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15 Corneal Topography
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189
post-treatment) and steep K while treating
hyperopia (should not be >48D posttreatment). Ectatic corneas tend to have higher
steep K values.
• Corneal astigmatism: The total corneal
astigmatism after considering posterior corneal astigmatism should be compared with the
manifest refraction to exclude causes of incongruence, such as lenticular astigmatism, posterior subcapsular cataract, tear lm
disturbance, etc. The axes of astigmatism are
also displayed.
• Q value: This value describes the shape of the
cornea, which is typically aspheric. The normal corneal asphericity ranges from −0.2 to
−0.3. A positive Q value indicates oblate cor-
nea, and a more negative value indicates
increased prolate shape.
• Thinnest location: This category gives an
idea about corneal thickness, but one should
refer to the thickness map to have a complete
picture of the case. It is very important to
study the relationship between the thinnest
location and the pachymetric apex according
to the thickness and location.
• Pupil center location: This is important when
carrying out decentration of the ablation prole, especially when treating hyperopia.
15.7.2.1 Red Flag Signs ofEctasia
onPentacam Map
(a) The elevation values on the front surface
map should not exceed 12 μm. Values
between +13μm and +15μm are suspicious,
and any value >+15μm is considered a risk
factor.
(b) The elevation values on the back surface map
should not exceed +17μm. Values between
+18μm and +20μm are suspicious, and any
value >+20μm is considered a risk factor.
(c) The difference between the back and front
surfaces (back–front) should not exceed
+5μm at the same point. For example: if the
back is +12μm and the front is +4μm at the
same point, it is suspicious, although both
values are within the normal limits.
(d) If there is any isolated island on either front
or back surfaces, it would be suspected, even
with values within the normal limits.
(e) In the pattern on the keratometric map, as
shown with Placido images, any inferior–
superior asymmetry arouses suspicion.
Compare the thickness at the apex with the
thickness at the thinnest location. A difference of >10μm that increases during followups is suspicious.
(f) An inferior–superior difference in the central
4mm zone of >30μm is abnormal.
(g) The difference between the examined cornea
and its fellow eye at the same point should be
<30μm.
15.8 Applications ofCorneal
Topography
(a) As a screening tool to identify regular and
irregular corneas and astigmatism.
(b) To identify corneas suitable for laser vision
correction and to determine the corneal
shape and thickness for planning the
surgery.
(c) Identify corneal ectatic disorders such as
keratoconus, pellucid marginal degeneration,
and keratoglobus.
(d) Planning intracorneal ring segments requires
adequate pachymetry in the mid-peripheral
cornea, measured on corneal topography
systems.
(e) Contact lens tting is based on the corneal
curvature and best-t sphere measurements.
(f) Comparison of corneal topography scans
over time indicates progression of corneal
ectasias.
15.9 Conclusion
Topography is an excellent tool to screen potentially borderline cases in clinical practice. Placido
disc-based devices are very useful tools; however, they are less sensitive to changes on the posterior surface of the cornea. Newer diagnostic
devices like elevation-based topographers, single
and dual Scheimpug imaging, and LED technology help one better understand the posterior
surface of the cornea and pachymetry. These
newer modalities can help diagnose ectatic dis-
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R. Deshmukh and S. Basu
ease in the preclinical stage, thus allowing early
treatment.
Funding Hyderabad Eye Research Foundation (HERF),
Hyderabad, India.
Disclosure None.
References
1. Ambrósio R, Belin MW. Imaging of the cornea: topography vs tomography. J Refract Surg.
2010;26(11):847–9.
2. Scheiner C.Oculus, Hoc Est: Fundamentum Opticum.
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3. Gatinel D, Hoang-Xuan T.Measurement of combined
corneal, internal, and total ocular optical quality
analysis in anterior segment pathology with the OPDscan and OPD-station. J Refract Surg. 2006;22(9
Suppl):S1014–20.
4. Ventura BV, Al-Mohtaseb Z, Wang L, Koch DD,
Weikert MP.Repeatability and comparability of corneal power and corneal astigmatism obtained from a
point-source color light-emitting diode topographer,
a Placido-based corneal topographer, and a lowcoherence reectometer. J Cataract Refract Surg.
