see the ratio in response to surgical intervention. And most of the studies show that though there is reversal of cupping, but actually there is no change in retinal nerve fiber layer thickness, and preoperative ratio reflects the true RNFL change damage in glaucoma patients. Diagnosis of pediatric glaucoma and juvenile glaucoma is very difficult, because most of the patients, they are uncooperative on visual field machines. And then one has to rely on fundus photography, fundus evaluation, and on OCT machines. So I just showed a very nice example of this case. 12-year-old Indian origin female. She came to us, she was having visual acuity of 20 by 20 in both eyes. She was diagnosed as juvenile open-angle glaucoma. And she was on Dorzox and atenolol in both eyes. And her previous — she was diagnosed as JOAG in 2011. And her previous scans were unreliable. When she presented to us, she had 23 and 25 in her eyes, and she had open-angle in both eyes under gonioscopy. If you look at her photograph, you can make out that her ratio was 0.7, in her right eye, while in left eye it was 0.8, with inferior rim thinning. And this patient, when she presented to us, she was quite cooperative, and we found the superior defect in HFA. The problem with this patient was that for six years, she was going to different ophthalmologists, and every time her OCT scans were taken by different machines. So none of the ophthalmologists were able to assess whether there was a true RNFL damage or whether the different machines were showing different OCT parameters. Luckily, we got the scans from her, which was done in 2011, and it showed a value of 84 in right eye and 87 in left eye. And when we did her OCT scan, the values were drastically reduced. It was 67 in right eye and 68 in left eye. So there was cross thinning of retinal nerve fiber layer thickness. And if this patient was serially followed on same machine, maybe we could have detected preperimetrical glaucoma and maybe the surgical intervention could have been done earlier. This is a second exam. This patient was operated at age of 2 years, trabeculotomy and trabeculectomy both done for primary child — for the glaucoma. And this patient didn’t have any OCT at that time. Didn’t have any handheld OCT at that time. So her records, documentation, showed that she had ratio of 0.8. And after a long follow-up, she came to us, and when we took the scan, it showed the CD ratio of 0.4 in right eye and 0.34 in left eye. And she was maintaining a visual acuity of 20 by 20 in both eyes. Though she was uncooperative on HFM. So by this we can interpret that there could be reversal of cupping in these patients, after surgical intervention. But whatever RNFL damage has been done, it would always remain permanent. So this is the poll question. Fifth for you. Do you always do OCT in cases of pediatric optic neuritis, optic nerve head drusen, and papilledema? Always, sometimes, very rare, or cannot comment? So let’s wait for the poll result from the audience. Yeah. Most of you have voted as sometimes. And we got equal votings for always and very rare option. So good. I would like to do OCT in all cases of pediatric neuritis, optic nerve head drusen, and papilledema. Because optic neuritis patient — there can be, once the optic neuritis resolves, there can be some thinning of retinal nerve fiber layer layer, which we can correlate with visual field testing. And in cases of optic nerve head drusen, some of the cases can have coexisting papilledema. And even in all these patients of optic neuritis and papilledema, along with mild disc edema, you can have some changes which I have already described previously, which can affect visual acuity. And some patients with optic neuritis later can see on follow-up — you can have multiple sclerosis being diagnosed. So it is better to always do OCT, and keep a record of all these patients. How to differentiate between optic nerve head drusen and optic nerve head papilledema? Some researchers have given this very nice sign of lumpy bumpy contour of optic nerve head drusen, in cases of — on OCT. And while some have described in papilledema a lazy V sign, or lazy position that is SHYPS sign, or subretinal hyporeflective space. And in the case of this subretinal hyporeflective space, it can be indicative of a severe edema. This is a nice picture that I have taken from a site. This patient had optic nerve head drusen, which was seen as pseudopapilledema on optic nerve head photograph, and it showed a hyporeflective scan, and on OCT scan, it was seen as a hyporeflective area. This scan is a pediatric patient who presented to us. Her retinal nerve fiber layer thickness in both eyes were increased to 143 and 133. And if you see in her TSNI, there is drastic increase in retinal nerve fiber layer thickness in both eyes, and there is increase in subretinal hyporeflective space, in extracted vertical tomogram. So this patient was diagnosed as papilledema, and later on, she was diagnosed with tubercular meningitis. This is my last poll question. What was the diagnosis of this pediatric patient? Optic nerve head drusen, optic atrophy, papilledema, or pseudopapilledema? Though it is very difficult to comment, just merely taking the scan into account in diagnosing pediatric diseases, we can have a poll on this question. And on the scan. Let’s see the audience poll. Yeah, absolutely correct. Most of you have diagnosed this as papilledema. Why this is papilledema? Because in pseudopapilledema, we would never