  Exoplanet transmission spectra provide rich information about the chemical
composition, clouds and temperature structure of exoplanet atmospheres. Most
exoplanet transmission spectra only span infrared wavelengths ($\gtrsim$ 1
$\rm{\mu m}$), which can preclude crucial atmospheric information from shorter
wavelengths. Here, we explore how retrieved atmospheric parameters from
exoplanet transmission spectra change with the addition of optical data. From a
sample of 14 giant planets with transit spectra from 0.3-4.5 $\rm{\mu m}$,
primarily from the Hubble and Spitzer space telescopes, we apply a free
chemistry retrieval to planetary spectra for wavelength ranges of 0.3-4.5
$\rm{\mu m}$, 0.6-4.5 $\rm{\mu m}$, and 1.1-4.5 $\rm{\mu m}$. We analyse the
posterior distributions of these retrievals and perform an information content
analysis, finding wavelengths below 0.6 $\rm{\mu m}$ are necessary to constrain
cloud scattering slope parameters ($\log{a}$ and $\gamma$) and alkali species
Na and K. There is limited improvement in the constraints on the remaining
atmospheric parameters. Across the population, we find limb temperatures are
retrieved colder than planetary equilibrium temperatures but have an overall
good agreement with Global Circulation Models. As JWST extends to a minimum
wavelength of 0.6 $\rm{\mu m}$, we demonstrate that exploration into
complementing JWST observations with optical HST data is important to further
our understanding of aerosol properties and alkali abundances in exoplanet
atmospheres.