2015;41(10):2242–50.
5. Liu Z, Huang AJ, Pugfelder SC. Evaluation of
corneal thickness and topography in normal eyes
using the Orbscan corneal topography system. Br J
Ophthalmol. 1999;83(7):774–8.
6. Oliveira CM, Ribeiro C, Franco S.Corneal imaging
with slit-scanning and Scheimpug imaging techniques. Clin Exp Optom. 2011;94(1):33–42.
7. Kanclerz P, Khoramnia R, Wang X. Current developments in corneal topography and tomography.
Diagnostics (Basel). 2021;11(8):1466.
8. Motlagh MN, Moshirfar M, Murri MS, Skanchy
DF, Momeni-Moghaddam H, Ronquillo YC, et al.
Pentacam® corneal tomography for screening of
refractive surgery candidates: a review of the literature, part I. Med Hypothesis Discov Innov
Ophthalmol. 2019;8(3):177–203.
9. Gatinel D, Malet J, Hoang-Xuan T, Azar DT.Corneal
elevation topography: best t sphere, elevation distance, asphericity, toricity, and clinical implications.
Cornea. 2011;30(5):508–15.
10. Belin MW, Khachikian SS.An introduction to understanding elevation-based topography: how elevation data are displayed—a review. Clin Experiment
Ophthalmol. 2009;37(1):14–29.
11. Ghemame M, Charpentier P, Mouriaux F. Corneal
topography in practice. J Fr Ophtalmol.
2020;43(1):67–79.
12. Rasheed K, Rabinowitz YS, Remba D, Remba
MJ. Interobserver and intraobserver reliability of a
classication scheme for corneal topographic patterns. Br J Ophthalmol. 1998;82(12):1401–6.
13. Shah RS, Khandelwal SS, Goshe JM, Haberman ID,
Randleman JB. Comparative postoperative topography pattern recognition analysis using axial vs
tangential curvature maps. J Cataract Refract Surg.
2020;46(10):1368–73.
14. Smadja D, Santhiago MR, Mello GR, Krueger RR,
Colin J, Touboul D.Inuence of the reference surface
shape for discriminating between normal corneas,
subclinical keratoconus, and keratoconus. J Refract
Surg. 2013;29(4):274–81.
15. Rousch C.Orbscan II Manual (Salt Lake City, Utha.
Orbtek).
Ocular Surface Examination
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SwatiSingh andSayanBasu
16.1 Introduction
The ocular surface comprises the cornea, limbus,
conjunctiva, eyelids, tear lm, and lacrimal gland
[1, 2]. The ocular surface examination should be
performed using the slit lamp and requires vital
dyes like Sodium uorescein and Lissamine
green. Different techniques for using a slit lamp
have been discussed in Chap. 14. This chapter
describes the examination techniques used to
arrive at a clinical diagnosis using devices readily
available in eye clinics.
S. Singh (*)
Kallam Anji Reddy Campus, LV Prasad Eye Institute,
Hyderabad, India
e-mail: swatisingh@lvpei.org
S. Basu
Shantilal Shanghvi Cornea Institute, Kallam Anji
Reddy Campus, LV Prasad Eye Institute, Hyderabad,
India
e-mail: sayanbasu@lvpei.org
16.2 Cornea andConjunctiva
16.2.1 Cornea
The normal cornea is transparent and has a
smooth, clear optical surface. The cornea measures 11–12mm horizontally and 9–11mm vertically [1]. One should examine the cornea under
white light and uorescein staining. Slit-lamp
evaluation of the cornea shows the ve layers
individually and allows pathology detection at
high magnication. Any epithelial irregularities
like defects and erosions would take up uorescein stain (Fig.16.1) [3]. Different grading systems are used for corneal uorescein staining, like
the National Eye Institute Scoring System and the
Oxford Ocular Surface Staining Score [3].