get such high values in retinal nerve fiber layer layer. If you see this, in sector analysis, it has gone above 300 microns. There is a very important entity in pediatric ophthalmology in which OCT has become a very good diagnostic and monitoring tool. That is idiopathic intracranial hypertension. And it is also shown to be a visual prognostic indicator in these cases. I will share you a very good example of a typical idiopathic intracranial hypertension, in a pediatric patient. Pediatric IH, quite different from adult IH. Usually adult IH — we will have — most of them, they will present with a complaint of headache and blurring and transient obscuration of vision. While in pediatric cases, this is not the routine symptom. Most of them, they will present with strabismus, and children rarely complain of transient obscuration of vision, though they can say that they have some decrease in visual acuity. So in this case, this was a 3-year-old male who presented to us with complaint of vomiting and headaches in 6 days. And there was squinting and turning of face noted by parents in 3 days. His extraocular movements were full, and there was esotropia of 20 prism diopter, and fundus examination showed edema. MRI showed empty sella turcica, and the MRI was suggestive of IH. This patient was evaluated by a neurologist, and found to be alleviated. So if you see — the scan of this patient, before the patient was started on treatment and before starting the treatment the optic nerve head parameters were 157 microns in right eye and in left eye it was 183 micrometer. After treatment, the optic nerve head and retinal nerve head parameters, retinal nerve fiber layer parameter decreased to 99 micrometers in right eye and 99 micrometers in left eye. Patient, after three months, there was no disc edema in fundus. His vision was 6×6 with Cardiff card in each eye, anterior segment was absolutely normal. And you can see in the extracted vertical tomogram and compare the pre and post-op treatment — in prescan, you can have increased subretinal hyporeflective space, which decreased down — or almost became normal — in scan, in the right hand side, after treatment. So definitely the OCT obviates need of repeated lumbar puncture. But one has to be very cautious, regarding the retinal nerve fiber layer — this decrease in retinal nerve fiber layer thickness. Whether this decrease suggests to you that edema is decreasing down, or whether there is any thinning process going on, which can lead to optic atrophy. Therefore serial OCT imaging and perimetry can be standard in monitoring papilledema in cases of pediatric patients. If you look at congenital optic disc anomalies, the studies have shown that retinal nerve fiber layer thickness is less in optic nerve hypoplastic patients. And these patients can have decreased macular thickness also. And there can be variations in various zones of ellipsoid, myoid, and interdigitation zones. Optic disc pit and optic nerve head coloboma can also have decreased retinal nerve fiber layer thickness. OCT — besides all these diagnostic modalities, it has also become a very good tool for monitoring vigabatrin toxicity, and we had a good paper published by Brooke et al., in which they have stated that retinal nerve fiber layer is decreased in children who have long-term therapy with vigabatrin. In retinopathy of prematurity, various authors have reported that retinal nerve fiber layer thickness can be less in patients with lower gestational age and adults who are having severe retinopathy of prematurity. And some authors have even taken measurements in schoolgoing children, and they found that retinal nerve fiber layer thickness was less in children with history of early prematurity and ROP treatment. OCT has also become a remarkable tool in optic nerve glioma patients. Retinal nerve fiber layer thickness loss can occur from optic atrophy, secondary to optic nerve glioma in children with neurofibromatosis. And OCT may be of value when patients are unable to perform routine perimetry. And instead of doing repeated perimetry and repeated MRI scan, OCT can act as a surrogate marker of visual function in optic nerve glioma cases. In optic neuritis patients, we can see thickening of the peripapillary retinal nerve fiber layer thickness in acute phase, and later there can be thinning once the edema is resolved. But again, one has to be very cautious regarding whether there is any thinning, cross thinning, of retinal nerve fiber layer. This is again an example of Leber’s hereditary optic neuropathy. This 13-year-old male patient presented to us with defective vision of 1 month duration. And we recorded his vision. It was 20 by 200 in both eyes. He was able to read only first plate in Ishihara charts. And MRI with or without contrast were normal. Funduscopic examination — if you see, in right eye, there is mild hyperemia, and there is some onset of temporal pallor. While left eye fundus photograph — there is cross pallor. If you see the OCT scan, there is marked thinning in left eye. And left eye with retinal nerve fiber layer thickness was 71 micrometers, while in right eye it was 119. And if you see the four sector analysis, this patient has characteristic pseudoedema in superior and inferior quadrants, in right eye, while in left eye, most of the quadrants had thinned out. This suggests that left eye was going — has gone into phase of atrophic stage, while right eye was still in some active stage. OCT is also very wonderful tool in diagnosing optic neuropathy in patients of syndromic craniosynostosis. Most of the optic neuropathies are more common in syndromic craniosynostosis, as compared to non-syndromic craniosynostosis. And these are measurements that provide adjunctive evidence for identifying optic neuropathy in these patients. And this appears to be more sensitive in detecting optic neuropathy — atrophy — than papilledema. Besides being a good diagnostic and imaging tool, OCT is also showing, as some central nervous system development indicator, and some researchers found that optic nerve head parameters were predictive of CNS development and pathology, with large vertical CD ratios associated with lower Bayley scales of infant department scores. These infant development scores take into account motor development and impairment in children ranging from 2 to 48 months. And they found that optic nerve parameters to be quite larger in patients with the slight neurodevelopmental disorders. While weak association has been reported like large vertical cup diameter and vertical CD ratio in patients with periventricular leukomalacia, and shallow cup is associated with posthemorrhagic hydrocephalus. So I would like to share two very rare and interesting cases, in our hospital. One case is OCT documentation on unilateral optic nerve aplasia, and second case is OCT documented optic atrophy in non-syndromic craniosynostosis. This girl presented to us with complaints of defective vision in her right eye since birth. And when we evaluated her, we found that left eye was absolutely normal. She was having 20/20 vision in left eye, while in right eye, she had microcornea. There was no perception of light. And the other anterior segment was normal. She was not having any microphthalmia. Only microcornea. And the OCT were normal in both eye. On gonioscopy, she had normal angles, and intraocular pressure was normal in both eyes. OCT showed absence of optic nerve head, and on MRI scan, there was absence of the anterior portion of the optic nerve head. And if you see, the OCT scan in right eye — she is having absolutely normal OCT scan. Almost all anatomical layer you can make out. But in right eye OCT, if you see, there was no optic nerve head. There was no fovea. There was atrophy of all retinal nerve fiber layer, and there was absence of myoid interdigitation in all zones. In the literature, 38 cases have been reported of optic nerve aplasia, but none of the cases have documented OCT in their series. The second case is also a very interesting case. Which was published last month in Journal of American Association for Pediatric Ophthalmology and Strabismus. And this case was OCT documented optic atrophy in non-syndromic craniosynostosis and lacunar skull. This 6-year-old boy, he presented to us just with complaint of mild redness in left eye. And you can make out easily the facial features of this boy, that he is having slight prominent forehead. Prominent eyes and scleral show. During initial presentation, we also missed all these findings. So this boy, though he had vision of 20 by 20, but his fundus examination showed gross pallor in both eyes. Color vision absolutely normal, normal visual field test, and he was absolutely a normal patient without any complaint of headache, without any complaint of vomiting. And his history and neurodevelopment was absolutely normal. On x-ray, he had various radiolucent thumbprints and when we did MRI of this patient, he had empty sella, and kinking and buckling of optic nerves, which were suggestive of various intracranial hypertension. And he was advised 3D reconstruction of the CT scan, which came to be a very amazing result that this patient had all cranial sutures fused, and he was diagnosed with craniosynostosis. And if you can see in these 3D pictures, he had an appearance which is characteristic of lacunar skull. And when we did OCT of this patient, it showed a drastic decrease in the retinal nerve fiber layer thickness in both eyes, of values of 37 and 36. So along with the MRI, CT report, and OCT findings, we thought that there was something which was going on, and which was responsible for his thinning of retinal nerve fiber layer. The patient was seen by a neurosurgeon, and he was operated, and he underwent release of sutural release and cranioplasty, and postoperatively, he was doing very well. Until now, the patient is in follow-up with us, maintaining a vision of 20 by 20, and with no other symptoms. And obviously, the RNFL values are the same. We can’t do anything of this decreased retinal nerve fiber layer thickness. So here this OCT has proven to be a diagnostic tool in pediatric ophthalmology. And we hope that in future various ethnic and pediatric age parameters will be incorporated in machines, so that pediatric ophthalmologists could better interpret their OCT scans. And more indications can be made in pediatric ophthalmology. But the last thing is very important to remember. That OCT sees what your eyes do not see. But no machine is better than the human eye and brain. And before giving a diagnosis and before interpreting any OCT scan, the clinical features of the children should be considered before giving any final diagnosis. So I think… Yeah. I conclude my presentation. And thank you, all of you, for joining me, and thank you, Cybersight, for giving this opportunity of learning and sharing knowledge across the globe. So I would welcome all of you to — if you are having any queries or any questions, you are welcome to answer.