Corneal scarring with an irregular surface will
show pooling of the dye and should be differentiated from staining. A high-resolution anterior segment optical coherence tomography (AS-OCT) of
the cornea can depict the abnormalities involving
the individual layers of the cornea and stromal
thickness and provide an infrared photograph of
the cornea for better appreciation of the stromal
opacication [4, 5] (Fig.16.2).
16.2.2 Limbus
The limbus is the transition zone between the
cornea and the sclera. It contains radially running
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024
T. Das, P. Satgunam (eds.), Ophthalmic Diagnostics, https://doi.org/10.1007/978-981-97-0138-4_16
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Fig. 16.1 Sodium uorescein-stained images of the cornea showing stain uptake patterns in pseudo-dendrites,
true dendrites, and corneal ulceration
S. Singh and S. Basu
brovascular ridges known as the palisades of
Vogt that contain limbal stem cells (Fig. 16.3)
[5]. The palisades of Vogt are more common in
the superior and inferior quadrants and better
appreciated in pigmented races. Limbal stem cell
deciency seen in chemical injury results in the
loss of the palisades of Vogt (Fig.16.4). The surface abnormalities that occur at the limbus are
pterygium, Horner-Trantas dots, hypertrophied
epithelium, and ocular surface malignancy [5].
16.2.3 Conjunctiva
Both the bulbar and palpebral conjunctiva should
be examined for any congestion, especially perilimbal congestion, and the presence of symblepharon. Everted upper and lower eyelid examination
exposes the lid margin and palpebral conjunctiva
better (Fig.16.5). Presence of follicles suggests
conjunctivitis, whereas papillae suggest allergic
conjunctivitis. For ocular surface diseases, conjunctival signs like congestion, scarring, symblepharon, and keratinization can suggest chronic
a
Fig. 16.2 Normal appearance of the cornea and limbus. The
healthy cornea is optically transparent (a) and surrounded
by the annular limbus, which separates it from the opaque
sclera. The limbus contains the palisades of Vogt (b), which
are nger-like projections of the stroma. The optical coher-
b
ence tomography (OCT) image of the normal cornea shows
a smooth, uniform stratied epithelium (c) with underlying
compact stroma. The OCT angiography image of the normal limbus shows linear anastomosing hairpin loops of the
limbal capillaries (d) with adjacent avascular corneal stroma
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Fig. 16.3 Top and bottom. Pigmented palisades of Vogt
in a healthy corneal limbus
cicatrizing conjunctivitis [6]. Subtle symblepharon are picked up by retracting the lower eyelid
and instructing the patient to look upward, which
better exposes forniceal, nasal symblepharon.
The upper and lower fornices must be examined
for foreign bodies and scarring, especially in eyes
Fig. 16.4 Limbal stem cell deciency after chemical
injury that resulted in conjunctivalization of the cornea is
seen in the inferonasal cornea (top) and symblepharon
formation with adherence between the palpebral conjunctiva and the cornea (bottom)
with mucous membrane pemphigoid with otherwise quiet eye. Lid margin conjunctival folds
suggest conjunctivochalasis.
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Fig. 16.5 Everted
upper eyelid showing
normal (upper panel)
and scarred tarsal
conjunctiva. In the
middle panel, the lid
margin can be seen as
distorted, scarred, and
having occluded
meibomian gland
openings. The lower
panel shows giant tarsal
papillae with a
cobblestone appearance
and ropy discharge
S. Singh and S. Basu
16.3 Ocular Adnexa
16.3.1 Eyelid andEyelid Margin
The eyelids should be examined in a closed and
open state for proper apposition evaluation.
These must be examined for any signs of lagophthalmos, ectropion, entropion, blepharitis, and
any signs of trauma. The entire eyelid margin
must be examined for evidence of edema, hordeolum, or chalazion.
The eyelid margin is inspected for three
parameters, namely apposition to the globe,
mucocutaneous junction, and appearance. The
normal lid sits apposed to the globe, where its
sharp inner border lies over the bulbar surface
where the tear lake resides as a reservoir. These
positions are altered in eyelid ectropion or entropion, and the tear lake reservoir is disturbed. The
mucocutaneous junction (MCJ) is the area where
the free lid epidermis meets the conjunctival epithelium (Fig.16.6) [7, 8]. This transition is situated at the posterior border of the meibomian
gland orices from where the lid wiper begins.
The lid wiper region is part of the eyelid margin
in contact with the globe and extends superiorly
from the MCJ to the sub-tarsal fold. Any disturbances in the lid wiper region can cause corneal
epitheliopathy, termed lid wiper epitheliopathy
(LWE; Fig. 16.7) [8]. LWE is observed in lid
16 Ocular Surface Examination
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195
over the lid wiper region [8]. Also, sometimes,
there can be conjunctivalization of the meibomian gland orices with associated gland blockade as a sign of meibomian gland dysfunction.
Any lid margin notching or thinning, especially in eyes with chemical injury, should also be
looked at. An inamed lid margin would have a
congested look with ne telangiectatic vessels
around the meibomian gland openings seen in
posterior blepharitis. The inferior lid margin
should be reected using a cotton-tipped applicator to better visualize the lower lid margin, lower
lash follicles, inferior punctum, and meibomian
glands.
Fig. 16.6 Normal appearance of posterior lid margin
showing a gray line and the mucocutaneous junction
(MCJ) at the posterior border of the meibomian gland
openings
Fig. 16.7 Normal lower eyelid with eyelashes arising
from the skin and oriented outwards (upper panel). The
lower panel shows aberrant distichiatic eyelashes located
at the meibomian gland openings as an extra row other
than normal eyelashes
16.3.2 Eyelashes
Examine the eyelashes for debris, akes, crusting, or collarettes. The normal orientation of the
eyelash is upwards and outwards. Misdirected
eyelashes like those in trichiasis or aberrant eyelashes like those in distichiatic can cause ocular
surface staining due to rubbing over the surface
epithelium (Fig.16.8) [9]. Distichiatic lashes can
be ne and light-colored and are best examined
using the slit lamp.
16.3.3 Periocular Skin
The periocular skin should be examined for any
hypo or hyperpigmentation, edema, or signs of
inammation. Contact dermatitis, especially in
patients using antiglaucoma medications, would
show edematous skin with or without erosion in
the medial compartment of the eyelids [6, 10].
16.3.4 Lacrimal Gland
margin keratinization (LMK), contact lens users,
and dry eye disease. The MCJ and lid wiper
region are examined using uorescein staining
under a cobalt blue lter where the conjunctival
epithelium has pooling of the dye (Fig.16.7). In
eyes with LMK, posterior migration of the MCJ
occurs and the keratinized epithelium encroaches
The lacrimal gland contributes to the aqueous
component of the tear lm via secretory ductules
opening into the conjunctiva overlying the palpebral lobe. Traditionally, Schirmer's test and tear
lm height or area measurement are considered
indicators for lacrimal gland function [11]. These
techniques give an indirect assessment of the lac-
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S. Singh and S. Basu
Fig. 16.8 Corneal staining in different ocular conditions. The upper panel shows diffuse inferior corneal
staining in the area of exposure in a patient with lagophthalmos. The lower panel shows interpalpebral staining
rimal gland activity. The palpebral lobes of the
lacrimal gland can be directly visualized during a
routine slit-lamp biomicroscopy session by asking the patient to look inferonasal. At the same
time, the upper eyelid is lifted superotemporally
[12]. The morphology can be divided into size
(exposed area), shape (convex or at), and overlying conjunctival appearance (engorged vessels,
whitish areas of subepithelial scarring, or symblepharon). The normal palpebral lobe is a
convex- shaped, raised pinkish lobular structure
with overlying normal conjunctiva (Fig. 16.9).
The lobe lies in the superotemporal fornix extend-
seen in aqueous decient dry eye disease, whereas sectoral temporal staining is seen in areas of contact with the
keratinized lid margin, which is suggestive of lid wiper
epitheliopathy
ing to or beyond the lateral canthus. The lobe is
visibly smaller in patients with Sjogren's
Syndrome (SS), whereas cicatrization over the
lobe is seen in patients with Stevens-Johnson
syndrome (SJS). Under a slit-lamp biomicroscope, a dry 2% sodium uorescein ophthalmic
strip is applied onto the exposed palpebral lobe.