>> So, Dr. Pawar, we have about 6 questions, if you want to stop sharing your screen.

DR PAWAR: So yeah. We’ve got a couple of questions. I had one question. In kids who have unilateral disc edema, do we need to perform MRI? Yeah. It depends. It is better to have MRI in all cases, because sometimes you can have some surprises. This unilateral disc edema — sometimes with atypical optic neuritis patients, they can present like this. So better to have optic — along with imaging — better to have the MRI and OCT scan. Another question, which I am getting, is: is there any relationship of retinal nerve fiber layer thickness with refractive error? Yeah, obviously. In extremes of myopia and hypermetropia, we see that in myopia, there is increase in scleral and retinal thinning, and as there is elongation of the globe, so there is mechanical stretching of the globe, and because of this stretching, in extremes of myopia, the patient can have — a pediatric patient — they show decreased RNFL thickness. But one has to be very careful when you are saying it that there is a decreased RNFL, because decreased RNFL thickness can be seen if there is coexisting glaucoma. So for those patients, it is better that you do a serial analysis. You focus more on your optic nerve head changes, and a serial analysis in high myopia is a better option. So having one more question. Do you have any experience or data of retinal nerve fiber layer thickness in children with amblyopia? Yeah, we did a study in our hospital, in the Indian pediatric population, in anisometropic amblyopia. And we found there were no significant differences in retinal nerve fiber layer thickness in amblyopic eyes compared to fellow eyes. We found some differences only in some quadrants of both eyes and in some optic nerve head parameters. But obviously there was no difference in RNFL thickness. A nice question. How do we interpret OCT results in the pediatric patient if the machine does not have normative data for children? Yeah, most of the machines, they do not have normative data. So then you have to rely on the existing literature, and according to your ethnic population. The Spectralis, as you have seen in my presentation — there was a scan from a pediatric patient, but the Spectralis never says that this scan — that we cannot give data, we cannot do color coding for pediatric patient less than 18 years of age. They give color coding saying that there is some linear proportion, and they also say that even these color codings are there, but you should be extremely cautious whenever you are interpreting RNFL results in children less than 18 years of age and adults more than 78 years of age. So one more question. I am getting — how to look for RNFL status on fundoscopy. And its reliability. In fundus examination, you can make some obvious changes, like slit lamp, some slit retinal nerve fiber layer defect, and some red shade defect in green light. But subtle changes, obviously, you can miss in this green light, and OCT will be a better option to look for these preperimetric glaucoma and for these retinal nerve fiber layer defects. One more question I had. What specific parameters you should be looking at on retinal nerve fiber layer thickness and optic nerve head to diagnose glaucoma? A good question. Mainly retinal nerve fiber layer thickness and inferior quadrant thickness should be looked in pediatric glaucoma. For RNFL parameters and for optic nerve head parameters, the vertical CD ratio, and rim area should be given importance. But regarding sensitivity and specificity of optic nerve head parameters in the pediatric population, I don’t think we are having any studies on that. So I think we are… We are done. And maybe with more questions we can… Yeah. I would be very happy to answer these questions, if you can send these questions to Cybersight, or either in your feedback form. Once again, thank you for joining me for this session. And I really do appreciate for you hearing me on these OCT parameters. Yeah. Have a wonderful day. Thanks a lot.

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April 5, 2017

Last Updated: October 31, 2022

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