The washout of uorescein stain across the
applied area is recorded till secretions start
appearing. Normally, 3–5 secretory ductules can
be observed in healthy individuals, whereas the
number of openings is reduced in individuals
with aqueous decient dry eye [13].
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Fig. 16.9 Right and left palpebral lobes of the lacrimal
gland in normal individuals. The lobes are convex-shaped
and have smooth overlying conjunctiva. The lower panel
16.3.5 Meibomian Gland
Meibomian glands are lipid-producing glands
that secrete a mixture of lipids and some proteins
onto the ocular surface. The structure of the meibomian glands can be evaluated using
transillumination infrared imaging, such as infrared meibography, and their function can be measured using lipid layer thickness (LLT) and
meibum quality or expressibility tests [11].
Normal meibomian glands are seen as whitish
vertically running glands within the tarsal plate.
Gland dropout and short glands suggest meibomian gland dysfunction [14, 15]. Meibum quality
shows the secretory openings seen as uorescein washout
areas—two on the right side and three on the left side
(marked with arrows)
is graded as 0 (clear uid), 1 (cloudy uid), 2
(cloudy particulate), or 3 (toothpaste-like). The
expressibility of meibum from the central eight
glands of the upper and lower eyelids is graded as
0 (all glands expressible), 1 (3 to 4 glands
expressible), 2 (1 to 2 glands expressible), and 3
(no glands expressible). The meibographic
appearance of normal glands is shown in
Fig. 16.10. The normal lipid layer thickness
(LLT) varies from 70 to 100 nm [16]. Values
<60nm are considered signs of lipid deciency.
However, the repeatability coefcient of the dry
eye diagnostic devices should be kept in mind
while interpreting LLT values [17].
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Fig. 16.10 Infrared meibography of the upper and lower
eyelids of a normal adult showing vertically running meibomian glands reaching up to the convex tarsal border.
16.4 Tear Film Assessment
Tear lm tests are crucial in identifying dry eye
disease and surface irregularities in ocular surface disorders. The tear lm break-up time
(TBUT) measures tear stability and can be
evaluated in an invasive and non-invasive manner
[18]. TBUT is the time taken for the precorneal
tear lm to break after one blink and is affected in
dry eye disease (both aqueous decient and evaporative types), corneal epithelial irregularities,
and surface inammation with diminished mucus
layer attachment to corneal microplicae. A drop
of uorescein is instilled in the conjunctival culde- sac, and the patient is instructed not to blink
afterward. The time taken for the appearance of
the rst dry spot is taken as TBUT.The reported
mean uorescein-TBUT values in normal subjects are 7.6±10.4s [11, 18]. One should repeat
the test if the values are <10s before labelling it
pathological. With the advent of non-invasive
tests, the accuracy of TBUT is better when tested
two or more times. Non-invasive TBUT (NIBUT)
Non-invasive tear break-up time (NIBUT; OD= 7.4 s;
OS=10s) and tear meniscus height were captured in the
oculus keratograph of the same individual
measures changes in the reected videokeratographic mires using topographic systems
(Fig.16.10). The Placido disc projects the mires
onto the cornea, and any changes in the mires’
regularity are taken as the onset of tear break-up.
In one study, the values of NIBUT for 236 healthy
individuals of South Indian origin were between
7s and 10s in 33% of individuals, and 7% had
NIBUT values <7s [19].
Tear volume is measured using the Schirmer
test (invasive) and tear meniscus height (TMH,
non-invasive) [20]. A commercially available
Whatman 41 lter paper strip is used for the
Schirmer test. The proximal part of the strip sits
in the conjunctival-cul-de-sac and is inserted in
the lateral one-third of the lower eyelid. Both
eyes are tested simultaneously, and the moistened
segment is measured at the end of 5 min. The
strip should not touch the cornea to avoid reex
tear activity. The Schirmer test can be performed
with open or closed eyes; however, there is less
variation with closed eyes [21]. The different
types of Schirmer tests are the Schirmer I (with-
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